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'15') (Obsoleted by RFC 5389) == Outdated reference: A later version (-15) exists of draft-ietf-dime-diameter-qos-01 == Outdated reference: A later version (-04) exists of draft-manner-nsis-nslp-auth-03 Summary: 2 errors (**), 0 flaws (~~), 6 warnings (==), 11 comments (--). 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: May 22, 2008 NSN 6 C. Aoun 8 E. Davies 9 Folly Consulting 10 November 19, 2007 12 NAT/Firewall NSIS Signaling Layer Protocol (NSLP) 13 draft-ietf-nsis-nslp-natfw-16.txt 15 Status of this Memo 17 By submitting this Internet-Draft, each author represents that any 18 applicable patent or other IPR claims of which he or she is aware 19 have been or will be disclosed, and any of which he or she becomes 20 aware will be disclosed, in accordance with Section 6 of BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that 24 other groups may also distribute working documents as Internet- 25 Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt. 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html. 38 This Internet-Draft will expire on May 22, 2008. 40 Copyright Notice 42 Copyright (C) The IETF Trust (2007). 44 Abstract 46 This memo defines the NSIS Signaling Layer Protocol (NSLP) for 47 Network Address Translators (NATs) and firewalls. This NSLP allows 48 hosts to signal on the data path for NATs and firewalls to be 49 configured according to the needs of the application data flows. It 50 enables hosts behind NATs to obtain a public reachable address and 51 hosts behind firewalls to receive data traffic. The overall 52 architecture is given by the framework and requirements defined by 53 the Next Steps in Signaling (NSIS) working group. The network 54 scenarios, the protocol itself, and examples for path-coupled 55 signaling are given in this memo. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 60 1.1. Scope and Background . . . . . . . . . . . . . . . . . . . 5 61 1.2. Terminology and Abbreviations . . . . . . . . . . . . . . 8 62 1.3. Middleboxes . . . . . . . . . . . . . . . . . . . . . . . 10 63 1.4. General Scenario for NATFW Traversal . . . . . . . . . . . 11 65 2. Network Deployment Scenarios using the NATFW NSLP . . . . . . 13 66 2.1. Firewall Traversal . . . . . . . . . . . . . . . . . . . . 13 67 2.2. NAT with two private Networks . . . . . . . . . . . . . . 14 68 2.3. NAT with Private Network on Sender Side . . . . . . . . . 15 69 2.4. NAT with Private Network on Receiver Side Scenario . . . . 15 70 2.5. Both End Hosts behind twice-NATs . . . . . . . . . . . . . 16 71 2.6. Both End Hosts Behind Same NAT . . . . . . . . . . . . . . 17 72 2.7. Multihomed Network with NAT . . . . . . . . . . . . . . . 18 73 2.8. Multihomed Network with Firewall . . . . . . . . . . . . . 19 75 3. Protocol Description . . . . . . . . . . . . . . . . . . . . . 20 76 3.1. Policy Rules . . . . . . . . . . . . . . . . . . . . . . . 20 77 3.2. Basic Protocol Overview . . . . . . . . . . . . . . . . . 21 78 3.2.1. Message Types . . . . . . . . . . . . . . . . . . . . 25 79 3.2.2. Classification of RESPONSE Messages . . . . . . . . . 25 80 3.2.3. NATFW NSLP Signaling Sessions . . . . . . . . . . . . 26 81 3.3. Basic Message Processing . . . . . . . . . . . . . . . . . 27 82 3.4. Calculation of Signaling Session Lifetime . . . . . . . . 27 83 3.5. Message Sequencing . . . . . . . . . . . . . . . . . . . . 30 84 3.6. Authentication, Authorization, and Policy Decisions . . . 31 85 3.7. Protocol Operations . . . . . . . . . . . . . . . . . . . 32 86 3.7.1. Creating Signaling Sessions . . . . . . . . . . . . . 32 87 3.7.2. Reserving External Addresses . . . . . . . . . . . . . 35 88 3.7.3. NATFW NSLP Signaling Session Refresh . . . . . . . . . 42 89 3.7.4. Deleting Signaling Sessions . . . . . . . . . . . . . 43 90 3.7.5. Reporting Asynchronous Events . . . . . . . . . . . . 44 91 3.7.6. Proxy Mode of Operation . . . . . . . . . . . . . . . 46 92 3.8. De-Multiplexing at NATs . . . . . . . . . . . . . . . . . 49 93 3.9. Reacting to Route Changes . . . . . . . . . . . . . . . . 51 94 3.10. Updating Policy Rules . . . . . . . . . . . . . . . . . . 51 96 4. NATFW NSLP Message Components . . . . . . . . . . . . . . . . 53 97 4.1. NSLP Header . . . . . . . . . . . . . . . . . . . . . . . 53 98 4.2. NSLP Objects . . . . . . . . . . . . . . . . . . . . . . . 54 99 4.2.1. Signaling Session Lifetime Object . . . . . . . . . . 55 100 4.2.2. External Address Object . . . . . . . . . . . . . . . 55 101 4.2.3. Extended Flow Information Object . . . . . . . . . . . 56 102 4.2.4. Information Code Object . . . . . . . . . . . . . . . 57 103 4.2.5. Nonce Object . . . . . . . . . . . . . . . . . . . . . 60 104 4.2.6. Message Sequence Number Object . . . . . . . . . . . . 60 105 4.2.7. Data Terminal Information Object . . . . . . . . . . . 61 106 4.2.8. ICMP Types Object . . . . . . . . . . . . . . . . . . 62 107 4.3. Message Formats . . . . . . . . . . . . . . . . . . . . . 63 108 4.3.1. CREATE . . . . . . . . . . . . . . . . . . . . . . . . 64 109 4.3.2. EXTERNAL (EXT) . . . . . . . . . . . . . . . . . . . . 64 110 4.3.3. RESPONSE . . . . . . . . . . . . . . . . . . . . . . . 65 111 4.3.4. NOTIFY . . . . . . . . . . . . . . . . . . . . . . . . 65 113 5. Security Considerations . . . . . . . . . . . . . . . . . . . 67 114 5.1. Authorization Framework . . . . . . . . . . . . . . . . . 67 115 5.1.1. Peer-to-Peer Relationship . . . . . . . . . . . . . . 67 116 5.1.2. Intra-Domain Relationship . . . . . . . . . . . . . . 68 117 5.1.3. End-to-Middle Relationship . . . . . . . . . . . . . . 69 118 5.2. Security Framework for the NAT/Firewall NSLP . . . . . . . 70 119 5.2.1. Security Protection between neighboring NATFW NSLP 120 Nodes . . . . . . . . . . . . . . . . . . . . . . . . 70 121 5.2.2. Security Protection between non-neighboring NATFW 122 NSLP Nodes . . . . . . . . . . . . . . . . . . . . . . 71 124 6. IAB Considerations on UNSAF . . . . . . . . . . . . . . . . . 73 126 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 74 128 8. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 76 130 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 77 132 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 78 133 10.1. Normative References . . . . . . . . . . . . . . . . . . . 78 134 10.2. Informative References . . . . . . . . . . . . . . . . . . 78 136 Appendix A. Selecting Signaling Destination Addresses for EXT . . 80 138 Appendix B. Applicability Statement on Data Receivers behind 139 Firewalls . . . . . . . . . . . . . . . . . . . . . . 81 141 Appendix C. Firewall and NAT Resources . . . . . . . . . . . . . 83 142 C.1. Wildcarding of Policy Rules . . . . . . . . . . . . . . . 83 143 C.2. Mapping to Firewall Rules . . . . . . . . . . . . . . . . 83 144 C.3. Mapping to NAT Bindings . . . . . . . . . . . . . . . . . 84 145 C.4. NSLP Handling of Twice-NAT . . . . . . . . . . . . . . . . 84 147 Appendix D. Assigned Numbers for Testing . . . . . . . . . . . . 86 149 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 87 150 Intellectual Property and Copyright Statements . . . . . . . . . . 88 152 1. Introduction 154 1.1. Scope and Background 156 Firewalls and Network Address Translators (NAT) have both been used 157 throughout the Internet for many years, and they will remain present 158 for the foreseeable future. Firewalls are used to protect networks 159 against certain types of attacks from internal networks and the 160 Internet, whereas NATs provide a virtual extension of the IP address 161 space. Both types of devices may be obstacles to some applications, 162 since they only allow traffic created by a limited set of 163 applications to traverse them, typically those that use protocols 164 with relatively predetermined and static properties (e.g., most HTTP 165 traffic, and other client/server applications). Other applications, 166 such as IP telephony and most other peer-to-peer applications, which 167 have more dynamic properties, create traffic that is unable to 168 traverse NATs and firewalls unassisted. In practice, the traffic of 169 many applications cannot traverse autonomous firewalls or NATs, even 170 when they have additional functionality which attempts to restore the 171 transparency of the network. 173 Several solutions to enable applications to traverse such entities 174 have been proposed and are currently in use. Typically, application 175 level gateways (ALG) have been integrated with the firewall or NAT to 176 configure the firewall or NAT dynamically. Another approach is 177 middlebox communication (MIDCOM). In this approach, ALGs external to 178 the firewall or NAT configure the corresponding entity via the MIDCOM 179 protocol [7]. Several other work-around solutions are available, 180 such as STUN [15]. However, all of these approaches introduce other 181 problems that are generally hard to solve, such as dependencies on 182 the type of NAT implementation (full-cone, symmetric, etc), or 183 dependencies on certain network topologies. 185 NAT and firewall (NATFW) signaling shares a property with Quality of 186 Service (QoS) signaling. The signaling of both must reach any device 187 on the data path that is involved in, respectively, NATFW or QoS 188 treatment of data packets. This means, that for both, NATFW and QoS, 189 it is convenient if signaling travels path-coupled, meaning that the 190 signaling messages follow exactly the same path that the data packets 191 take. RSVP [11] is an example of a current QoS signaling protocol 192 that is path-coupled. [21] proposes the use of RSVP as firewall 193 signaling protocol but does not include NATs. 195 This memo defines a path-coupled signaling protocol for NAT and 196 firewall configuration within the framework of NSIS, called the NATFW 197 NSIS Signaling Layer Protocol (NSLP). The general requirements for 198 NSIS are defined in [5] and the general framework of NSIS is outlined 199 in [4]. It introduces the split between an NSIS transport layer and 200 an NSIS signaling layer. The transport of NSLP messages is handled 201 by an NSIS Network Transport Layer Protocol (NTLP, with General 202 Internet Signaling Transport (GIST) [2] being the implementation of 203 the abstract NTLP). The signaling logic for QoS and NATFW signaling 204 is implemented in the different NSLPs. The QoS NSLP is defined in 205 [6]. 207 The NATFW NSLP is designed to request the dynamic configuration of 208 NATs and/or firewalls along the data path. Dynamic configuration 209 includes enabling data flows to traverse these devices without being 210 obstructed, as well as blocking of particular data flows at inbound 211 firewalls. Enabling data flows requires the loading of firewall 212 rules with an action that allows the data flow packets to be 213 forwarded and creating NAT bindings. Blocking of data flows requires 214 the loading of firewalls rules with an action that will deny 215 forwarding of the data flow packets. A simplified example for 216 enabling data flows: A source host sends a NATFW NSLP signaling 217 message towards its data destination. This message follows the data 218 path. Every NATFW NSLP-enabled NAT/firewall along the data path 219 intercepts these messages, processes them, and configures itself 220 accordingly. Thereafter, the actual data flow can traverse all these 221 configured firewalls/NATs. 223 It is necessary to distinguish between two different basic scenarios 224 when operating the NATFW NSLP, independent of the type of the 225 middleboxes to be configured. 227 1. Both, data sender and data receiver, are NSIS NATFW NSLP aware. 228 This includes the cases where the data sender is logically 229 decomposed from the NSIS initiator or the data receiver logically 230 decomposed from the NSIS receiver, but both sides support NSIS. 231 This scenario assumes deployment of NSIS all over the Internet, 232 or at least at all NATs and firewalls. This scenario is used as 233 base assumption, if not otherwise noted. 235 2. Only one end host or region of the network is NSIS NATFW NSLP 236 aware, either data receiver or data sender. This scenario is 237 referred to as proxy mode. 239 The NATFW NSLP has two basic signaling messages which are sufficient 240 to cope with the various possible scenarios likely to be encountered 241 before and after widespread deployment of NSIS: 243 CREATE message: The basic message for configuring a path outbound 244 from a data sender to a data receiver. 246 EXTERNAL (EXT) message: Used to locate inbound NATs/firewalls and 247 prime them to expect outbound signaling and at NATs to pre- 248 allocate a public address. This is used for data receivers behind 249 these devices to enable their reachability. 251 CREATE and EXT messages are sent by the NSIS initiator (NI) towards 252 the NSIS responder (NR). Both type of messages are acknowledged by a 253 subsequent RESPONSE message. This RESPONSE message is generated by 254 the NR if the requested configuration can be established, otherwise 255 the NR or any of the NSIS forwarders (NFs) can also generate such a 256 message if an error occurs. NFs and the NR can also generate 257 asynchronous messages to notify the NI, the so called NOTIFY 258 messages. 260 If the data receiver resides in a private addressing realm or 261 firewall, and needs to preconfigure the edge-NAT/edge-firewall to 262 provide a (publicly) reachable address for use by the data sender, a 263 combination of EXTERNAL and CREATE messages is used. 265 During the introduction of NSIS, it is likely that one or other of 266 the data sender and receiver will not be NSIS aware. In these cases, 267 the NATFW NSLP can utilize NSIS aware middleboxes on the path between 268 the data sender and data receiver to provide proxy NATFW NSLP 269 services (i.e., the proxy mode operation). Typically, these boxes 270 will be at the boundaries of the realms in which the end hosts are 271 located. 273 The CREATE and EXT messages create NATFW NSLP and NTLP state in NSIS 274 entities. NTLP state allows signaling messages to travel in the 275 forward (outbound) and the reverse (inbound) direction along the path 276 between a NAT/firewall NSLP sender and a corresponding receiver. 277 This state is managed using a soft-state mechanism, i.e., it expires 278 unless it is refreshed from time to time. The NAT bindings and 279 firewall rules being installed during the state setup are bound to 280 the particular signaling session. However, the exact local 281 implementation of the NAT bindings and firewall rules are NAT/ 282 firewall specific. 284 This memo is structured as follows. Section 2 describes the network 285 environment for NATFW NSLP signaling. Section 3 defines the NATFW 286 signaling protocol and Section 4 defines the message components and 287 the overall messages used in the protocol. The remaining parts of 288 the main body of the document, covers security considerations 289 Section 5, IAB considerations on UNilateral Self-Address Fixing 290 (UNSAF) [12] in Section 6 and IANA considerations in Section 7. 291 Please note that readers familiar with firewalls and NATs and their 292 possible location within networks can safely skip Section 2. 294 1.2. Terminology and Abbreviations 296 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 297 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 298 document are to be interpreted as described in [1]. 300 This document uses a number of terms defined in [5] and [4]. The 301 following additional terms are used: 303 o Policy rule: A policy rule is "a basic building block of a policy- 304 based system. It is the binding of a set of actions to a set of 305 conditions - where the conditions are evaluated to determine 306 whether the actions are performed" [16]. In the context of NSIS 307 NATFW NSLP, the conditions are the specification of a set of 308 packets to which the rule is applied. The set of actions always 309 contains just a single element per rule, and is limited to either 310 action "deny" or action "allow". 312 o Reserved policy rule: A policy rule stored at NATs or firewalls 313 for activation by a later, different signaling exchange. This 314 type of policy rule is kept in the NATFW NSLP and is not loaded 315 into the firewall or NAT engine, i.e., it does not affect the data 316 flow handling. 318 o Installed policy rule: A policy rule in operation at NATs or 319 firewalls. This type of rule is kept in the NATFW NSLP and is 320 loaded into the firewall or NAT engine, i.e., it is affecting the 321 data flow. 323 o Remembered policy rule: A policy rule stored at NATs and firewalls 324 for immediate use, as soon as the signaling exchange is 325 successfully completed. 327 o Firewall: A packet filtering device that matches packets against a 328 set of policy rules and applies the actions. In the context of 329 NSIS NATFW NSLP we refer to this device as a firewall. 331 o Network Address Translator: Network Address Translation is a 332 method by which IP addresses are mapped from one IP address realm 333 to another, in an attempt to provide transparent routing between 334 hosts (see [9]). Network Address Translators are devices that 335 perform this work by modifying packets passing through them. 337 o Middlebox: "A middlebox is defined as any intermediate device 338 performing functions other than the normal, standard functions of 339 an IP router on the datagram path between a source host and a 340 destination host" [10]. In the context of this document, the term 341 middlebox refers to firewalls and NATs only. Other types of 342 middlebox are outside of the scope of this document. 344 o Data Receiver (DR): The node in the network that is receiving the 345 data packets of a flow. 347 o Data Sender (DS): The node in the network that is sending the data 348 packets of a flow. 350 o NATFW NSLP peer or peer: An NSIS NATFW NSLP node with which an 351 NSIS adjacency has been created as defined in [2]. 353 o NATFW NSLP signaling session or signaling session: A signaling 354 session defines an association between the NI, NFs, and the NR 355 related to a data flow. All the NATFW NSLP peers on the path, 356 including the NI and the NR, use the same identifier to refer to 357 the state stored for the association. The same NI and NR may have 358 more than one signaling session active at any time. The state for 359 NATFW NSLP consists of NSLP state and associated policy rules at a 360 middlebox. 362 o Edge-NAT: An edge-NAT is a NAT device with a globally routable IP 363 address which is reachable from the public Internet. 365 o Edge-firewall: An edge-firewall is a firewall device that is 366 located on the border line of an administrative domain. 368 o Public Network: "A Global or Public Network is an address realm 369 with unique network addresses assigned by Internet Assigned 370 Numbers Authority (IANA) or an equivalent address registry. This 371 network is also referred as external network during NAT 372 discussions" [9]. 374 o Private/Local Network: "A private network is an address realm 375 independent of external network addresses. Private network may 376 also be referred alternately as Local Network. Transparent 377 routing between hosts in private realm and external realm is 378 facilitated by a NAT router" [9]. 380 o Public/Global IP address: An IP address located in the public 381 network according to Section 2.7 of [9]. 383 o Private/Local IP address: An IP address located in the private 384 network according to Section 2.8 of [9]. 386 o Signaling Destination Address (SDA): An IP address generally taken 387 from the public/global IP address range, although, the SDA may in 388 certain circumstances be part of the private/local IP address 389 range. This address is used in EXT signaling message exchanges, 390 if the data receiver's IP address is unknown. 392 1.3. Middleboxes 394 The term middlebox covers a range of devices which intercept the flow 395 of packets between end hosts and perform actions other than standard 396 forwarding expected in an IP router. As such, middleboxes fall into 397 a number of categories with a wide range of functionality, not all of 398 which is pertinent to the NATFW NSLP. Middlebox categories in the 399 scope of this memo are firewalls that filter data packets against a 400 set of filter rules, and NATs that translate packet addresses from 401 one address realm to another address realm. Other categories of 402 middleboxes, such as QoS traffic shapers, are out of scope of this 403 memo. 405 The term NAT used in this document is a placeholder for a range of 406 different NAT flavors. We consider the following types of NATs: 408 o Traditional NAT (basic NAT and NAPT) 410 o Bi-directional NAT 412 o Twice-NAT 414 o Multihomed NAT 416 For definitions and a detailed discussion about the characteristics 417 of each NAT type please see [9]. 419 All types of middleboxes under consideration here, use policy rules 420 to make a decision on data packet treatment. Policy rules consist of 421 a flow identifier which selects the packets to which the policy 422 applies and an associated action; data packets matching the flow 423 identifier are subjected to the policy rule action. A typical flow 424 identifier is the 5-tuple selector which matches the following fields 425 of a packet to configured values: 427 o Source and destination IP addresses 429 o Transport protocol number 431 o Transport source and destination port numbers 433 Actions for firewalls are usually one or more of: 435 o Allow: forward data packet 436 o Deny: block data packet and discard it 438 o Other actions such as logging, diverting, duplicating, etc 440 Actions for NATs include (amongst many others): 442 o Change source IP address and transport port number to a globally 443 routeable IP address and associated port number. 445 o Change destination IP address and transport port number to a 446 private IP address and associated port number. 448 It should be noted that a middlebox may contain two logical 449 representations of the policy rule. The policy rule has a 450 representation within the NATFW NSLP, comprising the message routing 451 information (MRI) of the NTLP and NSLP information (such as the rule 452 action). The other representation is the implementation of the NATFW 453 NSLP policy rule within the NAT and firewall engine of the particular 454 device. Refer to Appendix C for further details. 456 1.4. General Scenario for NATFW Traversal 458 The purpose of NSIS NATFW signaling is to enable communication 459 between endpoints across networks, even in the presence of NAT and 460 firewall middleboxes that have not been specially engineered to 461 facilitate communication with the application protocols used. This 462 removes the need to create and maintain application layer gateways 463 for specific protocols that have been commonly used to provide 464 transparency in previous generations of NAT and firewall middleboxes. 465 It is assumed that these middleboxes will be statically configured in 466 such a way that NSIS NATFW signaling messages themselves are allowed 467 to reach the locally installed NATFW NSLP daemon. NSIS NATFW NSLP 468 signaling is used to dynamically install additional policy rules in 469 all NATFW middleboxes along the data path that will allow 470 transmission of the application data flow(s). Firewalls are 471 configured to forward data packets matching the policy rule provided 472 by the NSLP signaling. NATs are configured to translate data packets 473 matching the policy rule provided by the NSLP signaling. An 474 additional capability, that is an exception to the primary goal of 475 NSIS NATFW signaling, is that the NATFW nodes can request blocking of 476 particular data flows instead of enabling these flows at inbound 477 firewalls. 479 The basic high-level picture of NSIS usage is that end hosts are 480 located behind middleboxes, meaning that there is a middlebox on the 481 data path from the end host in a private network and the external 482 network (NATFW in Figure 1). Applications located at these end hosts 483 try to establish communication with corresponding applications on 484 other such end hosts. They trigger the NSIS entity at the local host 485 to control provisioning for middlebox traversal along the prospective 486 data path (e.g., via an API call). The NSIS entity in turn uses NSIS 487 NATFW NSLP signaling to establish policy rules along the data path, 488 allowing the data to travel from the sender to the receiver 489 unobstructed. 491 Application Application Server (0, 1, or more) Application 493 +----+ +----+ +----+ 494 | +------------------------+ +------------------------+ | 495 +-+--+ +----+ +-+--+ 496 | | 497 | NSIS Entities NSIS Entities | 498 +-+--+ +----+ +-----+ +-+--+ 499 | +--------+ +----------------------------+ +-----+ | 500 +-+--+ +-+--+ +--+--+ +-+--+ 501 | | ------ | | 502 | | //// \\\\\ | | 503 +-+--+ +-+--+ |/ | +-+--+ +-+--+ 504 | | | | | Internet | | | | | 505 | +--------+ +-----+ +----+ +-----+ | 506 +----+ +----+ |\ | +----+ +----+ 507 \\\\ ///// 508 sender NATFW (1+) ------ NATFW (1+) receiver 510 Note that 1+ refers to one or more NATFW nodes. 512 Figure 1: Generic View of NSIS with NATs and/or Firewalls 514 For end-to-end NATFW signaling, it is necessary that each firewall 515 and each NAT along the path between the data sender and the data 516 receiver implements the NSIS NATFW NSLP. There might be several NATs 517 and FWs in various possible combinations on a path between two hosts. 518 Section 2 presents a number of likely scenarios with different 519 combinations of NATs and firewalls. 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. Using combined middleboxes typically 532 reduces the number of network elements needed. 534 NSIS initiators (NI) send NSIS NATFW NSLP signaling messages via the 535 regular data path to the NSIS responder (NR). On the data path, 536 NATFW NSLP signaling messages reach different NSIS nodes that 537 implement the NATFW NSLP. Each NATFW NSLP node processes the 538 signaling messages according to Section 3 and, if necessary, installs 539 policy rules for subsequent data packets. 541 Each of the following sub-sections introduces a different scenario 542 for a different set of middleboxes and their ordering within the 543 topology. It is assumed that each middlebox implements the NSIS 544 NATFW NSLP signaling protocol. 546 2.1. Firewall Traversal 548 This section describes a scenario with firewalls only; NATs are not 549 involved. Each end host is behind a firewall. The firewalls are 550 connected via the public Internet. Figure 2 shows the topology. The 551 part labeled "public" is the Internet connecting both firewalls. 553 +----+ //----\\ +----+ 554 NI -----| FW |---| |------| FW |--- NR 555 +----+ \\----// +----+ 557 private public private 559 FW: Firewall 560 NI: NSIS Initiator 561 NR: NSIS Responder 563 Figure 2: Firewall Traversal Scenario 565 Each firewall on the data path must provide traversal service for 566 NATFW NSLP in order to permit the NSIS message to reach the other end 567 host. All firewalls process NSIS signaling and establish appropriate 568 policy rules, so that the required data packet flow can traverse 569 them. 571 There are several very different ways to place firewalls in a network 572 topology. To distinguish firewalls located at network borders, such 573 as administrative domains, from others located internally, the term 574 edge-firewall is used. A similar distinction can be made for NATs, 575 with an edge-NAT fulfilling the equivalent role. 577 2.2. NAT with two private Networks 579 Figure 3 shows a scenario with NATs at both ends of the network. 580 Therefore, each application instance, the NSIS initiator and the NSIS 581 responder, are behind NATs. The outermost NAT, known as the edge-NAT 582 (MB2 and MB3), at each side is connected to the public Internet. The 583 NATs are generically labeled as MBX (for middlebox No. X), since 584 those devices certainly implement NAT functionality, but can 585 implement firewall functionality as well. 587 Only two middleboxes MB are shown in Figure 3 at each side, but in 588 general, any number of MBs on each side must be considered. 590 +----+ +----+ //----\\ +----+ +----+ 591 NI --| MB1|-----| MB2|---| |---| MB3|-----| MB4|--- NR 592 +----+ +----+ \\----// +----+ +----+ 594 private public private 596 MB: Middlebox 597 NI: NSIS Initiator 598 NR: NSIS Responder 600 Figure 3: NAT with two Private Networks Scenario 602 Signaling traffic from NI to NR has to traverse all the middleboxes 603 on the path (MB1 to MB4, in this order), and all the middleboxes must 604 be configured properly to allow NSIS signaling to traverse them. The 605 NATFW signaling must configure all middleboxes and consider any 606 address translation that will result from this configuration in 607 further signaling. The sender (NI) has to know the IP address of the 608 receiver (NR) in advance, otherwise it will not be possible to send 609 any NSIS signaling messages towards the responder. Note that this IP 610 address is not the private IP address of the responder but the NAT's 611 public IP address (here MB3's IP address). Instead a NAT binding 612 (including a public IP address) has to be previously installed on the 613 NAT MB3. This NAT binding subsequently allows packets reaching the 614 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 Scenario 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 policy rules 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 EXT message of the NATFW NSLP where the 795 NSIS responder is located behind these firewalls within the private 796 network. The EXT message is used to block a particular data flow on 797 an inbound firewall. NSIS must route the EXT message inbound from NR 798 to NI probably without knowing which path the data traffic will take 799 from NI to NR (see also Appendix B). 801 +----+ 802 NR -------| MB |\ 803 \ +----+ \ //---\\ 804 \ -| |-- NI 805 \ \\---// 806 \ +----+ | 807 --| MB |-------+ 808 +----+ 809 private 811 private public 813 MB: Middlebox 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, source/ 829 destination addresses, transport protocol, and source/destination 830 port numbers, plus an action, such as allow or deny. For NATs the 831 policy rule consists of the action 'translate this address' and 832 further mapping information, that might be, in the simplest case, 833 internal IP address and external IP address. 835 The NATFW NSLP carries, in conjunction with the NTLP's Message 836 Routing Information (MRI), the policy rules to be installed at NATFW 837 peers. This policy rule is an abstraction with respect to the real 838 policy rule to be installed at the respective firewall or NAT. It 839 conveys the initiator's request and must be mapped to the possible 840 configuration on the particular used NAT and/or firewall in use. For 841 pure firewalls one or more filter rules must be created and for pure 842 NATs one or more NAT bindings must be created. In mixed firewall and 843 NAT boxes, the policy rule must be mapped to filter rules and 844 bindings observing the ordering of the firewall and NAT engine. 845 Depending on the ordering, NAT before firewall or vice versa, the 846 firewall rules must carry public or private IP addresses. However, 847 the exact mapping depends on the implementation of the firewall or 848 NAT which is different for each vendor. 850 The policy rule at the NATFW NSLP level comprises the message routing 851 information (MRI) part, carried in the NTLP, and the information 852 available in the NATFW NSLP. The information provided by the NSLP is 853 stored in the 'extend flow information' (NATFW_EFI) and 'data 854 terminal information' (NATFW_DTINFO) objects, and the message type. 855 Additional information, such as the external IP address and port 856 number, stored in the NAT or firewall, will be used as well. The MRI 857 carries the filter part of the NAT/firewall-level policy rule that is 858 to be installed. 860 The NATFW NSLP specifies two actions for the policy rules: deny and 861 allow. A policy rule with action set to deny will result in all 862 packets matching this rule to be dropped. A policy rule with action 863 set to allow will result in all packets matching this rule to be 864 forwarded. 866 3.2. Basic Protocol Overview 868 The NSIS NATFW NSLP is carried over the General Internet Signaling 869 Transport (GIST, the implementation of the NTLP) defined in [2]. 870 NATFW NSLP messages are initiated by the NSIS initiator (NI), handled 871 by NSIS forwarders (NF) and received by the NSIS responder (NR). It 872 is required that at least NI and NR implement this NSLP, intermediate 873 NFs only implement this NSLP when they provide relevant middlebox 874 functions. NSIS forwarders that do not have any NATFW NSLP functions 875 just forward these packets as they have no interest in them. 877 A Data Sender (DS), intending to send data to a Data Receiver (DR) 878 has to start NATFW NSLP signaling. This causes the NI associated 879 with the data sender (DS) to launch NSLP signaling towards the 880 address of data receiver (DR) (see Figure 10). Although it is 881 expected that the DS and the NATFW NSLP NI will usually reside on the 882 same host, this specification does not rule out scenarios where the 883 DS and NI reside on different hosts, the so-called proxy mode (see 884 Section 3.7.6.) 886 +-------+ +-------+ +-------+ +-------+ 887 | DS/NI |<~~~| MB1/ |<~~~| MB2/ |<~~~| DR/NR | 888 | |--->| NF1 |--->| NF2 |--->| | 889 +-------+ +-------+ +-------+ +-------+ 891 ========================================> 892 Data Traffic Direction (outbound) 894 ---> : NATFW NSLP request signaling 895 ~~~> : NATFW NSLP response signaling 896 DS/NI : Data sender and NSIS initiator 897 DR/NR : Data receiver and NSIS responder 898 MB1 : Middlebox 1 and NSIS forwarder 1 899 MB2 : Middlebox 2 and NSIS forwarder 2 901 Figure 10: General NSIS signaling 903 The following list shows the normal sequence of NSLP events without 904 detailing the interaction with the NTLP and the interactions on the 905 the NTLP level. 907 o NSIS initiators generate NATFW NSLP CREATE/EXT messages and send 908 these towards the NSIS responder. This CREATE/EXT message is the 909 initial message which creates a new NATFW NSLP signaling session. 910 The NI and the NR will most likely already share an application 911 session before they start the NATFW NSLP signaling session. Note 912 the difference between both sessions. 914 o NSLP CREATE/EXT messages are processed each time a NF with NATFW 915 NSLP support is traversed. Each NF that is intercepting a CREATE/ 916 EXT message and is accepting it for further treatment is joining 917 the particular NATFW NSLP signaling session. These nodes process 918 the message, check local policies for authorization and 919 authentication, possibly create policy rules, and forward the 920 signaling message to the next NSIS node. The request message is 921 forwarded until it reaches the NSIS responder. 923 o NSIS responders will check received messages and process them if 924 applicable. NSIS responders generate RESPONSE messages and send 925 them hop-by-hop back to the NI via the same chain of NFs 926 (traversal of the same NF chain is guaranteed through the 927 established reverse message routing state in the NTLP). The NR is 928 also joining the NATFW NSLP signaling session if the CREATE/EXT 929 message is accepted. 931 o The RESPONSE message is processed at each NF that has been 932 included in the prior NATFW NSLP signaling session setup. 934 o If the NI has received a successful RESPONSE message and if the 935 signaling NATFW NSLP session started with a CREATE message, the 936 data sender can start sending its data flow to the data receiver. 937 If the Ni has received a successful RESPONSE message and if the 938 signaling NATFW NSLP session started with a EXT message, the data 939 receiver is ready to receive further CREATE messages. 941 Because NATFW NSLP signaling follows the data path from DS to DR, 942 this immediately enables communication between both hosts for 943 scenarios with only firewalls on the data path or NATs on the sender 944 side. For scenarios with NATs on the receiver side certain problems 945 arise, as described in Section 2.4. 947 When the NR and the NI are located in different address realms and 948 the NR is located behind a NAT, the NI cannot signal to the NR 949 address directly. The DR/NR are not reachable from the NIs using the 950 private address of the NR and thus NATFW signaling messages cannot be 951 sent to the NR/DR's address. Therefore, the NR must first obtain a 952 NAT binding that provides an address that is reachable for the NI. 953 Once the NR has acquired a public IP address, it forwards this 954 information to the DS via a separate protocol. This application 955 layer signaling, which is out of scope of the NATFW NSLP, may involve 956 third parties that assist in exchanging these messages. 958 The same holds partially true for NRs located behind firewalls that 959 block all traffic by default. In this case, NR must tell its inbound 960 firewalls of inbound NATFW NSLP signaling and corresponding data 961 traffic. Once the NR has informed the inbound firewalls, it can 962 start its application level signaling to initiate communication with 963 the NI. This application layer signaling, which is out of scope of 964 the NATFW NSLP, may involve third parties that assist in exchanging 965 these messages. This mechanism can be used by machines hosting 966 services behind firewalls as well. In this case, the NR informs the 967 inbound firewalls as described, but does not need to communicate this 968 to the NIs. 970 NATFW NSLP signaling supports this scenario by using the EXT message 972 1. The DR acquires a public address by signaling on the reverse path 973 (DR towards DS) and thus making itself available to other hosts. 974 This process of acquiring public addresses is called reservation. 975 During this process the DR reserves publicly reachable addresses 976 and ports suitable for further usage in application level 977 signaling and the publicly reachable address for further NATFW 978 NSLP signaling. However, the data traffic will not be allowed to 979 use this address/port initially (see next point). In the process 980 of reservation the DR becomes the NI for the messages necessary 981 to obtain the publicly reachable IP address, i.e., the NI for 982 this specific NATFW NSLP signaling session. 984 2. Now on the side of DS, the NI creates a new NATFW NSLP signaling 985 session and signals directly to the public IP address of DR. 986 This public IP address is used as NR's address, as the NI would 987 do if there is no NAT in between, and creates policy rules at 988 middleboxes. Note, that the reservation will only allow 989 forwarding of signaling messages, but not data flow packets. 990 Policy rules allowing forwarding of data flow packets set up by 991 the prior EXT message signaling will be activated when the 992 signaling from NI towards NR is confirmed with a positive 993 RESPONSE message. The EXTERNAL (EXT) message is described 994 inSection 3.7.2. 996 +-------+ +-------+ +-------+ +-------+ 997 | DS/NI |<~~~| MB1/ |<~~~| NR | | DR | 998 | |--->| NF1 |--->| | | | 999 +-------+ +-------+ +-------+ +-------+ 1001 ========================================> 1002 Data Traffic Direction (outbound) 1004 ---> : NATFW NSLP request signaling 1005 ~~~> : NATFW NSLP response signaling 1006 DS/NI : Data sender and NSIS initiator 1007 DR/NR : Data receiver and NSIS responder 1008 MB1 : Middlebox 1 and NSIS forwarder 1 1009 MB2 : Middlebox 2 and NSIS forwarder 2 1011 Figure 11: A NSIS proxy mode signaling 1013 The above usage assumes that both ends of a communication support 1014 NSIS, but fails when NSIS is only deployed at one end of the path. 1015 In this case only one of the receiving or sending side is NSIS aware 1016 and not both at the same time. NATFW NSLP supports this scenario 1017 (i.e., the DR does not support NSIS) by using a proxy mode, as 1018 described in Section 3.7.6; the proxy mode operation also supports 1019 scenarios with a data sender that does not support NSIS, i.e. the 1020 data receiver must act to enable data flows towards itself. 1022 The basic functionality of the NATFW NSLP provides for opening 1023 firewall pin holes and creating NAT bindings to enable data flows to 1024 traverse these devices. Firewalls are normally expected to work on a 1025 'deny-all' policy, meaning that traffic not explicitly matching any 1026 firewall filter rule will be blocked. Similarly, the normal behavior 1027 of NATs is to block all traffic that does not match any already 1028 configured/installed binding or NATFW NSLP session. However, some 1029 scenarios require support of firewalls having 'allow-all' policies, 1030 allowing data traffic to traverse the firewall unless it is blocked 1031 explicitly. Data receivers can utilize NATFW NSLP's EXT message with 1032 action set to 'deny' to install policy rules at inbound firewalls to 1033 block unwanted traffic. 1035 The protocol works on a soft-state basis, meaning that whatever state 1036 is installed or reserved on a middlebox will expire, and thus be de- 1037 installed or forgotten after a certain period of time. To prevent 1038 premature removal of state that is needed for ongoing communication, 1039 the NATFW NI involved will have to specifically request a NATFW NSLP 1040 signaling session extension. An explicit NATFW NSLP state deletion 1041 capability is also provided by the protocol. 1043 If the actions requested by a NATFW NSLP message cannot be carried 1044 out, NFs and the NR must return a failure, such that appropriate 1045 actions can be taken. They can do this either during a the request 1046 message handling (synchronously) by sending an error RESPONSE 1047 message, or at any time (asynchronously) by sending a notification 1048 message. 1050 The next sections define the NATFW NSLP message types and formats, 1051 protocol operations, and policy rule operations. 1053 3.2.1. Message Types 1055 The protocol uses four messages types: 1057 o CREATE: a request message used for creating, changing, refreshing, 1058 and deleting NATFW NSLP signaling sessions, i.e., open the data 1059 path from DS to DR. 1061 o EXTERNAL (EXT): a request message used for reserving, changing, 1062 refreshing, and deleting EXT NATFW NSLP signaling sessions. EXT 1063 messages are forwarded to the edge-NAT or edge-firewall and allow 1064 inbound CREATE messages to be forwarded to the NR. Additionally, 1065 EXT messages reserve an external address and, if applicable, port 1066 number at an edge-NAT. 1068 o NOTIFY: an asynchronous message used by NATFW peers to alert 1069 inbound NATFW peers about specific events (especially failures). 1071 o RESPONSE: used as a response to CREATE and EXT request messages. 1073 3.2.2. Classification of RESPONSE Messages 1075 RESPONSE messages will be generated synchronously to CREATE and EXT 1076 messages by NSIS Forwarders and Responders to report success or 1077 failure of operations or some information relating to the NATFW NSLP 1078 signaling session or a node. RESPONSE messages MUST NOT be generated 1079 for any other message, such as NOTIFY and RESPONSE. 1081 All RESPONSE messages MUST carry a NATFW_INFO object which contains a 1082 severity class code and a response code (see Section 4.2.4). This 1083 section defines terms for groups of RESPONSE messages depending on 1084 the severity class. 1086 o Successful RESPONSE: Messages carrying NATFW_INFO with severity 1087 class 'Success' (0x2). 1089 o Informational RESPONSE: Messages carrying NATFW_INFO with severity 1090 class 'Informational' (0x1) (only used with NOTIFY messages). 1092 o Error RESPONSE: Messages carrying NATFW_INFO with severity class 1093 other than 'Success' or 'Informational'. 1095 3.2.3. NATFW NSLP Signaling Sessions 1097 A NATFW NSLP signaling session defines an association between the NI, 1098 NFs, and the NR related to a data flow. This association is created 1099 when the initial CREATE or EXT message is successfully received at 1100 the NFs or the NR. There is signaling NATFW NSLP session state 1101 stored at the NTLP layer and at the NATFW NSLP level. The NATFW NSLP 1102 signaling session state for the NATFW NSLP comprises NSLP state and 1103 the associated policy rules at a middlebox. 1105 The NATFW NSLP signaling session is identified by the session ID 1106 (plus other information at the NTLP level). The session ID is 1107 generated by the NI before the initial CREATE or EXT message is sent. 1108 The value of the session ID MUST generated in a random way, i.e., the 1109 output MUST NOT be easily guessable by third parties. The session ID 1110 is not stored in any NATFW NSLP message but passed on to the NTLP. 1112 A NATFW NSLP signaling session can conceptually be in different 1113 states, implementations may use other or even more states. The 1114 signaling session can have these states at a node: 1116 o Pending: The NATFW NSLP signaling session has been created and the 1117 node is waiting for a RESPONSE message to the CREATE or EXT 1118 message. A NATFW NSLP signaling session in state 'Pending' MUST 1119 be marked as 'Dead' if no corresponding RESPONSE message has been 1120 received within the time of the locally granted NATFW NSLP 1121 signaling session lifetime of the forwarded CREATE or EXT message 1122 (as described in Section 3.4). 1124 o Established: The NATFW NSLP signaling session is established, i.e, 1125 the signaling has been successfully performed and the lifetime of 1126 NATFW NSLP signaling session is counted from now on. A NATFW NSLP 1127 signaling session in state 'Established' MUST be marked as 'Dead' 1128 if no refresh message has been received within the time of the 1129 locally granted NATFW NSLP signaling session lifetime of the 1130 RESPONSE message (as described in Section 3.4). 1132 o Dead: Either the NATFW NSLP signaling session is timed out or the 1133 node has received an error RESPONSE message for the NATFW NSLP 1134 signaling session and the NATFW NSLP signaling session can be 1135 deleted. 1137 o Transit: The node has received an asynchronous message, i.e., a 1138 NOTIFY, and can delete the NATFW NSLP signaling session if needed. 1139 When a node has received a NOTIFY message (for instance, 1140 indicating a route change) it marks it as 'Transit' and deletes 1141 this NATFW NSLP signaling session if it is unused for some time 1142 specific to the local node. This idle time does not need to be 1143 fixed, since it can depend on the node local maintenance cycle, 1144 i.e., the NATFW NSLP signaling session could be deleted if the 1145 node runs it garbage collection cycle. 1147 3.3. Basic Message Processing 1149 All NATFW messages are subject to some basic message processing when 1150 received at a node, independent of message type. Initially, the 1151 syntax of the NSLP message is checked and a RESPONSE message with an 1152 appropriate error of class 'Protocol error' (0x1) code is generated 1153 if any problem is detected. If a message is delivered to the NATFW 1154 NSLP, this implies that the NTLP layer has been able to correlate it 1155 with the SID and MRI entries in its database. There is therefore 1156 enough information to identify the source of the message and routing 1157 information to route the message back to the NI through an 1158 established chain of NTLP messaging associations. The message is not 1159 further forwarded if any error in the syntax is detected. The 1160 specific response codes stemming from the processing of objects are 1161 described in the respective object definition section (see 1162 Section 4). After passing this check, the NATFW NSLP node performs 1163 authentication/authorization related checks described in Section 3.6. 1164 Further processing is executed only if these tests have been 1165 successfully passed, otherwise the processing stops and an error 1166 RESPONSE is returned. 1168 Further message processing stops whenever an error RESPONSE message 1169 is generated, and the EXT or CREATE message is discarded. 1171 3.4. Calculation of Signaling Session Lifetime 1173 NATFW NSLP signaling sessions, and the corresponding policy rules 1174 which may have been installed, are maintained via a soft-state 1175 mechanism. Each signaling session is assigned a signaling session 1176 lifetime and the signaling session is kept alive as long as the 1177 lifetime is valid. After the expiration of the signaling session 1178 lifetime, signaling sessions and policy rules MUST be removed 1179 automatically and resources bound to them MUST be freed as well. 1180 Signaling session lifetime is handled at every NATFW NSLP node. The 1181 NSLP forwarders and NSLP responder MUST NOT trigger signaling session 1182 lifetime extension refresh messages (see Section 3.7.3): this is the 1183 task of the NSIS initiator. 1185 The NSIS initiator MUST choose a NATFW NSLP signaling session 1186 lifetime value (expressed in seconds) before sending any message, 1187 including the initial message which creates the NATFW NSLP signaling 1188 session, to other NSLP nodes. The NATFW NSLP signaling session 1189 lifetime value is calculated based on: 1191 o the number of lost refresh messages that NFs should cope with; 1193 o the end-to-end delay between the NI and NR; 1195 o network vulnerability due to NATFW NSLP signaling session 1196 hijacking ([8]), NATFW NSLP signaling session hijacking is made 1197 easier when the NI does not explicitly remove the NATFW NSLP 1198 signaling session); 1200 o the user application's data exchange duration, in terms of time 1201 and networking needs. This duration is modeled as M x R, with R 1202 the message refresh period (in seconds) and M as a multiplier for 1203 R; 1205 o the load on the signaling plane. Short lifetimes imply more 1206 frequent signaling messages. 1208 o the acceptable time for a NATFW NSLP signaling session to be 1209 present after it is no longer actually needed. For example, if 1210 the existence of the NATFW NSLP signaling session implies a 1211 monetary cost and teardown cannot be guaranteed, shorter lifetimes 1212 would be preferable. 1214 o the lease time of the NI's IP address. The chosen NATFW NSLP 1215 signaling session lifetime must be larger than the lease time, 1216 otherwise the IP address can be re-assigned to a different node. 1217 This node may receive unwanted traffic, although it never has 1218 requested a NAT/firewall configuration, which might be an issue in 1219 mobile environments. 1221 The RSVP specification [11] provides an appropriate algorithm for 1222 calculating the NATFW NSLP signaling session lifetime as well as 1223 means to avoid refresh message synchronization between NATFW NSLP 1224 signaling sessions. [11] recommends: 1226 1. The refresh message timer to be randomly set to a value in the 1227 range [0.5R, 1.5R]. 1229 2. To avoid premature loss of state, lt (with lt being the NATFW 1230 NSLP signaling session lifetime) must satisfy lt >= (K + 1231 0.5)*1.5*R, where K is a small integer. Then in the worst case, 1232 K-1 successive messages may be lost without state being deleted. 1233 Currently K = 3 is suggested as the default. However, it may be 1234 necessary to set a larger K value for hops with high loss rate. 1235 Other algorithms could be used to define the relation between the 1236 NATFW NSLP signaling session lifetime and the refresh message 1237 period; the algorithm provided is only given as an example. 1239 This requested NATFW NSLP signaling session lifetime value lt is 1240 stored in the NATFW_LT object of the NSLP message. 1242 NSLP forwarders can execute the following behavior with respect to 1243 the lifetime handling: 1245 Requested signaling session lifetime acceptable: 1247 No changes to the NATFW NSLP signaling session lifetime values are 1248 needed. The CREATE or EXT message is forwarded. 1250 Signaling session lifetime can be lowered: 1252 The NSLP responder MAY also lower the requested NATFW NSLP 1253 signaling session lifetime to an acceptable value (based on its 1254 local policies). If an NF changes the NATFW NSLP signaling 1255 session lifetime value, it MUST store the new value in the 1256 NATFW_LT object. The CREATE or EXT message is forwarded. 1258 Requested signaling session lifetime is too big: 1260 The NSLP responder MAY reject the requested NATFW NSLP signaling 1261 session lifetime value as being too big and MUST generate an error 1262 RESPONSE message of class 'Signaling session failures' (0x6) with 1263 response code 'Requested lifetime is too big' (0x02) upon 1264 rejection. Lowering the lifetime is preferred instead of 1265 generating an error message. 1267 Requested signaling session lifetime is too small: 1269 The NSLP responder MAY reject the requested NATFW NSLP signaling 1270 session lifetime value as being to small and MUST generate an 1271 error RESPONSE message of class 'Signaling session failures' (0x6) 1272 with response code 'Requested lifetime is too small' (0x10) upon 1273 rejection. 1275 NFs MUST NOT increase the NATFW NSLP signaling session lifetime 1276 value. Messages can be rejected on the basis of the NATFW NSLP 1277 signaling session lifetime being too long when a NATFW NSLP signaling 1278 session is first created and also on refreshes. 1280 The NSLP responder generates a successful RESPONSE for the received 1281 CREATE or EXT message, sets the NATFW NSLP signaling session lifetime 1282 value in the NATFW_LT object to the above granted lifetime and sends 1283 the message back towards NSLP initiator. 1285 Each NSLP forwarder processes the RESPONSE message, reads and stores 1286 the granted NATFW NSLP signaling session lifetime value. The 1287 forwarders MUST accept the granted NATFW NSLP signaling session 1288 lifetime, as long as this value is less than or equal to the 1289 acceptable value. The acceptable value refers to the value accepted 1290 by the NSLP forwarder when processing the CREATE or EXT message. For 1291 received values greater than the acceptable value, NSLP forwarders 1292 MUST generate a RESPONSE message of class 'Signaling session 1293 failures' (0x6) with response code 'Requested lifetime is too big' 1294 (0x02). For received values lower than the values acceptable by the 1295 node local policy, NSLP forwarders MUST generate a RESPONSE message 1296 of class 'Signaling session failures' (0x6) with response code 1297 'Requested lifetime is too small' (0x10). Figure 12 shows the 1298 procedure with an example, where an initiator requests 60 seconds 1299 lifetime in the CREATE message and the lifetime is shortened along 1300 the path by the forwarder to 20 seconds and by the responder to 15 1301 seconds. When the NSLP forwarder receives the RESPONSE message with 1302 a NATFW NSLP signaling session lifetime value of 15 seconds it checks 1303 whether this value is lower or equal to the acceptable value. 1305 +-------+ CREATE(lt=60s) +-------------+ CREATE(lt=20s) +--------+ 1306 | |---------------->| NSLP |---------------->| | 1307 | NI | | forwarder | | NR | 1308 | |<----------------| check 15<20 |<----------------| | 1309 +-------+ RESPONSE(lt=15s)+-------------+ RESPONSE(lt=15s)+--------+ 1311 lt = lifetime 1313 Figure 12: Signaling Session Lifetime Setting Example 1315 3.5. Message Sequencing 1317 NATFW NSLP messages need to carry an identifier so that all nodes 1318 along the path can distinguish messages sent at different points in 1319 time. Messages can be lost along the path or duplicated. So all 1320 NATFW NSLP nodes should be able to identify either old messages that 1321 have been received before (duplicated), or the case that messages 1322 have been lost before (loss). For message replay protection it is 1323 necessary to keep information about messages that have already been 1324 received and requires every NATFW NSLP message to carry a message 1325 sequence number (MSN), see also Section 4.2.6. 1327 The MSN MUST be set by the NI and MUST NOT be set or modified by any 1328 other node. The initial value for the MSN MUST be generated randomly 1329 and MUST be unique only within the NATFW NSLP signaling session for 1330 which it is used. The NI MUST increment the MSN by one for every 1331 message sent. Once the MSN has reached the maximum value, the next 1332 value it takes is zero. All NATFW NSLP nodes MUST use the algorithm 1333 defined in [3] to detect MSN wrap-arounds. 1335 NSIS forwarders and the responder store the MSN from the initial 1336 CREATE or EXT packet which creates the NATFW NSLP signaling session 1337 as the start value for the NATFW NSLP signaling session. NFs and NRs 1338 MUST include the received MSN value in the corresponding RESPONSE 1339 message that they generate. 1341 When receiving a CREATE or EXT message, a NATFW NSLP node uses the 1342 MSN given in the message to determine whether the state being 1343 requested is different to the state already installed. The message 1344 MUST be discarded if the received MSN value is equal to or lower than 1345 the stored MSN value. Such a received MSN value can indicate a 1346 duplicated and delayed message or replayed message. If the received 1347 MSN value is greater than the already stored MSN value, the NATFW 1348 NSLP MUST update its stored state accordingly, if permitted by all 1349 security checks (see Section 3.6), and stores the updated MSN value 1350 accordingly. 1352 3.6. Authentication, Authorization, and Policy Decisions 1354 NATFW NSLP nodes receiving signaling messages MUST first check 1355 whether this message is authenticated and authorized to perform the 1356 requested action. NATFW NSLP nodes requiring more information than 1357 provided MUST generate an error RESPONSE of class 'Permanent failure' 1358 (0x5) with response code 'Authentication failed' (0x01) or with 1359 response code 'Authorization failed' (0x02). 1361 The NATFW NSLP is expected to run in various environments, such as 1362 IP-based telephone systems, enterprise networks, home networks, etc. 1363 The requirements on authentication and authorization are quite 1364 different between these use cases. While a home gateway, or an 1365 Internet cafe, using NSIS may well be happy with a "NATFW signaling 1366 coming from inside the network" policy for authorization of 1367 signaling, enterprise networks are likely to require more strongly 1368 authenticated/authorized signaling. This enterprise scenario may 1369 require the use of an infrastructure and administratively assigned 1370 identities to operate the NATFW NSLP. 1372 Once the NI is authenticated and authorized, another step is 1373 performed. The requested policy rule for the NATFW NSLP signaling 1374 session is checked against a set of policy rules, i.e., whether the 1375 requesting NI is allowed to request the policy rule to be loaded in 1376 the device. If this fails the NF or NR must send an error RESPONSE 1377 of class 'Permanent failure' (0x5) and with response code 1378 'Authorization failed' (0x02). 1380 3.7. Protocol Operations 1382 This section defines the protocol operations including, how to create 1383 NATFW NSLP signaling sessions, maintain them, and how to reserve 1384 addresses. 1386 3.7.1. Creating Signaling Sessions 1388 Allowing two hosts to exchange data even in the presence of 1389 middleboxes is realized in the NATFW NSLP by use of the CREATE 1390 message. The NI (either the data sender or a proxy) generates a 1391 CREATE message as defined in Section 4.3.1 and hands it to the NTLP. 1392 The NTLP forwards the whole message on the basis of the message 1393 routing information (MRI) towards the NR. Each NSIS forwarder along 1394 the path that implements NATFW NSLP, processes the NSLP message. 1395 Forwarding is thus managed NSLP hop-by-hop but may pass transparently 1396 through NSIS forwarders which do not contain NATFW NSLP functionality 1397 and non-NSIS aware routers between NSLP hop way points. When the 1398 message reaches the NR, the NR can accept the request or reject it. 1399 The NR generates a response to CREATE and this response is 1400 transported hop-by-hop towards the NI. NATFW NSLP forwarders may 1401 reject requests at any time. Figure 13 sketches the message flow 1402 between NI (DS in this example), a NF (e.g., NAT), and NR (DR in this 1403 example). 1405 NI Private Network NF Public Internet NR 1406 | | | 1407 | CREATE | | 1408 |----------------------------->| | 1409 | | | 1410 | | | 1411 | | CREATE | 1412 | |--------------------------->| 1413 | | | 1414 | | RESPONSE | 1415 | RESPONSE |<---------------------------| 1416 |<-----------------------------| | 1417 | | | 1418 | | | 1420 Figure 13: CREATE message flow with success RESPONSE 1422 There are several processing rules for a NATFW peer when generating 1423 and receiving CREATE messages, since this message type is used for 1424 creating new NATFW NSLP signaling session, updating existing, 1425 extending the lifetime and deleting NATFW NSLP signaling session. 1426 The three latter functions operate in the same way for all kinds of 1427 CREATE message, and are therefore described in separate sections: 1429 o Extending the lifetime of NATFW NSLP signaling sessions is 1430 described in Section 3.7.3. 1432 o Deleting NATFW NSLP signaling sessions is described in 1433 Section 3.7.4. 1435 o Updating policy rules is described in Section 3.10. 1437 For an initial CREATE message creating a new NATFW NSLP signaling 1438 session, the processing of CREATE messages is different for every 1439 NATFW node type: 1441 o NSLP initiator: An NI only generates CREATE messages and hands 1442 them over to the NTLP. The NI should never receive CREATE 1443 messages and MUST discard it. 1445 o NATFW NSLP forwarder: NFs that are unable to forward the CREATE 1446 message to the next hop MUST generate an error RESPONSE of class 1447 'Permanent failure' (0x6) with response code 'Did not reach the 1448 NR' (0x07). This case may occur if the NTLP layer cannot find an 1449 NATFW NSLP peer, either another NF or the NR, and returns an error 1450 via the GIST API. The NSLP message processing at the NFs depends 1451 on the middlebox type: 1453 * NAT: When the initial CREATE message is received at the public 1454 side of the NAT, it looks for a reservation made in advance, by 1455 using a EXT message (see Section 3.7.2). The matching process 1456 considers the received MRI information and the stored MRI 1457 information, as described in Section 3.8. If no matching 1458 reservation can be found, i.e. no reservation has been made in 1459 advance, the NSLP MUST return an error RESPONSE of class 1460 'Signaling session failure' (0x6) with response code 'No 1461 reservation found matching the MRI of the CREATE request' 1462 (0x03) MUST be generated. If there is a matching reservation, 1463 the NSLP stores the data sender's address (and if applicable 1464 port number) as part of the source address of the policy rule 1465 ('the remembered policy rule') to be loaded and forwards the 1466 message with the destination address set to the internal 1467 (private in most cases) address of NR. When the initial CREATE 1468 message is received at the private side, the NAT binding is 1469 allocated, but not activated (see also Appendix C.3). The MRI 1470 information is updated to reflect the address, and if 1471 applicable port, translation. The NSLP message is forwarded 1472 towards the NR with source address set to the NAT's external 1473 address from the newly remembered binding. 1475 * Firewall: When the initial CREATE message is received, the NSLP 1476 just remembers the requested policy rule, but does not install 1477 any policy rule. Afterwards, the message is forwarded towards 1478 the NR. 1480 * Combined NAT and firewall: Processing at combined firewall and 1481 NAT middleboxes is the same as in the NAT case. No policy 1482 rules are installed. Implementations MUST take into account 1483 the order of packet processing in the firewall and NAT 1484 functions within the device. This will be referred to as 1485 'order of functions' and is generally different depending on 1486 whether the packet arrives at the external or internal side of 1487 the middlebox. 1489 o NSLP receiver: NRs receiving initial CREATE messages MUST reply 1490 with a success RESPONSE of class 'Success' (0x2) with response 1491 code set to 'All successfully processed' (0x01), if they accept 1492 the CREATE message. Otherwise they MUST generate a RESPONSE 1493 message with a suitable response code. RESPONSE messages are sent 1494 back NSLP hop-by-hop towards the NI, irrespective of the response 1495 codes, either success or error. 1497 Remembered policy rules at middleboxes MUST be only installed upon 1498 receiving a corresponding successful RESPONSE message with the same 1499 SID and MSN as the CREATE message that caused them to be remembered. 1500 This is a countermeasure to several problems, for example, wastage of 1501 resources due to loading policy rules at intermediate NFs when the 1502 CREATE message does not reach the final NR for some reason. 1504 Processing of a RESPONSE message is different for every NSIS node 1505 type: 1507 o NSLP initiator: After receiving a successful RESPONSE, the data 1508 path is configured and the DS can start sending its data to the 1509 DR. After receiving an error RESPONSE message, the NI MAY try to 1510 generate the CREATE message again or give up and report the 1511 failure to the application, depending on the error condition. 1513 o NSLP forwarder: NFs install the remembered policy rules, if a 1514 successful RESPONSE message with matching SID and MSN is received. 1515 If an ERROR RESPONSE message with matching SID and MSN is 1516 received, the NATFW NSLP session is marked as dead, no policy rule 1517 is installed and the remembered rule is discarded. 1519 o NSIS responder: The NR should never receive RESPONSE messages and 1520 MUST silently drop any such messages received. 1522 3.7.2. Reserving External Addresses 1524 NSIS signaling is intended to travel end-to-end, even in the presence 1525 of NATs and firewalls on-path. This works well in cases where the 1526 data sender is itself behind a NAT or a firewall as described in 1527 Section 3.7.1. For scenarios where the data receiver is located 1528 behind a NAT or a firewall and it needs to receive data flows from 1529 outside its own network (usually referred to as inbound flows, see 1530 Figure 5) the problem is more troublesome. 1532 NSIS signaling, as well as subsequent data flows, are directed to a 1533 particular destination IP address that must be known in advance and 1534 reachable. Data receivers must tell the local NSIS infrastructure 1535 (i.e., the inbound firewalls/NATs) about incoming NATFW NSLP 1536 signaling and data flows before they can receive these flows. It is 1537 necessary to differentiate between data receivers behind NATs and 1538 behind firewalls for understanding the further NATFW procedures. 1539 Data receivers that are only behind firewalls already have a public 1540 IP address and they need only to be reachable for NATFW signaling. 1541 Unlike data receivers behind just firewalls, data receivers behind 1542 NATs do not have public IP addresses; consequently they are not 1543 reachable for NATFW signaling by entities outside their addressing 1544 realm. 1546 The preceding discussion addresses the situation where a DR node that 1547 wants to be reachable is unreachable because the NAT lacks a suitable 1548 rule with the 'allow' action which would forward inbound data. 1549 However, in certain scenarios, a node situated behind inbound 1550 firewalls that do not block inbound data traffic (firewalls with 1551 "default to allow") unless requested might wish to prevent traffic 1552 being sent to it from specified addresses. In this case, NSIS NATFW 1553 signaling can be used to achieve this by installing a policy rule 1554 with its action set to 'deny' using the same mechanisms as for 1555 'allow' rules. 1557 The required result is obtained by sending a EXTERNAL (EXT) message 1558 in the inbound direction of the intended data flow. When using this 1559 functionality the NSIS initiator for the 'Reserve External Address' 1560 signaling is typically the node that will become the DR for the 1561 eventual data flow. To distinguish this initiator from the usual 1562 case where the NI is associated with the DS, the NI is denoted by NI+ 1563 and the NSIS responder is similarly denoted by NR+. 1565 Public Internet Private Address 1566 Space 1568 Edge 1569 NI(DS) NAT/FW NAT NR(DR) 1570 NR+ NI+ 1572 | | | | 1573 | | | | 1574 | | | | 1575 | | EXT[(DTInfo)] | EXT[(DTInfo)] | 1576 | |<----------------------|<----------------------| 1577 | | | | 1578 | |RESPONSE[Success/Error]|RESPONSE[Success/Error]| 1579 | |---------------------->|---------------------->| 1580 | | | | 1581 | | | | 1583 ============================================================> 1584 Data Traffic Direction 1586 Figure 14: Reservation message flow for DR behind NAT or firewall 1588 Figure 14 shows the EXT message flow for enabling inbound NATFW NSLP 1589 signaling messages. In this case the roles of the different NSIS 1590 entities are: 1592 o The data receiver (DR) for the anticipated data traffic is the 1593 NSIS initiator (NI+) for the EXTERNAL (EXT) message, but becomes 1594 the NSIS responder (NR) for following CREATE messages. 1596 o The actual data sender (DS) will be the NSIS initiator (NI) for 1597 later CREATE messages and may be the NSIS target of the signaling 1598 (NR+). 1600 o It may be necessary to use a signaling destination address (SDA) 1601 as the actual target of the EXT message (NR+) if the DR is located 1602 behind a NAT and the address of the DS is unknown. The SDA is an 1603 arbitrary address in the outermost address realm on the other side 1604 of the NAT from the DR. Typically this will be a suitable public 1605 IP address when the 'outside' realm is the public Internet. This 1606 choice of address causes the EXT message to be routed through the 1607 NATs towards the outermost realm and would force interception of 1608 the message by the outermost NAT in the network at the boundary 1609 between the private address and the public address realm (the 1610 edge-NAT). It may also be intercepted by other NATs and firewalls 1611 on the path to the edge-NAT. 1613 Basically, there are two different signaling scenarios. Either 1615 1. the DR behind the NAT/firewall knows the IP address of the DS in 1616 advance, 1618 2. or the address of DS is not known in advance. 1620 Case 1 requires the NATFW NSLP to request the path-coupled message 1621 routing method (PC-MRM) from the NTLP. The EXT message MUST be sent 1622 with PC-MRM (see Section 5.8.1 in [2]) with the direction set to 1623 'upstream' (inbound). The handling of case 2 depends on the 1624 situation of DR: If DR is solely located behind a firewall, the EXT 1625 message MUST be sent with the PC-MRM, direction 'upstream' (inbound), 1626 and data flow source IP address set to wildcard. If DR is located 1627 behind a NAT, the EXT message MUST be sent with the loose-end message 1628 routing method (LE-MRM, see Section 5.8.2 in [2]), the destination- 1629 address set to the signaling destination address (SDA, see also 1630 Appendix A). For scenarios with DR being behind a firewall, special 1631 conditions apply (applicability statement, Appendix B). The data 1632 receiver is challenged to determine whether it is solely located 1633 behind firewalls or NATs, for choosing the right message routing 1634 method. This decision can depend on a local configuration parameter, 1635 possibly given through DHCP, or it could be discovered through other 1636 non-NSLP related testing of the network configuration. 1638 For case 2 with NAT, the NI+ (which could be on the data receiver DR 1639 or on any other host within the private network) sends the EXT 1640 message targeted to the signaling destination address. The message 1641 routing for the EXT message is in the reverse direction to the normal 1642 message routing used for path-coupled signaling where the signaling 1643 is sent outbound (as opposed to inbound in this case). When 1644 establishing NAT bindings (and an NATFW NSLP signaling session) the 1645 signaling direction does not matter since the data path is modified 1646 through route pinning due to the external IP address at the NAT. 1647 Subsequent NSIS messages (and also data traffic) will travel through 1648 the same NAT boxes. However, this is only valid for the NAT boxes, 1649 but not for any intermediate firewall. That is the reason for having 1650 a separate CREATE message enabling the reservations made with EXT at 1651 the NATs and either enabling prior reservations or creating new 1652 pinholes at the firewalls which are encountered on the outbound path 1653 depending on whether the inbound and outbound routes coincide. 1655 The EXT signaling message creates an NSIS NATFW signaling session at 1656 any intermediate NSIS NATFW peer(s) encountered, independent of the 1657 message routing method used. Furthermore, it has to be ensured that 1658 the edge-NAT or edge-firewall device is discovered as part of this 1659 process. The end host cannot be assumed to know this device - 1660 instead the NAT or firewall box itself is assumed to know that it is 1661 located at the outer perimeter of the network. Forwarding of the EXT 1662 message beyond this entity is not necessary, and MUST be prohibited 1663 as it may provide information on the capabilities of internal hosts. 1664 It should be noted, that it is the outermost NAT or firewall that is 1665 the edge-device that must be found during this discovery process. 1666 For instance, when there are a NAT and afterwards a firewall on the 1667 outbound path at the network border, the firewall is the edge- 1668 firewall. All messages must be forwarded to the topology-wise 1669 outermost edge-device, to ensure that this devices knows about the 1670 NATFW NSLP signaling sessions for incoming CREATE messages. However, 1671 the NAT is still the edge-NAT because it has a public globally 1672 routable IP address on its public side: this is not affected by any 1673 firewall between the edge-NAT and the public network. 1675 Possible edge arrangements are: 1677 Public Net ----------------- Private net -------------- 1679 | Public Net|--|Edge-FW|--|FW|...|FW|--|DR| 1681 | Public Net|--|Edge-FW|--|Edge-NAT|...|NAT or FW|--|DR| 1683 | Public Net|--|Edge-NAT|--|NAT or FW|...|NAT or FW|--|DR| 1685 The edge-NAT or edge-firewall device closest to the public realm 1686 responds to the EXT message with a successful RESPONSE message. An 1687 edge-NAT includes an NATFW_EXT_IP object (see Section 4.2.2), 1688 carrying the public reachable IP address, and if applicable port 1689 number. 1691 There are several processing rules for a NATFW peer when generating 1692 and receiving EXT messages, since this message type is used for 1693 creating new reserve NATFW NSLP signaling sessions, updating 1694 existing, extending the lifetime and deleting NATFW NSLP signaling 1695 session. The three latter functions operate in the same way for all 1696 kinds of CREATE and EXT messages, and are therefore described in 1697 separate sections: 1699 o Extending the lifetime of NATFW NSLP signaling sessions is 1700 described in Section 3.7.3. 1702 o Deleting NATFW NSLP signaling sessions is described in 1703 Section 3.7.4. 1705 o Updating policy rules is described in Section 3.10. 1707 The NI+ MUST include a NATFW_DTINFO object in the EXT message when 1708 using the LE-MRM. The LE-MRM does not include enough information for 1709 some types of NATs (basically, those NATs which also translate port 1710 numbers) to perform the address translation. This information is 1711 provided in the NATFW_DTINFO (see Section 4.2.7). This information 1712 MUST include at least the 'dst port number' and 'protocol' fields, in 1713 the NATFW_DTINFO object as these may be required by en-route NATs, 1714 depending on the type of the NAT. All other fields MAY be set by the 1715 NI+ to restrict the set of possible NIs. An edge-NAT will use the 1716 information provided in the NATFW_DTINFO object to allow only NATFW 1717 CREATE message with the MRI matching ('src IPv4/v6 address', 'src 1718 port number', 'protocol') to be forwarded. A NAT requiring 1719 information carried in the NATFW_DTINFO can generate a number of 1720 error RESPONSE messages of class 'Signaling session failures' (0x6): 1722 o 'Requested policy rule denied due to policy conflict' (0x04) 1724 o 'NATFW_DTINFO object is required' (0x07) 1726 o 'Requested value in sub_ports field in NATFW_EFI not permitted' 1727 (0x08) 1729 o 'Requested IP protocol not supported' (0x09) 1731 o 'Plain IP policy rules not permitted -- need transport layer 1732 information' (0x0A) 1734 o 'source IP address range is too large' (0x0C) 1736 o 'destination IP address range is too large' (0x0D) 1738 o 'source L4-port range is too large' (0x0E) 1740 o 'destination L4-port range is too large' (0x0F) 1742 Processing of EXT messages is specific to the NSIS node type: 1744 o NSLP initiator: NI+ only generate EXT messages. When the data 1745 sender's address information is known in advance the NI+ can 1746 include a NATFW_DTINFO object in the EXT message, if not anyway 1747 required to do so (see above). When the data sender's IP address 1748 is not known, the NI+ MUST NOT include a NATFW_DTINFO object. The 1749 NI should never receive EXT messages and MUST silently discard it. 1751 o NSLP forwarder: The NSLP message processing at NFs depends on the 1752 middlebox type: 1754 * NAT: NATs check whether the message is received at the external 1755 (public in most cases) address or at the internal (private) 1756 address. If received at the external an NF MUST generate an 1757 error RESPONSE of class 'Protocol error' (0x3) with response 1758 code 'Received EXT request message on external side' (0x0B). 1759 If received at the internal (private address) and the NATFW_EFI 1760 object contains the action 'deny', an error RESPONSE of class 1761 'Protocol error' (0x3) with response code 'Requested rule 1762 action not applicable' (0x06) MUST be generated. If received 1763 at the internal address, an IP address, and if applicable one 1764 or more ports, are reserved. If it is an edge-NAT and there is 1765 no edge-firewall beyond, the NSLP message is not forwarded any 1766 further and a successful RESPONSE message is generated 1767 containing an NATFW_EXT_IP object holding the translated 1768 address, and if applicable port, information from the binding 1769 reserved as a result of the EXT message. The RESPONSE message 1770 is sent back towards the NI+. If it is not an edge-NAT, the 1771 NSLP message is forwarded further using the translated IP 1772 address as signaling source address in the LE-MRM and 1773 translated port in the NATFW_DTINFO object in the field 'DR 1774 port number', i.e., the NATFW_DTINFO object is updated to 1775 reflect the translated port number. The edge-NAT or any other 1776 NAT MUST reject EXT messages not carrying a NATFW_DTINFO object 1777 or if the address information within this object is invalid or 1778 is not compliant with local policies (e.g., the information 1779 provided relates to a range of addresses ('wildcarded') but the 1780 edge-NAT requires exact information about DS' IP address and 1781 port) with the above mentioned response codes. 1783 * Firewall: Non edge-firewalls remember the requested policy 1784 rule, keep NATFW NSLP signaling session state, and forward the 1785 message. Edge-firewalls stop forwarding the EXT message. The 1786 policy rule is immediately loaded if the action in the 1787 NATFW_EFI object is set to 'deny' and the node is an edge- 1788 firewall. The policy rule is remembered, but not activated, if 1789 the action in the NATFW_EFI object is set to 'allow'. In both 1790 cases, a successful RESPONSE message is generated. If the 1791 action is 'allow', and the NATFW_DTINFO object is included, and 1792 the MRM is set to LE-MRM in the request, additionally an 1793 NATFW_EXT_IP object is included in the RESPONSE message, 1794 holding the translated address, and if applicable port, 1795 information. This information is obtained from the 1796 NATFW_DTINFO object's 'DR port number' and the source-address 1797 of the LE-MRM. 1799 * Combined NAT and firewall: Processing at combined firewall and 1800 NAT middleboxes is the same as in the NAT case. 1802 o NSLP receiver: This type of message should never be received by 1803 any NR+ and it MUST generate an error RESPONSE message of class 1804 'Permanent failure' (0x5) with response code 'No edge-device here' 1805 (0x06). 1807 Processing of a RESPONSE message is different for every NSIS node 1808 type: 1810 o NSLP initiator: Upon receiving a successful RESPONSE message, the 1811 NI+ can rely on the requested configuration for future inbound 1812 NATFW NSLP signaling sessions. If the response contains an 1813 NATFW_EXT_IP object, the NI can use IP address and port pairs 1814 carried for further application signaling. After receiving a 1815 error RESPONSE message, the NI+ MAY try to generate the EXT 1816 message again or give up and report the failure to the 1817 application, depending on the error condition. 1819 o NSLP forwarder: NFs simply forward this message as long as they 1820 keep state for the requested reservation, if the RESPONSE message 1821 contains NATFW_INFO object with class set to 'Success' (0x2). If 1822 the RESPONSE message contains NATFW_INFO object with class set not 1823 to 'Success' (0x2), the NATFW NSLP signaling session is marked as 1824 dead. 1826 o NSIS responder: This type of message should never be received by 1827 any NR+. The NF should never receive response messages and MUST 1828 silently discard it. 1830 Reservations with action 'allow' made with EXT MUST be enabled by a 1831 subsequent CREATE message. A reservation made with EXT (independent 1832 of selected action) is kept alive as long as the NI+ refreshes the 1833 particular NATFW NSLP signaling session and it can be reused for 1834 multiple, different CREATE messages. An NI+ may decide to teardown a 1835 reservation immediately after receiving a CREATE message. This 1836 implies that a new NATFW NSLP signaling session must be created for 1837 each new CREATE message. The CREATE message does not re-use the 1838 NATFW NSLP signaling session created by REA. 1840 Without using CREATE Section 3.7.1 or EXT in proxy mode Section 3.7.6 1841 no data traffic will be forwarded to DR beyond the edge-NAT or edge- 1842 firewall. The only function of EXT is to ensure that subsequent 1843 CREATE messages traveling towards the NR will be forwarded across the 1844 public-private boundary towards the DR. Correlation of incoming 1845 CREATE messages to EXT reservation states is described in 1846 Section 3.8. 1848 3.7.3. NATFW NSLP Signaling Session Refresh 1850 NATFW NSLP signaling sessions are maintained on a soft-state basis. 1851 After a specified timeout, sessions and corresponding policy rules 1852 are removed automatically by the middlebox, if they are not 1853 refreshed. Soft-state is created by CREATE and EXT and the 1854 maintenance of this state must be done by these messages. State 1855 created by CREATE must be maintained by CREATE, state created by EXT 1856 must be maintained by EXT. Refresh messages, are messages carrying 1857 the same session ID as the initial message and a NATFW_LT lifetime 1858 object with a lifetime greater than zero. Messages with the same SID 1859 but carrying a different MRI are treated as updates of the policy 1860 rules and are processed as defined in Section 3.10. Every refresh 1861 CREATE or EXT message MUST be acknowledged by an appropriate response 1862 message generated by the NR. Upon reception by each NSIS forwarder, 1863 the state for the given session ID is extended by the NATFW NSLP 1864 signaling session refresh period, a period of time calculated based 1865 on a proposed refresh message period. The lifetime extension of a 1866 NATFW NSLP signaling session is calculated as current local time plus 1867 proposed lifetime value (NATFW NSLP signaling session refresh 1868 period). Section 3.4 defines the process of calculating lifetimes in 1869 detail. 1871 NI Public Internet NAT Private address NR 1873 | | space | 1874 | CREATE[lifetime > 0] | | 1876 |----------------------------->| | 1877 | | | 1878 | | | 1879 | | CREATE[lifetime > 0] | 1880 | |--------------------------->| 1881 | | | 1882 | | RESPONSE[Success/Error] | 1883 | RESPONSE[Success/Error] |<---------------------------| 1884 |<-----------------------------| | 1885 | | | 1886 | | | 1888 Figure 16: Successful Refresh Message Flow, CREATE as example 1890 Processing of NATFW NSLP signaling session refresh CREATE and EXT 1891 messages is different for every NSIS node type: 1893 o NSLP initiator: The NI/NI+ can generate NATFW NSLP signaling 1894 session refresh CREATE/EXT messages before the NATFW NSLP 1895 signaling session times out. The rate at which the refresh 1896 CREATE/EXT messages are sent and their relation to the NATFW NSLP 1897 signaling session state lifetime is discussed further in 1898 Section 3.4. 1900 o NSLP forwarder: Processing of this message is independent of the 1901 middlebox type and is as described in Section 3.4. 1903 o NSLP responder: NRs accepting a NATFW NSLP signaling session 1904 refresh CREATE/EXT message generate a successful RESPONSE message, 1905 including the granted lifetime value of Section 3.4 in a NATFW_LT 1906 object. 1908 3.7.4. Deleting Signaling Sessions 1910 NATFW NSLP signaling sessions can be deleted at any time. NSLP 1911 initiators can trigger this deletion by using a CREATE or EXT 1912 messages with a lifetime value set to 0, as shown in Figure 17. 1913 Whether a CREATE or EXT message type is used, depends on how the 1914 NATFW NSLP signaling session was created. 1916 NI Public Internet NAT Private address NR 1918 | | space | 1919 | CREATE[lifetime=0] | | 1920 |----------------------------->| | 1921 | | | 1922 | | CREATE[lifetime=0] | 1923 | |--------------------------->| 1924 | | | 1926 Figure 17: Delete message flow, CREATE as example 1928 NSLP nodes receiving this message delete the NATFW NSLP signaling 1929 session immediately. Policy rules associated with this particular 1930 NATFW NSLP signaling session MUST be also deleted immediately. This 1931 message is forwarded until it reaches the final NR. The CREATE/EXT 1932 message with a lifetime value of 0, does not generate any response, 1933 neither positive nor negative, since there is no NSIS state left at 1934 the nodes along the path. 1936 NSIS initiators can use CREATE/EXT message with lifetime set to zero 1937 in an aggregated way, such that a single CREATE or EXT message is 1938 terminating multiple NATFW NSLP signaling sessions. NIs can follow 1939 this procedure if the like to aggregate NATFW NSLP signaling session 1940 deletion requests: The NI uses the CREATE or EXT message with the 1941 session ID set to zero and the MRI's source-address set to its used 1942 IP address. All other fields of the respective NATFW NSLP signaling 1943 sessions to be terminated are set as well, otherwise these fields are 1944 completely wildcarded. The NSLP message is transferred to the NTLP 1945 requesting 'explicit routing' as described in Sections 5.2.1 and 1946 7.1.4. in [2]. 1948 The outbound NF receiving such an aggregated CREATE or EXT message 1949 MUST reject it with an error RESPONSE of class 'Permanent failure' 1950 (0x5) with response code 'Authentication failed' (0x01) if the 1951 authentication fails and with an error RESPONSE of class 'Permanent 1952 failure' (0x5) with response code 'Authorization failed' (0x02) if 1953 the authorization fails. Per NATFW NSLP signaling session proof of 1954 ownership, as it is defined in this memo, is not possible anymore 1955 when using this aggregated way. However, the outbound NF can use the 1956 relationship between the information of the received CREATE or EXT 1957 message and the GIST messaging association where the request has been 1958 received. The outbound NF MUST only accept this aggregated CREATE or 1959 EXT message through already established GIST messaging associations 1960 with the NI. The outbound NF MUST NOT propagate this aggregated 1961 CREATE or EXT message but it MAY generate and forward per NATFW NSLP 1962 signaling session CREATE or EXT messages. 1964 3.7.5. Reporting Asynchronous Events 1966 NATFW NSLP forwarders and NATFW NSLP responders must have the ability 1967 to report asynchronous events to other NATFW NSLP nodes, especially 1968 to allow reporting back to the NATFW NSLP initiator. Such 1969 asynchronous events may be premature NATFW NSLP signaling session 1970 termination, changes in local policies, route change or any other 1971 reason that indicates change of the NATFW NSLP signaling session 1972 state. 1974 NFs and NRs may generate NOTIFY messages upon asynchronous events, 1975 with a NATFW_INFO object indicating the reason for event. These 1976 reasons can be carried in the NATFW_INFO object (class MUST be set to 1977 'Informational' (0x1)) within the NOTIFY message. This list shows 1978 the response codes and the associated actions to take at NFs and the 1979 NI: 1981 o 'Route change: possible route change on the outbound path' (0x01): 1982 Follow instructions in Section 3.9. This MUST be sent inbound. 1984 o 'Re-authentication required' (0x02): The NI should re-send the 1985 authentication. This MUST be sent inbound. 1987 o 'NATFW node is going down soon' (0x03): The NI and other NFs 1988 should be prepared for a service interruption at any time. This 1989 message MAY be sent inbound and outbound. 1991 o 'NATFW signaling session lifetime expired' (0x04): The NATFW 1992 signaling session has been expired and the signaling session is 1993 invalid now. NFs MUST mark the signaling session as 'Dead'. This 1994 message MAY be sent inbound and outbound. 1996 NOTIFY messages are always sent hop-by-hop inbound towards NI until 1997 they reach NI or outbound towards the NR as indicated in the list 1998 above. 2000 The initial processing when receiving a NOTIFY message is the same 2001 for all NATFW nodes: NATFW nodes MUST only accept NOTIFY messages 2002 through already established NTLP messaging associations. The further 2003 processing is different for each NATFW NSLP node type and depends on 2004 the events notified: 2006 o NSLP initiator: NIs analyze the notified event and behave 2007 appropriately based on the event type. NIs MUST NOT generate 2008 NOTIFY messages. 2010 o NSLP forwarder: NFs analyze the notified event and behave based on 2011 the above description per response code. NFs SHOULD generate 2012 NOTIFY messages upon asynchronous events and forward them inbound 2013 towards the NI or outbound towards the NR, depending on the 2014 received direction, i.e., inbound messages MUST be forwarded 2015 further inbound and outbound messages MUST be forwarded further 2016 inbound. NFs MUST silently discard NOTIFY messages that have been 2017 received outbound but are only allowed to be sent inbound, e.g. 2018 'Re-authentication required' (0x02). 2020 o NSLP responder: NRs SHOULD generate NOTIFY messages upon 2021 asynchronous events including a response code based on the 2022 reported event. The NR MUST silently discard NOTIFY messages that 2023 have been received outbound but are only allowed to be sent 2024 inbound, e.g. 'Re-authentication required' (0x02), 2026 NATFW NSLP forwarders, keeping multiple NATFW NSLP signaling sessions 2027 at the same time, can experience problems when shutting down service 2028 suddenly. This sudden shutdown can be result of node local failure, 2029 for instance, due to a hardware failure. This NF generates NOTIFY 2030 messages for each of the NATFW NSLP signaling sessions and tries to 2031 send them inbound. Due to the number of NOTIFY messages to be sent, 2032 the shutdown of the node may be unnecessarily prolonged, since not 2033 all messages can be sent at the same time. This case can be 2034 described as a NOTIFY storm, if a multitude of NATFW NSLP signaling 2035 sessions is involved. 2037 To avoid the need of generating per NATFW NSLP signaling session 2038 NOTIFY messages in such a scenario described or similar cases, NFs 2039 SHOULD follow this procedure: The NF uses the NOTIFY message with the 2040 session ID in the NTLP set to zero, with the MRI completely 2041 wildcarded, using the 'explicit routing' as described in Sections 2042 5.2.1 and 7.1.4. in [2]. The inbound NF receiving this type of 2043 NOTIFY immediately regards all NATFW NSLP signaling sessions from 2044 that peer matching the MRI as void. This message will typically 2045 result in multiple NOTIFY messages at the inbound NF, i.e., the NF 2046 can generate per terminated NATFW NSLP signaling session a NOTIFY 2047 message. However, a NF MAY aggregate again the NOTIFY messages as 2048 described here. 2050 3.7.6. Proxy Mode of Operation 2052 Some migration scenarios need specialized support to cope with cases 2053 where NSIS is only deployed in same areas of the Internet. End-to- 2054 end signaling is going to fail without NSIS support at or near both 2055 data sender and data receiver terminals. A proxy mode of operation 2056 is needed. This proxy mode of operation must terminate the NATFW 2057 NSLP signaling as topologically close to the terminal for which it is 2058 proxying and proxy all messages. This NATFW NSLP node doing the 2059 proxying of the signaling messages becomes either the NI or the NR 2060 for the particular NATFW NSLP signaling session, depending on whether 2061 it is the DS or DR that does not support NSIS. Typically, the edge- 2062 NAT or the edge-firewall would be used to proxy NATFW NSLP messages. 2064 This proxy mode operation does not require any new CREATE or EXT 2065 message type, but relies on extended CREATE and EXT message types. 2066 They are called respectively CREATE-PROXY and EXT-PROXY and are 2067 distinguished by setting the P flag in the NSLP header to P=1. This 2068 flag instructs edge-NATs and edge-firewalls receiving them to operate 2069 in proxy mode for the NATFW NSLP signaling session in question. The 2070 semantics of the CREATE and EXT message types are not changed and the 2071 behavior of the various node types is as defined in Section 3.7.1 and 2072 Section 3.7.2, except for the proxying node. The following 2073 paragraphs describe the proxy mode operation for data receivers 2074 behind middleboxes and data senders behind middleboxes. 2076 3.7.6.1. Proxying for a Data Sender 2078 The NATFW NSLP gives the NR the ability to install state on the 2079 inbound path towards the data sender for outbound data packets, even 2080 when only the receiving side is running NSIS (as shown in Figure 18). 2081 The goal of the method described is to trigger the edge-NAT/ 2082 edge-firewall to generate a CREATE message on behalf of the data 2083 receiver. In this case, an NR can signal towards the network border 2084 as it is performed in the standard EXT message handling scenario as 2085 in Section 3.7.2. The message is forwarded until the edge-NAT/ 2086 edge-firewall is reached. A public IP address and port number is 2087 reserved at an edge-NAT/edge-firewall. As shown in Figure 18, unlike 2088 the standard EXT message handling case, the edge-NAT/edge-firewall is 2089 triggered to send a CREATE message on a new reverse path which 2090 traverse several firewalls or NATs. The new reverse path for CREATE 2091 is necessary to handle routing asymmetries between the edge-NAT/ 2092 edge-firewall and DR. It must be stressed that the semantics of the 2093 CREATE and EXT messages is not changed, i.e., each is processed as 2094 described earlier. 2096 DS Public Internet NAT/FW Private address NR 2097 No NI NF space NI+ 2098 NR+ 2100 | | EXT-PROXY[(DTInfo)] | 2101 | |<------------------------- | 2102 | | RESPONSE[Error/Success] | 2103 | | ---------------------- > | 2104 | | CREATE | 2105 | | ------------------------> | 2106 | | RESPONSE[Error/Success] | 2107 | | <---------------------- | 2108 | | | 2110 Figure 18: EXT Triggering Sending of CREATE Message 2112 A NATFW_NONCE object, carried in the EXT and CREATE message, is used 2113 to build the relationship between received CREATEs at the message 2114 initiator. An NI+ uses the presence of the NATFW_NONCE object to 2115 correlate it to the particular EXT-PROXY. The absence of a NONCE 2116 object indicates a CREATE initiated by the DS and not by the edge- 2117 NAT. Therefore, these processing rules of EXT-PROXY messages are 2118 added to the regular EXT processing: 2120 o NSLP initiator (NI+): The NI+ MUST choose a random value and place 2121 it in the NATFW_NONCE object. 2123 o NSLP forwarder being either edge-NAT or edge-firewall: When the NF 2124 accepts a EXT_PROXY message, it generates a successful RESPONSE 2125 message as if it were the NR and additionally, it generates a 2126 CREATE message as defined in Section 3.7.1 and includes a 2127 NATFW_NONCE object having the same value as of the received 2128 NATFW_NONCE object. The NF MUST NOT generate a CREATE-PROXY 2129 message. The NF MUST refresh the CREATE message signaling session 2130 only if a EXT-PROXY refresh message has been received first. This 2131 also includes tearing down signaling sessions, i.e., the NF must 2132 teardown the CREATE signaling session only if a EXT-PROXY message 2133 with lifetime set to 0 has been received first. 2135 The scenario described in this section challenges the data receiver 2136 because it must make a correct assumption about the data sender's 2137 ability to use NSIS NATFW NSLP signaling. It is possible for the DR 2138 to make the wrong assumption in two different ways: 2140 a) the DS is NSIS unaware but the DR assumes the DS to be NSIS 2141 aware and 2143 b) the DS is NSIS aware but the DR assumes the DS to be NSIS 2144 unaware. 2146 Case a) will result in middleboxes blocking the data traffic, since 2147 DS will never send the expected CREATE message. Case b) will result 2148 in the DR successfully requesting proxy mode support by the edge-NAT 2149 or edge-firewall. The edge-NAT/edge-firewall will send CREATE 2150 messages and DS will send CREATE messages as well. Both CREATE 2151 messages are handled as separated NATFW NSLP signaling sessions and 2152 therefore the common rules per NATFW NSLP signaling session apply; 2153 the NATFW_NONCE object is used to differentiate CREATE messages 2154 generated by the edge-NAT/edge-firewall from NI initiated CREATE 2155 messages. It is the NR's responsibility to decide whether to 2156 teardown the EXT-PROXY signaling sessions in the case where the data 2157 sender's side is NSIS aware, but was incorrectly assumed not to be so 2158 by the DR. It is RECOMMENDED that a DR behind NATs uses the proxy 2159 mode of operation by default, unless the DR knows that the DS is NSIS 2160 aware. The DR MAY cache information about data senders which it has 2161 found to be NSIS aware in past NATFW NSLP signaling sessions. 2163 There is a possible race condition between the RESPONSE message to 2164 the EXT-PROXY and the CREATE message generated by the edge-NAT. The 2165 CREATE message can arrive earlier than the RESPONSE message. An NI+ 2166 MUST accept CREATE messages generated by the edge-NAT even if the 2167 RESPONSE message to the EXT-PROXY was not received. 2169 3.7.6.2. Proxying for a Data Receiver 2171 As with data receivers behind middleboxes, data senders behind 2172 middleboxes can require proxy mode support. The issue here is that 2173 there is no NSIS support at the data receiver's side and, by default, 2174 there will be no response to CREATE messages. This scenario requires 2175 the last NSIS NATFW NSLP aware node to terminate the forwarding and 2176 to proxy the response to the CREATE message, meaning that this node 2177 is generating RESPONSE messages. This last node may be an edge-NAT/ 2178 edge-firewall, or any other NATFW NSLP peer, that detects that there 2179 is no NR available (probably as a result of GIST timeouts but there 2180 may be other triggers). 2182 DS Private Address NAT/FW Public Internet NR 2183 NI Space NF no NR 2185 | | | 2186 | CREATE-PROXY | | 2187 |------------------------------>| | 2188 | | | 2189 | RESPONSE[SUCCESS/ERROR] | | 2190 |<------------------------------| | 2191 | | | 2193 Figure 19: Proxy Mode CREATE Message Flow 2195 The processing of CREATE-PROXY messages and RESPONSE messages is 2196 similar to Section 3.7.1, except that forwarding is stopped at the 2197 edge-NAT/edge-firewall. The edge-NAT/edge-firewall responds back to 2198 NI according the situation (error/success) and will be the NR for 2199 future NATFW NSLP communication. 2201 The NI can choose the proxy mode of operation although the DR is NSIS 2202 aware. The CREATE-PROXY mode would not configure all NATs and 2203 firewalls along the data path, since it is terminated at the edge- 2204 device. Any device beyond this point will never receive any NATFW 2205 NSLP signaling for this flow. 2207 3.8. De-Multiplexing at NATs 2209 Section 3.7.2 describes how NSIS nodes behind NATs can obtain a 2210 public reachable IP address and port number at a NAT and and how the 2211 resulting mapping rule can be activated by using CREATE messages (see 2212 Section 3.7.1). The information about the public IP address/port 2213 number can be transmitted via an application level signaling protocol 2214 and/or third party to the communication partner that would like to 2215 send data toward the host behind the NAT. However, NSIS signaling 2216 flows are sent towards the address of the NAT at which this 2217 particular IP address and port number is allocated and not directly 2218 to the allocated IP address and port number. The NATFW NSLP 2219 forwarder at this NAT needs to know how the incoming NSLP CREATE 2220 messages are related to reserved addresses, meaning how to de- 2221 multiplex incoming NSIS CREATE messages. 2223 The de-multiplexing method uses information stored at the local NATFW 2224 NSLP node and the of the policy rule. The policy rule uses the LE- 2225 MRM MRI source-address (see [2]) as the flow destination IP address 2226 and the network-layer-version as IP version. The external IP address 2227 at the NAT is stored as the external flow destination IP address. 2228 All other parameters of the policy rule other than the flow 2229 destination IP address are wildcarded if no NATFW_DTINFO object is 2230 included in the EXT message. The LE-MRM MRI destination-address MUST 2231 NOT be used in the policy rule, since it is solely a signaling 2232 destination address. 2234 If the NATFW_DTINFO object is included in the EXT message, the policy 2235 rule is filled with further information. The 'dst port number' field 2236 of the NATFW_DTINFO is stored as the flow destination port number. 2237 The 'protocol' field is stored as the flow protocol. The 'src port 2238 number' field is stored as the flow source port number. The 'data 2239 sender's IPv4 address' is stored as the flow source IP address. Note 2240 that some of these field can contain wildcards. 2242 When receiving a CREATE message at the NATFW NSLP it uses the flow 2243 information stored in the MRI to do the matching process. This table 2244 shows the parameters to be compared against each others. Note that 2245 not all parameters can be present in a MRI at the same time. 2247 +-------------------------------+--------------------------------+ 2248 | Flow parameter (Policy Rule) | MRI parameter (CREATE message) | 2249 +-------------------------------+--------------------------------+ 2250 | IP version | network-layer-version | 2251 | | | 2252 | Protocol | IP-protocol | 2253 | | | 2254 | source IP address (w) | source-address (w) | 2255 | | | 2256 | external IP address | destination-address | 2257 | | | 2258 | destination IP address (n/u) | N/A | 2259 | | | 2260 | source port number (w) | L4-source-port (w) | 2261 | | | 2262 | external port number (w) | L4-destination-port (w) | 2263 | | | 2264 | destination port number (n/u) | N/A | 2265 | | | 2266 | IPsec SPI | ipsec-SPI | 2267 +-------------------------------+--------------------------------+ 2269 Table entries marked with (w) can be wildcarded and entries marked 2270 with (n/u) are not used for the matching. 2272 Table 1 2274 3.9. Reacting to Route Changes 2276 The NATFW NSLP needs to react to route changes in the data path. 2277 This assumes the capability to detect route changes, to perform NAT 2278 and firewall configuration on the new path and possibly to tear down 2279 NATFW NSLP signaling session state on the old path. The detection of 2280 route changes is described in Section 7 of [2] and the NATFW NSLP 2281 relies on notifications about route changes by the NTLP. This 2282 notification will be conveyed by the API between NTLP and NSLP, which 2283 is out of scope of this memo. 2285 A NATFW NSLP node other than the NI or NI+ detecting a route change, 2286 by means described in the NTLP specification or others, generates a 2287 NOTIFY message indicating this change and sends this inbound towards 2288 NI. Intermediate NFs on the way to the NI can use this information 2289 to decide later if their NATFW NSLP signaling session can be deleted 2290 locally, if they do not receive an update within a certain time 2291 period, as described in Section 3.2.3. It is important to consider 2292 the transport limitations of NOTIFY messages as mandated in 2293 Section 3.7.5. 2295 The NI receiving this NOTIFY message MAY generate a new CREATE or EXT 2296 message and sends it towards the NATFW NSLP signaling session's NI as 2297 for the initial message using the same session ID. All the remaining 2298 processing and message forwarding, such as NSLP next hop discovery, 2299 is subject to regular NSLP processing as described in the particular 2300 sections. Normal routing will guide the new CREATE or EXT message to 2301 the correct NFs along the changed route. NFs that were on the 2302 original path receiving these new CREATE or EXT messages (see also 2303 Section 3.10), can use the session ID to update the existing NATFW 2304 NSLP signaling session, whereas NFs that were not on the original 2305 path will create new state for this NATFW NSLP signaling session. 2306 The next section describes how policy rules are updated. 2308 3.10. Updating Policy Rules 2310 NSIS initiators can request an update of the installed/reserved 2311 policy rules at any time within a NATFW NSLP signaling session. 2312 Updates to policy rules can be required due to node mobility (NI is 2313 moving from one IP address to another), route changes (this can 2314 result in a different NAT mapping at a different NAT device), or the 2315 wish of the NI to simply change the rule. NIs can update policy 2316 rules in existing NATFW NSLP signaling sessions by sending an 2317 appropriate CREATE or EXT message (similar to Section 3.4) with 2318 modified message routing information (MRI) as compared with that 2319 installed previously, but using the existing session ID to identify 2320 the intended target of the update. With respect to authorization and 2321 authentication, this update CREATE or EXT message is treated in 2322 exactly the same way as any initial message. Therefore, any node 2323 along in the NATFW NSLP signaling session can reject the update with 2324 an error RESPONSE message, as defined in the previous sections. 2326 The message processing and forwarding is executed as defined in the 2327 particular sections. A NF or the NR receiving an update, simply 2328 replaces the installed policy rules installed in the firewall/NAT. 2329 The local procedures on how to update the MRI in the firewall/NAT is 2330 out of scope of this memo 2332 4. NATFW NSLP Message Components 2334 A NATFW NSLP message consists of a NSLP header and one or more 2335 objects following the header. The NSLP header is carried in all 2336 NATFW NSLP message and objects are Type-Length-Value (TLV) encoded 2337 using big endian (network ordered) binary data representations. 2338 Header and objects are aligned to 32 bit boundaries and object 2339 lengths that are not multiples of 32 bits must be padded to the next 2340 higher 32 bit multiple. 2342 The whole NSLP message is carried as payload of a NTLP message. 2344 Note that the notation 0x is used to indicate hexadecimal numbers. 2346 4.1. NSLP Header 2348 All GIST NSLP-Data objects for the NATFW NSLP MUST contain this 2349 common header as the first 32 bits of the object (this is not the 2350 same as the GIST Common Header). It contains two fields, the NSLP 2351 message type and a reserved field. The total length is 32 bits. The 2352 layout of the NSLP header is defined by Figure 20. 2354 0 1 2 3 2355 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 2356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2357 | Message type |P| reserved | reserved | 2358 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2360 Figure 20: Common NSLP header 2362 The reserved field MUST be set to zero in the NATFW NSLP header 2363 before sending and MUST be ignored during processing of the header. 2365 The defined messages types are: 2367 o IANA-TBD(1) : CREATE 2369 o IANA-TBD(2) : EXTERNAL(EXT) 2371 o IANA-TBD(3) : RESPONSE 2373 o IANA-TBD(4) : NOTIFY 2375 If a message with another type is received, an error RESPONSE of 2376 class 'Protocol error' (0x3) with response code 'Illegal message 2377 type' (0x01) MUST be generated. 2379 The P flag indicates the usage of proxy mode. If proxy mode is used 2380 it MUST be set to 1. Proxy mode usage is only allowed in combination 2381 with the message types CREATE and EXT, P=1 MUST NOT be set with 2382 message types other than CREATE and EXT. The P flag MUST be ignored 2383 when processing messages with type RESPONSE. An error RESPONSE 2384 message of class 'Protocol error' (0x3) and type 'Bad flags value' 2385 (0x03) MUST be generated, if the P flag is set in NOTIFY messages. 2387 4.2. NSLP Objects 2389 NATFW NSLP objects use a common header format defined by Figure 21. 2390 The object header contains two fields, the NSLP object type and the 2391 object length. Its total length is 32 bits. 2393 0 1 2 3 2394 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 2395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2396 |A|B|r|r| Object Type |r|r|r|r| Object Length | 2397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2399 Figure 21: Common NSLP object header 2401 The object length field contains the total length of the object 2402 without the object header. The unit is a word, consisting of 4 2403 octets. The particular values of type and length for each NSLP 2404 object are listed in the subsequent sections that define the NSLP 2405 objects. An error RESPONSE of class 'Protocol error' (0x3) with 2406 response code 'Wrong object length' (0x07) MUST be generated if the 2407 length given for the object in the object header did not match the 2408 length of the object data present. The two leading bits of the NSLP 2409 object header are used to signal the desired treatment for objects 2410 whose treatment has not been defined in this memo (see [2], Section 2411 A.2.1), i.e., the Object Type has not been defined. NATFW NSLP uses 2412 a subset of the categories defined in GIST: 2414 o AB=00 ("Mandatory"): If the object is not understood, the entire 2415 message containing it MUST be rejected with an error RESPONSE of 2416 class 'Protocol error' (0x3) with response code 'Unknown object 2417 present' (0x06). 2419 o AB=01 ("Optional"): If the object is not understood, it should be 2420 deleted and then the rest of the message processed as usual. 2422 o AB=10 ("Forward"): If the object is not understood, it should be 2423 retained unchanged in any message forwarded as a result of message 2424 processing, but not stored locally. 2426 The combination AB=11 MUST NOT be used and an error RESPONSE of class 2427 'Protocol error' (0x3) with response code 'Invalid Flag-Field 2428 combination' (0x09) MUST be generated. 2430 The following sections do not repeat the common NSLP object header, 2431 they just list the type and the length. 2433 4.2.1. Signaling Session Lifetime Object 2435 The signaling session lifetime object carries the requested or 2436 granted lifetime of a NATFW NSLP signaling session measured in 2437 seconds. 2439 Type: NATFW_LT (IANA-TBD) 2441 Length: 1 2443 0 1 2 3 2444 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 2445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2446 | NATFW NSLP signaling session lifetime | 2447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2449 Figure 22: Signaling Session Lifetime object 2451 4.2.2. External Address Object 2453 The external address object can be included in RESPONSE messages 2454 (Section 4.3.3) only. It carries the publicly reachable IP address, 2455 and if applicable port number, at an edge-NAT. 2457 Type: NATFW_EXT_IP (IANA-TBD) 2459 Length: 2 2461 0 1 2 3 2462 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 2463 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2464 | port number | reserved | 2465 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2466 | IPv4 address | 2467 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2469 Figure 23: External Address Object for IPv4 addresses 2471 Please note that the field 'port number' MUST be set to 0 if only an 2472 IP address has been reserved, for instance, by a traditional NAT. A 2473 port number of 0 MUST be ignored in processing this object. 2475 4.2.3. Extended Flow Information Object 2477 In general, flow information is kept in the message routing 2478 information (MRI) of the NTLP. Nevertheless, some additional 2479 information may be required for NSLP operations. The 'extended flow 2480 information' object carries this additional information about the 2481 action of the policy rule for firewalls/NATs and contiguous port . 2483 Type: NATFW_EFI (IANA-TBD) 2485 Length: 1 2487 0 1 2 3 2488 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 2489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2490 | rule action | sub_ports | 2491 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2493 Figure 24: Extended Flow Information 2495 This object has two fields, 'rule action' and 'sub_ports'. The 'rule 2496 action' field has these meanings: 2498 o 0x0001: Allow: A policy rule with this action allows data traffic 2499 to traverse the middlebox and the NATFW NSLP MUST allow NSLP 2500 signaling to be forwarded. 2502 o 0x0002: Deny: A policy rule with this action blocks data traffic 2503 from traversing the middlebox and the NATFW NSLP MUST NOT allow 2504 NSLP signaling to be forwarded. 2506 If the 'rule action' field contains neither 0x0001 nor 0x0002, an 2507 error RESPONSE of class 'Signaling session error' (0x6) with response 2508 code 'Unknown policy rule action' (0x05) MUST be generated. 2510 The 'sub_ports' field contains the number of contiguous transport 2511 layer ports to which this rule applies. The default value of this 2512 field is 0, i.e., only the port specified in the NTLP's MRM or 2513 NATFW_DTINFO object is used for the policy rule. A value of 1 2514 indicates that additionally to the port specified in the NTLP's MRM 2515 (port1), a second port (port2) is used. This value of port 2 is 2516 calculated as: port2 = port1 + 1. Other values than 0 or 1 MUST NOT 2517 be used in this field and an error RESPONSE of class 'Signaling 2518 session error' (0x6) with response code 'Requested value in sub_ports 2519 field in NATFW_EFI not permitted' (0x08) MUST be generated. Further 2520 version of this memo may allow other values for the 'sub_ports' 2521 field. This two contiguous port numbered ports, can be used by 2522 legacy voice over IP equipment. This legacy equipment assumes that 2523 two adjacent port numbers for its RTP/RTCP flows respectively. 2525 4.2.4. Information Code Object 2527 This object carries the response code, which may be indications for 2528 either a successful or failed CREATE or EXT message depending on the 2529 value of the 'response code' field. 2531 Type: NATFW_INFO (IANA-TBD) 2533 Length: 1 2535 0 1 2 3 2536 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 2537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2538 | Resv. | Class | Response Code |r|r|r|r| Object Type | 2539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2541 Figure 25: Information Code Object 2543 The field 'resv.' is reserved for future extensions and MUST be set 2544 to zero when generating such an object and MUST be ignored when 2545 receiving. The 'Object Type' field contains the type of the object 2546 causing the error. The value of 'Object Type' is set to 0, if no 2547 object is concerned and the leading fours bits marked with 'r' are 2548 always set to zero and ignored. The 4 bit class field contains the 2549 severity class. The following classes are defined: 2551 o 0x1: Informational (NOTIFY only) 2553 o 0x2: Success 2555 o 0x3: Protocol error 2557 o 0x4: Transient failure 2559 o 0x5: Permanent failure 2561 o 0x6: Signaling session failures 2563 Within each severity class a number of responses values are defined 2564 o Informational: 2566 * 0x01: Route change: possible route change on the outbound path. 2568 * 0x02: Re-authentication required. 2570 * 0x03: NATFW node is going down soon. 2572 o Success: 2574 * 0x01: All successfully processed. 2576 o Protocol error: 2578 * 0x01: Illegal message type: the type given in the Message Type 2579 field of the NSLP header is unknown. 2581 * 0x02: Wrong message length: the length given for the message in 2582 the NSLP header does not match the length of the message data. 2584 * 0x03: Bad flags value: an undefined flag or combination of 2585 flags was set in the NSLP header. 2587 * 0x04: Mandatory object missing: an object required in a message 2588 of this type was missing. 2590 * 0x05: Illegal object present: an object was present which must 2591 not be used in a message of this type. 2593 * 0x06: Unknown object present: an object of an unknown type was 2594 present in the message. 2596 * 0x07: Wrong object length: the length given for the object in 2597 the object header did not match the length of the object data 2598 present. 2600 * 0x08: Unknown object field value: a field in an object had an 2601 unknown value. 2603 * 0x09: Invalid Flag-Field combination: An object contains an 2604 invalid combination of flags and/or fields. 2606 * 0x0A: Duplicate object present. 2608 * 0x0B: Received EXT request message on external side. 2610 o Transient failure: 2612 * 0x01: Requested resources temporarily not available. 2614 o Permanent failure: 2616 * 0x01: Authentication failed. 2618 * 0x02: Authorization failed. 2620 * 0x03: Unable to agree transport security with peer. 2622 * 0x04: Internal or system error. 2624 * 0x05: No NAT here. 2626 * 0x06: No edge-device here. 2628 * 0x07: Did not reach the NR. 2630 o Signaling session failures: 2632 * 0x01: Session terminated asynchronously. 2634 * 0x02: Requested lifetime is too big. 2636 * 0x03: No reservation found matching the MRI of the CREATE 2637 request. 2639 * 0x04: Requested policy rule denied due to policy conflict. 2641 * 0x05: Unknown policy rule action. 2643 * 0x06: Requested rule action not applicable. 2645 * 0x07: NATFW_DTINFO object is required. 2647 * 0x08: Requested value in sub_ports field in NATFW_EFI not 2648 permitted. 2650 * 0x09: Requested IP protocol not supported. 2652 * 0x0A: Plain IP policy rules not permitted -- need transport 2653 layer information. 2655 * 0x0B: ICMP type value not permitted. 2657 * 0x0C: source IP address range is too large. 2659 * 0x0D: destination IP address range is too large. 2661 * 0x0E: source L4-port range is too large. 2663 * 0x0F: destination L4-port range is too large. 2665 * 0x10: Requested lifetime is too small. 2667 4.2.5. Nonce Object 2669 This object carries the nonce value as described in Section 3.7.6. 2671 Type: NATFW_NONCE (IANA-TBD) 2673 Length: 1 2675 0 1 2 3 2676 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 2677 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2678 | nonce | 2679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2681 Figure 26: Nonce Object 2683 4.2.6. Message Sequence Number Object 2685 This object carries the MSN value as described in Section 3.5. 2687 Type: NATFW_MSN (IANA-TBD) 2689 Length: 1 2691 0 1 2 3 2692 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 2693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2694 | message sequence number | 2695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2697 Figure 27: Message Sequence Number Object 2699 4.2.7. Data Terminal Information Object 2701 The 'data terminal information' object carries additional information 2702 possibly needed during EXT operations. EXT messages are transported 2703 by the NTLP using the Loose-End message routing method (LE-MRM). The 2704 LE-MRM contains only DR's IP address and a signaling destination 2705 address (destination address). This destination address is used for 2706 message routing only and is not necessarily reflecting the address of 2707 the data sender. This object contains information about (if 2708 applicable) DR's port number (the destination port number), DS' port 2709 number (the source port number), the used transport protocol, the 2710 prefix length of the IP address, and DS' IP address. 2712 Type: NATFW_DTINFO (IANA-TBD) 2714 Length: variable. Maximum 3. 2716 0 1 2 3 2717 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 2718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2719 |I|P|S| reserved | sender prefix | protocol | 2720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2721 : DR port number | DS port number : 2722 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2723 : IPsec SPI : 2724 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2725 | data sender's IPv4 address | 2726 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2728 Figure 28: Data Terminal IPv4 Address Object 2730 The flags are: 2732 o I: I=1 means that 'protocol' should be interpreted. 2734 o P: P=1 means that 'dst port number' and 'src port number' are 2735 present and should be interpreted. 2737 o S: S=1 means that SPI is present and should be interpreted. 2739 The SPI field is only present if S is set. The port numbers are only 2740 present if P is set. The flags P and S MUST NOT be set at the same 2741 time. An error RESPONSE of class 'Protocol error' (0x3) with 2742 response code 'Invalid Flag-Field combination' (0x09) MUST be 2743 generated if they are both set. If either P or S is set, I MUST be 2744 set as well and the protocol field MUST carry the particular 2745 protocol. An error RESPONSE of class 'Protocol error' (0x3) with 2746 response code 'Invalid Flag-Field combination' (0x09) MUST be 2747 generated if S or P is set but I is not set. 2749 The fields MUST be interpreted according these rules: 2751 o (data) sender prefix: This parameter indicates the prefix length 2752 of the 'data sender's IP address' in bits. For instance, a full 2753 IPv4 address requires 'sender prefix' to be set to 32. A value of 2754 0 indicates an IP address wildcard. 2756 o protocol: The IPv4 protocol field. This field MUST be interpreted 2757 if I=1, otherwise it MUST be set to 0 and MUST be ignored. 2759 o DR port number: The port number at the data receiver (DR), i.e., 2760 the destination port. A value of 0 indicates a port wildcard, 2761 i.e., the destination port number is not known. Any other value 2762 indicates the destination port number. 2764 o DS port number: The port number at the data sender (DS), i.e., the 2765 source port. A value of 0 indicates a port wildcard, i.e., the 2766 source port number is not known. Any other value indicates the 2767 source port number. 2769 o data sender's IPv4 address: The source IP address of the data 2770 sender. This field MUST be set to zero if no IP address is 2771 provided, i.e., a complete wildcard is desired (see dest prefix 2772 field above). 2774 4.2.8. ICMP Types Object 2776 The 'ICMP types' object contains additional information needed to 2777 configure a NAT of firewall with rules to control ICMP traffic. The 2778 object contains a number of values of the ICMP Type field for which a 2779 filter action should be set up: 2781 Type: NATFW_ICMP_TYPES (IANA-TBD) 2783 Length: Variable = ((Number of Types carried + 1) + 3) DIV 4 2785 Where DIV is an integer division. 2787 0 1 2 3 2788 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 2789 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2790 | Count | Type | Type | ........ | 2791 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2792 | ................ | 2793 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2794 | ........ | Type | (Padding) | 2795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2797 Figure 29: ICMP Types Object 2799 The fields MUST be interpreted according these rules: 2801 count: 8 bit integer specifying the number of 'Type' entries in 2802 the object. 2804 type: 8 bit field specifying an ICMP Type value to which this rule 2805 applies. 2807 padding: Sufficient 0 bits to pad out the last word so that the 2808 total size of object is an even multiple of words. Ignored on 2809 reception. 2811 4.3. Message Formats 2813 This section defines the content of each NATFW NSLP message type. 2814 The message types are defined in Section 4.1. 2816 Basically, each message is constructed of NSLP header and one or more 2817 NSLP objects. The order of objects is not defined, meaning that 2818 objects may occur in any sequence. Objects are marked either with 2819 mandatory (M) or optional (O). Where (M) implies that this 2820 particular object MUST be included within the message and where (O) 2821 implies that this particular object is OPTIONAL within the message. 2822 Objects defined in this memo carry always the flag combination AB=00 2823 in the NSLP object header. An error RESPONSE message of class 2824 'Protocol error' (0x3) with response code 'Mandatory object missing' 2825 (0x02) MUST be generated if a mandatory declared object is missing. 2826 An error RESPONSE message of class 'Protocol error' (0x3) with 2827 response code 'Illegal object present' (0x05) MUST be generated if an 2828 object was present which must not be used in a message of this type. 2829 An error RESPONSE message of class 'Protocol error' (0x3) with 2830 response code 'Duplicate object present' (0x0A) MUST be generated if 2831 an object appears more than once in a message. 2833 Each section elaborates the required settings and parameters to be 2834 set by the NSLP for the NTLP, for instance, how the message routing 2835 information is set. 2837 4.3.1. CREATE 2839 The CREATE message is used to create NATFW NSLP signaling sessions 2840 and to create policy rules. Furthermore, CREATE messages are used to 2841 refresh NATFW NSLP signaling sessions and to delete them. 2843 The CREATE message carries these objects: 2845 o Signaling Session Lifetime object (M) 2847 o Extended flow information object (M) 2849 o Message sequence number object (M) 2851 o Nonce object (M) if P flag set to 1 in the NSLP header, otherwise 2852 (O) 2854 o ICMP Types Object (O) 2856 The message routing information in the NTLP MUST be set to DS as 2857 source address and DR as destination address. All other parameters 2858 MUST be set according the required policy rule. CREATE messages MUST 2859 be transported by using the path-coupled MRM with direction set to 2860 'downstream' (outbound). 2862 4.3.2. EXTERNAL (EXT) 2864 The EXTERNAL (EXT) message is used to a) reserve an external IP 2865 address/port at NATs, b) to notify firewalls about NSIS capable DRs, 2866 or c) to block incoming data traffic at inbound firewalls. 2868 The EXT message carries these objects: 2870 o Signaling Session Lifetime object (M) 2872 o Message sequence number object (M) 2874 o Extended flow information object (M) 2876 o Data terminal information object (M) 2878 o Nonce object [M if P flag set to 1 in the NSLP header, otherwise 2879 (O) 2881 o ICMP Types Object (O) 2882 The selected message routing method of the EXT message depends on a 2883 number of considerations. Section 3.7.2 describes it exhaustively 2884 how to select the correct method. EXT messages can be transported 2885 via the path-coupled message routing method (PC-MRM) or via the 2886 loose-end message routing method (LE-MRM). In the case of PC-MRM, 2887 the source-address is set to DS' address and the destination address 2888 is set to DR's address, the direction is set to inbound. In the case 2889 of LE-MRM, the destination-address is set to DR's address or to the 2890 signaling destination address. The source-address is set to DS's 2891 address. 2893 4.3.3. RESPONSE 2895 RESPONSE messages are responses to CREATE and EXT messages. RESPONSE 2896 messages MUST NOT be generated for any other message, such as NOTIFY 2897 and RESPONSE. 2899 The RESPONSE message for the class 'Success' (0x2) carries these 2900 objects: 2902 o Signaling Session Lifetime object (M) 2904 o Message sequence number object (M) 2906 o Information code object (M) 2908 o External address object (O) 2910 The RESPONSE message for other classes than 'Success' (0x2) carries 2911 these objects: 2913 o Message sequence number object (M) 2915 o Information code object (M) 2917 This message is routed towards the NI hop-by-hop, using existing NTLP 2918 messaging associations. The MRM used for this message MUST be the 2919 same as MRM used by the corresponding CREATE or EXT message. 2921 4.3.4. NOTIFY 2923 The NOTIFY messages is used to report asynchronous events happening 2924 along the signaled path to other NATFW NSLP nodes. 2926 The NOTIFY message carries this object: 2928 o Information code object (M). 2930 The NOTIFY message is routed towards the NI hop-by-hop using the 2931 existing inbound node messaging association entry within the node's 2932 Message Routing State table. The MRM used for this message MUST be 2933 the same as MRM used by the corresponding CREATE or EXT message. 2935 5. Security Considerations 2937 Security is of major concern particularly in case of firewall 2938 traversal. This section provides security considerations for the 2939 NAT/firewall traversal and is organized as follows. 2941 In Section 5.1 we describe the participating entities relate to each 2942 other from a security point of view. This subsection also motivates 2943 a particular authorization model. 2945 Security threats that focus on NSIS in general are described in [8] 2946 and they are applicable to this document as well. 2948 Finally, we illustrate how the security requirements that were 2949 created based on the security threats can be fulfilled by specific 2950 security mechanisms. These aspects will be elaborated in 2951 Section 5.2. 2953 5.1. Authorization Framework 2955 The NATFW NSLP is a protocol which may involve a number of NSIS nodes 2956 and is, as such, not a two-party protocol. Figure 1 and Figure 2 of 2957 [8] already depict the possible set of communication patterns. In 2958 this section we will re-evaluate these communication patters with 2959 respect to the NATFW NSLP protocol interaction. 2961 The security solutions for providing authorization have a direct 2962 impact on the treatment of different NSLPs. As it can be seen from 2963 the QoS NSLP [6] and the corresponding Diameter QoS work [19] 2964 accounting and charging seems to play an important role for QoS 2965 reservations, whereas monetary aspects might only indirectly effect 2966 authorization decisions for NAT and firewall signaling. Hence, there 2967 are differences in the semantic of authorization handling between QoS 2968 and NATFW signaling. A NATFW aware node will most likely want to 2969 authorize the entity (e.g., user or machine) requesting the 2970 establishment of pinholes or NAT bindings. The outcome of the 2971 authorization decision is either allowed or disallowed whereas a QoS 2972 authorization decision might indicate that a different set of QoS 2973 parameters is authorization (see [19] as an example). 2975 5.1.1. Peer-to-Peer Relationship 2977 Starting with the simplest scenario, it is assumed that neighboring 2978 nodes are able to authenticate each other and to establish keying 2979 material to protect the signaling message communication. The nodes 2980 will have to authorize each other, additionally to the 2981 authentication. We use the term 'Security Context' as a placeholder 2982 for referring to the entire security procedure, the necessary 2983 infrastructure that needs to be in place in order for this to work 2984 (e.g., key management) and the established security related state. 2985 The required long-term key (symmetric or asymmetric keys) used for 2986 authentication are either made available using an out-of-band 2987 mechanism between the two NSIS NATFW nodes or they are dynamically 2988 established using mechanisms not further specified in this document. 2989 Note that the deployment environment will most likely have an impact 2990 on the choice of credentials being used. The choice of these 2991 credentials used is also outside the scope of this document. 2993 +------------------------+ +-------------------------+ 2994 |Network A | | Network B| 2995 | +---------+ +---------+ | 2996 | +-///-+ Middle- +---///////----+ Middle- +-///-+ | 2997 | | | box 1 | Security | box 2 | | | 2998 | | +---------+ Context +---------+ | | 2999 | | Security | | Security | | 3000 | | Context | | Context | | 3001 | | | | | | 3002 | +--+---+ | | +--+---+ | 3003 | | Host | | | | Host | | 3004 | | A | | | | B | | 3005 | +------+ | | +------+ | 3006 +------------------------+ +-------------------------+ 3008 Figure 30: Peer-to-Peer Relationship 3010 Figure 30 shows a possible relationship between participating NSIS 3011 aware nodes. Host A might be, for example, a host in an enterprise 3012 network that has keying material established (e.g., a shared secret) 3013 with the company's firewall (Middlebox 1). The network administrator 3014 of Network A (company network) has created access control lists for 3015 Host A (or whatever identifiers a particular company wants to use). 3016 Exactly the same procedure might also be used between Host B and 3017 Middlebox 2 in Network B. For the communication between Middlebox 1 3018 and Middlebox 2 a security context is also assumed in order to allow 3019 authentication, authorization and signaling message protection to be 3020 successful. 3022 5.1.2. Intra-Domain Relationship 3024 In larger corporations, for example, a middlebox is used to protect 3025 individual departments. In many cases, the entire enterprise is 3026 controlled by a single (or a small number of) security department, 3027 which gives instructions to the department administrators. In such a 3028 scenario, the previously discussed peer-to-peer relationship might be 3029 prevalent. Sometimes it might be necessary to preserve 3030 authentication and authorization information within the network. As 3031 a possible solution, a centralized approach could be used, whereby an 3032 interaction between the individual middleboxes and a central entity 3033 (for example a policy decision point - PDP) takes place. As an 3034 alternative, individual middleboxes exchange the authorization 3035 decision with another middlebox within the same trust domain. 3036 Individual middleboxes within an administrative domain may exploit 3037 their relationship instead of requesting authentication and 3038 authorization of the signaling initiator again and again. Figure 31 3039 illustrates a network structure which uses a centralized entity. 3041 +-----------------------------------------------------------+ 3042 | Network A | 3043 | +---------+ +---------+ 3044 | +----///--------+ Middle- +------///------++ Middle- +--- 3045 | | Security | box 2 | Security | box 2 | 3046 | | Context +----+----+ Context +----+----+ 3047 | +----+----+ | | | 3048 | | Middle- +--------+ +---------+ | | 3049 | | box 1 | | | | | 3050 | +----+----+ | | | | 3051 | | Security | +----+-----+ | | 3052 | | Context | | Policy | | | 3053 | +--+---+ +-----------+ Decision +----------+ | 3054 | | Host | | Point | | 3055 | | A | +----------+ | 3056 | +------+ | 3057 +-----------------------------------------------------------+ 3059 Figure 31: Intra-domain Relationship 3061 The interaction between individual middleboxes and a policy decision 3062 point (or AAA server) is outside the scope of this document. 3064 5.1.3. End-to-Middle Relationship 3066 The peer-to-peer relationship between neighboring NSIS NATFW NSLP 3067 nodes might not always be sufficient. Network B might require 3068 additional authorization of the signaling message initiator (in 3069 addition to the authorization of the neighboring node). If 3070 authentication and authorization information is not attached to the 3071 initial signaling message then the signaling message arriving at 3072 Middlebox 2 would result in an error message being created, which 3073 indicates the additional authorization requirement. In many cases 3074 the signaling message initiator might already be aware of the 3075 additionally required authorization before the signaling message 3076 exchange is executed. 3078 Figure 32 shows this scenario. 3080 +--------------------+ +---------------------+ 3081 | Network A | |Network B | 3082 | | Security | | 3083 | +---------+ Context +---------+ | 3084 | +-///-+ Middle- +---///////----+ Middle- +-///-+ | 3085 | | | box 1 | +-------+ box 2 | | | 3086 | | +---------+ | +---------+ | | 3087 | |Security | | | Security | | 3088 | |Context | | | Context | 3089 | | | | | | | 3090 | +--+---+ | | | +--+---+ | 3091 | | Host +----///----+------+ | | Host | | 3092 | | A | | Security | | B | | 3093 | +------+ | Context | +------+ | 3094 +--------------------+ +---------------------+ 3096 Figure 32: End-to-Middle Relationship 3098 5.2. Security Framework for the NAT/Firewall NSLP 3100 The following list of security requirements has been created to 3101 ensure proper secure operation of the NATFW NSLP. 3103 5.2.1. Security Protection between neighboring NATFW NSLP Nodes 3105 Based on the analyzed threats it is RECOMMENDED to provide, between 3106 neighboring NATFW NSLP nodes, the following mechanism: 3108 o data origin authentication 3110 o replay protection 3112 o integrity protection and 3114 o optionally confidentiality protection 3116 It is RECOMMENDED to use the authentication and key exchange security 3117 mechanisms provided in [2] between neighboring nodes when sending 3118 NATFW signaling messages. The proposed security mechanisms of GIST 3119 provide support for authentication and key exchange in addition to 3120 denial of service protection. Depending on the chosen security 3121 protocol, support for multiple authentication protocols might be 3122 provided. If security between neighboring nodes is desired than the 3123 usage of C-MODE for the delivery of data packets and the usage of 3124 D-MODE only to discover the next NATFW NSLP aware node along the path 3125 is highly RECOMMENDED. Almost all security threats at the NATFW NSLP 3126 layer can be prevented by using a mutually authenticated Transport 3127 Layer secured connection and by relying on authorization by the 3128 neighboring NATFW NSLP entities. 3130 The NATFW NSLP relies on an established security association between 3131 neighboring peers to prevent unauthorized nodes to modify or delete 3132 installed state. Between non-neighboring nodes the session ID (SID) 3133 carried in the NTLP is used to show ownership of a NATFW NSLP 3134 signaling session. The session ID MUST be generated in a random way 3135 and thereby prevent an off-path adversary to mount targeted attacks. 3136 Hence, an adversary would have to learn the randomly generated 3137 session ID to perform an attack. In a mobility environment a former 3138 on-path node that is now off-path can perform an attack. Messages 3139 for a particular NATFW NSLP signaling session are handled by the NTLP 3140 to the NATFW NSLP for further processing. Messages carrying a 3141 different session ID not associated with any NATFW NSLP are subject 3142 to the regular processing for new NATFW NSLP signaling sessions. 3144 5.2.2. Security Protection between non-neighboring NATFW NSLP Nodes 3146 Based on the security threats and the listed requirements it was 3147 noted that some threats also demand authentication and authorization 3148 of a NATFW signaling entity (including the initiator) towards a non- 3149 neighboring node. This mechanism mainly demands entity 3150 authentication. Additionally, security protection of certain 3151 payloads may be required between non-neighboring signaling entities 3152 and the Cryptographic Message Syntax (CMS) [14] might be a potential 3153 solution. Payload protection using CMS is not described in this 3154 document. The most important information exchanged at the NATFW NSLP 3155 is information related to the establishment for firewall pinholes and 3156 NAT bindings. This information can, however, not be protected over 3157 multiple NSIS NATFW NSLP hops since this information might change 3158 depending on the capability of each individual NATFW NSLP node. 3160 Some scenarios might also benefit from the usage of authorization 3161 tokens. Their purpose is to associate two different signaling 3162 protocols (e.g., SIP and NSIS) and their authorization decision. 3163 These tokens are obtained by non-NSIS protocols, such as SIP or as 3164 part of network access authentication. When a NAT or firewall along 3165 the path receives the token it might be verified locally or passed to 3166 the AAA infrastructure. Examples of authorization tokens can be 3167 found in RFC 3520 [17] and RFC 3521 [18]. Figure 33 shows an example 3168 of this protocol interaction. 3170 An authorization token is provided by the SIP proxy, which acts as 3171 the assertion generating entity and gets delivered to the end host 3172 with proper authentication and authorization. When the NATFW 3173 signaling message is transmitted towards the network, the 3174 authorization token is attached to the signaling messages to refer to 3175 the previous authorization decision. The assertion verifying entity 3176 needs to process the token or it might be necessary to interact with 3177 the assertion granting entity using HTTP (or other protocols). As a 3178 result of a successfully authorization by a NATFW NSLP node, the 3179 requested action is executed and later a RESPONSE message is 3180 generated. 3182 +----------------+ Trust Relationship +----------------+ 3183 | +------------+ |<.......................>| +------------+ | 3184 | | Protocol | | | | Assertion | | 3185 | | requesting | | HTTP, SIP Request | | Granting | | 3186 | | authz | |------------------------>| | Entity | | 3187 | | assertions | |<------------------------| +------------+ | 3188 | +------------+ | Artifact/Assertion | Entity Cecil | 3189 | ^ | +----------------+ 3190 | | | ^ ^| 3191 | | | . || HTTP, 3192 | | | Trust . || other 3193 | API Access | Relationship. || protocols 3194 | | | . || 3195 | | | . || 3196 | | | v |v 3197 | v | +----------------+ 3198 | +------------+ | | +------------+ | 3199 | | Protocol | | NSIS NATFW CREATE + | | Assertion | | 3200 | | using authz| | Assertion/Artifact | | Verifying | | 3201 | | assertion | | ----------------------- | | Entity | | 3202 | +------------+ | | +------------+ | 3203 | Entity Alice | <---------------------- | Entity Bob | 3204 +----------------+ RESPONSE +----------------+ 3206 Figure 33: Authorization Token Usage 3208 Threats against the usage of authorization tokens have been mentioned 3209 in [8]. Hence, it is required to provide confidentiality protection 3210 to avoid allowing an eavesdropper to learn the token and to use it in 3211 another NATFW NSLP signaling session (replay attack). The token 3212 itself also needs to be protected against tempering. 3214 To harmonize the usage of authorization tokens in NSLPs a separate 3215 document is available, see [20]. 3217 6. IAB Considerations on UNSAF 3219 UNilateral Self-Address Fixing (UNSAF) is described in [12] as a 3220 process at originating endpoints that attempt to determine or fix the 3221 address (and port) by which they are known to another endpoint. 3222 UNSAF proposals, such as STUN [15] are considered as a general class 3223 of workarounds for NAT traversal and as solutions for scenarios with 3224 no middlebox communication. 3226 This memo specifies a path-coupled middlebox communication protocol, 3227 i.e., the NSIS NATFW NSLP. NSIS in general and the NATFW NSLP are 3228 not intended as a short-term workaround, but more as a long-term 3229 solution for middlebox communication. In NSIS, endpoints are 3230 involved in allocating, maintaining, and deleting addresses and ports 3231 at the middlebox. However, the full control of addresses and ports 3232 at the middlebox is at the NATFW NSLP daemon located to the 3233 respective NAT. 3235 Therefore, this document addresses the UNSAF considerations in [12] 3236 by proposing a long-term alternative solution. 3238 7. IANA Considerations 3240 This section provides guidance to the Internet Assigned Numbers 3241 Authority (IANA) regarding registration of values related to the 3242 NATFW NSLP, in accordance with BCP 26 RFC 2434 [13]. 3244 The NATFW NSLP requires IANA to create a number of new registries. 3245 These registries may require further coordination with the registries 3246 of the NTLP [2] and the QoS NSLP [6]. 3248 NATFW NSLP Message Type Registry 3250 The NATFW NSLP Message Type is a 8 bit value. The allocation of 3251 values for new message types requires standards action. Updates and 3252 deletion of values from the registry is not possible. This 3253 specification defines four NATFW NSLP message types, which form the 3254 initial contents of this registry. IANA is requested to add these 3255 four NATFW NSLP Message Types: CREATE, EXT, RESPONSE, and NOTIFY. 3257 NATFW NSLP Header Flag Registry 3259 NATFW NSLP messages have a messages-specific 8 bit flags/reserved 3260 field in their header. The registration of flags is subject to IANA 3261 registration. The allocation of values for flag types requires 3262 standards action. Updates and deletion of values from the registry 3263 is not possible. This specification defines only one flag, the P 3264 flag in Figure 20. 3266 NSLP Object Type Registry 3268 [Delete this part if already done by another NSLP: 3270 A new registry is to be created for NSLP Message Objects. This is a 3271 12-bit field (giving values from 0 to 4095). This registry is shared 3272 between a number of NSLPs. Allocation policies are as follows: 3274 0-1023: Standards Action 3276 1024-1999: Specification Required 3278 2000-2047: Private/Experimental Use 3280 2048-4095: Reserved 3282 When a new object is defined, the extensibility bits (A/B) must also 3283 be defined.] 3285 This document defines 8 objects for the NATFW NSLP: NATFW_LT, 3286 NATFW_EXT_IP, NATFW_EFI, NATFW_INFO, NATFW_NONCE, NATFW_MSN, 3287 NATFW_DTINFO, NATFW_ICMP_TYPES. IANA is request to assigned values 3288 for them from NSLP Object Type registry and to replace the 3289 corresponding IANA-TBD tags with the numeric values. 3291 NSLP Response Code Registry 3293 In addition it defines a number of Response Codes for the NATFW NSLP. 3294 These can be found in Section 4.2.4 and are to be assigned values 3295 from NSLP Response Code registry. The allocation of values for 3296 Response Codes Codes requires standards action. IANA is request to 3297 assigned values for them from NSLP Response Code registry. 3299 Furthermore, IANA is requested to add a new value to the NSLP 3300 Identifiers (NSLPID) registry defined in [2] for the NATFW NSLP. 3302 8. Open Issues 3304 A more detailed list of open issue can be found at: 3305 https://kobe.netlab.nec.de/roundup/nsis-natfw-nslp/index 3307 9. Acknowledgments 3309 We would like to thank the following individuals for their 3310 contributions to this document at different stages: 3312 o Marcus Brunner and Henning Schulzrinne for work on work on IETF 3313 drafts which lead us to start with this document, 3315 o Miquel Martin for his help on the initial version of this 3316 document, 3318 o Srinath Thiruvengadam and Ali Fessi work for their work on the 3319 NAT/firewall threats draft, 3321 o Henning Peters for his comments and suggestions, 3323 o and the NSIS working group. 3325 10. References 3327 10.1. Normative References 3329 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 3330 Levels", BCP 14, RFC 2119, March 1997. 3332 [2] Schulzrinne, H. and R. Hancock, "GIST: General Internet 3333 Signalling Transport", draft-ietf-nsis-ntlp-14 (work in 3334 progress), July 2007. 3336 [3] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, 3337 August 1996. 3339 10.2. Informative References 3341 [4] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den 3342 Bosch, "Next Steps in Signaling (NSIS): Framework", RFC 4080, 3343 June 2005. 3345 [5] Brunner, M., "Requirements for Signaling Protocols", RFC 3726, 3346 April 2004. 3348 [6] Manner, J., "NSLP for Quality-of-Service Signaling", 3349 draft-ietf-nsis-qos-nslp-15 (work in progress), July 2007. 3351 [7] Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A., and A. 3352 Rayhan, "Middlebox communication architecture and framework", 3353 RFC 3303, August 2002. 3355 [8] Tschofenig, H. and D. Kroeselberg, "Security Threats for Next 3356 Steps in Signaling (NSIS)", RFC 4081, June 2005. 3358 [9] Srisuresh, P. and M. Holdrege, "IP Network Address Translator 3359 (NAT) Terminology and Considerations", RFC 2663, August 1999. 3361 [10] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and Issues", 3362 RFC 3234, February 2002. 3364 [11] Braden, B., Zhang, L., Berson, S., Herzog, S., and S. Jamin, 3365 "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional 3366 Specification", RFC 2205, September 1997. 3368 [12] Daigle, L. and IAB, "IAB Considerations for UNilateral Self- 3369 Address Fixing (UNSAF) Across Network Address Translation", 3370 RFC 3424, November 2002. 3372 [13] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 3373 Considerations Section in RFCs", BCP 26, RFC 2434, 3374 October 1998. 3376 [14] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852, 3377 July 2004. 3379 [15] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy, "STUN 3380 - Simple Traversal of User Datagram Protocol (UDP) Through 3381 Network Address Translators (NATs)", RFC 3489, March 2003. 3383 [16] Westerinen, A., Schnizlein, J., Strassner, J., Scherling, M., 3384 Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry, J., and 3385 S. Waldbusser, "Terminology for Policy-Based Management", 3386 RFC 3198, November 2001. 3388 [17] Hamer, L-N., Gage, B., Kosinski, B., and H. Shieh, "Session 3389 Authorization Policy Element", RFC 3520, April 2003. 3391 [18] Hamer, L-N., Gage, B., and H. Shieh, "Framework for Session 3392 Set-up with Media Authorization", RFC 3521, April 2003. 3394 [19] Zorn, G., "Diameter Quality of Service Application", 3395 draft-ietf-dime-diameter-qos-01 (work in progress), July 2007. 3397 [20] Manner, J., "Authorization for NSIS Signaling Layer Protocols", 3398 draft-manner-nsis-nslp-auth-03 (work in progress), March 2007. 3400 [21] Roedig, U., Goertz, M., Karten, M., and R. Steinmetz, "RSVP as 3401 firewall Signalling Protocol", Proceedings of the 6th IEEE 3402 Symposium on Computers and Communications, Hammamet, 3403 Tunisia pp. 57 to 62, IEEE Computer Society Press, July 2001. 3405 Appendix A. Selecting Signaling Destination Addresses for EXT 3407 As with all other message types, EXT messages need a reachable IP 3408 address of the data sender on the GIST level. For the path-coupled 3409 MRM the source-address of GIST is the reachable IP address (i.e., the 3410 real IP address of the data sender, or a wildcard). While this is 3411 straight forward, it is not necessarily so for the loose-end MRM. 3412 Many applications do not provide the IP address of the communication 3413 counterpart, i.e., either the data sender or both a data sender and 3414 receiver. For the EXT messages, the case of data sender is of 3415 interest only. The rest of this section is giving informational 3416 guidance about determining a good destination-address of the LE-MRM 3417 in GIST for EXT messages. 3419 This signaling destination address (SDA, the destination-address in 3420 GIST) can be the data sender, but for applications which do not 3421 provide an address upfront, the destination address has to be chosen 3422 independently, as it is unknown at the time when the NATFW NSLP 3423 signaling has to start. Choosing the 'correct' destination IP 3424 address may be difficult and it is possible that there is no 'right 3425 answer' for all applications relying on the NATFW NSLP. 3427 Whenever possible it is RECOMMENDED to chose the data sender's IP 3428 address as SDA. It necessary to differentiate between the received 3429 IP addresses on the data sender. Some application level signaling 3430 protocols (e.g., SIP) have the ability to transfer multiple contact 3431 IP addresses of the data sender. For instance, private IP address, 3432 public IP address at NAT, and public IP address at a relay. It is 3433 RECOMMENDED to use all non-private IP addresses as SDAs. 3435 A different SDA must be chosen, should the IP address of the data 3436 sender be unknown. This can have multiple reasons: The application 3437 level signaling protocol cannot determine any data sender IP address 3438 at this point of time or the data receiver is server behind a NAT, 3439 i.e., accepting inbound packets from any host. In this case, the 3440 NATFW NSLP can be instructed to use the public IP address of an 3441 application server or any other node. Choosing the SDA in this case 3442 is out of the scope of the NATFW NSLP and depends on the 3443 application's choice. The local network can provide a network-SDA, 3444 i.e., a SDA which is only meaningful to the local network. This will 3445 ensure that GIST packets with destination-address set to this 3446 network-SDA are going to be routed to a edge-NAT or edge-firewall. 3448 Appendix B. Applicability Statement on Data Receivers behind Firewalls 3450 Section 3.7.2 describes how data receivers behind middleboxes can 3451 instruct inbound firewalls/NATs to forward NATFW NSLP signaling 3452 towards them. Finding an inbound edge-NAT in address environment 3453 with NAT'ed addresses is quite easy. It is only required to find 3454 some edge-NAT, as the data traffic will be route-pinned to the NAT, 3455 which is done with the LE-MRM. Locating the appropriate edge- 3456 firewall with the PC-MRM, sent inbound is difficult. For cases with 3457 a single, symmetric route from the Internet to the data receiver, it 3458 is quite easy; simply follow the default route in the inbound 3459 direction. 3461 +------+ Data Flow 3462 +-------| EFW1 +----------+ <=========== 3463 | +------+ ,--+--. 3464 +--+--+ / \ 3465 NI+-----| FW1 | (Internet )----NR+/NI/DS 3466 NR +--+--+ \ / 3467 | +------+ `--+--' 3468 +-------| EFW2 +----------+ 3469 +------+ 3471 ~~~~~~~~~~~~~~~~~~~~~> 3472 Signaling Flow 3474 Figure 34: Data receiver behind multiple, parallel located firewalls 3476 When a data receiver, and thus NR, is located in a network site that 3477 is multihomed with several independently firewalled connections to 3478 the public Internet (as shown in Figure 34), the specific firewall 3479 through which the data traffic will be routed has to be ascertained. 3480 NATFW NSLP signaling messages sent from the NI+/NR during the EXT 3481 message exchange towards the NR+ must be routed by the NTLP to the 3482 edge-firewall that will be passed by the data traffic as well. The 3483 NTLP would need to be aware about the routing within the Internet to 3484 determine the path between DS and DR. Out of this, the NTLP could 3485 determine which of the edge-firewalls, either EFW1 or EFW2, must be 3486 selected to forward the NATFW NSLP signaling. Signaling to the wrong 3487 edge-firewall, as shown in Figure 34, would install the NATFW NSLP 3488 policy rules at the wrong device. This causes either a blocked data 3489 flow (when the policy rule is 'allow') or an ongoing attack (when the 3490 policy rule is 'deny'). Requiring the NTLP to know all about the 3491 routing within the Internet is definitely a tough challenge and 3492 usually not possible. In such described case, the NTLP must 3493 basically give up and return an error to the NSLP level, indicating 3494 that the next hop discovery is not possible. 3496 Appendix C. Firewall and NAT Resources 3498 This section gives some examples on how NATFW NSLP policy rules could 3499 be mapped to real firewall or NAT resources. The firewall rules and 3500 NAT bindings are described in a natural way, i.e., in a way one will 3501 find it in common implementation. 3503 C.1. Wildcarding of Policy Rules 3505 The policy rule/MRI to be installed can be wildcarded to some degree. 3506 Wildcarding applies to IP address, transport layer port numbers, and 3507 the IP payload (or next header in IPv6). Processing of wildcarding 3508 splits into the NTLP and the NATFW NSLP layer. The processing at the 3509 NTLP layer is independent of the NSLP layer processing and per layer 3510 constraints apply. For wildcarding in the NTLP see Section 5.8 of 3511 [2]. 3513 Wildcarding at the NATFW NSLP level is always a node local policy 3514 decision. A signaling message carrying a wildcarded MRI (and thus 3515 policy rule) arriving at an NSLP node can be rejected if the local 3516 policy does not allow the request. For instance, a MRI with IP 3517 addresses set (not wildcarded), transport protocol TCP, and TCP port 3518 numbers completely wildcarded. Now the local policy allows only 3519 requests for TCP with all ports set and not wildcarded. The request 3520 is going to be rejected. 3522 C.2. Mapping to Firewall Rules 3524 This section describes how a NSLP policy rule signaled with a CREATE 3525 message is mapped to a firewall rule. The MRI is set as follows: 3527 o network-layer-version=IPv4 3529 o source-address=192.0.2.100, prefix-length=32 3531 o destination-address=192.0.50.5, prefix-length=32 3533 o IP-protocol=UDP 3535 o L4-source-port=34543, L4-destination-port=23198 3537 The NATFW_EFI object is set to action=allow and sub_ports=0. 3539 The resulting policy rule (firewall rule) to be installed might look 3540 like: allow udp from 192.0.2.100 port=34543 to 192.0.50.5 port=23198 3542 C.3. Mapping to NAT Bindings 3544 This section describes how a NSLP policy rule signaled with a EXT 3545 message is mapped to a NAT binding. It is assumed that the EXT 3546 message is sent by a NI+ being located behind a NAT and does contain 3547 a NATFW_DTINFO object. The MRI is set following using the signaling 3548 destination address, since the IP address of the real data sender is 3549 not known: 3551 o network-layer-version=IPv4 3553 o source-address= 192.168.5.100 3555 o destination-address=SDA 3557 o IP-protocol=UDP 3559 The NATFW_EFI object is set to action=allow and sub_ports=0. The 3560 NATFW_DTINFO object contains these parameters: 3562 o P=1 3564 o dest prefix=0 3566 o protocol=UDP 3568 o dst port number = 20230, src port number=0 3570 o src IP=0.0.0.0 3572 The edge-NAT allocates the external IP 192.0.2.79 and port 45000. 3574 The resulting policy rule (NAT binding) to be installed could look 3575 like: translate from any to 192.0.2.79 port=45000 to 192.168.5.100 3576 port=20230 3578 C.4. NSLP Handling of Twice-NAT 3580 The dynamic configuration of twice-NATs requires application level 3581 support, as stated in Section 2.5. The NATFW NSLP cannot be used for 3582 configuring twice-NATs if application level support is needed. 3583 Assuming application level support performing the configuration of 3584 the twice-NAT and the NATFW NSLP being installed at this devices, the 3585 NATFW NSLP must be able to traverse it. The NSLP is probably able to 3586 traverse the twice-NAT, as any other data traffic, but the flow 3587 information stored in the NTLP's MRI will be invalidated through the 3588 translation of source and destination address. The NATFW NSLP 3589 implementation on the twice-NAT MUST intercept NATFW NSLP and NTLP 3590 signaling messages as any other NATFW NSLP node does. For the given 3591 signaling flow, the NATFW NSLP node MUST look up the corresponding IP 3592 address translation and modify the NTLP/NSLP signaling accordingly. 3593 The modification results in an updated MRI with respect to the source 3594 and destination IP addresses. 3596 Appendix D. Assigned Numbers for Testing 3598 NOTE: This section MUST be removed before publication. 3600 This section defines temporarily used values of the NATFW NSLP for 3601 testing the different implementations. 3603 Values for the NATFW NSLP message types: 3605 o CREATE: 0x01 3607 o EXT: 0x02 3609 o RESPONSE: 0x03 3611 o NOTIFY: 0x04 3613 Values for the NSLP object types 3615 o NATFW_LT: 0x00F1 3617 o NATFW_EXT_IP: 0x00F2 3619 o NATFW_EFI: 0x00F3 3621 o NATFW_INFO: 0x00F4 3623 o NATFW_NONCE: 0x00F5 3625 o NATFW_MSN: 0x00F6 3627 o NATFW_DTINFO: 0x00F7 3629 o NATFW_ICMP_TYPES: 0x00F9 3631 1345 3633 Authors' Addresses 3635 Martin Stiemerling 3636 NEC Europe Ltd. and University of Goettingen 3637 Kurfuersten-Anlage 36 3638 Heidelberg 69115 3639 Germany 3641 Phone: +49 (0) 6221 4342 113 3642 Email: stiemerling@netlab.nec.de 3643 URI: http://www.stiemerling.org 3645 Hannes Tschofenig 3646 Nokia Siemens Networks 3647 Otto-Hahn-Ring 6 3648 Munich 81739 3649 Germany 3651 Phone: 3652 Email: Hannes.Tschofenig@nsn.com 3653 URI: http://www.tschofenig.com 3655 Cedric Aoun 3656 Paris 3657 France 3659 Email: cedric@caoun.net 3661 Elwyn Davies 3662 Folly Consulting 3663 Soham 3664 UK 3666 Phone: +44 7889 488 335 3667 Email: elwynd@dial.pipex.com 3669 Full Copyright Statement 3671 Copyright (C) The IETF Trust (2007). 3673 This document is subject to the rights, licenses and restrictions 3674 contained in BCP 78, and except as set forth therein, the authors 3675 retain all their rights. 3677 This document and the information contained herein are provided on an 3678 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 3679 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 3680 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 3681 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 3682 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 3683 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 3685 Intellectual Property 3687 The IETF takes no position regarding the validity or scope of any 3688 Intellectual Property Rights or other rights that might be claimed to 3689 pertain to the implementation or use of the technology described in 3690 this document or the extent to which any license under such rights 3691 might or might not be available; nor does it represent that it has 3692 made any independent effort to identify any such rights. Information 3693 on the procedures with respect to rights in RFC documents can be 3694 found in BCP 78 and BCP 79. 3696 Copies of IPR disclosures made to the IETF Secretariat and any 3697 assurances of licenses to be made available, or the result of an 3698 attempt made to obtain a general license or permission for the use of 3699 such proprietary rights by implementers or users of this 3700 specification can be obtained from the IETF on-line IPR repository at 3701 http://www.ietf.org/ipr. 3703 The IETF invites any interested party to bring to its attention any 3704 copyrights, patents or patent applications, or other proprietary 3705 rights that may cover technology that may be required to implement 3706 this standard. Please address the information to the IETF at 3707 ietf-ipr@ietf.org. 3709 Acknowledgment 3711 Funding for the RFC Editor function is provided by the IETF 3712 Administrative Support Activity (IASA).