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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NSIS Working Group M. Stiemerling 3 Internet-Draft NEC 4 Intended status: Standards Track H. Tschofenig 5 Expires: August 18, 2008 Nokia Siemens Networks 6 C. Aoun 7 E. Davies 8 Folly Consulting 9 February 15, 2008 11 NAT/Firewall NSIS Signaling Layer Protocol (NSLP) 12 draft-ietf-nsis-nslp-natfw-18.txt 14 Status of this Memo 16 By submitting this Internet-Draft, each author represents that any 17 applicable patent or other IPR claims of which he or she is aware 18 have been or will be disclosed, and any of which he or she becomes 19 aware will be disclosed, in accordance with Section 6 of BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF), its areas, and its working groups. Note that 23 other groups may also distribute working documents as Internet- 24 Drafts. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 The list of current Internet-Drafts can be accessed at 32 http://www.ietf.org/ietf/1id-abstracts.txt. 34 The list of Internet-Draft Shadow Directories can be accessed at 35 http://www.ietf.org/shadow.html. 37 This Internet-Draft will expire on August 18, 2008. 39 Copyright Notice 41 Copyright (C) The IETF Trust (2008). 43 Abstract 45 This memo defines the NSIS Signaling Layer Protocol (NSLP) for 46 Network Address Translators (NATs) and firewalls. This NSLP allows 47 hosts to signal on the data path for NATs and firewalls to be 48 configured according to the needs of the application data flows. For 49 instance, it enables hosts behind NATs to obtain a public reachable 50 address and hosts behind firewalls to receive data traffic. The 51 overall architecture is given by the framework and requirements 52 defined by the Next Steps in Signaling (NSIS) working group. The 53 network scenarios, the protocol itself, and examples for path-coupled 54 signaling are given in this memo. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 59 1.1. Scope and Background . . . . . . . . . . . . . . . . . . . 5 60 1.2. Terminology and Abbreviations . . . . . . . . . . . . . . 8 61 1.3. Middleboxes . . . . . . . . . . . . . . . . . . . . . . . 9 62 1.4. General Scenario for NATFW Traversal . . . . . . . . . . . 11 64 2. Network Deployment Scenarios using the NATFW NSLP . . . . . . 13 65 2.1. Firewall Traversal . . . . . . . . . . . . . . . . . . . . 13 66 2.2. NAT with two private Networks . . . . . . . . . . . . . . 14 67 2.3. NAT with Private Network on Sender Side . . . . . . . . . 15 68 2.4. NAT with Private Network on Receiver Side Scenario . . . . 15 69 2.5. Both End Hosts behind twice-NATs . . . . . . . . . . . . . 16 70 2.6. Both End Hosts Behind Same NAT . . . . . . . . . . . . . . 17 71 2.7. Multihomed Network with NAT . . . . . . . . . . . . . . . 18 72 2.8. Multihomed Network with Firewall . . . . . . . . . . . . . 19 74 3. Protocol Description . . . . . . . . . . . . . . . . . . . . . 20 75 3.1. Policy Rules . . . . . . . . . . . . . . . . . . . . . . . 20 76 3.2. Basic Protocol Overview . . . . . . . . . . . . . . . . . 21 77 3.2.1. Signaling for Outbound Traffic . . . . . . . . . . . . 21 78 3.2.2. Signaling for Inbound Traffic . . . . . . . . . . . . 22 79 3.2.3. Signaling for Proxy Mode . . . . . . . . . . . . . . . 23 80 3.2.4. Blocking Traffic . . . . . . . . . . . . . . . . . . . 25 81 3.2.5. State and Error Maintenance . . . . . . . . . . . . . 25 82 3.2.6. Message Types . . . . . . . . . . . . . . . . . . . . 26 83 3.2.7. Classification of RESPONSE Messages . . . . . . . . . 26 84 3.2.8. NATFW NSLP Signaling Sessions . . . . . . . . . . . . 27 85 3.3. Basic Message Processing . . . . . . . . . . . . . . . . . 28 86 3.4. Calculation of Signaling Session Lifetime . . . . . . . . 28 87 3.5. Message Sequencing . . . . . . . . . . . . . . . . . . . . 31 88 3.6. Authentication, Authorization, and Policy Decisions . . . 32 89 3.7. Protocol Operations . . . . . . . . . . . . . . . . . . . 33 90 3.7.1. Creating Signaling Sessions . . . . . . . . . . . . . 33 91 3.7.2. Reserving External Addresses . . . . . . . . . . . . . 36 92 3.7.3. NATFW NSLP Signaling Session Refresh . . . . . . . . . 43 93 3.7.4. Deleting Signaling Sessions . . . . . . . . . . . . . 44 94 3.7.5. Reporting Asynchronous Events . . . . . . . . . . . . 46 95 3.7.6. Proxy Mode of Operation . . . . . . . . . . . . . . . 47 96 3.8. De-Multiplexing at NATs . . . . . . . . . . . . . . . . . 51 97 3.9. Reacting to Route Changes . . . . . . . . . . . . . . . . 53 98 3.10. Updating Policy Rules . . . . . . . . . . . . . . . . . . 53 100 4. NATFW NSLP Message Components . . . . . . . . . . . . . . . . 55 101 4.1. NSLP Header . . . . . . . . . . . . . . . . . . . . . . . 55 102 4.2. NSLP Objects . . . . . . . . . . . . . . . . . . . . . . . 56 103 4.2.1. Signaling Session Lifetime Object . . . . . . . . . . 57 104 4.2.2. External Address Object . . . . . . . . . . . . . . . 57 105 4.2.3. Extended Flow Information Object . . . . . . . . . . . 58 106 4.2.4. Information Code Object . . . . . . . . . . . . . . . 59 107 4.2.5. Nonce Object . . . . . . . . . . . . . . . . . . . . . 62 108 4.2.6. Message Sequence Number Object . . . . . . . . . . . . 62 109 4.2.7. Data Terminal Information Object . . . . . . . . . . . 63 110 4.2.8. ICMP Types Object . . . . . . . . . . . . . . . . . . 64 111 4.3. Message Formats . . . . . . . . . . . . . . . . . . . . . 65 112 4.3.1. CREATE . . . . . . . . . . . . . . . . . . . . . . . . 66 113 4.3.2. EXTERNAL . . . . . . . . . . . . . . . . . . . . . . . 66 114 4.3.3. RESPONSE . . . . . . . . . . . . . . . . . . . . . . . 67 115 4.3.4. NOTIFY . . . . . . . . . . . . . . . . . . . . . . . . 67 117 5. Security Considerations . . . . . . . . . . . . . . . . . . . 69 118 5.1. Authorization Framework . . . . . . . . . . . . . . . . . 69 119 5.1.1. Peer-to-Peer Relationship . . . . . . . . . . . . . . 69 120 5.1.2. Intra-Domain Relationship . . . . . . . . . . . . . . 70 121 5.1.3. End-to-Middle Relationship . . . . . . . . . . . . . . 71 122 5.2. Security Framework for the NAT/Firewall NSLP . . . . . . . 72 123 5.2.1. Security Protection between neighboring NATFW NSLP 124 Nodes . . . . . . . . . . . . . . . . . . . . . . . . 72 125 5.2.2. Security Protection between non-neighboring NATFW 126 NSLP Nodes . . . . . . . . . . . . . . . . . . . . . . 73 128 6. IAB Considerations on UNSAF . . . . . . . . . . . . . . . . . 75 130 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 76 132 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 78 134 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 79 135 9.1. Normative References . . . . . . . . . . . . . . . . . . . 79 136 9.2. Informative References . . . . . . . . . . . . . . . . . . 79 138 Appendix A. Selecting Signaling Destination Addresses for 139 EXTERNAL . . . . . . . . . . . . . . . . . . . . . . 81 141 Appendix B. Applicability Statement on Data Receivers behind 142 Firewalls . . . . . . . . . . . . . . . . . . . . . . 82 144 Appendix C. Firewall and NAT Resources . . . . . . . . . . . . . 84 145 C.1. Wildcarding of Policy Rules . . . . . . . . . . . . . . . 84 146 C.2. Mapping to Firewall Rules . . . . . . . . . . . . . . . . 84 147 C.3. Mapping to NAT Bindings . . . . . . . . . . . . . . . . . 85 148 C.4. NSLP Handling of Twice-NAT . . . . . . . . . . . . . . . . 85 150 Appendix D. Protocols Numbers for Testing . . . . . . . . . . . . 87 152 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 88 153 Intellectual Property and Copyright Statements . . . . . . . . . . 89 155 1. Introduction 157 1.1. Scope and Background 159 Firewalls and Network Address Translators (NAT) have both been used 160 throughout the Internet for many years, and they will remain present 161 for the foreseeable future. Firewalls are used to protect networks 162 against certain types of attacks from internal networks and the 163 Internet, whereas NATs provide a virtual extension of the IP address 164 space. Both types of devices may be obstacles to some applications, 165 since they only allow traffic created by a limited set of 166 applications to traverse them, typically those that use protocols 167 with relatively predetermined and static properties (e.g., most HTTP 168 traffic, and other client/server applications). Other applications, 169 such as IP telephony and most other peer-to-peer applications, which 170 have more dynamic properties, create traffic that is unable to 171 traverse NATs and firewalls unassisted. In practice, the traffic of 172 many applications cannot traverse autonomous firewalls or NATs, even 173 when they have additional functionality which attempts to restore the 174 transparency of the network. 176 Several solutions to enable applications to traverse such entities 177 have been proposed and are currently in use. Typically, application 178 level gateways (ALG) have been integrated with the firewall or NAT to 179 configure the firewall or NAT dynamically. Another approach is 180 middlebox communication (MIDCOM). In this approach, ALGs external to 181 the firewall or NAT configure the corresponding entity via the MIDCOM 182 protocol [7]. Several other work-around solutions are available, 183 such as STUN [14]. However, all of these approaches introduce other 184 problems that are generally hard to solve, such as dependencies on 185 the type of NAT implementation (full-cone, symmetric, etc), or 186 dependencies on certain network topologies. 188 NAT and firewall (NATFW) signaling shares a property with Quality of 189 Service (QoS) signaling. The signaling of both must reach any device 190 on the data path that is involved in, respectively, NATFW or QoS 191 treatment of data packets. This means, that for both, NATFW and QoS, 192 it is convenient if signaling travels path-coupled, meaning that the 193 signaling messages follow exactly the same path that the data packets 194 take. RSVP [11] is an example of a current QoS signaling protocol 195 that is path-coupled. [19] proposes the use of RSVP as firewall 196 signaling protocol but does not include NATs. 198 This memo defines a path-coupled signaling protocol for NAT and 199 firewall configuration within the framework of NSIS, called the NATFW 200 NSIS Signaling Layer Protocol (NSLP). The general requirements for 201 NSIS are defined in [5] and the general framework of NSIS is outlined 202 in [4]. It introduces the split between an NSIS transport layer and 203 an NSIS signaling layer. The transport of NSLP messages is handled 204 by an NSIS Network Transport Layer Protocol (NTLP, with General 205 Internet Signaling Transport (GIST) [2] being the implementation of 206 the abstract NTLP). The signaling logic for QoS and NATFW signaling 207 is implemented in the different NSLPs. The QoS NSLP is defined in 208 [6]. 210 The NATFW NSLP is designed to request the dynamic configuration of 211 NATs and/or firewalls along the data path. Dynamic configuration 212 includes enabling data flows to traverse these devices without being 213 obstructed, as well as blocking of particular data flows at inbound 214 firewalls. Enabling data flows requires the loading of firewall 215 rules with an action that allows the data flow packets to be 216 forwarded and creating NAT bindings. Blocking of data flows requires 217 the loading of firewalls rules with an action that will deny 218 forwarding of the data flow packets. A simplified example for 219 enabling data flows: A source host sends a NATFW NSLP signaling 220 message towards its data destination. This message follows the data 221 path. Every NATFW NSLP-enabled NAT/firewall along the data path 222 intercepts this message, processes them, and configures itself 223 accordingly. Thereafter, the actual data flow can traverse all these 224 configured firewalls/NATs. 226 It is necessary to distinguish between two different basic scenarios 227 when operating the NATFW NSLP, independent of the type of the 228 middleboxes to be configured. 230 1. Both, data sender and data receiver, are NSIS NATFW NSLP aware. 231 This includes the cases where the data sender is logically 232 decomposed from the initiator of the NSIS signaling (the so- 233 called NSIS initiator) or the data receiver logically decomposed 234 from the receiver of the NSIS signaling (the so-called NSIS 235 receiver), but both sides support NSIS. This scenario assumes 236 deployment of NSIS all over the Internet, or at least at all NATs 237 and firewalls. This scenario is used as base assumption, if not 238 otherwise noted. 240 2. Only one end host or region of the network is NSIS NATFW NSLP 241 aware, either data receiver or data sender. This scenario is 242 referred to as proxy mode. 244 The NATFW NSLP has two basic signaling messages which are sufficient 245 to cope with the various possible scenarios likely to be encountered 246 before and after widespread deployment of NSIS: 248 CREATE message: Send by the data sender for configuring a path 249 outbound from a data sender to a data receiver. 251 EXTERNAL message: Used by data receiver to locate inbound NATs/ 252 firewalls and prime them to expect outbound signaling and at NATs 253 to pre-allocate a public address. This is used for data receivers 254 behind these devices to enable their reachability. 256 CREATE and EXTERNAL messages are sent by the NSIS initiator (NI) 257 towards the NSIS responder (NR). Both type of messages are 258 acknowledged by a subsequent RESPONSE message. This RESPONSE message 259 is generated by the NR if the requested configuration can be 260 established, otherwise the NR or any of the NSIS forwarders (NFs) can 261 also generate such a message if an error occurs. NFs and the NR can 262 also generate asynchronous messages to notify the NI, the so called 263 NOTIFY messages. 265 If the data receiver resides in a private addressing realm or behind 266 a firewall, and needs to preconfigure the edge-NAT/edge-firewall to 267 provide a (publicly) reachable address for use by the data sender, a 268 combination of EXTERNAL and CREATE messages is used. 270 During the introduction of NSIS, it is likely that one or the other 271 of the data sender and receiver will not be NSIS aware. In these 272 cases, the NATFW NSLP can utilize NSIS aware middleboxes on the path 273 between the data sender and data receiver to provide proxy NATFW NSLP 274 services (i.e., the proxy mode). Typically, these boxes will be at 275 the boundaries of the realms in which the end hosts are located. 277 The CREATE and EXTERNAL messages create NATFW NSLP and NTLP state in 278 NSIS entities. NTLP state allows signaling messages to travel in the 279 forward (outbound) and the reverse (inbound) direction along the path 280 between a NAT/firewall NSLP sender and a corresponding receiver. 281 This state is managed using a soft-state mechanism, i.e., it expires 282 unless it is refreshed from time to time. The NAT bindings and 283 firewall rules being installed during the state setup are bound to 284 the particular signaling session. However, the exact local 285 implementation of the NAT bindings and firewall rules are NAT/ 286 firewall specific and it is out of scope of this memo. 288 This memo is structured as follows. Section 2 describes the network 289 environment for NATFW NSLP signaling. Section 3 defines the NATFW 290 signaling protocol and Section 4 defines the message components and 291 the overall messages used in the protocol. The remaining parts of 292 the main body of the document cover security considerations 293 Section 5, IAB considerations on UNilateral Self-Address Fixing 294 (UNSAF) [12] in Section 6 and IANA considerations in Section 7. 295 Please note that readers familiar with firewalls and NATs and their 296 possible location within networks can safely skip Section 2. 298 1.2. Terminology and Abbreviations 300 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 301 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 302 document are to be interpreted as described in [1]. 304 This document uses a number of terms defined in [5] and [4]. The 305 following additional terms are used: 307 o Policy rule: A policy rule is "a basic building block of a policy- 308 based system. It is the binding of a set of actions to a set of 309 conditions - where the conditions are evaluated to determine 310 whether the actions are performed" [15]. In the context of NSIS 311 NATFW NSLP, the conditions are the specification of a set of 312 packets to which the rule is applied. The set of actions always 313 contains just a single element per rule, and is limited to either 314 action "deny" or action "allow". 316 o Reserved policy rule: A policy rule stored at NATs or firewalls 317 for activation by a later, different signaling exchange. This 318 type of policy rule is kept in the NATFW NSLP and is not loaded 319 into the firewall or NAT engine, i.e., it does not affect the data 320 flow handling. 322 o Installed policy rule: A policy rule in operation at NATs or 323 firewalls. This type of rule is kept in the NATFW NSLP and is 324 loaded into the firewall or NAT engine, i.e., it is affecting the 325 data flow. 327 o Remembered policy rule: A policy rule stored at NATs and firewalls 328 for immediate use, as soon as the signaling exchange is 329 successfully completed. 331 o Firewall: A packet filtering device that matches packets against a 332 set of policy rules and applies the actions. 334 o Network Address Translator: Network Address Translation is a 335 method by which IP addresses are mapped from one IP address realm 336 to another, in an attempt to provide transparent routing between 337 hosts (see [9]). Network Address Translators are devices that 338 perform this work by modifying packets passing through them. 340 o Data Receiver (DR): The node in the network that is receiving the 341 data packets of a flow. 343 o Data Sender (DS): The node in the network that is sending the data 344 packets of a flow. 346 o NATFW NSLP peer or peer: An NSIS NATFW NSLP node with which an 347 NTLP adjacency has been created as defined in [2]. 349 o NATFW NSLP signaling session or signaling session: A signaling 350 session defines an association between the NI, NFs, and the NR 351 related to a data flow. All the NATFW NSLP peers on the path, 352 including the NI and the NR, use the same identifier to refer to 353 the state stored for the association. The same NI and NR may have 354 more than one signaling session active at any time. The state for 355 NATFW NSLP consists of NSLP state and associated policy rules at a 356 middlebox. 358 o Edge-NAT: An edge-NAT is a NAT device with a globally routable IP 359 address which is reachable from the public Internet. 361 o Edge-firewall: An edge-firewall is a firewall device that is 362 located on the border line of an administrative domain. 364 o Public Network: "A Global or Public Network is an address realm 365 with unique network addresses assigned by Internet Assigned 366 Numbers Authority (IANA) or an equivalent address registry. This 367 network is also referred as external network during NAT 368 discussions" [9]. 370 o Private/Local Network: "A private network is an address realm 371 independent of external network addresses. Private network may 372 also be referred alternately as Local Network. Transparent 373 routing between hosts in private realm and external realm is 374 facilitated by a NAT router" [9]. 376 o Public/Global IP address: An IP address located in the public 377 network according to Section 2.7 of [9]. 379 o Private/Local IP address: An IP address located in the private 380 network according to Section 2.8 of [9]. 382 o Signaling Destination Address (SDA): An IP address generally taken 383 from the public/global IP address range, although, the SDA may in 384 certain circumstances be part of the private/local IP address 385 range. This address is used in EXTERNAL signaling message 386 exchanges, if the data receiver's IP address is unknown. 388 1.3. Middleboxes 390 The term middlebox covers a range of devices and is well-defined in 391 [10]: "A middlebox is defined as any intermediate device performing 392 functions other than the normal, standard functions of an IP router 393 on the datagram path between source host and a destination host". As 394 such, middleboxes fall into a number of categories with a wide range 395 of functionality, not all of which is pertinent to the NATFW NSLP. 396 Middlebox categories in the scope of this memo are firewalls that 397 filter data packets against a set of filter rules, and NATs that 398 translate packet addresses from one address realm to another address 399 realm. Other categories of middleboxes, such as QoS traffic shapers, 400 are out of scope of this memo. 402 The term NAT used in this document is a placeholder for a range of 403 different NAT flavors. We consider the following types of NATs: 405 o Traditional NAT (basic NAT and NAPT) 407 o Bi-directional NAT 409 o Twice-NAT 411 o Multihomed NAT 413 For definitions and a detailed discussion about the characteristics 414 of each NAT type please see [9]. 416 All types of middleboxes under consideration here, use policy rules 417 to make a decision on data packet treatment. Policy rules consist of 418 a flow identifier which selects the packets to which the policy 419 applies and an associated action; data packets matching the flow 420 identifier are subjected to the policy rule action. A typical flow 421 identifier is the 5-tuple selector which matches the following fields 422 of a packet to configured values: 424 o Source and destination IP addresses 426 o Transport protocol number 428 o Transport source and destination port numbers 430 Actions for firewalls are usually one or more of: 432 o Allow: forward data packet 434 o Deny: block data packet and discard it 436 o Other actions such as logging, diverting, duplicating, etc 438 Actions for NATs include (amongst many others): 440 o Change source IP address and transport port number to a globally 441 routable IP address and associated port number. 443 o Change destination IP address and transport port number to a 444 private IP address and associated port number. 446 It should be noted that a middlebox may contain two logical 447 representations of the policy rule. The policy rule has a 448 representation within the NATFW NSLP, comprising the message routing 449 information (MRI) of the NTLP and NSLP information (such as the rule 450 action). The other representation is the implementation of the NATFW 451 NSLP policy rule within the NAT and firewall engine of the particular 452 device. Refer to Appendix C for further details. 454 1.4. General Scenario for NATFW Traversal 456 The purpose of NSIS NATFW signaling is to enable communication 457 between endpoints across networks, even in the presence of NAT and 458 firewall middleboxes that have not been specially engineered to 459 facilitate communication with the application protocols used. This 460 removes the need to create and maintain application layer gateways 461 for specific protocols that have been commonly used to provide 462 transparency in previous generations of NAT and firewall middleboxes. 463 It is assumed that these middleboxes will be statically configured in 464 such a way that NSIS NATFW signaling messages themselves are allowed 465 to reach the locally installed NATFW NSLP daemon. NSIS NATFW NSLP 466 signaling is used to dynamically install additional policy rules in 467 all NATFW middleboxes along the data path that will allow 468 transmission of the application data flow(s). Firewalls are 469 configured to forward data packets matching the policy rule provided 470 by the NSLP signaling. NATs are configured to translate data packets 471 matching the policy rule provided by the NSLP signaling. An 472 additional capability, that is an exception to the primary goal of 473 NSIS NATFW signaling, is that the NATFW nodes can request blocking of 474 particular data flows instead of enabling these flows at inbound 475 firewalls. 477 The basic high-level picture of NSIS usage is that end hosts are 478 located behind middleboxes, meaning that there is at least one 479 middlebox on the data path from the end host in a private network to 480 the external network (NATFW in Figure 1). Applications located at 481 these end hosts try to establish communication with corresponding 482 applications on other such end hosts. They trigger the NSIS entity 483 at the local host to control provisioning for middlebox traversal 484 along the prospective data path (e.g., via an API call). The NSIS 485 entity in turn uses NSIS NATFW NSLP signaling to establish policy 486 rules along the data path, allowing the data to travel from the 487 sender to the receiver unobstructed. 489 Application Application Server (0, 1, or more) Application 491 +----+ +----+ +----+ 492 | +------------------------+ +------------------------+ | 493 +-+--+ +----+ +-+--+ 494 | | 495 | NSIS Entities NSIS Entities | 496 +-+--+ +----+ +-----+ +-+--+ 497 | +--------+ +----------------------------+ +-----+ | 498 +-+--+ +-+--+ +--+--+ +-+--+ 499 | | ------ | | 500 | | //// \\\\\ | | 501 +-+--+ +-+--+ |/ | +-+--+ +-+--+ 502 | | | | | Internet | | | | | 503 | +--------+ +-----+ +----+ +-----+ | 504 +----+ +----+ |\ | +----+ +----+ 505 \\\\ ///// 506 sender NATFW (1+) ------ NATFW (1+) receiver 508 Note that 1+ refers to one or more NATFW nodes. 510 Figure 1: Generic View of NSIS with NATs and/or firewalls 512 For end-to-end NATFW signaling, it is necessary that each firewall 513 and each NAT along the path between the data sender and the data 514 receiver implements the NSIS NATFW NSLP. There might be several NATs 515 and FWs in various possible combinations on a path between two hosts. 516 Section 2 presents a number of likely scenarios with different 517 combinations of NATs and firewalls. However, the scenarios given in 518 the following sections are not limiting the scope of the NATFW NSLP 519 to them only, but they are examples only. 521 2. Network Deployment Scenarios using the NATFW NSLP 523 This section introduces several scenarios for middlebox placement 524 within IP networks. Middleboxes are typically found at various 525 different locations, including at enterprise network borders, within 526 enterprise networks, as mobile phone network gateways, etc. Usually, 527 middleboxes are placed more towards the edge of networks than in 528 network cores. Firewalls and NATs may be found at these locations 529 either alone, or they may be combined; other categories of 530 middleboxes may also be found at such locations, possibly combined 531 with the NATs and/or firewalls. 533 NSIS initiators (NI) send NSIS NATFW NSLP signaling messages via the 534 regular data path to the NSIS responder (NR). On the data path, 535 NATFW NSLP signaling messages reach different NSIS nodes that 536 implement the NATFW NSLP. Each NATFW NSLP node processes the 537 signaling messages according to Section 3 and, if necessary, installs 538 policy rules for subsequent data packets. 540 Each of the following sub-sections introduces a different scenario 541 for a different set of middleboxes and their ordering within the 542 topology. It is assumed that each middlebox implements the NSIS 543 NATFW NSLP signaling protocol. 545 2.1. Firewall Traversal 547 This section describes a scenario with firewalls only; NATs are not 548 involved. Each end host is behind a firewall. The firewalls are 549 connected via the public Internet. Figure 2 shows the topology. The 550 part labeled "public" is the Internet connecting both firewalls. 552 +----+ //----\\ +----+ 553 NI -----| FW |---| |------| FW |--- NR 554 +----+ \\----// +----+ 556 private public private 558 FW: Firewall 559 NI: NSIS Initiator 560 NR: NSIS Responder 562 Figure 2: Firewall Traversal Scenario 564 Each firewall on the data path must provide traversal service for 565 NATFW NSLP in order to permit the NSIS message to reach the other end 566 host. All firewalls process NSIS signaling and establish appropriate 567 policy rules, so that the required data packet flow can traverse 568 them. 570 There are several very different ways to place firewalls in a network 571 topology. To distinguish firewalls located at network borders, such 572 as administrative domains, from others located internally, the term 573 edge-firewall is used. A similar distinction can be made for NATs, 574 with an edge-NAT fulfilling the equivalent role. 576 2.2. NAT with two private Networks 578 Figure 3 shows a scenario with NATs at both ends of the network. 579 Therefore, each application instance, the NSIS initiator and the NSIS 580 responder, are behind NATs. The outermost NAT, known as the edge-NAT 581 (MB2 and MB3), at each side is connected to the public Internet. The 582 NATs are generically labeled as MBX (for middlebox No. X), since 583 those devices certainly implement NAT functionality, but can 584 implement firewall functionality as well. 586 Only two middleboxes MB are shown in Figure 3 at each side, but in 587 general, any number of MBs on each side must be considered. 589 +----+ +----+ //----\\ +----+ +----+ 590 NI --| MB1|-----| MB2|---| |---| MB3|-----| MB4|--- NR 591 +----+ +----+ \\----// +----+ +----+ 593 private public private 595 MB: Middlebox 596 NI: NSIS Initiator 597 NR: NSIS Responder 599 Figure 3: NAT with two Private Networks Scenario 601 Signaling traffic from NI to NR has to traverse all the middleboxes 602 on the path (MB1 to MB4, in this order), and all the middleboxes must 603 be configured properly to allow NSIS signaling to traverse them. The 604 NATFW signaling must configure all middleboxes and consider any 605 address translation that will result from this configuration in 606 further signaling. The sender (NI) has to know the IP address of the 607 receiver (NR) in advance, otherwise it will not be possible to send 608 any NSIS signaling messages towards the responder. Note that this IP 609 address is not the private IP address of the responder but the NAT's 610 public IP address (here MB3's IP address). Instead a NAT binding 611 (including a public IP address) has to be previously installed on the 612 NAT MB3. This NAT binding subsequently allows packets reaching the 613 NAT to be forwarded to the receiver within the private address realm. 615 The receiver might have a number of ways to learn its public IP 616 address and port number (including the NATFW NSLP) and might need to 617 signal this information to the sender using the application level 618 signaling protocol. 620 2.3. NAT with Private Network on Sender Side 622 This scenario shows an application instance at the sending node that 623 is behind one or more NATs (shown as generic MB, see discussion in 624 Section 2.2). The receiver is located in the public Internet. 626 +----+ +----+ //----\\ 627 NI --| MB |-----| MB |---| |--- NR 628 +----+ +----+ \\----// 630 private public 632 MB: Middlebox 633 NI: NSIS Initiator 634 NR: NSIS Responder 636 Figure 4: NAT with Private Network on Sender Side 638 The traffic from NI to NR has to traverse middleboxes only on the 639 sender's side. The receiver has a public IP address. The NI sends 640 its signaling message directly to the address of the NSIS responder. 641 Middleboxes along the path intercept the signaling messages and 642 configure the a accordingly. 644 The data sender does not necessarily know whether the receiver is 645 behind a NAT or not, hence, it is the receiving side that has to 646 detect whether itself is behind a NAT or not. 648 2.4. NAT with Private Network on Receiver Side Scenario 650 The application instance receiving data is behind one or more NATs 651 shown as MB (see discussion in Section 2.2). 653 //----\\ +----+ +----+ 654 NI ---| |---| MB |-----| MB |--- NR 655 \\----// +----+ +----+ 657 public private 659 MB: Middlebox 660 NI: NSIS Initiator 661 NR: NSIS Responder 663 Figure 5: NAT with Private Network on Receiver Scenario 665 Initially, the NSIS responder must determine its publicly reachable 666 IP address at the external middlebox and notify the NSIS initiator 667 about this address. One possibility is that an application level 668 protocol is used, meaning that the public IP address is signaled via 669 this protocol to the NI. Afterwards the NI can start its signaling 670 towards the NR and therefore establish the path via the middleboxes 671 in the receiver side private network. 673 This scenario describes the use case for the EXTERNAL message of the 674 NATFW NSLP. 676 2.5. Both End Hosts behind twice-NATs 678 This is a special case, where the main problem arises from the need 679 to detect that both end hosts are logically within the same address 680 space, but are also in two partitions of the address realm on either 681 side of a twice-NAT (see [9] for a discussion of twice-NAT 682 functionality). 684 Sender and receiver are both within a single private address realm 685 but the two partitions potentially have overlapping IP address 686 ranges. Figure 6 shows the arrangement of NATs. 688 public 690 +----+ +----+ //----\\ 691 NI --| MB |--+--| MB |---| | 692 +----+ | +----+ \\----// 693 | 694 | +----+ 695 +--| MB |------------ NR 696 +----+ 698 private 700 MB: Middlebox 701 NI: NSIS Initiator 702 NR: NSIS Responder 704 Figure 6: NAT to Public, Sender and Receiver on either side of a 705 twice-NAT Scenario 707 The middleboxes shown in Figure 6 are twice-NATs, i.e., they map IP 708 addresses and port numbers on both sides, meaning the mapping of 709 source and destination address at the private and public interfaces. 711 This scenario requires the assistance of application level entities, 712 such as a DNS server. The application level entities must handle 713 requests that are based on symbolic names, and configure the 714 middleboxes so that data packets are correctly forwarded from NI to 715 NR. The configuration of those middleboxes may require other 716 middlebox communication protocols, such as MIDCOM [7]. NSIS 717 signaling is not required in the twice-NAT only case, since 718 middleboxes of the twice-NAT type are normally configured by other 719 means. Nevertheless, NSIS signaling might be useful when there are 720 also firewalls on the path. In this case NSIS will not configure any 721 policy rule at twice-NATs, but will configure policy rules at the 722 firewalls on the path. The NSIS signaling protocol must be at least 723 robust enough to survive this scenario. This requires that twice- 724 NATs must implement the NATFW NSLP also and participate in NATFW 725 signaling sessions but they do not change the configuration of the 726 NAT, i.e., they only read the address mapping information out of the 727 NAT and translate the Message Routing Information (MRI, [2]) within 728 the NSLP and NTLP accordingly. For more information see Appendix C.4 730 2.6. Both End Hosts Behind Same NAT 732 When NSIS initiator and NSIS responder are behind the same NAT (thus 733 being in the same address realm, see Figure 7), they are most likely 734 not aware of this fact. As in Section 2.4 the NSIS responder must 735 determine its public IP address in advance and transfer it to the 736 NSIS initiator. Afterwards, the NSIS initiator can start sending the 737 signaling messages to the responder's public IP address. During this 738 process, a public IP address will be allocated for the NSIS initiator 739 at the same middlebox as for the responder. Now, the NSIS signaling 740 and the subsequent data packets will traverse the NAT twice: from 741 initiator to public IP address of responder (first time) and from 742 public IP address of responder to responder (second time). 744 NI public 745 \ +----+ //----\\ 746 +-| MB |----| | 747 / +----+ \\----// 748 NR 749 private 751 MB: Middlebox 752 NI: NSIS Initiator 753 NR: NSIS Responder 755 Figure 7: NAT to Public, Both Hosts Behind Same NAT 757 2.7. Multihomed Network with NAT 759 The previous sub-sections sketched network topologies where several 760 NATs and/or firewalls are ordered sequentially on the path. This 761 section describes a multihomed scenario with two NATs placed on 762 alternative paths to the public network. 764 +----+ //---\\ 765 NI -------| MB |---| | 766 \ +----+ \\-+-// 767 \ | 768 \ +----- NR 769 \ | 770 \ +----+ //-+-\\ 771 --| MB |---| | 772 +----+ \\---// 774 private public 776 MB: Middlebox 777 NI: NSIS Initiator 778 NR: NSIS Responder 779 Figure 8: Multihomed Network with Two NATs 781 Depending on the destination, either one or the other middlebox is 782 used for the data flow. Which middlebox is used, depends on local 783 policy or routing decisions. NATFW NSLP must be able to handle this 784 situation properly, see Section 3.7.2 for an extended discussion of 785 this topic with respect to NATs. 787 2.8. Multihomed Network with Firewall 789 This section describes a multihomed scenario with two firewalls 790 placed on alternative paths to the public network (Figure 9). The 791 routing in the private and public network decides which firewall is 792 being taken for data flows. Depending on the data flow's direction, 793 either outbound or inbound, a different firewall could be traversed. 794 This is a challenge for the EXTERNAL message of the NATFW NSLP where 795 the NSIS responder is located behind these firewalls within the 796 private network. The EXTERNAL message is used to block a particular 797 data flow on an inbound firewall. NSIS must route the EXTERNAL 798 message inbound from NR to NI probably without knowing which path the 799 data traffic will take from NI to NR (see also Appendix B). 801 +----+ 802 NR -------| FW |\ 803 \ +----+ \ //---\\ 804 \ -| |-- NI 805 \ \\---// 806 \ +----+ | 807 --| FW |-------+ 808 +----+ 809 private 811 private public 813 FW: Firewall 814 NI: NSIS Initiator 815 NR: NSIS Responder 817 Figure 9: Multihomed Network with two firewalls 819 3. Protocol Description 821 This section defines messages, objects, and protocol semantics for 822 the NATFW NSLP. 824 3.1. Policy Rules 826 Policy rules, bound to a NATFW NSLP signaling session, are the 827 building blocks of middlebox devices considered in the NATFW NSLP. 828 For firewalls the policy rule usually consists of a 5-tuple and an 829 action such as allow or deny. The information contained in the tuple 830 includes source/destination addresses, transport protocol and source/ 831 destination port numbers. For NATs the policy rule consists of the 832 action 'translate this address' and further mapping information, that 833 might be, in the simplest case, internal IP address and external IP 834 address. 836 The NATFW NSLP carries, in conjunction with the NTLP's Message 837 Routing Information (MRI), the policy rules to be installed at NATFW 838 peers. This policy rule is an abstraction with respect to the real 839 policy rule to be installed at the respective firewall or NAT. It 840 conveys the initiator's request and must be mapped to the possible 841 configuration on the particular used NAT and/or firewall in use. For 842 pure firewalls one or more filter rules must be created and for pure 843 NATs one or more NAT bindings must be created. In mixed firewall and 844 NAT boxes, the policy rule must be mapped to filter rules and 845 bindings observing the ordering of the firewall and NAT engine. 846 Depending on the ordering, NAT before firewall or vice versa, the 847 firewall rules must carry public or private IP addresses. However, 848 the exact mapping depends on the implementation of the firewall or 849 NAT which is possibly different for each implementation. 851 The policy rule at the NATFW NSLP level comprises the message routing 852 information (MRI) part, carried in the NTLP, and the information 853 available in the NATFW NSLP. The information provided by the NSLP is 854 stored in the 'extend flow information' (NATFW_EFI) and 'data 855 terminal information' (NATFW_DTINFO) objects, and the message type. 856 Additional information, such as the external IP address and port 857 number, stored in the NAT or firewall, will be used as well. The MRI 858 carries the filter part of the NAT/firewall-level policy rule that is 859 to be installed. 861 The NATFW NSLP specifies two actions for the policy rules: deny and 862 allow. A policy rule with action set to deny will result in all 863 packets matching this rule to be dropped. A policy rule with action 864 set to allow will result in all packets matching this rule to be 865 forwarded. 867 3.2. Basic Protocol Overview 869 The NSIS NATFW NSLP is carried over the General Internet Signaling 870 Transport (GIST, the implementation of the NTLP) defined in [2]. 871 NATFW NSLP messages are initiated by the NSIS initiator (NI), handled 872 by NSIS forwarders (NF) and received by the NSIS responder (NR). It 873 is required that at least NI and NR implement this NSLP, intermediate 874 NFs only implement this NSLP when they provide relevant middlebox 875 functions. NSIS forwarders that do not have any NATFW NSLP functions 876 just forward these packets as they have no interest in them. 878 3.2.1. Signaling for Outbound Traffic 880 A Data Sender (DS), intending to send data to a Data Receiver (DR) 881 has to start NATFW NSLP signaling. This causes the NI associated 882 with the data sender (DS) to launch NSLP signaling towards the 883 address of data receiver (DR) (see Figure 10). Although it is 884 expected that the DS and the NATFW NSLP NI will usually reside on the 885 same host, this specification does not rule out scenarios where the 886 DS and NI reside on different hosts, the so-called proxy mode (see 887 Section 3.7.6.) 889 +-------+ +-------+ +-------+ +-------+ 890 | DS/NI |<~~~| MB1/ |<~~~| MB2/ |<~~~| DR/NR | 891 | |--->| NF1 |--->| NF2 |--->| | 892 +-------+ +-------+ +-------+ +-------+ 894 ========================================> 895 Data Traffic Direction (outbound) 897 ---> : NATFW NSLP request signaling 898 ~~~> : NATFW NSLP response signaling 899 DS/NI : Data sender and NSIS initiator 900 DR/NR : Data receiver and NSIS responder 901 MB1 : Middlebox 1 and NSIS forwarder 1 902 MB2 : Middlebox 2 and NSIS forwarder 2 904 Figure 10: General NSIS signaling 906 The following list shows the normal sequence of NSLP events without 907 detailing the interaction with the NTLP and the interactions on the 908 the NTLP level. 910 o NSIS initiators generate NATFW NSLP CREATE/EXTERNAL messages and 911 send these towards the NSIS responder. This CREATE/EXTERNAL 912 message is the initial message which creates a new NATFW NSLP 913 signaling session. The NI and the NR will most likely already 914 share an application session before they start the NATFW NSLP 915 signaling session. Note well the difference between both 916 sessions. 918 o NSLP CREATE/EXTERNAL messages are processed each time a NF with 919 NATFW NSLP support is traversed. Each NF that is intercepting a 920 CREATE/EXTERNAL message and is accepting it for further treatment 921 is joining the particular NATFW NSLP signaling session. These 922 nodes process the message, check local policies for authorization 923 and authentication, possibly create policy rules, and forward the 924 signaling message to the next NSIS node. The request message is 925 forwarded until it reaches the NSIS responder. 927 o NSIS responders will check received messages and process them if 928 applicable. NSIS responders generate RESPONSE messages and send 929 them hop-by-hop back to the NI via the same chain of NFs 930 (traversal of the same NF chain is guaranteed through the 931 established reverse message routing state in the NTLP). The NR is 932 also joining the NATFW NSLP signaling session if the CREATE/ 933 EXTERNAL message is accepted. 935 o The RESPONSE message is processed at each NF that has been 936 included in the prior NATFW NSLP signaling session setup. 938 o If the NI has received a successful RESPONSE message and if the 939 signaling NATFW NSLP session started with a CREATE message, the 940 data sender can start sending its data flow to the data receiver. 941 If the NI has received a successful RESPONSE message and if the 942 signaling NATFW NSLP session started with a EXTERNAL message, the 943 data receiver is ready to receive further CREATE messages. 945 Because NATFW NSLP signaling follows the data path from DS to DR, 946 this immediately enables communication between both hosts for 947 scenarios with only firewalls on the data path or NATs on the sender 948 side. For scenarios with NATs on the receiver side certain problems 949 arise, as described in Section 2.4. 951 3.2.2. Signaling for Inbound Traffic 953 When the NR and the NI are located in different address realms and 954 the NR is located behind a NAT, the NI cannot signal to the NR 955 address directly. The DR/NR is not reachable from other NIs using 956 the private address of the NR and thus NATFW signaling messages 957 cannot be sent to the NR/DR's address. Therefore, the NR must first 958 obtain a NAT binding that provides an address that is reachable for 959 the NI. Once the NR has acquired a public IP address, it forwards 960 this information to the DS via a separate protocol. This application 961 layer signaling, which is out of scope of the NATFW NSLP, may involve 962 third parties that assist in exchanging these messages. 964 The same holds partially true for NRs located behind firewalls that 965 block all traffic by default. In this case, NR must tell its inbound 966 firewalls of inbound NATFW NSLP signaling and corresponding data 967 traffic. Once the NR has informed the inbound firewalls, it can 968 start its application level signaling to initiate communication with 969 the NI. This mechanism can be used by machines hosting services 970 behind firewalls as well. In this case, the NR informs the inbound 971 firewalls as described, but does not need to communicate this to the 972 NIs. 974 NATFW NSLP signaling supports this scenario by using the EXTERNAL 975 message 977 1. The DR acquires a public address by signaling on the reverse path 978 (DR towards DS) and thus making itself available to other hosts. 979 This process of acquiring public addresses is called reservation. 980 During this process the DR reserves publicly reachable addresses 981 and ports suitable for further usage in application level 982 signaling and the publicly reachable address for further NATFW 983 NSLP signaling. However, the data traffic will not be allowed to 984 use this address/port initially (see next point). In the process 985 of reservation the DR becomes the NI for the messages necessary 986 to obtain the publicly reachable IP address, i.e., the NI for 987 this specific NATFW NSLP signaling session. 989 2. Now on the side of DS, the NI creates a new NATFW NSLP signaling 990 session and signals directly to the public IP address of DR. 991 This public IP address is used as NR's address, as the NI would 992 do if there is no NAT in between, and creates policy rules at 993 middleboxes. Note, that the reservation will only allow 994 forwarding of signaling messages, but not data flow packets. 995 Policy rules allowing forwarding of data flow packets set up by 996 the prior EXTERNAL message signaling will be activated when the 997 signaling from NI towards NR is confirmed with a positive 998 RESPONSE message. The EXTERNAL message is described in 999 Section 3.7.2. 1001 3.2.3. Signaling for Proxy Mode 1002 administrative domain 1003 ----------------------------------\ 1004 | 1005 +-------+ +-------+ +-------+ | +-------+ 1006 | DS/NI |<~~~| MB1/ |<~~~| MB2/ | | | DR | 1007 | |--->| NF1 |--->| NR | | | | 1008 +-------+ +-------+ +-------+ | +-------+ 1009 | 1010 ----------------------------------/ 1012 ========================================> 1013 Data Traffic Direction (outbound) 1015 ---> : NATFW NSLP request signaling 1016 ~~~> : NATFW NSLP response signaling 1017 DS/NI : Data sender and NSIS initiator 1018 DR/NR : Data receiver and NSIS responder 1019 MB1 : Middlebox 1 and NSIS forwarder 1 1020 MB2 : Middlebox 2 and NSIS responder 1022 Figure 11: proxy mode signaling for data sender 1024 The above usage assumes that both ends of a communication support 1025 NSIS, but fails when NSIS is only deployed at one end of the path. 1026 In this case only one of the sending Figure 11 or receiving Figure 12 1027 side is NSIS aware and not both at the same time. NATFW NSLP 1028 supports both scenarios (i.e., either the DS or DR do not support 1029 NSIS) by using a proxy mode, as described in Section 3.7.6 1030 administrative domain 1031 / ---------------------------------- 1032 | 1033 +-------+ | +-------+ +-------+ +-------+ 1034 | DS | | | MB2/ |~~~>| MB1/ |~~~>| DR | 1035 | | | | NR |<---| NF1 |<---| | 1036 +-------+ | +-------+ +-------+ +-------+ 1037 | 1038 \---------------------------------- 1040 ========================================> 1041 Data Traffic Direction (inbound) 1043 ---> : NATFW NSLP request signaling 1044 ~~~> : NATFW NSLP response signaling 1045 DS/NI : Data sender and NSIS initiator 1046 DR/NR : Data receiver and NSIS responder 1047 MB1 : Middlebox 1 and NSIS forwarder 1 1048 MB2 : Middlebox 2 and NSIS responder 1050 Figure 12: proxy mode signaling for data receiver 1052 3.2.4. Blocking Traffic 1054 The basic functionality of the NATFW NSLP provides for opening 1055 firewall pin holes and creating NAT bindings to enable data flows to 1056 traverse these devices. Firewalls are normally expected to work on a 1057 'deny-all' policy, meaning that traffic not explicitly matching any 1058 firewall filter rule will be blocked. Similarly, the normal behavior 1059 of NATs is to block all traffic that does not match any already 1060 configured/installed binding or NATFW NSLP session. However, some 1061 scenarios require support of firewalls having 'allow-all' policies, 1062 allowing data traffic to traverse the firewall unless it is blocked 1063 explicitly. Data receivers can utilize NATFW NSLP's EXTERNAL message 1064 with action set to 'deny' to install policy rules at inbound 1065 firewalls to block unwanted traffic. 1067 3.2.5. State and Error Maintenance 1069 The protocol works on a soft-state basis, meaning that whatever state 1070 is installed or reserved on a middlebox will expire, and thus be de- 1071 installed or forgotten after a certain period of time. To prevent 1072 premature removal of state that is needed for ongoing communication, 1073 the NATFW NI involved will have to specifically request a NATFW NSLP 1074 signaling session extension. An explicit NATFW NSLP state deletion 1075 capability is also provided by the protocol. 1077 If the actions requested by a NATFW NSLP message cannot be carried 1078 out, NFs and the NR must return a failure, such that appropriate 1079 actions can be taken. They can do this either during a the request 1080 message handling (synchronously) by sending an error RESPONSE 1081 message, or at any time (asynchronously) by sending a NOTIFY 1082 notification message. 1084 The next sections define the NATFW NSLP message types and formats, 1085 protocol operations, and policy rule operations. 1087 3.2.6. Message Types 1089 The protocol uses four messages types: 1091 o CREATE: a request message used for creating, changing, refreshing, 1092 and deleting NATFW NSLP signaling sessions, i.e., open the data 1093 path from DS to DR. 1095 o EXTERNAL: a request message used for reserving, changing, 1096 refreshing, and deleting EXTERNAL NATFW NSLP signaling sessions. 1097 EXTERNAL messages are forwarded to the edge-NAT or edge-firewall 1098 and allow inbound CREATE messages to be forwarded to the NR. 1099 Additionally, EXTERNAL messages reserve an external address and, 1100 if applicable, port number at an edge-NAT. 1102 o NOTIFY: an asynchronous message used by NATFW peers to alert other 1103 NATFW peers about specific events (especially failures). 1105 o RESPONSE: used as a response to CREATE and EXTERNAL request 1106 messages. 1108 3.2.7. Classification of RESPONSE Messages 1110 RESPONSE messages will be generated synchronously to CREATE and 1111 EXTERNAL messages by NSIS Forwarders and Responders to report success 1112 or failure of operations or some information relating to the NATFW 1113 NSLP signaling session or a node. RESPONSE messages MUST NOT be 1114 generated for any other message, such as NOTIFY and RESPONSE. 1116 All RESPONSE messages MUST carry a NATFW_INFO object which contains a 1117 severity class code and a response code (see Section 4.2.4). This 1118 section defines terms for groups of RESPONSE messages depending on 1119 the severity class. 1121 o Successful RESPONSE: Messages carrying NATFW_INFO with severity 1122 class 'Success' (0x2). 1124 o Informational RESPONSE: Messages carrying NATFW_INFO with severity 1125 class 'Informational' (0x1) (only used with NOTIFY messages). 1127 o Error RESPONSE: Messages carrying NATFW_INFO with severity class 1128 other than 'Success' or 'Informational'. 1130 3.2.8. NATFW NSLP Signaling Sessions 1132 A NATFW NSLP signaling session defines an association between the NI, 1133 NFs, and the NR related to a data flow. This association is created 1134 when the initial CREATE or EXTERNAL message is successfully received 1135 at the NFs or the NR. There is signaling NATFW NSLP session state 1136 stored at the NTLP layer and at the NATFW NSLP level. The NATFW NSLP 1137 signaling session state for the NATFW NSLP comprises NSLP state and 1138 the associated policy rules at a middlebox. 1140 The NATFW NSLP signaling session is identified by the session ID 1141 (plus other information at the NTLP level). The session ID is 1142 generated by the NI before the initial CREATE or EXTERNAL message is 1143 sent. The value of the session ID MUST generated in a random way, 1144 i.e., the output MUST NOT be easily guessable by third parties. The 1145 session ID is not stored in any NATFW NSLP message but passed on to 1146 the NTLP. 1148 A NATFW NSLP signaling session can conceptually be in different 1149 states, implementations may use other or even more states. The 1150 signaling session can have these states at a node: 1152 o Pending: The NATFW NSLP signaling session has been created and the 1153 node is waiting for a RESPONSE message to the CREATE or EXTERNAL 1154 message. A NATFW NSLP signaling session in state 'Pending' MUST 1155 be marked as 'Dead' if no corresponding RESPONSE message has been 1156 received within the time of the locally granted NATFW NSLP 1157 signaling session lifetime of the forwarded CREATE or EXTERNAL 1158 message (as described in Section 3.4). 1160 o Established: The NATFW NSLP signaling session is established, i.e, 1161 the signaling has been successfully performed and the lifetime of 1162 NATFW NSLP signaling session is counted from now on. A NATFW NSLP 1163 signaling session in state 'Established' MUST be marked as 'Dead' 1164 if no refresh message has been received within the time of the 1165 locally granted NATFW NSLP signaling session lifetime of the 1166 RESPONSE message (as described in Section 3.4). 1168 o Dead: Either the NATFW NSLP signaling session is timed out or the 1169 node has received an error RESPONSE message for the NATFW NSLP 1170 signaling session and the NATFW NSLP signaling session can be 1171 deleted. 1173 o Transit: The node has received an asynchronous message, i.e., a 1174 NOTIFY, and can delete the NATFW NSLP signaling session if needed 1175 after some time. When a node has received a NOTIFY message, it 1176 marks the signaling session as 'transit'. This signaling session 1177 SHOULD NOT be deleted before a minimum hold time of 30 second, 1178 i.e., it can be removed after 30 seconds or more. 1180 3.3. Basic Message Processing 1182 All NATFW messages are subject to some basic message processing when 1183 received at a node, independent of the message type. Initially, the 1184 syntax of the NSLP message is checked and a RESPONSE message with an 1185 appropriate error of class 'Protocol error' (0x3) code is generated 1186 if any problem is detected. If a message is delivered to the NATFW 1187 NSLP, this implies that the NTLP layer has been able to correlate it 1188 with the SID and MRI entries in its database. There is therefore 1189 enough information to identify the source of the message and routing 1190 information to route the message back to the NI through an 1191 established chain of NTLP messaging associations. The message is not 1192 further forwarded if any error in the syntax is detected. The 1193 specific response codes stemming from the processing of objects are 1194 described in the respective object definition section (see 1195 Section 4). After passing this check, the NATFW NSLP node performs 1196 authentication/authorization related checks described in Section 3.6. 1197 Further processing is executed only if these tests have been 1198 successfully passed, otherwise the processing stops and an error 1199 RESPONSE is returned. 1201 Further message processing stops whenever an error RESPONSE message 1202 is generated, and the EXTERNAL or CREATE message is discarded. 1204 3.4. Calculation of Signaling Session Lifetime 1206 NATFW NSLP signaling sessions, and the corresponding policy rules 1207 which may have been installed, are maintained via a soft-state 1208 mechanism. Each signaling session is assigned a signaling session 1209 lifetime and the signaling session is kept alive as long as the 1210 lifetime is valid. After the expiration of the signaling session 1211 lifetime, signaling sessions and policy rules MUST be removed 1212 automatically and resources bound to them MUST be freed as well. 1213 Signaling session lifetime is handled at every NATFW NSLP node. The 1214 NSLP forwarders and NSLP responder MUST NOT trigger signaling session 1215 lifetime extension refresh messages (see Section 3.7.3): this is the 1216 task of the NSIS initiator. 1218 The NSIS initiator MUST choose a NATFW NSLP signaling session 1219 lifetime value (expressed in seconds) before sending any message, 1220 including the initial message which creates the NATFW NSLP signaling 1221 session, to other NSLP nodes. The NATFW NSLP signaling session 1222 lifetime value is calculated based on: 1224 o the number of lost refresh messages that NFs should cope with; 1226 o the end-to-end delay between the NI and NR; 1228 o network vulnerability due to NATFW NSLP signaling session 1229 hijacking ([8]), NATFW NSLP signaling session hijacking is made 1230 easier when the NI does not explicitly remove the NATFW NSLP 1231 signaling session); 1233 o the user application's data exchange duration, in terms of time 1234 and networking needs. This duration is modeled as R, with R the 1235 message refresh period (in seconds); 1237 o the load on the signaling plane. Short lifetimes imply more 1238 frequent signaling messages. 1240 o the acceptable time for a NATFW NSLP signaling session to be 1241 present after it is no longer actually needed. For example, if 1242 the existence of the NATFW NSLP signaling session implies a 1243 monetary cost and teardown cannot be guaranteed, shorter lifetimes 1244 would be preferable; 1246 o the lease time of the NI's IP address. The lease time of the IP 1247 address must be larger than chosen NATFW NSLP signaling session 1248 lifetime, otherwise the IP address can be re-assigned to a 1249 different node. This node may receive unwanted traffic, although 1250 it never has requested a NAT/firewall configuration, which might 1251 be an issue in environments with mobile hosts. 1253 The RSVP specification [11] provides an appropriate algorithm for 1254 calculating the NATFW NSLP signaling session lifetime as well as 1255 means to avoid refresh message synchronization between NATFW NSLP 1256 signaling sessions. [11] recommends: 1258 1. The refresh message timer to be randomly set to a value in the 1259 range [0.5R, 1.5R]. 1261 2. To avoid premature loss of state, lt (with lt being the NATFW 1262 NSLP signaling session lifetime) must satisfy lt >= (K + 1263 0.5)*1.5*R, where K is a small integer. Then in the worst case, 1264 K-1 successive messages may be lost without state being deleted. 1265 Currently K = 3 is suggested as the default. However, it may be 1266 necessary to set a larger K value for hops with high loss rate. 1267 Other algorithms could be used to define the relation between the 1268 NATFW NSLP signaling session lifetime and the refresh message 1269 period; the algorithm provided is only given as an example. 1271 This requested NATFW NSLP signaling session lifetime value lt is 1272 stored in the NATFW_LT object of the NSLP message. 1274 NSLP forwarders and the NSLP responder can execute the following 1275 behavior with respect to the requested lifetime handling: 1277 Requested signaling session lifetime acceptable: 1279 No changes to the NATFW NSLP signaling session lifetime values are 1280 needed. The CREATE or EXTERNAL message is forwarded, if 1281 applicable. 1283 Signaling session lifetime can be lowered: 1285 An NSLP forwarded or the NSLP responder MAY also lower the 1286 requested NATFW NSLP signaling session lifetime to an acceptable 1287 value (based on its local policies). If an NF changes the NATFW 1288 NSLP signaling session lifetime value, it MUST store the new value 1289 in the NATFW_LT object. The CREATE or EXTERNAL message is 1290 forwarded. 1292 Requested signaling session lifetime is too big: 1294 An NSLP forwarded or the NSLP responder MAY reject the requested 1295 NATFW NSLP signaling session lifetime value as being too big and 1296 MUST generate an error RESPONSE message of class 'Signaling 1297 session failure' (0x6) with response code 'Requested lifetime is 1298 too big' (0x02) upon rejection. Lowering the lifetime is 1299 preferred instead of generating an error message. 1301 Requested signaling session lifetime is too small: 1303 An NSLP forwarded or the NSLP responder MAY reject the requested 1304 NATFW NSLP signaling session lifetime value as being to small and 1305 MUST generate an error RESPONSE message of class 'Signaling 1306 session failure' (0x6) with response code 'Requested lifetime is 1307 too small' (0x10) upon rejection. 1309 NFs or the NR MUST NOT increase the NATFW NSLP signaling session 1310 lifetime value. Messages can be rejected on the basis of the NATFW 1311 NSLP signaling session lifetime being too long when a NATFW NSLP 1312 signaling session is first created and also on refreshes. 1314 The NSLP responder generates a successful RESPONSE for the received 1315 CREATE or EXTERNAL message, sets the NATFW NSLP signaling session 1316 lifetime value in the NATFW_LT object to the above granted lifetime 1317 and sends the message back towards NSLP initiator. 1319 Each NSLP forwarder processes the RESPONSE message, reads and stores 1320 the granted NATFW NSLP signaling session lifetime value. The 1321 forwarders MUST accept the granted NATFW NSLP signaling session 1322 lifetime, if the lifetime value is within the acceptable range. The 1323 acceptable value refers to the value accepted by the NSLP forwarder 1324 when processing the CREATE or EXTERNAL message. For received values 1325 greater than the acceptable value, NSLP forwarders MUST generate a 1326 RESPONSE message of class 'Signaling session failure' (0x6) with 1327 response code 'Modified lifetime is too big' (0x11). For received 1328 values lower than the values acceptable by the node local policy, 1329 NSLP forwarders MUST generate a RESPONSE message of class 'Signaling 1330 session failure' (0x6) with response code 'Modified lifetime is too 1331 small' (0x12). 1333 Figure 13 shows the procedure with an example, where an initiator 1334 requests 60 seconds lifetime in the CREATE message and the lifetime 1335 is shortened along the path by the forwarder to 20 seconds and by the 1336 responder to 15 seconds. When the NSLP forwarder receives the 1337 RESPONSE message with a NATFW NSLP signaling session lifetime value 1338 of 15 seconds it checks whether this value is lower or equal to the 1339 acceptable value. 1341 +-------+ CREATE(lt=60s) +-------------+ CREATE(lt=20s) +--------+ 1342 | |---------------->| NSLP |---------------->| | 1343 | NI | | forwarder | | NR | 1344 | |<----------------| check 15<20 |<----------------| | 1345 +-------+ RESPONSE(lt=15s)+-------------+ RESPONSE(lt=15s)+--------+ 1347 lt = lifetime 1349 Figure 13: Signaling Session Lifetime Setting Example 1351 3.5. Message Sequencing 1353 NATFW NSLP messages need to carry an identifier so that all nodes 1354 along the path can distinguish messages sent at different points in 1355 time. Messages can be lost along the path or duplicated. So all 1356 NATFW NSLP nodes should be able to identify either old messages that 1357 have been received before (duplicated), or the case that messages 1358 have been lost before (loss). For message replay protection it is 1359 necessary to keep information about messages that have already been 1360 received and requires every NATFW NSLP message to carry a message 1361 sequence number (MSN), see also Section 4.2.6. 1363 The MSN MUST be set by the NI and MUST NOT be set or modified by any 1364 other node. The initial value for the MSN MUST be generated randomly 1365 and MUST be unique only within the NATFW NSLP signaling session for 1366 which it is used. The NI MUST increment the MSN by one for every 1367 message sent. Once the MSN has reached the maximum value, the next 1368 value it takes is zero. All NATFW NSLP nodes MUST use the algorithm 1369 defined in [3] to detect MSN wrap-arounds. 1371 NSIS forwarders and the responder store the MSN from the initial 1372 CREATE or EXTERNAL packet which creates the NATFW NSLP signaling 1373 session as the start value for the NATFW NSLP signaling session. NFs 1374 and NRs MUST include the received MSN value in the corresponding 1375 RESPONSE message that they generate. 1377 When receiving a CREATE or EXTERNAL message, a NATFW NSLP node uses 1378 the MSN given in the message to determine whether the state being 1379 requested is different to the state already installed. The message 1380 MUST be discarded if the received MSN value is equal to or lower than 1381 the stored MSN value. Such a received MSN value can indicate a 1382 duplicated and delayed message or replayed message. If the received 1383 MSN value is greater than the already stored MSN value, the NATFW 1384 NSLP MUST update its stored state accordingly, if permitted by all 1385 security checks (see Section 3.6), and store the updated MSN value 1386 accordingly. 1388 3.6. Authentication, Authorization, and Policy Decisions 1390 NATFW NSLP nodes receiving signaling messages MUST first check 1391 whether this message is authenticated and authorized to perform the 1392 requested action. NATFW NSLP nodes requiring more information than 1393 provided MUST generate an error RESPONSE of class 'Permanent failure' 1394 (0x5) with response code 'Authentication failed' (0x01) or with 1395 response code 'Authorization failed' (0x02). 1397 The NATFW NSLP is expected to run in various environments, such as 1398 IP-based telephone systems, enterprise networks, home networks, etc. 1399 The requirements on authentication and authorization are quite 1400 different between these use cases. While a home gateway, or an 1401 Internet cafe, using NSIS may well be happy with a "NATFW signaling 1402 coming from inside the network" policy for authorization of 1403 signaling, enterprise networks are likely to require more strongly 1404 authenticated/authorized signaling. This enterprise scenario may 1405 require the use of an infrastructure and administratively assigned 1406 identities to operate the NATFW NSLP. 1408 Once the NI is authenticated and authorized, another step is 1409 performed. The requested policy rule for the NATFW NSLP signaling 1410 session is checked against a set of policy rules, i.e., whether the 1411 requesting NI is allowed to request the policy rule to be loaded in 1412 the device. If this fails the NF or NR must send an error RESPONSE 1413 of class 'Permanent failure' (0x5) and with response code 1414 'Authorization failed' (0x02). 1416 3.7. Protocol Operations 1418 This section defines the protocol operations including, how to create 1419 NATFW NSLP signaling sessions, maintain them, delete them, and how to 1420 reserve addresses. 1422 3.7.1. Creating Signaling Sessions 1424 Allowing two hosts to exchange data even in the presence of 1425 middleboxes is realized in the NATFW NSLP by use of the CREATE 1426 message. The NI (either the data sender or a proxy) generates a 1427 CREATE message as defined in Section 4.3.1 and hands it to the NTLP. 1428 The NTLP forwards the whole message on the basis of the message 1429 routing information (MRI) towards the NR. Each NSIS forwarder along 1430 the path that implements NATFW NSLP, processes the NSLP message. 1431 Forwarding is done hop-by-hop but may pass transparently through NSIS 1432 forwarders which do not contain NATFW NSLP functionality and non-NSIS 1433 aware routers between NSLP hop way points. When the message reaches 1434 the NR, the NR can accept the request or reject it. The NR generates 1435 a response to CREATE and this response is transported hop-by-hop 1436 towards the NI. NATFW NSLP forwarders may reject requests at any 1437 time. Figure 14 sketches the message flow between NI (DS in this 1438 example), a NF (e.g., NAT), and NR (DR in this example). 1440 NI Private Network NF Public Internet NR 1441 | | | 1442 | CREATE | | 1443 |----------------------------->| | 1444 | | | 1445 | | | 1446 | | CREATE | 1447 | |--------------------------->| 1448 | | | 1449 | | RESPONSE | 1450 | RESPONSE |<---------------------------| 1451 |<-----------------------------| | 1452 | | | 1453 | | | 1455 Figure 14: CREATE message flow with success RESPONSE 1457 There are several processing rules for a NATFW peer when generating 1458 and receiving CREATE messages, since this message type is used for 1459 creating new NATFW NSLP signaling session, updating existing, 1460 extending the lifetime and deleting NATFW NSLP signaling session. 1461 The three latter functions operate in the same way for all kinds of 1462 CREATE message, and are therefore described in separate sections: 1464 o Extending the lifetime of NATFW NSLP signaling sessions is 1465 described in Section 3.7.3. 1467 o Deleting NATFW NSLP signaling sessions is described in 1468 Section 3.7.4. 1470 o Updating policy rules is described in Section 3.10. 1472 For an initial CREATE message creating a new NATFW NSLP signaling 1473 session, the processing of CREATE messages is different for every 1474 NATFW node type: 1476 o NSLP initiator: An NI only generates CREATE messages and hands 1477 them over to the NTLP. The NI should never receive CREATE 1478 messages and MUST discard it. 1480 o NATFW NSLP forwarder: NFs that are unable to forward the CREATE 1481 message to the next hop MUST generate an error RESPONSE of class 1482 'Permanent failure' (0x6) with response code 'Did not reach the 1483 NR' (0x07). This case may occur if the NTLP layer cannot find an 1484 NATFW NSLP peer, either another NF or the NR, and returns an error 1485 via the GIST API. The NSLP message processing at the NFs depends 1486 on the middlebox type: 1488 * NAT: When the initial CREATE message is received at the public 1489 side of the NAT, it looks for a reservation made in advance, by 1490 using a EXTERNAL message (see Section 3.7.2). The matching 1491 process considers the received MRI information and the stored 1492 MRI information, as described in Section 3.8. If no matching 1493 reservation can be found, i.e., no reservation has been made in 1494 advance, the NSLP MUST return an error RESPONSE of class 1495 'Signaling session failure' (0x6) with response code 'No 1496 reservation found matching the MRI of the CREATE request' 1497 (0x03). If there is a matching reservation, the NSLP stores 1498 the data sender's address (and if applicable port number) as 1499 part of the source address of the policy rule ('the remembered 1500 policy rule') to be loaded and forwards the message with the 1501 destination address set to the internal (private in most cases) 1502 address of NR. When the initial CREATE message is received at 1503 the private side, the NAT binding is allocated, but not 1504 activated (see also Appendix C.3). An error RESPONSE message 1505 is generated, if the requested policy rule cannot be installed 1506 later on, with of class 'Signaling session failure' (0x6) with 1507 response code 'Requested policy rule denied due to policy 1508 conflict' (0x4). The MRI information is updated to reflect the 1509 address, and if applicable port, translation. The NSLP message 1510 is forwarded towards the NR with source address set to the 1511 NAT's external address from the newly remembered binding. 1513 * Firewall: When the initial CREATE message is received, the NSLP 1514 just remembers the requested policy rule, but does not install 1515 any policy rule. Afterwards, the message is forwarded towards 1516 the NR. An error RESPONSE message is generated, if the 1517 requested policy rule cannot be installed later on, with of 1518 class 'Signaling session failure' (0x6) with response code 1519 'Requested policy rule denied due to policy conflict' (0x4). 1521 * Combined NAT and firewall: Processing at combined firewall and 1522 NAT middleboxes is the same as in the NAT case. No policy 1523 rules are installed. Implementations MUST take into account 1524 the order of packet processing in the firewall and NAT 1525 functions within the device. This will be referred to as 1526 'order of functions' and is generally different depending on 1527 whether the packet arrives at the external or internal side of 1528 the middlebox. 1530 o NSLP receiver: NRs receiving initial CREATE messages MUST reply 1531 with a success RESPONSE of class 'Success' (0x2) with response 1532 code set to 'All successfully processed' (0x01), if they accept 1533 the CREATE message. Otherwise they MUST generate a RESPONSE 1534 message with a suitable response code. RESPONSE messages are sent 1535 back NSLP hop-by-hop towards the NI, irrespective of the response 1536 codes, either success or error. 1538 Remembered policy rules at middleboxes MUST be only installed upon 1539 receiving a corresponding successful RESPONSE message with the same 1540 SID as the CREATE message that caused them to be remembered. This is 1541 a countermeasure to several problems, for example, wastage of 1542 resources due to loading policy rules at intermediate NFs when the 1543 CREATE message does not reach the final NR for some reason. 1545 Processing of a RESPONSE message is different for every NSIS node 1546 type: 1548 o NSLP initiator: After receiving a successful RESPONSE, the data 1549 path is configured and the DS can start sending its data to the 1550 DR. After receiving an error RESPONSE message, the NI MAY try to 1551 generate the CREATE message again or give up and report the 1552 failure to the application, depending on the error condition. 1554 o NSLP forwarder: NFs install the remembered policy rules, if a 1555 successful RESPONSE message with matching SID is received. If an 1556 ERROR RESPONSE message with matching SID is received, the NATFW 1557 NSLP session is marked as dead, no policy rule is installed and 1558 the remembered rule is discarded. 1560 o NSIS responder: The NR should never receive RESPONSE messages and 1561 MUST silently drop any such messages received. 1563 NFs and the NR can also tear down the CREATE session at any time by 1564 generating a NOTIFY message with the appropriate response code set. 1566 3.7.2. Reserving External Addresses 1568 NSIS signaling is intended to travel end-to-end, even in the presence 1569 of NATs and firewalls on-path. This works well in cases where the 1570 data sender is itself behind a NAT or a firewall as described in 1571 Section 3.7.1. For scenarios where the data receiver is located 1572 behind a NAT or a firewall and it needs to receive data flows from 1573 outside its own network (usually referred to as inbound flows, see 1574 Figure 5) the problem is more troublesome. 1576 NSIS signaling, as well as subsequent data flows, are directed to a 1577 particular destination IP address that must be known in advance and 1578 reachable. Data receivers must tell the local NSIS infrastructure 1579 (i.e., the inbound firewalls/NATs) about incoming NATFW NSLP 1580 signaling and data flows before they can receive these flows. It is 1581 necessary to differentiate between data receivers behind NATs and 1582 behind firewalls for understanding the further NATFW procedures. 1583 Data receivers that are only behind firewalls already have a public 1584 IP address and they need only to be reachable for NATFW signaling. 1585 Unlike data receivers behind just firewalls, data receivers behind 1586 NATs do not have public IP addresses; consequently they are not 1587 reachable for NATFW signaling by entities outside their addressing 1588 realm. 1590 The preceding discussion addresses the situation where a DR node that 1591 wants to be reachable is unreachable because the NAT lacks a suitable 1592 rule with the 'allow' action which would forward inbound data. 1593 However, in certain scenarios, a node situated behind inbound 1594 firewalls that do not block inbound data traffic (firewalls with 1595 "default to allow") unless requested might wish to prevent traffic 1596 being sent to it from specified addresses. In this case, NSIS NATFW 1597 signaling can be used to achieve this by installing a policy rule 1598 with its action set to 'deny' using the same mechanisms as for 1599 'allow' rules. 1601 The required result is obtained by sending a EXTERNAL message in the 1602 inbound direction of the intended data flow. When using this 1603 functionality the NSIS initiator for the 'Reserve External Address' 1604 signaling is typically the node that will become the DR for the 1605 eventual data flow. To distinguish this initiator from the usual 1606 case where the NI is associated with the DS, the NI is denoted by NI+ 1607 and the NSIS responder is similarly denoted by NR+. 1609 Public Internet Private Address 1610 Space 1612 Edge 1613 NI(DS) NAT/FW NAT NR(DR) 1614 NR+ NI+ 1616 | | | | 1617 | | | | 1618 | | | | 1619 | | EXTERNAL[(DTInfo)] | EXTERNAL[(DTInfo)] | 1620 | |<----------------------|<----------------------| 1621 | | | | 1622 | |RESPONSE[Success/Error]|RESPONSE[Success/Error]| 1623 | |---------------------->|---------------------->| 1624 | | | | 1625 | | | | 1627 ============================================================> 1628 Data Traffic Direction 1630 Figure 15: Reservation message flow for DR behind NAT or firewall 1632 Figure 15 shows the EXTERNAL message flow for enabling inbound NATFW 1633 NSLP signaling messages. In this case the roles of the different 1634 NSIS entities are: 1636 o The data receiver (DR) for the anticipated data traffic is the 1637 NSIS initiator (NI+) for the EXTERNAL message, but becomes the 1638 NSIS responder (NR) for following CREATE messages. 1640 o The actual data sender (DS) will be the NSIS initiator (NI) for 1641 later CREATE messages and may be the NSIS target of the signaling 1642 (NR+). 1644 o It may be necessary to use a signaling destination address (SDA) 1645 as the actual target of the EXTERNAL message (NR+) if the DR is 1646 located behind a NAT and the address of the DS is unknown. The 1647 SDA is an arbitrary address in the outermost address realm on the 1648 other side of the NAT from the DR. Typically this will be a 1649 suitable public IP address when the 'outside' realm is the public 1650 Internet. This choice of address causes the EXTERNAL message to 1651 be routed through the NATs towards the outermost realm and would 1652 force interception of the message by the outermost NAT in the 1653 network at the boundary between the private address and the public 1654 address realm (the edge-NAT). It may also be intercepted by other 1655 NATs and firewalls on the path to the edge-NAT. 1657 Basically, there are two different signaling scenarios. Either 1659 1. the DR behind the NAT/firewall knows the IP address of the DS in 1660 advance, 1662 2. or the address of DS is not known in advance. 1664 Case 1 requires the NATFW NSLP to request the path-coupled message 1665 routing method (PC-MRM) from the NTLP. The EXTERNAL message MUST be 1666 sent with PC-MRM (see Section 5.8.1 in [2]) with the direction set to 1667 'upstream' (inbound). The handling of case 2 depends on the 1668 situation of DR: If DR is solely located behind a firewall, the 1669 EXTERNAL message MUST be sent with the PC-MRM, direction 'upstream' 1670 (inbound), and data flow source IP address set to wildcard. If DR is 1671 located behind a NAT, the EXTERNAL message MUST be sent with the 1672 loose-end message routing method (LE-MRM, see Section 5.8.2 in [2]), 1673 the destination-address set to the signaling destination address 1674 (SDA, see also Appendix A). For scenarios with DR being behind a 1675 firewall, special conditions apply (see applicability statement in 1676 Appendix B). The data receiver is challenged to determine whether it 1677 is solely located behind firewalls or NATs, for choosing the right 1678 message routing method. This decision can depend on a local 1679 configuration parameter, possibly given through DHCP, or it could be 1680 discovered through other non-NSLP related testing of the network 1681 configuration. It is RECOMMENDED to use the PC-MRM with the known 1682 data sender's IP address. This gives GIST the best possible handled 1683 to route the message 'upstream' (outbound). It is RECOMMENDED to use 1684 the LE-MRM, if and only if the data sender's IP address is not known 1685 and the data receiver is behind a NAT. 1687 For case 2 with NAT, the NI+ (which could be on the data receiver DR 1688 or on any other host within the private network) sends the EXTERNAL 1689 message targeted to the signaling destination address. The message 1690 routing for the EXTERNAL message is in the reverse direction to the 1691 normal message routing used for path-coupled signaling where the 1692 signaling is sent outbound (as opposed to inbound in this case). 1693 When establishing NAT bindings (and an NATFW NSLP signaling session) 1694 the signaling direction does not matter since the data path is 1695 modified through route pinning due to the external IP address at the 1696 NAT. Subsequent NSIS messages (and also data traffic) will travel 1697 through the same NAT boxes. However, this is only valid for the NAT 1698 boxes, but not for any intermediate firewall. That is the reason for 1699 having a separate CREATE message enabling the reservations made with 1700 EXTERNAL at the NATs and either enabling prior reservations or 1701 creating new pinholes at the firewalls which are encountered on the 1702 outbound path depending on whether the inbound and outbound routes 1703 coincide. 1705 The EXTERNAL signaling message creates an NSIS NATFW signaling 1706 session at any intermediate NSIS NATFW peer(s) encountered, 1707 independent of the message routing method used. Furthermore, it has 1708 to be ensured that the edge-NAT or edge-firewall device is discovered 1709 as part of this process. The end host cannot be assumed to know this 1710 device - instead the NAT or firewall box itself is assumed to know 1711 that it is located at the outer perimeter of the network. Forwarding 1712 of the EXTERNAL message beyond this entity is not necessary, and MUST 1713 be prohibited as it may provide information on the capabilities of 1714 internal hosts. It should be noted, that it is the outermost NAT or 1715 firewall that is the edge-device that must be found during this 1716 discovery process. For instance, when there are a NAT and afterwards 1717 a firewall on the outbound path at the network border, the firewall 1718 is the edge-firewall. All messages must be forwarded to the 1719 topology-wise outermost edge-device, to ensure that this devices 1720 knows about the NATFW NSLP signaling sessions for incoming CREATE 1721 messages. However, the NAT is still the edge-NAT because it has a 1722 public globally routable IP address on its public side: this is not 1723 affected by any firewall between the edge-NAT and the public network. 1725 Possible edge arrangements are: 1727 Public Net ----------------- Private net -------------- 1729 | Public Net|--|Edge-FW|--|FW|...|FW|--|DR| 1731 | Public Net|--|Edge-FW|--|Edge-NAT|...|NAT or FW|--|DR| 1733 | Public Net|--|Edge-NAT|--|NAT or FW|...|NAT or FW|--|DR| 1735 The edge-NAT or edge-firewall device closest to the public realm 1736 responds to the EXTERNAL message with a successful RESPONSE message. 1737 An edge-NAT includes an NATFW_EXTERNAL-IP object (see Section 4.2.2), 1738 carrying the public reachable IP address, and if applicable port 1739 number. 1741 There are several processing rules for a NATFW peer when generating 1742 and receiving EXTERNAL messages, since this message type is used for 1743 creating new reserve NATFW NSLP signaling sessions, updating 1744 existing, extending the lifetime and deleting NATFW NSLP signaling 1745 session. The three latter functions operate in the same way for all 1746 kinds of CREATE and EXTERNAL messages, and are therefore described in 1747 separate sections: 1749 o Extending the lifetime of NATFW NSLP signaling sessions is 1750 described in Section 3.7.3. 1752 o Deleting NATFW NSLP signaling sessions is described in 1753 Section 3.7.4. 1755 o Updating policy rules is described in Section 3.10. 1757 The NI+ MUST always include a NATFW_DTINFO object in the EXTERNAL 1758 message. Especially, the LE-MRM does not include enough information 1759 for some types of NATs (basically, those NATs which also translate 1760 port numbers) to perform the address translation. This information 1761 is provided in the NATFW_DTINFO (see Section 4.2.7). This 1762 information MUST include at least the 'dst port number' and 1763 'protocol' fields, in the NATFW_DTINFO object as these may be 1764 required by en-route NATs, depending on the type of the NAT. All 1765 other fields MAY be set by the NI+ to restrict the set of possible 1766 NIs. An edge-NAT will use the information provided in the 1767 NATFW_DTINFO object to allow only NATFW CREATE message with the MRI 1768 matching ('src IPv4/v6 address', 'src port number', 'protocol') to be 1769 forwarded. A NAT requiring information carried in the NATFW_DTINFO 1770 can generate a number of error RESPONSE messages of class 'Signaling 1771 session failure' (0x6): 1773 o 'Requested policy rule denied due to policy conflict' (0x04) 1775 o 'NATFW_DTINFO object is required' (0x07) 1777 o 'Requested value in sub_ports field in NATFW_EFI not permitted' 1778 (0x08) 1780 o 'Requested IP protocol not supported' (0x09) 1782 o 'Plain IP policy rules not permitted -- need transport layer 1783 information' (0x0A) 1785 o 'source IP address range is too large' (0x0C) 1787 o 'destination IP address range is too large' (0x0D) 1789 o 'source L4-port range is too large' (0x0E) 1790 o 'destination L4-port range is too large' (0x0F) 1792 Processing of EXTERNAL messages is specific to the NSIS node type: 1794 o NSLP initiator: NI+ only generate EXTERNAL messages. When the 1795 data sender's address information is known in advance the NI+ can 1796 include a NATFW_DTINFO object in the EXTERNAL message, if not 1797 anyway required to do so (see above). When the data sender's IP 1798 address is not known, the NI+ MUST NOT include an IP address in 1799 the NATFW_DTINFO object. The NI should never receive EXTERNAL 1800 messages and MUST silently discard it. 1802 o NSLP forwarder: The NSLP message processing at NFs depends on the 1803 middlebox type: 1805 * NAT: NATs check whether the message is received at the external 1806 (public in most cases) address or at the internal (private) 1807 address. If received at the external an NF MUST generate an 1808 error RESPONSE of class 'Protocol error' (0x3) with response 1809 code 'Received EXTERNAL request message on external side' 1810 (0x0B). If received at the internal (private address) and the 1811 NATFW_EFI object contains the action 'deny', an error RESPONSE 1812 of class 'Protocol error' (0x3) with response code 'Requested 1813 rule action not applicable' (0x06) MUST be generated. If 1814 received at the internal address, an IP address, and if 1815 applicable one or more ports, are reserved. If it is an edge- 1816 NAT and there is no edge-firewall beyond, the NSLP message is 1817 not forwarded any further and a successful RESPONSE message is 1818 generated containing an NATFW_EXTERNAL-IP object holding the 1819 translated address, and if applicable port, information from 1820 the binding reserved as a result of the EXTERNAL message. The 1821 RESPONSE message is sent back towards the NI+. If it is not an 1822 edge-NAT, the NSLP message is forwarded further using the 1823 translated IP address as signaling source address in the LE-MRM 1824 and translated port in the NATFW_DTINFO object in the field 'DR 1825 port number', i.e., the NATFW_DTINFO object is updated to 1826 reflect the translated port number. The edge-NAT or any other 1827 NAT MUST reject EXTERNAL messages not carrying a NATFW_DTINFO 1828 object or if the address information within this object is 1829 invalid or is not compliant with local policies (e.g., the 1830 information provided relates to a range of addresses 1831 ('wildcarded') but the edge-NAT requires exact information 1832 about DS' IP address and port) with the above mentioned 1833 response codes. 1835 * Firewall: Non edge-firewalls remember the requested policy 1836 rule, keep NATFW NSLP signaling session state, and forward the 1837 message. Edge-firewalls stop forwarding the EXTERNAL message. 1839 The policy rule is immediately loaded if the action in the 1840 NATFW_EFI object is set to 'deny' and the node is an edge- 1841 firewall. The policy rule is remembered, but not activated, if 1842 the action in the NATFW_EFI object is set to 'allow'. In both 1843 cases, a successful RESPONSE message is generated. If the 1844 action is 'allow', and the NATFW_DTINFO object is included, and 1845 the MRM is set to LE-MRM in the request, additionally an 1846 NATFW_EXTERNAL-IP object is included in the RESPONSE message, 1847 holding the translated address, and if applicable port, 1848 information. This information is obtained from the 1849 NATFW_DTINFO object's 'DR port number' and the source-address 1850 of the LE-MRM. 1852 * Combined NAT and firewall: Processing at combined firewall and 1853 NAT middleboxes is the same as in the NAT case. 1855 o NSLP receiver: This type of message should never be received by 1856 any NR+ and it MUST generate an error RESPONSE message of class 1857 'Permanent failure' (0x5) with response code 'No edge-device here' 1858 (0x06). 1860 Processing of a RESPONSE message is different for every NSIS node 1861 type: 1863 o NSLP initiator: Upon receiving a successful RESPONSE message, the 1864 NI+ can rely on the requested configuration for future inbound 1865 NATFW NSLP signaling sessions. If the response contains an 1866 NATFW_EXTERNAL-IP object, the NI can use IP address and port pairs 1867 carried for further application signaling. After receiving a 1868 error RESPONSE message, the NI+ MAY try to generate the EXTERNAL 1869 message again or give up and report the failure to the 1870 application, depending on the error condition. 1872 o NSLP forwarder: NFs simply forward this message as long as they 1873 keep state for the requested reservation, if the RESPONSE message 1874 contains NATFW_INFO object with class set to 'Success' (0x2). If 1875 the RESPONSE message contains NATFW_INFO object with class set not 1876 to 'Success' (0x2), the NATFW NSLP signaling session is marked as 1877 dead. 1879 o NSIS responder: This type of message should never be received by 1880 any NR+. The NF should never receive response messages and MUST 1881 silently discard it. 1883 NFs and the NR can also tear down the EXTERNAL session at any time by 1884 generating a NOTIFY message with the appropriate response code set. 1886 Reservations with action 'allow' made with EXTERNAL MUST be enabled 1887 by a subsequent CREATE message. A reservation made with EXTERNAL 1888 (independent of selected action) is kept alive as long as the NI+ 1889 refreshes the particular NATFW NSLP signaling session and it can be 1890 reused for multiple, different CREATE messages. An NI+ may decide to 1891 teardown a reservation immediately after receiving a CREATE message. 1892 This implies that a new NATFW NSLP signaling session must be created 1893 for each new CREATE message. The CREATE message does not re-use the 1894 NATFW NSLP signaling session created by EXTERNAL. 1896 Without using CREATE (see Section 3.7.1) or EXTERNAL in proxy mode 1897 (see Section 3.7.6) no data traffic will be forwarded to DR beyond 1898 the edge-NAT or edge-firewall. The only function of EXTERNAL is to 1899 ensure that subsequent CREATE messages traveling towards the NR will 1900 be forwarded across the public-private boundary towards the DR. 1901 Correlation of incoming CREATE messages to EXTERNAL reservation 1902 states is described in Section 3.8. 1904 3.7.3. NATFW NSLP Signaling Session Refresh 1906 NATFW NSLP signaling sessions are maintained on a soft-state basis. 1907 After a specified timeout, sessions and corresponding policy rules 1908 are removed automatically by the middlebox, if they are not 1909 refreshed. Soft-state is created by CREATE and EXTERNAL and the 1910 maintenance of this state must be done by these messages. State 1911 created by CREATE must be maintained by CREATE, state created by 1912 EXTERNAL must be maintained by EXTERNAL. Refresh messages, are 1913 messages carrying the same session ID as the initial message and a 1914 NATFW_LT lifetime object with a lifetime greater than zero. Messages 1915 with the same SID but carrying a different MRI are treated as updates 1916 of the policy rules and are processed as defined in Section 3.10. 1917 Every refresh CREATE or EXTERNAL message MUST be acknowledged by an 1918 appropriate response message generated by the NR. Upon reception by 1919 each NSIS forwarder, the state for the given session ID is extended 1920 by the NATFW NSLP signaling session refresh period, a period of time 1921 calculated based on a proposed refresh message period. The new 1922 (extended) lifetime of a NATFW NSLP signaling session is calculated 1923 as current local time plus proposed lifetime value (NATFW NSLP 1924 signaling session refresh period). Section 3.4 defines the process 1925 of calculating lifetimes in detail. 1927 NI Public Internet NAT Private address NR 1929 | | space | 1930 | CREATE[lifetime > 0] | | 1932 |----------------------------->| | 1933 | | | 1934 | | | 1935 | | CREATE[lifetime > 0] | 1936 | |--------------------------->| 1937 | | | 1938 | | RESPONSE[Success/Error] | 1939 | RESPONSE[Success/Error] |<---------------------------| 1940 |<-----------------------------| | 1941 | | | 1942 | | | 1944 Figure 17: Successful Refresh Message Flow, CREATE as example 1946 Processing of NATFW NSLP signaling session refresh CREATE and 1947 EXTERNAL messages is different for every NSIS node type: 1949 o NSLP initiator: The NI/NI+ can generate NATFW NSLP signaling 1950 session refresh CREATE/EXTERNAL messages before the NATFW NSLP 1951 signaling session times out. The rate at which the refresh 1952 CREATE/EXTERNAL messages are sent and their relation to the NATFW 1953 NSLP signaling session state lifetime is discussed further in 1954 Section 3.4. 1956 o NSLP forwarder: Processing of this message is independent of the 1957 middlebox type and is as described in Section 3.4. 1959 o NSLP responder: NRs accepting a NATFW NSLP signaling session 1960 refresh CREATE/EXTERNAL message generate a successful RESPONSE 1961 message, including the granted lifetime value of Section 3.4 in a 1962 NATFW_LT object. 1964 3.7.4. Deleting Signaling Sessions 1966 NATFW NSLP signaling sessions can be deleted at any time. NSLP 1967 initiators can trigger this deletion by using a CREATE or EXTERNAL 1968 messages with a lifetime value set to 0, as shown in Figure 18. 1969 Whether a CREATE or EXTERNAL message type is used, depends on how the 1970 NATFW NSLP signaling session was created. 1972 NI Public Internet NAT Private address NR 1974 | | space | 1975 | CREATE[lifetime=0] | | 1976 |----------------------------->| | 1977 | | | 1978 | | CREATE[lifetime=0] | 1979 | |--------------------------->| 1980 | | | 1982 Figure 18: Delete message flow, CREATE as example 1984 NSLP nodes receiving this message delete the NATFW NSLP signaling 1985 session immediately. Policy rules associated with this particular 1986 NATFW NSLP signaling session MUST be also deleted immediately. This 1987 message is forwarded until it reaches the final NR. The CREATE/ 1988 EXTERNAL message with a lifetime value of 0, does not generate any 1989 response, neither positive nor negative, since there is no NSIS state 1990 left at the nodes along the path. 1992 NSIS initiators can use CREATE/EXTERNAL message with lifetime set to 1993 zero in an aggregated way, such that a single CREATE or EXTERNAL 1994 message is terminating multiple NATFW NSLP signaling sessions. NIs 1995 can follow this procedure if they like to aggregate NATFW NSLP 1996 signaling session deletion requests: The NI uses the CREATE or 1997 EXTERNAL message with the session ID set to zero and the MRI's 1998 source-address set to its used IP address. All other fields of the 1999 respective NATFW NSLP signaling sessions to be terminated are set as 2000 well, otherwise these fields are completely wildcarded. The NSLP 2001 message is transferred to the NTLP requesting 'explicit routing' as 2002 described in Sections 5.2.1 and 7.1.4. in [2]. 2004 The outbound NF receiving such an aggregated CREATE or EXTERNAL 2005 message MUST reject it with an error RESPONSE of class 'Permanent 2006 failure' (0x5) with response code 'Authentication failed' (0x01) if 2007 the authentication fails and with an error RESPONSE of class 2008 'Permanent failure' (0x5) with response code 'Authorization failed' 2009 (0x02) if the authorization fails. Per NATFW NSLP signaling session 2010 proof of ownership, as it is defined in this memo, is not possible 2011 anymore when using this aggregated way. However, the outbound NF can 2012 use the relationship between the information of the received CREATE 2013 or EXTERNAL message and the GIST messaging association where the 2014 request has been received. The outbound NF MUST only accept this 2015 aggregated CREATE or EXTERNAL message through already established 2016 GIST messaging associations with the NI. The outbound NF MUST NOT 2017 propagate this aggregated CREATE or EXTERNAL message but it MAY 2018 generate and forward per NATFW NSLP signaling session CREATE or 2019 EXTERNAL messages. 2021 3.7.5. Reporting Asynchronous Events 2023 NATFW NSLP forwarders and NATFW NSLP responders must have the ability 2024 to report asynchronous events to other NATFW NSLP nodes, especially 2025 to allow reporting back to the NATFW NSLP initiator. Such 2026 asynchronous events may be premature NATFW NSLP signaling session 2027 termination, changes in local policies, route change or any other 2028 reason that indicates change of the NATFW NSLP signaling session 2029 state. 2031 NFs and NRs may generate NOTIFY messages upon asynchronous events, 2032 with a NATFW_INFO object indicating the reason for event. These 2033 reasons can be carried in the NATFW_INFO object (class MUST be set to 2034 'Informational' (0x1)) within the NOTIFY message. This list shows 2035 the response codes and the associated actions to take at NFs and the 2036 NI: 2038 o 'Route change: possible route change on the outbound path' (0x01): 2039 Follow instructions in Section 3.9. This MUST be sent inbound. 2041 o 'Re-authentication required' (0x02): The NI should re-send the 2042 authentication. This MUST be sent inbound. 2044 o 'NATFW node is going down soon' (0x03): The NI and other NFs 2045 should be prepared for a service interruption at any time. This 2046 message MAY be sent inbound and outbound. 2048 o 'NATFW signaling session lifetime expired' (0x04): The NATFW 2049 signaling session has been expired and the signaling session is 2050 invalid now. NFs MUST mark the signaling session as 'Dead'. This 2051 message MAY be sent inbound and outbound. 2053 o 'NATFW signaling session terminated' (0x05): The NATFW signaling 2054 session has been terminated by any reason and the signaling 2055 session is invalid now. NFs MUST mark the signaling session as 2056 'Dead'. This message MAY be sent inbound and outbound. 2058 NOTIFY messages are always sent hop-by-hop inbound towards NI until 2059 they reach NI or outbound towards the NR as indicated in the list 2060 above. 2062 The initial processing when receiving a NOTIFY message is the same 2063 for all NATFW nodes: NATFW nodes MUST only accept NOTIFY messages 2064 through already established NTLP messaging associations. The further 2065 processing is different for each NATFW NSLP node type and depends on 2066 the events notified: 2068 o NSLP initiator: NIs analyze the notified event and behave 2069 appropriately based on the event type. NIs MUST NOT generate 2070 NOTIFY messages. 2072 o NSLP forwarder: NFs analyze the notified event and behave based on 2073 the above description per response code. NFs SHOULD generate 2074 NOTIFY messages upon asynchronous events and forward them inbound 2075 towards the NI or outbound towards the NR, depending on the 2076 received direction, i.e., inbound messages MUST be forwarded 2077 further inbound and outbound messages MUST be forwarded further 2078 outbound. NFs MUST silently discard NOTIFY messages that have 2079 been received outbound but are only allowed to be sent inbound, 2080 e.g. 'Re-authentication required' (0x02). 2082 o NSLP responder: NRs SHOULD generate NOTIFY messages upon 2083 asynchronous events including a response code based on the 2084 reported event. The NR MUST silently discard NOTIFY messages that 2085 have been received outbound but are only allowed to be sent 2086 inbound, e.g. 'Re-authentication required' (0x02), 2088 NATFW NSLP forwarders, keeping multiple NATFW NSLP signaling sessions 2089 at the same time, can experience problems when shutting down service 2090 suddenly. This sudden shutdown can be result of node local failure, 2091 for instance, due to a hardware failure. This NF generates NOTIFY 2092 messages for each of the NATFW NSLP signaling sessions and tries to 2093 send them inbound. Due to the number of NOTIFY messages to be sent, 2094 the shutdown of the node may be unnecessarily prolonged, since not 2095 all messages can be sent at the same time. This case can be 2096 described as a NOTIFY storm, if a multitude of NATFW NSLP signaling 2097 sessions is involved. 2099 To avoid the need of generating per NATFW NSLP signaling session 2100 NOTIFY messages in such a scenario described or similar cases, NFs 2101 SHOULD follow this procedure: The NF uses the NOTIFY message with the 2102 session ID in the NTLP set to zero, with the MRI completely 2103 wildcarded, using the 'explicit routing' as described in Sections 2104 5.2.1 and 7.1.4. in [2]. The inbound NF receiving this type of 2105 NOTIFY immediately regards all NATFW NSLP signaling sessions from 2106 that peer matching the MRI as void. This message will typically 2107 result in multiple NOTIFY messages at the inbound NF, i.e., the NF 2108 can generate per terminated NATFW NSLP signaling session a NOTIFY 2109 message. However, a NF MAY aggregate again the NOTIFY messages as 2110 described here. 2112 3.7.6. Proxy Mode of Operation 2114 Some migration scenarios need specialized support to cope with cases 2115 where NSIS is only deployed in same areas of the Internet. End-to- 2116 end signaling is going to fail without NSIS support at or near both 2117 data sender and data receiver terminals. A proxy mode of operation 2118 is needed. This proxy mode of operation must terminate the NATFW 2119 NSLP signaling topologically-wise as close as possible to the 2120 terminal for which it is proxying and proxy all messages. This NATFW 2121 NSLP node doing the proxying of the signaling messages becomes either 2122 the NI or the NR for the particular NATFW NSLP signaling session, 2123 depending on whether it is the DS or DR that does not support NSIS. 2124 Typically, the edge-NAT or the edge-firewall would be used to proxy 2125 NATFW NSLP messages. 2127 This proxy mode operation does not require any new CREATE or EXTERNAL 2128 message type, but relies on extended CREATE and EXTERNAL message 2129 types. They are called respectively CREATE-PROXY and EXTERNAL-PROXY 2130 and are distinguished by setting the P flag in the NSLP header to 2131 P=1. This flag instructs edge-NATs and edge-firewalls receiving them 2132 to operate in proxy mode for the NATFW NSLP signaling session in 2133 question. The semantics of the CREATE and EXTERNAL message types are 2134 not changed and the behavior of the various node types is as defined 2135 in Section 3.7.1 and Section 3.7.2, except for the proxying node. 2136 The following paragraphs describe the proxy mode operation for data 2137 receivers behind middleboxes and data senders behind middleboxes. 2139 3.7.6.1. Proxying for a Data Sender 2141 The NATFW NSLP gives the NR the ability to install state on the 2142 inbound path towards the data sender for outbound data packets, even 2143 when only the receiving side is running NSIS (as shown in Figure 19). 2144 The goal of the method described is to trigger the edge-NAT/ 2145 edge-firewall to generate a CREATE message on behalf of the data 2146 receiver. In this case, an NR can signal towards the network border 2147 as it is performed in the standard EXTERNAL message handling scenario 2148 as in Section 3.7.2. The message is forwarded until the edge-NAT/ 2149 edge-firewall is reached. A public IP address and port number is 2150 reserved at an edge-NAT/edge-firewall. As shown in Figure 19, unlike 2151 the standard EXTERNAL message handling case, the edge-NAT/ 2152 edge-firewall is triggered to send a CREATE message on a new reverse 2153 path which traverse several firewalls or NATs. The new reverse path 2154 for CREATE is necessary to handle routing asymmetries between the 2155 edge-NAT/edge-firewall and DR. It must be stressed that the 2156 semantics of the CREATE and EXTERNAL messages is not changed, i.e., 2157 each is processed as described earlier. 2159 DS Public Internet NAT/FW Private address DR 2160 No NI NF space NR 2161 NR+ NI+ 2163 | | EXTERNAL-PROXY[(DTInfo)] | 2164 | |<------------------------- | 2165 | | RESPONSE[Error/Success] | 2166 | | ---------------------- > | 2167 | | CREATE | 2168 | | ------------------------> | 2169 | | RESPONSE[Error/Success] | 2170 | | <---------------------- | 2171 | | | 2173 Figure 19: EXTERNAL Triggering Sending of CREATE Message 2175 A NATFW_NONCE object, carried in the EXTERNAL and CREATE message, is 2176 used to build the relationship between received CREATEs at the 2177 message initiator. An NI+ uses the presence of the NATFW_NONCE 2178 object to correlate it to the particular EXTERNAL-PROXY. The absence 2179 of a NONCE object indicates a CREATE initiated by the DS and not by 2180 the edge-NAT. The two signaling sessions, i.e., the session for 2181 EXTERNAL-PROXY and the session for CREATE, are not independent. The 2182 primary session is the EXTERNAL-PROXY session. The CREATE session is 2183 secondary to the EXTERNAL-PROXY session, i.e., the CREATE session is 2184 valid as long as the EXTERNAL-PROXY session is the signaling states 2185 'Established' or 'Transit'. There is no CREATE session in any other 2186 signaling state of the EXTERNAL-PROXY, i.e., 'pending' or 'dead'. 2187 This ensures a faith-sharing between both signaling sessions. 2189 These processing rules of EXTERNAL-PROXY messages are added to the 2190 regular EXTERNAL processing: 2192 o NSLP initiator (NI+): The NI+ MUST take the session ID (SID) value 2193 of the EXTERNAL-PROXY session as the nonce value of the 2194 NATFW_NONCE object. 2196 o NSLP forwarder being either edge-NAT or edge-firewall: When the NF 2197 accepts a EXTERNAL-PROXY message, it generates a successful 2198 RESPONSE message as if it were the NR and additionally, it 2199 generates a CREATE message as defined in Section 3.7.1 and 2200 includes a NATFW_NONCE object having the same value as of the 2201 received NATFW_NONCE object. The NF MUST NOT generate a CREATE- 2202 PROXY message. The NF MUST refresh the CREATE message signaling 2203 session only if a EXTERNAL-PROXY refresh message has been received 2204 first. This also includes tearing down signaling sessions, i.e., 2205 the NF must teardown the CREATE signaling session only if a 2206 EXTERNAL-PROXY message with lifetime set to 0 has been received 2207 first. 2209 The scenario described in this section challenges the data receiver 2210 because it must make a correct assumption about the data sender's 2211 ability to use NSIS NATFW NSLP signaling. It is possible for the DR 2212 to make the wrong assumption in two different ways: 2214 a) the DS is NSIS unaware but the DR assumes the DS to be NSIS 2215 aware and 2217 b) the DS is NSIS aware but the DR assumes the DS to be NSIS 2218 unaware. 2220 Case a) will result in middleboxes blocking the data traffic, since 2221 DS will never send the expected CREATE message. Case b) will result 2222 in the DR successfully requesting proxy mode support by the edge-NAT 2223 or edge-firewall. The edge-NAT/edge-firewall will send CREATE 2224 messages and DS will send CREATE messages as well. Both CREATE 2225 messages are handled as separated NATFW NSLP signaling sessions and 2226 therefore the common rules per NATFW NSLP signaling session apply; 2227 the NATFW_NONCE object is used to differentiate CREATE messages 2228 generated by the edge-NAT/edge-firewall from NI initiated CREATE 2229 messages. It is the NR's responsibility to decide whether to 2230 teardown the EXTERNAL-PROXY signaling sessions in the case where the 2231 data sender's side is NSIS aware, but was incorrectly assumed not to 2232 be so by the DR. It is RECOMMENDED that a DR behind NATs uses the 2233 proxy mode of operation by default, unless the DR knows that the DS 2234 is NSIS aware. The DR MAY cache information about data senders which 2235 it has found to be NSIS aware in past NATFW NSLP signaling sessions. 2237 There is a possible race condition between the RESPONSE message to 2238 the EXTERNAL-PROXY and the CREATE message generated by the edge-NAT. 2239 The CREATE message can arrive earlier than the RESPONSE message. An 2240 NI+ MUST accept CREATE messages generated by the edge-NAT even if the 2241 RESPONSE message to the EXTERNAL-PROXY was not received. 2243 3.7.6.2. Proxying for a Data Receiver 2245 As with data receivers behind middleboxes, data senders behind 2246 middleboxes can require proxy mode support. The issue here is that 2247 there is no NSIS support at the data receiver's side and, by default, 2248 there will be no response to CREATE messages. This scenario requires 2249 the last NSIS NATFW NSLP aware node to terminate the forwarding and 2250 to proxy the response to the CREATE message, meaning that this node 2251 is generating RESPONSE messages. This last node may be an edge-NAT/ 2252 edge-firewall, or any other NATFW NSLP peer, that detects that there 2253 is no NR available (probably as a result of GIST timeouts but there 2254 may be other triggers). 2256 DS Private Address NAT/FW Public Internet NR 2257 NI Space NF no NR 2259 | | | 2260 | CREATE-PROXY | | 2261 |------------------------------>| | 2262 | | | 2263 | RESPONSE[SUCCESS/ERROR] | | 2264 |<------------------------------| | 2265 | | | 2267 Figure 20: Proxy Mode CREATE Message Flow 2269 The processing of CREATE-PROXY messages and RESPONSE messages is 2270 similar to Section 3.7.1, except that forwarding is stopped at the 2271 edge-NAT/edge-firewall. The edge-NAT/edge-firewall responds back to 2272 NI according to the situation (error/success) and will be the NR for 2273 future NATFW NSLP communication. 2275 The NI can choose the proxy mode of operation although the DR is NSIS 2276 aware. The CREATE-PROXY mode would not configure all NATs and 2277 firewalls along the data path, since it is terminated at the edge- 2278 device. Any device beyond this point will never receive any NATFW 2279 NSLP signaling for this flow. 2281 3.8. De-Multiplexing at NATs 2283 Section 3.7.2 describes how NSIS nodes behind NATs can obtain a 2284 public reachable IP address and port number at a NAT and and how the 2285 resulting mapping rule can be activated by using CREATE messages (see 2286 Section 3.7.1). The information about the public IP address/port 2287 number can be transmitted via an application level signaling protocol 2288 and/or third party to the communication partner that would like to 2289 send data toward the host behind the NAT. However, NSIS signaling 2290 flows are sent towards the address of the NAT at which this 2291 particular IP address and port number is allocated and not directly 2292 to the allocated IP address and port number. The NATFW NSLP 2293 forwarder at this NAT needs to know how the incoming NSLP CREATE 2294 messages are related to reserved addresses, meaning how to de- 2295 multiplex incoming NSIS CREATE messages. 2297 The de-multiplexing method uses information stored at the local NATFW 2298 NSLP node and in the policy rule. The policy rule uses the LE-MRM 2299 MRI source-address (see [2]) as the flow destination IP address and 2300 the network-layer-version as IP version. The external IP address at 2301 the NAT is stored as the external flow destination IP address. All 2302 other parameters of the policy rule other than the flow destination 2303 IP address are wildcarded if no NATFW_DTINFO object is included in 2304 the EXTERNAL message. The LE-MRM MRI destination-address MUST NOT be 2305 used in the policy rule, since it is solely a signaling destination 2306 address. 2308 If the NATFW_DTINFO object is included in the EXTERNAL message, the 2309 policy rule is filled with further information. The 'dst port 2310 number' field of the NATFW_DTINFO is stored as the flow destination 2311 port number. The 'protocol' field is stored as the flow protocol. 2312 The 'src port number' field is stored as the flow source port number. 2313 The 'data sender's IPv4 address' is stored as the flow source IP 2314 address. Note that some of these field can contain wildcards. 2316 When receiving a CREATE message at the NATFW NSLP it uses the flow 2317 information stored in the MRI to do the matching process. This table 2318 shows the parameters to be compared against each others. Note that 2319 not all parameters can be present in a MRI at the same time. 2321 +-------------------------------+--------------------------------+ 2322 | Flow parameter (Policy Rule) | MRI parameter (CREATE message) | 2323 +-------------------------------+--------------------------------+ 2324 | IP version | network-layer-version | 2325 | | | 2326 | Protocol | IP-protocol | 2327 | | | 2328 | source IP address (w) | source-address (w) | 2329 | | | 2330 | external IP address | destination-address | 2331 | | | 2332 | destination IP address (n/u) | N/A | 2333 | | | 2334 | source port number (w) | L4-source-port (w) | 2335 | | | 2336 | external port number (w) | L4-destination-port (w) | 2337 | | | 2338 | destination port number (n/u) | N/A | 2339 | | | 2340 | IPsec-SPI | ipsec-SPI | 2341 +-------------------------------+--------------------------------+ 2343 Table entries marked with (w) can be wildcarded and entries marked 2344 with (n/u) are not used for the matching. 2346 Table 1 2348 3.9. Reacting to Route Changes 2350 The NATFW NSLP needs to react to route changes in the data path. 2351 This assumes the capability to detect route changes, to perform NAT 2352 and firewall configuration on the new path and possibly to tear down 2353 NATFW NSLP signaling session state on the old path. The detection of 2354 route changes is described in Section 7 of [2] and the NATFW NSLP 2355 relies on notifications about route changes by the NTLP. This 2356 notification will be conveyed by the API between NTLP and NSLP, which 2357 is out of scope of this memo. 2359 A NATFW NSLP node other than the NI or NI+ detecting a route change, 2360 by means described in the NTLP specification or others, generates a 2361 NOTIFY message indicating this change and sends this inbound towards 2362 NI. Intermediate NFs on the way to the NI can use this information 2363 to decide later if their NATFW NSLP signaling session can be deleted 2364 locally, if they do not receive an update within a certain time 2365 period, as described in Section 3.2.8. It is important to consider 2366 the transport limitations of NOTIFY messages as mandated in 2367 Section 3.7.5. 2369 The NI receiving this NOTIFY message MAY generate a new CREATE or 2370 EXTERNAL message and send it towards the NATFW NSLP signaling 2371 session's NI as for the initial message using the same session ID. 2372 All the remaining processing and message forwarding, such as NSLP 2373 next hop discovery, is subject to regular NSLP processing as 2374 described in the particular sections. Normal routing will guide the 2375 new CREATE or EXTERNAL message to the correct NFs along the changed 2376 route. NFs that were on the original path receiving these new CREATE 2377 or EXTERNAL messages (see also Section 3.10), can use the session ID 2378 to update the existing NATFW NSLP signaling session, whereas NFs that 2379 were not on the original path will create new state for this NATFW 2380 NSLP signaling session. The next section describes how policy rules 2381 are updated. 2383 3.10. Updating Policy Rules 2385 NSIS initiators can request an update of the installed/reserved 2386 policy rules at any time within a NATFW NSLP signaling session. 2387 Updates to policy rules can be required due to node mobility (NI is 2388 moving from one IP address to another), route changes (this can 2389 result in a different NAT mapping at a different NAT device), or the 2390 wish of the NI to simply change the rule. NIs can update policy 2391 rules in existing NATFW NSLP signaling sessions by sending an 2392 appropriate CREATE or EXTERNAL message (similar to Section 3.4) with 2393 modified message routing information (MRI) as compared with that 2394 installed previously, but using the existing session ID to identify 2395 the intended target of the update. With respect to authorization and 2396 authentication, this update CREATE or EXTERNAL message is treated in 2397 exactly the same way as any initial message. Therefore, any node 2398 along in the NATFW NSLP signaling session can reject the update with 2399 an error RESPONSE message, as defined in the previous sections. 2401 The message processing and forwarding is executed as defined in the 2402 particular sections. A NF or the NR receiving an update, simply 2403 replaces the installed policy rules installed in the firewall/NAT. 2404 The local procedures on how to update the MRI in the firewall/NAT is 2405 out of scope of this memo. 2407 4. NATFW NSLP Message Components 2409 A NATFW NSLP message consists of a NSLP header and one or more 2410 objects following the header. The NSLP header is carried in all 2411 NATFW NSLP messages and objects are Type-Length-Value (TLV) encoded 2412 using big endian (network ordered) binary data representations. 2413 Header and objects are aligned to 32 bit boundaries and object 2414 lengths that are not multiples of 32 bits must be padded to the next 2415 higher 32 bit multiple. 2417 The whole NSLP message is carried as payload of a NTLP message. 2419 Note that the notation 0x is used to indicate hexadecimal numbers. 2421 4.1. NSLP Header 2423 All GIST NSLP-Data objects for the NATFW NSLP MUST contain this 2424 common header as the first 32 bits of the object (this is not the 2425 same as the GIST Common Header). It contains two fields, the NSLP 2426 message type and a reserved field. The total length is 32 bits. The 2427 layout of the NSLP header is defined by Figure 21. 2429 0 1 2 3 2430 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2432 | Message type |P| reserved | reserved | 2433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2435 Figure 21: Common NSLP header 2437 The reserved field MUST be set to zero in the NATFW NSLP header 2438 before sending and MUST be ignored during processing of the header. 2440 The defined messages types are: 2442 o IANA-TBD(1) : CREATE 2444 o IANA-TBD(2) : EXTERNAL 2446 o IANA-TBD(3) : RESPONSE 2448 o IANA-TBD(4) : NOTIFY 2450 If a message with another type is received, an error RESPONSE of 2451 class 'Protocol error' (0x3) with response code 'Illegal message 2452 type' (0x01) MUST be generated. 2454 The P flag indicates the usage of proxy mode. If proxy mode is used 2455 it MUST be set to 1. Proxy mode usage MUST only be used in 2456 combination with the message types CREATE and EXTERNAL. The P flag 2457 MUST be ignored when processing messages with type RESPONSE or 2458 NOTIFY. 2460 4.2. NSLP Objects 2462 NATFW NSLP objects use a common header format defined by Figure 22. 2463 The object header contains two fields, the NSLP object type and the 2464 object length. Its total length is 32 bits. 2466 0 1 2 3 2467 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2468 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2469 |A|B|r|r| Object Type |r|r|r|r| Object Length | 2470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2472 Figure 22: Common NSLP object header 2474 The object length field contains the total length of the object 2475 without the object header. The unit is a word, consisting of 4 2476 octets. The particular values of type and length for each NSLP 2477 object are listed in the subsequent sections that define the NSLP 2478 objects. An error RESPONSE of class 'Protocol error' (0x3) with 2479 response code 'Wrong object length' (0x07) MUST be generated if the 2480 length given for the object in the object header did not match the 2481 length of the object data present. The two leading bits of the NSLP 2482 object header are used to signal the desired treatment for objects 2483 whose treatment has not been defined in this memo (see [2], Section 2484 A.2.1), i.e., the Object Type has not been defined. NATFW NSLP uses 2485 a subset of the categories defined in GIST: 2487 o AB=00 ("Mandatory"): If the object is not understood, the entire 2488 message containing it MUST be rejected with an error RESPONSE of 2489 class 'Protocol error' (0x3) with response code 'Unknown object 2490 present' (0x06). 2492 o AB=01 ("Optional"): If the object is not understood, it should be 2493 deleted and then the rest of the message processed as usual. 2495 o AB=10 ("Forward"): If the object is not understood, it should be 2496 retained unchanged in any message forwarded as a result of message 2497 processing, but not stored locally. 2499 The combination AB=11 MUST NOT be used and an error RESPONSE of class 2500 'Protocol error' (0x3) with response code 'Invalid Flag-Field 2501 combination' (0x09) MUST be generated. 2503 The following sections do not repeat the common NSLP object header, 2504 they just list the type and the length. 2506 4.2.1. Signaling Session Lifetime Object 2508 The signaling session lifetime object carries the requested or 2509 granted lifetime of a NATFW NSLP signaling session measured in 2510 seconds. 2512 Type: NATFW_LT (IANA-TBD) 2514 Length: 1 2516 0 1 2 3 2517 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2518 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2519 | NATFW NSLP signaling session lifetime | 2520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2522 Figure 23: Signaling Session Lifetime object 2524 4.2.2. External Address Object 2526 The external address object can be included in RESPONSE messages 2527 (Section 4.3.3) only. It carries the publicly reachable IP address, 2528 and if applicable port number, at an edge-NAT. 2530 Type: NATFW_EXTERNAL-IP (IANA-TBD) 2532 Length: 2 2534 0 1 2 3 2535 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2537 | port number | reserved | 2538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2539 | IPv4 address | 2540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2542 Figure 24: External Address Object for IPv4 addresses 2544 Please note that the field 'port number' MUST be set to 0 if only an 2545 IP address has been reserved, for instance, by a traditional NAT. A 2546 port number of 0 MUST be ignored in processing this object. 2548 4.2.3. Extended Flow Information Object 2550 In general, flow information is kept in the message routing 2551 information (MRI) of the NTLP. Nevertheless, some additional 2552 information may be required for NSLP operations. The 'extended flow 2553 information' object carries this additional information about the 2554 action of the policy rule for firewalls/NATs and contiguous port . 2556 Type: NATFW_EFI (IANA-TBD) 2558 Length: 1 2560 0 1 2 3 2561 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2563 | rule action | sub_ports | 2564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2566 Figure 25: Extended Flow Information 2568 This object has two fields, 'rule action' and 'sub_ports'. The 'rule 2569 action' field has these meanings: 2571 o 0x0001: Allow: A policy rule with this action allows data traffic 2572 to traverse the middlebox and the NATFW NSLP MUST allow NSLP 2573 signaling to be forwarded. 2575 o 0x0002: Deny: A policy rule with this action blocks data traffic 2576 from traversing the middlebox and the NATFW NSLP MUST NOT allow 2577 NSLP signaling to be forwarded. 2579 If the 'rule action' field contains neither 0x0001 nor 0x0002, an 2580 error RESPONSE of class 'Signaling session failure' (0x6) with 2581 response code 'Unknown policy rule action' (0x05) MUST be generated. 2583 The 'sub_ports' field contains the number of contiguous transport 2584 layer ports to which this rule applies. The default value of this 2585 field is 0, i.e., only the port specified in the NTLP's MRM or 2586 NATFW_DTINFO object is used for the policy rule. A value of 1 2587 indicates that additionally to the port specified in the NTLP's MRM 2588 (port1), a second port (port2) is used. This value of port 2 is 2589 calculated as: port2 = port1 + 1. Other values than 0 or 1 MUST NOT 2590 be used in this field and an error RESPONSE of class 'Signaling 2591 session failure' (0x6) with response code 'Requested value in 2592 sub_ports field in NATFW_EFI not permitted' (0x08) MUST be generated. 2593 This two contiguous port numbered ports, can be used by legacy voice 2594 over IP equipment. This legacy equipment assumes that two adjacent 2595 port numbers for its RTP/RTCP flows respectively. 2597 4.2.4. Information Code Object 2599 This object carries the response code, which may be indications for 2600 either a successful or failed CREATE or EXTERNAL message depending on 2601 the value of the 'response code' field. 2603 Type: NATFW_INFO (IANA-TBD) 2605 Length: 1 2607 0 1 2 3 2608 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2609 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2610 | Resv. | Class | Response Code |r|r|r|r| Object Type | 2611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2613 Figure 26: Information Code Object 2615 The field 'resv.' is reserved for future extensions and MUST be set 2616 to zero when generating such an object and MUST be ignored when 2617 receiving. The 'Object Type' field contains the type of the object 2618 causing the error. The value of 'Object Type' is set to 0, if no 2619 object is concerned. The leading fours bits marked with 'r' are 2620 always set to zero and ignored. The 4 bit class field contains the 2621 severity class. The following classes are defined: 2623 o 0x1: Informational (NOTIFY only) 2625 o 0x2: Success 2627 o 0x3: Protocol error 2629 o 0x4: Transient failure 2631 o 0x5: Permanent failure 2633 o 0x6: Signaling session failure 2635 Within each severity class a number of responses values are defined 2637 o Informational: 2639 * 0x01: Route change: possible route change on the outbound path. 2641 * 0x02: Re-authentication required. 2643 * 0x03: NATFW node is going down soon. 2645 * 0x04: NATFW signaling session lifetime expired. 2647 * 0x05: NATFW signaling session terminated. 2649 o Success: 2651 * 0x01: All successfully processed. 2653 o Protocol error: 2655 * 0x01: Illegal message type: the type given in the Message Type 2656 field of the NSLP header is unknown. 2658 * 0x02: Wrong message length: the length given for the message in 2659 the NSLP header does not match the length of the message data. 2661 * 0x03: Bad flags value: an undefined flag or combination of 2662 flags was set in the NSLP header. 2664 * 0x04: Mandatory object missing: an object required in a message 2665 of this type was missing. 2667 * 0x05: Illegal object present: an object was present which must 2668 not be used in a message of this type. 2670 * 0x06: Unknown object present: an object of an unknown type was 2671 present in the message. 2673 * 0x07: Wrong object length: the length given for the object in 2674 the object header did not match the length of the object data 2675 present. 2677 * 0x08: Unknown object field value: a field in an object had an 2678 unknown value. 2680 * 0x09: Invalid Flag-Field combination: An object contains an 2681 invalid combination of flags and/or fields. 2683 * 0x0A: Duplicate object present. 2685 * 0x0B: Received EXTERNAL request message on external side. 2687 o Transient failure: 2689 * 0x01: Requested resources temporarily not available. 2691 o Permanent failure: 2693 * 0x01: Authentication failed. 2695 * 0x02: Authorization failed. 2697 * 0x04: Internal or system error. 2699 * 0x06: No edge-device here. 2701 * 0x07: Did not reach the NR. 2703 o Signaling session failure: 2705 * 0x01: Session terminated asynchronously. 2707 * 0x02: Requested lifetime is too big. 2709 * 0x03: No reservation found matching the MRI of the CREATE 2710 request. 2712 * 0x04: Requested policy rule denied due to policy conflict. 2714 * 0x05: Unknown policy rule action. 2716 * 0x06: Requested rule action not applicable. 2718 * 0x07: NATFW_DTINFO object is required. 2720 * 0x08: Requested value in sub_ports field in NATFW_EFI not 2721 permitted. 2723 * 0x09: Requested IP protocol not supported. 2725 * 0x0A: Plain IP policy rules not permitted -- need transport 2726 layer information. 2728 * 0x0B: ICMP type value not permitted. 2730 * 0x0C: source IP address range is too large. 2732 * 0x0D: destination IP address range is too large. 2734 * 0x0E: source L4-port range is too large. 2736 * 0x0F: destination L4-port range is too large. 2738 * 0x10: Requested lifetime is too small. 2740 * 0x11: Modified lifetime is too big. 2742 * 0x12: Modified lifetime is too small. 2744 4.2.5. Nonce Object 2746 This object carries the nonce value as described in Section 3.7.6. 2748 Type: NATFW_NONCE (IANA-TBD) 2750 Length: 1 2752 0 1 2 3 2753 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2754 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2755 | nonce | 2756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2758 Figure 27: Nonce Object 2760 4.2.6. Message Sequence Number Object 2762 This object carries the MSN value as described in Section 3.5. 2764 Type: NATFW_MSN (IANA-TBD) 2766 Length: 1 2768 0 1 2 3 2769 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2770 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2771 | message sequence number | 2772 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2774 Figure 28: Message Sequence Number Object 2776 4.2.7. Data Terminal Information Object 2778 The 'data terminal information' object carries additional information 2779 possibly needed during EXTERNAL operations. EXTERNAL messages are 2780 transported by the NTLP using the Loose-End message routing method 2781 (LE-MRM). The LE-MRM contains only DR's IP address and a signaling 2782 destination address (destination address). This destination address 2783 is used for message routing only and is not necessarily reflecting 2784 the address of the data sender. This object contains information 2785 about (if applicable) DR's port number (the destination port number), 2786 DS' port number (the source port number), the used transport 2787 protocol, the prefix length of the IP address, and DS' IP address. 2789 Type: NATFW_DTINFO (IANA-TBD) 2791 Length: variable. Maximum 3. 2793 0 1 2 3 2794 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2796 |I|P|S| reserved | sender prefix | protocol | 2797 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2798 : DR port number | DS port number : 2799 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2800 : IPsec-SPI : 2801 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2802 | data sender's IPv4 address | 2803 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2805 Figure 29: Data Terminal IPv4 Address Object 2807 The flags are: 2809 o I: I=1 means that 'protocol' should be interpreted. 2811 o P: P=1 means that 'dst port number' and 'src port number' are 2812 present and should be interpreted. 2814 o S: S=1 means that SPI is present and should be interpreted. 2816 The SPI field is only present if S is set. The port numbers are only 2817 present if P is set. The flags P and S MUST NOT be set at the same 2818 time. An error RESPONSE of class 'Protocol error' (0x3) with 2819 response code 'Invalid Flag-Field combination' (0x09) MUST be 2820 generated if they are both set. If either P or S is set, I MUST be 2821 set as well and the protocol field MUST carry the particular 2822 protocol. An error RESPONSE of class 'Protocol error' (0x3) with 2823 response code 'Invalid Flag-Field combination' (0x09) MUST be 2824 generated if S or P is set but I is not set. 2826 The fields MUST be interpreted according to these rules: 2828 o (data) sender prefix: This parameter indicates the prefix length 2829 of the 'data sender's IP address' in bits. For instance, a full 2830 IPv4 address requires 'sender prefix' to be set to 32. A value of 2831 0 indicates an IP address wildcard. 2833 o protocol: The IP protocol field. This field MUST be interpreted 2834 if I=1, otherwise it MUST be set to 0 and MUST be ignored. 2836 o DR port number: The port number at the data receiver (DR), i.e., 2837 the destination port. A value of 0 indicates a port wildcard, 2838 i.e., the destination port number is not known. Any other value 2839 indicates the destination port number. 2841 o DS port number: The port number at the data sender (DS), i.e., the 2842 source port. A value of 0 indicates a port wildcard, i.e., the 2843 source port number is not known. Any other value indicates the 2844 source port number. 2846 o data sender's IPv4 address: The source IP address of the data 2847 sender. This field MUST be set to zero if no IP address is 2848 provided, i.e., a complete wildcard is desired (see dest prefix 2849 field above). 2851 4.2.8. ICMP Types Object 2853 The 'ICMP types' object contains additional information needed to 2854 configure a NAT of firewall with rules to control ICMP traffic. The 2855 object contains a number of values of the ICMP Type field for which a 2856 filter action should be set up: 2858 Type: NATFW_ICMP_TYPES (IANA-TBD) 2860 Length: Variable = ((Number of Types carried + 1) + 3) DIV 4 2862 Where DIV is an integer division. 2864 0 1 2 3 2865 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2867 | Count | Type | Type | ........ | 2868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2869 | ................ | 2870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2871 | ........ | Type | (Padding) | 2872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2874 Figure 30: ICMP Types Object 2876 The fields MUST be interpreted according to these rules: 2878 count: 8 bit integer specifying the number of 'Type' entries in 2879 the object. 2881 type: 8 bit field specifying an ICMP Type value to which this rule 2882 applies. 2884 padding: Sufficient 0 bits to pad out the last word so that the 2885 total size of object is an even multiple of words. Ignored on 2886 reception. 2888 4.3. Message Formats 2890 This section defines the content of each NATFW NSLP message type. 2891 The message types are defined in Section 4.1. 2893 Basically, each message is constructed of NSLP header and one or more 2894 NSLP objects. The order of objects is not defined, meaning that 2895 objects may occur in any sequence. Objects are marked either with 2896 mandatory (M) or optional (O). Where (M) implies that this 2897 particular object MUST be included within the message and where (O) 2898 implies that this particular object is OPTIONAL within the message. 2899 Objects defined in this memo always carry the flag combination AB=00 2900 in the NSLP object header. An error RESPONSE message of class 2901 'Protocol error' (0x3) with response code 'Mandatory object missing' 2902 (0x04) MUST be generated if a mandatory declared object is missing. 2903 An error RESPONSE message of class 'Protocol error' (0x3) with 2904 response code 'Illegal object present' (0x05) MUST be generated if an 2905 object was present which must not be used in a message of this type. 2906 An error RESPONSE message of class 'Protocol error' (0x3) with 2907 response code 'Duplicate object present' (0x0A) MUST be generated if 2908 an object appears more than once in a message. 2910 Each section elaborates the required settings and parameters to be 2911 set by the NSLP for the NTLP, for instance, how the message routing 2912 information is set. 2914 4.3.1. CREATE 2916 The CREATE message is used to create NATFW NSLP signaling sessions 2917 and to create policy rules. Furthermore, CREATE messages are used to 2918 refresh NATFW NSLP signaling sessions and to delete them. 2920 The CREATE message carries these objects: 2922 o Signaling Session Lifetime object (M) 2924 o Extended flow information object (M) 2926 o Message sequence number object (M) 2928 o Nonce object (M) if P flag set to 1 in the NSLP header, otherwise 2929 (O) 2931 o ICMP Types Object (O) 2933 The message routing information in the NTLP MUST be set to DS as 2934 source address and DR as destination address. All other parameters 2935 MUST be set according the required policy rule. CREATE messages MUST 2936 be transported by using the path-coupled MRM with direction set to 2937 'downstream' (outbound). 2939 4.3.2. EXTERNAL 2941 The EXTERNAL message is used to a) reserve an external IP address/ 2942 port at NATs, b) to notify firewalls about NSIS capable DRs, or c) to 2943 block incoming data traffic at inbound firewalls. 2945 The EXTERNAL message carries these objects: 2947 o Signaling Session Lifetime object (M) 2949 o Message sequence number object (M) 2951 o Extended flow information object (M) 2953 o Data terminal information object (M) 2955 o Nonce object (M) if P flag set to 1 in the NSLP header, otherwise 2956 (O) 2958 o ICMP Types Object (O) 2959 The selected message routing method of the EXTERNAL message depends 2960 on a number of considerations. Section 3.7.2 describes it 2961 exhaustively how to select the correct method. EXTERNAL messages can 2962 be transported via the path-coupled message routing method (PC-MRM) 2963 or via the loose-end message routing method (LE-MRM). In the case of 2964 PC-MRM, the source-address is set to DS' address and the destination 2965 address is set to DR's address, the direction is set to inbound. In 2966 the case of LE-MRM, the destination-address is set to DR's address or 2967 to the signaling destination address. The source-address is set to 2968 DS's address. 2970 4.3.3. RESPONSE 2972 RESPONSE messages are responses to CREATE and EXTERNAL messages. 2973 RESPONSE messages MUST NOT be generated for any other message, such 2974 as NOTIFY and RESPONSE. 2976 The RESPONSE message for the class 'Success' (0x2) carries these 2977 objects: 2979 o Signaling Session Lifetime object (M) 2981 o Message sequence number object (M) 2983 o Information code object (M) 2985 o External address object (O) 2987 The RESPONSE message for other classes than 'Success' (0x2) carries 2988 these objects: 2990 o Message sequence number object (M) 2992 o Information code object (M) 2994 This message is routed towards the NI hop-by-hop, using existing NTLP 2995 messaging associations. The MRM used for this message MUST be the 2996 same as MRM used by the corresponding CREATE or EXTERNAL message. 2998 4.3.4. NOTIFY 3000 The NOTIFY messages is used to report asynchronous events happening 3001 along the signaled path to other NATFW NSLP nodes. 3003 The NOTIFY message carries this object: 3005 o Information code object (M). 3007 The NOTIFY message is routed towards the NI hop-by-hop using the 3008 existing inbound node messaging association entry within the node's 3009 Message Routing State table. The MRM used for this message MUST be 3010 the same as MRM used by the corresponding CREATE or EXTERNAL message. 3012 5. Security Considerations 3014 Security is of major concern particularly in case of firewall 3015 traversal. This section provides security considerations for the 3016 NAT/firewall traversal and is organized as follows. 3018 In Section 5.1 we describe how the participating entities relate to 3019 each other from a security point of view. This subsection also 3020 motivates a particular authorization model. 3022 Security threats that focus on NSIS in general are described in [8] 3023 and they are applicable to this document as well. 3025 Finally, we illustrate how the security requirements that were 3026 created based on the security threats can be fulfilled by specific 3027 security mechanisms. These aspects will be elaborated in 3028 Section 5.2. 3030 5.1. Authorization Framework 3032 The NATFW NSLP is a protocol which may involve a number of NSIS nodes 3033 and is, as such, not a two-party protocol. Figure 1 and Figure 2 of 3034 [8] already depict the possible set of communication patterns. In 3035 this section we will re-evaluate these communication patters with 3036 respect to the NATFW NSLP protocol interaction. 3038 The security solutions for providing authorization have a direct 3039 impact on the treatment of different NSLPs. As it can be seen from 3040 the QoS NSLP [6] and the corresponding Diameter QoS work [18] 3041 accounting and charging seems to play an important role for QoS 3042 reservations, whereas monetary aspects might only indirectly effect 3043 authorization decisions for NAT and firewall signaling. Hence, there 3044 are differences in the semantic of authorization handling between QoS 3045 and NATFW signaling. A NATFW aware node will most likely want to 3046 authorize the entity (e.g., user or machine) requesting the 3047 establishment of pinholes or NAT bindings. The outcome of the 3048 authorization decision is either allowed or disallowed whereas a QoS 3049 authorization decision might indicate that a different set of QoS 3050 parameters is authorization (see [18] as an example). 3052 5.1.1. Peer-to-Peer Relationship 3054 Starting with the simplest scenario, it is assumed that neighboring 3055 nodes are able to authenticate each other and to establish keying 3056 material to protect the signaling message communication. The nodes 3057 will have to authorize each other, additionally to the 3058 authentication. We use the term 'Security Context' as a placeholder 3059 for referring to the entire security procedure, the necessary 3060 infrastructure that needs to be in place in order for this to work 3061 (e.g., key management) and the established security related state. 3062 The required long-term key (symmetric or asymmetric keys) used for 3063 authentication are either made available using an out-of-band 3064 mechanism between the two NSIS NATFW nodes or they are dynamically 3065 established using mechanisms not further specified in this document. 3066 Note that the deployment environment will most likely have an impact 3067 on the choice of credentials being used. The choice of these 3068 credentials used is also outside the scope of this document. 3070 +------------------------+ +-------------------------+ 3071 |Network A | | Network B| 3072 | +---------+ +---------+ | 3073 | +-///-+ Middle- +---///////----+ Middle- +-///-+ | 3074 | | | box 1 | Security | box 2 | | | 3075 | | +---------+ Context +---------+ | | 3076 | | Security | | Security | | 3077 | | Context | | Context | | 3078 | | | | | | 3079 | +--+---+ | | +--+---+ | 3080 | | Host | | | | Host | | 3081 | | A | | | | B | | 3082 | +------+ | | +------+ | 3083 +------------------------+ +-------------------------+ 3085 Figure 31: Peer-to-Peer Relationship 3087 Figure 31 shows a possible relationship between participating NSIS 3088 aware nodes. Host A might be, for example, a host in an enterprise 3089 network that has keying material established (e.g., a shared secret) 3090 with the company's firewall (Middlebox 1). The network administrator 3091 of Network A (company network) has created access control lists for 3092 Host A (or whatever identifiers a particular company wants to use). 3093 Exactly the same procedure might also be used between Host B and 3094 Middlebox 2 in Network B. For the communication between Middlebox 1 3095 and Middlebox 2 a security context is also assumed in order to allow 3096 authentication, authorization and signaling message protection to be 3097 successful. 3099 5.1.2. Intra-Domain Relationship 3101 In larger corporations, for example, a middlebox is used to protect 3102 individual departments. In many cases, the entire enterprise is 3103 controlled by a single (or a small number of) security department, 3104 which gives instructions to the department administrators. In such a 3105 scenario, the previously discussed peer-to-peer relationship might be 3106 prevalent. Sometimes it might be necessary to preserve 3107 authentication and authorization information within the network. As 3108 a possible solution, a centralized approach could be used, whereby an 3109 interaction between the individual middleboxes and a central entity 3110 (for example a policy decision point - PDP) takes place. As an 3111 alternative, individual middleboxes exchange the authorization 3112 decision with another middlebox within the same trust domain. 3113 Individual middleboxes within an administrative domain may exploit 3114 their relationship instead of requesting authentication and 3115 authorization of the signaling initiator again and again. Figure 32 3116 illustrates a network structure which uses a centralized entity. 3118 +-----------------------------------------------------------+ 3119 | Network A | 3120 | +---------+ +---------+ 3121 | +----///--------+ Middle- +------///------++ Middle- +--- 3122 | | Security | box 2 | Security | box 2 | 3123 | | Context +----+----+ Context +----+----+ 3124 | +----+----+ | | | 3125 | | Middle- +--------+ +---------+ | | 3126 | | box 1 | | | | | 3127 | +----+----+ | | | | 3128 | | Security | +----+-----+ | | 3129 | | Context | | Policy | | | 3130 | +--+---+ +-----------+ Decision +----------+ | 3131 | | Host | | Point | | 3132 | | A | +----------+ | 3133 | +------+ | 3134 +-----------------------------------------------------------+ 3136 Figure 32: Intra-domain Relationship 3138 The interaction between individual middleboxes and a policy decision 3139 point (or AAA server) is outside the scope of this document. 3141 5.1.3. End-to-Middle Relationship 3143 The peer-to-peer relationship between neighboring NSIS NATFW NSLP 3144 nodes might not always be sufficient. Network B might require 3145 additional authorization of the signaling message initiator (in 3146 addition to the authorization of the neighboring node). If 3147 authentication and authorization information is not attached to the 3148 initial signaling message then the signaling message arriving at 3149 Middlebox 2 would result in an error message being created, which 3150 indicates the additional authorization requirement. In many cases 3151 the signaling message initiator might already be aware of the 3152 additionally required authorization before the signaling message 3153 exchange is executed. 3155 Figure 33 shows this scenario. 3157 +--------------------+ +---------------------+ 3158 | Network A | |Network B | 3159 | | Security | | 3160 | +---------+ Context +---------+ | 3161 | +-///-+ Middle- +---///////----+ Middle- +-///-+ | 3162 | | | box 1 | +-------+ box 2 | | | 3163 | | +---------+ | +---------+ | | 3164 | |Security | | | Security | | 3165 | |Context | | | Context | 3166 | | | | | | | 3167 | +--+---+ | | | +--+---+ | 3168 | | Host +----///----+------+ | | Host | | 3169 | | A | | Security | | B | | 3170 | +------+ | Context | +------+ | 3171 +--------------------+ +---------------------+ 3173 Figure 33: End-to-Middle Relationship 3175 5.2. Security Framework for the NAT/Firewall NSLP 3177 The following list of security requirements has been created to 3178 ensure proper secure operation of the NATFW NSLP. 3180 5.2.1. Security Protection between neighboring NATFW NSLP Nodes 3182 Based on the analyzed threats it is RECOMMENDED to provide, between 3183 neighboring NATFW NSLP nodes, the following mechanism: 3185 o data origin authentication 3187 o replay protection 3189 o integrity protection and 3191 o optionally confidentiality protection 3193 It is RECOMMENDED to use the authentication and key exchange security 3194 mechanisms provided in [2] between neighboring nodes when sending 3195 NATFW signaling messages. The proposed security mechanisms of GIST 3196 provide support for authentication and key exchange in addition to 3197 denial of service protection. Depending on the chosen security 3198 protocol, support for multiple authentication protocols might be 3199 provided. If security between neighboring nodes is desired than the 3200 usage of C-MODE for the delivery of data packets and the usage of 3201 D-MODE only to discover the next NATFW NSLP aware node along the path 3202 is highly RECOMMENDED. Almost all security threats at the NATFW NSLP 3203 layer can be prevented by using a mutually authenticated Transport 3204 Layer secured connection and by relying on authorization by the 3205 neighboring NATFW NSLP entities. 3207 The NATFW NSLP relies on an established security association between 3208 neighboring peers to prevent unauthorized nodes to modify or delete 3209 installed state. Between non-neighboring nodes the session ID (SID) 3210 carried in the NTLP is used to show ownership of a NATFW NSLP 3211 signaling session. The session ID MUST be generated in a random way 3212 and thereby prevent an off-path adversary to mount targeted attacks. 3213 Hence, an adversary would have to learn the randomly generated 3214 session ID to perform an attack. In a mobility environment a former 3215 on-path node that is now off-path can perform an attack. Messages 3216 for a particular NATFW NSLP signaling session are handled by the NTLP 3217 to the NATFW NSLP for further processing. Messages carrying a 3218 different session ID not associated with any NATFW NSLP are subject 3219 to the regular processing for new NATFW NSLP signaling sessions. 3221 5.2.2. Security Protection between non-neighboring NATFW NSLP Nodes 3223 Based on the security threats and the listed requirements it was 3224 noted that some threats also demand authentication and authorization 3225 of a NATFW signaling entity (including the initiator) towards a non- 3226 neighboring node. This mechanism mainly demands entity 3227 authentication. The most important information exchanged at the 3228 NATFW NSLP is information related to the establishment for firewall 3229 pinholes and NAT bindings. This information can, however, not be 3230 protected over multiple NSIS NATFW NSLP hops since this information 3231 might change depending on the capability of each individual NATFW 3232 NSLP node. 3234 Some scenarios might also benefit from the usage of authorization 3235 tokens. Their purpose is to associate two different signaling 3236 protocols (e.g., SIP and NSIS) and their authorization decision. 3237 These tokens are obtained by non-NSIS protocols, such as SIP or as 3238 part of network access authentication. When a NAT or firewall along 3239 the path receives the token it might be verified locally or passed to 3240 the AAA infrastructure. Examples of authorization tokens can be 3241 found in RFC 3520 [16] and RFC 3521 [17]. Figure 34 shows an example 3242 of this protocol interaction. 3244 An authorization token is provided by the SIP proxy, which acts as 3245 the assertion generating entity and gets delivered to the end host 3246 with proper authentication and authorization. When the NATFW 3247 signaling message is transmitted towards the network, the 3248 authorization token is attached to the signaling messages to refer to 3249 the previous authorization decision. The assertion verifying entity 3250 needs to process the token or it might be necessary to interact with 3251 the assertion granting entity using HTTP (or other protocols). As a 3252 result of a successfully authorization by a NATFW NSLP node, the 3253 requested action is executed and later a RESPONSE message is 3254 generated. 3256 +----------------+ Trust Relationship +----------------+ 3257 | +------------+ |<.......................>| +------------+ | 3258 | | Protocol | | | | Assertion | | 3259 | | requesting | | HTTP, SIP Request | | Granting | | 3260 | | authz | |------------------------>| | Entity | | 3261 | | assertions | |<------------------------| +------------+ | 3262 | +------------+ | Artifact/Assertion | Entity Cecil | 3263 | ^ | +----------------+ 3264 | | | ^ ^| 3265 | | | . || HTTP, 3266 | | | Trust . || other 3267 | API Access | Relationship. || protocols 3268 | | | . || 3269 | | | . || 3270 | | | v |v 3271 | v | +----------------+ 3272 | +------------+ | | +------------+ | 3273 | | Protocol | | NSIS NATFW CREATE + | | Assertion | | 3274 | | using authz| | Assertion/Artifact | | Verifying | | 3275 | | assertion | | ----------------------- | | Entity | | 3276 | +------------+ | | +------------+ | 3277 | Entity Alice | <---------------------- | Entity Bob | 3278 +----------------+ RESPONSE +----------------+ 3280 Figure 34: Authorization Token Usage 3282 Threats against the usage of authorization tokens have been mentioned 3283 in [8]. Hence, it is required to provide confidentiality protection 3284 to avoid allowing an eavesdropper to learn the token and to use it in 3285 another NATFW NSLP signaling session (replay attack). The token 3286 itself also needs to be protected against tempering. 3288 6. IAB Considerations on UNSAF 3290 UNilateral Self-Address Fixing (UNSAF) is described in [12] as a 3291 process at originating endpoints that attempt to determine or fix the 3292 address (and port) by which they are known to another endpoint. 3293 UNSAF proposals, such as STUN [14] are considered as a general class 3294 of workarounds for NAT traversal and as solutions for scenarios with 3295 no middlebox communication. 3297 This memo specifies a path-coupled middlebox communication protocol, 3298 i.e., the NSIS NATFW NSLP. NSIS in general and the NATFW NSLP are 3299 not intended as a short-term workaround, but more as a long-term 3300 solution for middlebox communication. In NSIS, endpoints are 3301 involved in allocating, maintaining, and deleting addresses and ports 3302 at the middlebox. However, the full control of addresses and ports 3303 at the middlebox is at the NATFW NSLP daemon located at the 3304 respective NAT. 3306 Therefore, this document addresses the UNSAF considerations in [12] 3307 by proposing a long-term alternative solution. 3309 7. IANA Considerations 3311 This section provides guidance to the Internet Assigned Numbers 3312 Authority (IANA) regarding registration of values related to the 3313 NATFW NSLP, in accordance with BCP 26 RFC 2434 [13]. 3315 The NATFW NSLP requires IANA to create a number of new registries. 3316 These registries may require further coordination with the registries 3317 of the NTLP [2] and the QoS NSLP [6]. 3319 NATFW NSLP Message Type Registry 3321 The NATFW NSLP Message Type is a 8 bit value. The allocation of 3322 values for new message types requires standards action. Updates and 3323 deletion of values from the registry is not possible. This 3324 specification defines four NATFW NSLP message types, which form the 3325 initial contents of this registry. IANA is requested to add these 3326 four NATFW NSLP Message Types: CREATE, EXT, RESPONSE, and NOTIFY. 3328 NATFW NSLP Header Flag Registry 3330 NATFW NSLP messages have a messages-specific 8 bit flags/reserved 3331 field in their header. The registration of flags is subject to IANA 3332 registration. The allocation of values for flag types requires 3333 standards action. Updates and deletion of values from the registry 3334 is not possible. This specification defines only one flag, the P 3335 flag in Figure 21. 3337 NSLP Object Type Registry 3339 [Delete this part if already done by another NSLP: 3341 A new registry is to be created for NSLP Message Objects. This is a 3342 12-bit field (giving values from 0 to 4095). This registry is shared 3343 between a number of NSLPs. Allocation policies are as follows: 3345 0-1023: Standards Action 3347 1024-1999: Specification Required 3349 2000-2047: Private/Experimental Use 3351 2048-4095: Reserved 3353 When a new object is defined, the extensibility bits (A/B) must also 3354 be defined.] 3356 This document defines 8 objects for the NATFW NSLP: NATFW_LT, 3357 NATFW_EXTERNAL-IP, NATFW_EFI, NATFW_INFO, NATFW_NONCE, NATFW_MSN, 3358 NATFW_DTINFO, NATFW_ICMP_TYPES. IANA is request to assigned values 3359 for them from NSLP Object Type registry and to replace the 3360 corresponding IANA-TBD tags with the numeric values. 3362 NSLP Response Code Registry 3364 In addition it defines a number of Response Codes for the NATFW NSLP. 3365 These can be found in Section 4.2.4 and are to be assigned values 3366 from NSLP Response Code registry. The allocation of values for 3367 Response Codes Codes requires standards action. IANA is request to 3368 assigned values for them from NSLP Response Code registry. 3370 GIST NSLPID 3372 This specification defines an NSLP for use with GIST and thus 3373 requires an assigned NSLP identifier. IANA is requested to add a new 3374 value to the NSLP Identifiers (NSLPID) registry defined in [2] for 3375 the NATFW NSLP. 3377 IPv4 and IPv6 Router Alert Option (RAO) value 3379 The GIST specification also requires that each NSLP-ID be associated 3380 with specific Router Alert Option (RAO) value. For the purposes of 3381 the NATFW NSLP, just a single IPv4 RAO value and a single IPv6 RAO 3382 must be allocated. 3384 8. Acknowledgments 3386 We would like to thank the following individuals for their 3387 contributions to this document at different stages: 3389 o Marcus Brunner and Henning Schulzrinne for their work on IETF 3390 drafts which lead us to start with this document; 3392 o Miquel Martin for his large contribution on the initial version of 3393 this document and one of the first prototype implemenations; 3395 o Srinath Thiruvengadam and Ali Fessi work for their work on the 3396 NAT/firewall threats draft; 3398 o Henning Peters for his comments and suggestions; 3400 o and the NSIS working group. 3402 9. References 3404 9.1. Normative References 3406 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 3407 Levels", BCP 14, RFC 2119, March 1997. 3409 [2] Schulzrinne, H. and R. Hancock, "GIST: General Internet 3410 Signalling Transport", draft-ietf-nsis-ntlp-15 (work in 3411 progress), February 2008. 3413 [3] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, 3414 August 1996. 3416 9.2. Informative References 3418 [4] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den 3419 Bosch, "Next Steps in Signaling (NSIS): Framework", RFC 4080, 3420 June 2005. 3422 [5] Brunner, M., "Requirements for Signaling Protocols", RFC 3726, 3423 April 2004. 3425 [6] Manner, J., Karagiannis, G., and A. McDonald, "NSLP for 3426 Quality-of-Service Signaling", draft-ietf-nsis-qos-nslp-16 3427 (work in progress), February 2008. 3429 [7] Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A., and A. 3430 Rayhan, "Middlebox communication architecture and framework", 3431 RFC 3303, August 2002. 3433 [8] Tschofenig, H. and D. Kroeselberg, "Security Threats for Next 3434 Steps in Signaling (NSIS)", RFC 4081, June 2005. 3436 [9] Srisuresh, P. and M. Holdrege, "IP Network Address Translator 3437 (NAT) Terminology and Considerations", RFC 2663, August 1999. 3439 [10] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and Issues", 3440 RFC 3234, February 2002. 3442 [11] Braden, B., Zhang, L., Berson, S., Herzog, S., and S. Jamin, 3443 "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional 3444 Specification", RFC 2205, September 1997. 3446 [12] Daigle, L. and IAB, "IAB Considerations for UNilateral Self- 3447 Address Fixing (UNSAF) Across Network Address Translation", 3448 RFC 3424, November 2002. 3450 [13] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 3451 Considerations Section in RFCs", BCP 26, RFC 2434, 3452 October 1998. 3454 [14] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy, "STUN 3455 - Simple Traversal of User Datagram Protocol (UDP) Through 3456 Network Address Translators (NATs)", RFC 3489, March 2003. 3458 [15] Westerinen, A., Schnizlein, J., Strassner, J., Scherling, M., 3459 Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry, J., and 3460 S. Waldbusser, "Terminology for Policy-Based Management", 3461 RFC 3198, November 2001. 3463 [16] Hamer, L-N., Gage, B., Kosinski, B., and H. Shieh, "Session 3464 Authorization Policy Element", RFC 3520, April 2003. 3466 [17] Hamer, L-N., Gage, B., and H. Shieh, "Framework for Session 3467 Set-up with Media Authorization", RFC 3521, April 2003. 3469 [18] Sun, D., McCann, P., Tschofenig, H., Tsou, T., Doria, A., and 3470 G. Zorn, "Diameter Quality of Service Application", 3471 draft-ietf-dime-diameter-qos-04 (work in progress), 3472 January 2008. 3474 [19] Roedig, U., Goertz, M., Karten, M., and R. Steinmetz, "RSVP as 3475 firewall Signalling Protocol", Proceedings of the 6th IEEE 3476 Symposium on Computers and Communications, Hammamet, 3477 Tunisia pp. 57 to 62, IEEE Computer Society Press, July 2001. 3479 Appendix A. Selecting Signaling Destination Addresses for EXTERNAL 3481 As with all other message types, EXTERNAL messages need a reachable 3482 IP address of the data sender on the GIST level. For the path- 3483 coupled MRM the source-address of GIST is the reachable IP address 3484 (i.e., the real IP address of the data sender, or a wildcard). While 3485 this is straight forward, it is not necessarily so for the loose-end 3486 MRM. Many applications do not provide the IP address of the 3487 communication counterpart, i.e., either the data sender or both a 3488 data sender and receiver. For the EXTERNAL messages, the case of 3489 data sender is of interest only. The rest of this section gives 3490 informational guidance about determining a good destination-address 3491 of the LE-MRM in GIST for EXTERNAL messages. 3493 This signaling destination address (SDA, the destination-address in 3494 GIST) can be the data sender, but for applications which do not 3495 provide an address upfront, the destination address has to be chosen 3496 independently, as it is unknown at the time when the NATFW NSLP 3497 signaling has to start. Choosing the 'correct' destination IP 3498 address may be difficult and it is possible that there is no 'right 3499 answer' for all applications relying on the NATFW NSLP. 3501 Whenever possible it is RECOMMENDED to chose the data sender's IP 3502 address as SDA. It is necessary to differentiate between the 3503 received IP addresses on the data sender. Some application level 3504 signaling protocols (e.g., SIP) have the ability to transfer multiple 3505 contact IP addresses of the data sender. For instance, private IP 3506 address, public IP address at NAT, and public IP address at a relay. 3507 It is RECOMMENDED to use all non-private IP addresses as SDAs. 3509 A different SDA must be chosen, if the IP address of the data sender 3510 is unknown. This can have multiple reasons: The application level 3511 signaling protocol cannot determine any data sender IP address at 3512 this point of time or the data receiver is server behind a NAT, i.e., 3513 accepting inbound packets from any host. In this case, the NATFW 3514 NSLP can be instructed to use the public IP address of an application 3515 server or any other node. Choosing the SDA in this case is out of 3516 the scope of the NATFW NSLP and depends on the application's choice. 3517 The local network can provide a network-SDA, i.e., a SDA which is 3518 only meaningful to the local network. This will ensure that GIST 3519 packets with destination-address set to this network-SDA are going to 3520 be routed to a edge-NAT or edge-firewall. 3522 Appendix B. Applicability Statement on Data Receivers behind Firewalls 3524 Section 3.7.2 describes how data receivers behind middleboxes can 3525 instruct inbound firewalls/NATs to forward NATFW NSLP signaling 3526 towards them. Finding an inbound edge-NAT in address environment 3527 with NAT'ed addresses is quite easy. It is only required to find 3528 some edge-NAT, as the data traffic will be route-pinned to the NAT. 3529 Locating the appropriate edge-firewall with the PC-MRM, sent inbound 3530 is difficult. For cases with a single, symmetric route from the 3531 Internet to the data receiver, it is quite easy; simply follow the 3532 default route in the inbound direction. 3534 +------+ Data Flow 3535 +-------| EFW1 +----------+ <=========== 3536 | +------+ ,--+--. 3537 +--+--+ / \ 3538 NI+-----| FW1 | (Internet )----NR+/NI/DS 3539 NR +--+--+ \ / 3540 | +------+ `--+--' 3541 +-------| EFW2 +----------+ 3542 +------+ 3544 ~~~~~~~~~~~~~~~~~~~~~> 3545 Signaling Flow 3547 Figure 35: Data receiver behind multiple, parallel located firewalls 3549 When a data receiver, and thus NR, is located in a network site that 3550 is multihomed with several independently firewalled connections to 3551 the public Internet (as shown in Figure 35), the specific firewall 3552 through which the data traffic will be routed has to be ascertained. 3553 NATFW NSLP signaling messages sent from the NI+/NR during the 3554 EXTERNAL message exchange towards the NR+ must be routed by the NTLP 3555 to the edge-firewall that will be passed by the data traffic as well. 3556 The NTLP would need to be aware about the routing within the Internet 3557 to determine the path between DS and DR. Out of this, the NTLP could 3558 determine which of the edge-firewalls, either EFW1 or EFW2, must be 3559 selected to forward the NATFW NSLP signaling. Signaling to the wrong 3560 edge-firewall, as shown in Figure 35, would install the NATFW NSLP 3561 policy rules at the wrong device. This causes either a blocked data 3562 flow (when the policy rule is 'allow') or an ongoing attack (when the 3563 policy rule is 'deny'). Requiring the NTLP to know all about the 3564 routing within the Internet is definitely a tough challenge and 3565 usually not possible. In such described case, the NTLP must 3566 basically give up and return an error to the NSLP level, indicating 3567 that the next hop discovery is not possible. 3569 Appendix C. Firewall and NAT Resources 3571 This section gives some examples on how NATFW NSLP policy rules could 3572 be mapped to real firewall or NAT resources. The firewall rules and 3573 NAT bindings are described in a natural way, i.e., in a way one will 3574 find it in common implementations. 3576 C.1. Wildcarding of Policy Rules 3578 The policy rule/MRI to be installed can be wildcarded to some degree. 3579 Wildcarding applies to IP address, transport layer port numbers, and 3580 the IP payload (or next header in IPv6). Processing of wildcarding 3581 splits into the NTLP and the NATFW NSLP layer. The processing at the 3582 NTLP layer is independent of the NSLP layer processing and per layer 3583 constraints apply. For wildcarding in the NTLP see Section 5.8 of 3584 [2]. 3586 Wildcarding at the NATFW NSLP level is always a node local policy 3587 decision. A signaling message carrying a wildcarded MRI (and thus 3588 policy rule) arriving at an NSLP node can be rejected if the local 3589 policy does not allow the request. For instance, a MRI with IP 3590 addresses set (not wildcarded), transport protocol TCP, and TCP port 3591 numbers completely wildcarded. Now the local policy allows only 3592 requests for TCP with all ports set and not wildcarded. The request 3593 is going to be rejected. 3595 C.2. Mapping to Firewall Rules 3597 This section describes how a NSLP policy rule signaled with a CREATE 3598 message is mapped to a firewall rule. The MRI is set as follows: 3600 o network-layer-version=IPv4 3602 o source-address=192.0.2.100, prefix-length=32 3604 o destination-address=192.0.50.5, prefix-length=32 3606 o IP-protocol=UDP 3608 o L4-source-port=34543, L4-destination-port=23198 3610 The NATFW_EFI object is set to action=allow and sub_ports=0. 3612 The resulting policy rule (firewall rule) to be installed might look 3613 like: allow udp from 192.0.2.100 port=34543 to 192.0.50.5 port=23198 3615 C.3. Mapping to NAT Bindings 3617 This section describes how a NSLP policy rule signaled with a 3618 EXTERNAL message is mapped to a NAT binding. It is assumed that the 3619 EXTERNAL message is sent by a NI+ being located behind a NAT and does 3620 contain a NATFW_DTINFO object. The MRI is set following using the 3621 signaling destination address, since the IP address of the real data 3622 sender is not known: 3624 o network-layer-version=IPv4 3626 o source-address= 192.168.5.100 3628 o destination-address=SDA 3630 o IP-protocol=UDP 3632 The NATFW_EFI object is set to action=allow and sub_ports=0. The 3633 NATFW_DTINFO object contains these parameters: 3635 o P=1 3637 o dest prefix=0 3639 o protocol=UDP 3641 o dst port number = 20230, src port number=0 3643 o src IP=0.0.0.0 3645 The edge-NAT allocates the external IP 192.0.2.79 and port 45000. 3647 The resulting policy rule (NAT binding) to be installed could look 3648 like: translate udp from any to 192.0.2.79 port=45000 to 3649 192.168.5.100 port=20230 3651 C.4. NSLP Handling of Twice-NAT 3653 The dynamic configuration of twice-NATs requires application level 3654 support, as stated in Section 2.5. The NATFW NSLP cannot be used for 3655 configuring twice-NATs if application level support is needed. 3656 Assuming application level support performing the configuration of 3657 the twice-NAT and the NATFW NSLP being installed at this devices, the 3658 NATFW NSLP must be able to traverse it. The NSLP is probably able to 3659 traverse the twice-NAT, as any other data traffic, but the flow 3660 information stored in the NTLP's MRI will be invalidated through the 3661 translation of source and destination address. The NATFW NSLP 3662 implementation on the twice-NAT MUST intercept NATFW NSLP and NTLP 3663 signaling messages as any other NATFW NSLP node does. For the given 3664 signaling flow, the NATFW NSLP node MUST look up the corresponding IP 3665 address translation and modify the NTLP/NSLP signaling accordingly. 3666 The modification results in an updated MRI with respect to the source 3667 and destination IP addresses. 3669 Appendix D. Protocols Numbers for Testing 3671 NOTE for the RFC editor: This section MUST be removed before 3672 publication. 3674 This section defines temporarily used values of the NATFW NSLP for 3675 testing the different implementations. 3677 Values for the NATFW NSLP message types: 3679 o CREATE: 0x01 3681 o EXTERNAL: 0x02 3683 o RESPONSE: 0x03 3685 o NOTIFY: 0x04 3687 Values for the NSLP object types 3689 o NATFW_LT: 0x00F1 3691 o NATFW_EXTERNAL-IP: 0x00F2 3693 o NATFW_EFI: 0x00F3 3695 o NATFW_INFO: 0x00F4 3697 o NATFW_NONCE: 0x00F5 3699 o NATFW_MSN: 0x00F6 3701 o NATFW_DTINFO: 0x00F7 3703 o NATFW_ICMP_TYPES: 0x00F9 3705 1345 3707 Authors' Addresses 3709 Martin Stiemerling 3710 NEC Europe Ltd. and University of Goettingen 3711 Kurfuersten-Anlage 36 3712 Heidelberg 69115 3713 Germany 3715 Phone: +49 (0) 6221 4342 113 3716 Email: stiemerling@netlab.nec.de 3717 URI: http://www.stiemerling.org 3719 Hannes Tschofenig 3720 Nokia Siemens Networks 3721 Linnoitustie 6 3722 Espoo 02600 3723 Finland 3725 Phone: +358 (50) 4871445 3726 Email: Hannes.Tschofenig@nsn.com 3727 URI: http://www.tschofenig.com 3729 Cedric Aoun 3730 Paris 3731 France 3733 Email: cedric@caoun.net 3735 Elwyn Davies 3736 Folly Consulting 3737 Soham 3738 UK 3740 Phone: +44 7889 488 335 3741 Email: elwynd@dial.pipex.com 3743 Full Copyright Statement 3745 Copyright (C) The IETF Trust (2008). 3747 This document is subject to the rights, licenses and restrictions 3748 contained in BCP 78, and except as set forth therein, the authors 3749 retain all their rights. 3751 This document and the information contained herein are provided on an 3752 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 3753 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 3754 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 3755 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 3756 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 3757 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 3759 Intellectual Property 3761 The IETF takes no position regarding the validity or scope of any 3762 Intellectual Property Rights or other rights that might be claimed to 3763 pertain to the implementation or use of the technology described in 3764 this document or the extent to which any license under such rights 3765 might or might not be available; nor does it represent that it has 3766 made any independent effort to identify any such rights. Information 3767 on the procedures with respect to rights in RFC documents can be 3768 found in BCP 78 and BCP 79. 3770 Copies of IPR disclosures made to the IETF Secretariat and any 3771 assurances of licenses to be made available, or the result of an 3772 attempt made to obtain a general license or permission for the use of 3773 such proprietary rights by implementers or users of this 3774 specification can be obtained from the IETF on-line IPR repository at 3775 http://www.ietf.org/ipr. 3777 The IETF invites any interested party to bring to its attention any 3778 copyrights, patents or patent applications, or other proprietary 3779 rights that may cover technology that may be required to implement 3780 this standard. Please address the information to the IETF at 3781 ietf-ipr@ietf.org. 3783 Acknowledgment 3785 Funding for the RFC Editor function is provided by the IETF 3786 Administrative Support Activity (IASA).