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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PCP Working Group M. Boucadair 3 Internet-Draft France Telecom 4 Updates: 6887 (if approved) R. Penno 5 Intended status: Standards Track D. Wing 6 Expires: July 26, 2015 P. Patil 7 T. Reddy 8 Cisco 9 January 22, 2015 11 PCP Server Selection 12 draft-ietf-pcp-server-selection-10 14 Abstract 16 The document specifies the behavior to be followed by a PCP client to 17 contact its PCP server(s) when one or several PCP server IP addresses 18 are configured. 20 This document updates RFC6887. 22 Requirements Language 24 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 25 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 26 document are to be interpreted as described in RFC 2119 [RFC2119]. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on July 26, 2015. 45 Copyright Notice 47 Copyright (c) 2015 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 3. IP Address Selection: PCP Server with Multiple IP Addresses . 3 65 4. IP Address Selection: Multiple PCP Servers . . . . . . . . . 4 66 5. Example: Multiple PCP Servers on a Single Interface . . . . . 5 67 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 68 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 69 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 70 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 71 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 72 9.2. Informative References . . . . . . . . . . . . . . . . . 8 73 Appendix A. Multi-homing . . . . . . . . . . . . . . . . . . . . 9 74 A.1. IPv6 Multi-homing . . . . . . . . . . . . . . . . . . . . 9 75 A.2. IPv4 Multi-homing . . . . . . . . . . . . . . . . . . . . 10 77 1. Introduction 79 A host may have multiple network interfaces (e.g., 3G, IEEE 802.11, 80 etc.); each configured with different PCP servers. Each PCP server 81 learned must be associated with the interface on which it was 82 learned. Generic multi-interface considerations are documented in 83 Section 8.4 of [RFC6887]. Multiple PCP server IP addresses may be 84 configured on a PCP client in some deployment contexts such as multi- 85 homing (see Appendix A). A PCP server may also have multiple IP 86 addresses associated with it. It is out of scope of this document to 87 enumerate all deployment scenarios that require multiple PCP server 88 IP addresses to be configured. 90 If a PCP client discovers multiple PCP server IP addresses, it needs 91 to determine which actions it needs to undertake (e.g., whether PCP 92 entries are to be installed in all or a subset of discovered IP 93 addresses, whether some PCP entries are to be removed, etc.). This 94 document makes the following assumptions: 96 o There is no requirement that multiple PCP servers configured on 97 the same interface have the same capabilities. 99 o PCP requests to different PCP servers are independent, the result 100 of a PCP request to one PCP server does not influence another. 102 o The configuration mechanism must distinguish IP addresses that 103 belong to the same PCP server. 105 This document specifies the behavior to be followed by a PCP client 106 [RFC6887] to contact its PCP server(s) [RFC6887] when it is 107 configured with one or several PCP server IP addresses (e.g., using 108 DHCP [RFC7291]). This document does not make any assumption on the 109 type of these IP addresses (i.e., unicast/anycast). 111 2. Terminology 113 This document makes use of the following terms: 115 o PCP client: denotes a PCP software instance responsible for 116 issuing PCP requests to a PCP server. Refer to [RFC6887]. 117 o PCP server: denotes a software instance that receives and 118 processes PCP requests from a PCP client. A PCP server can be co- 119 located with or be separated from the function it controls (e.g., 120 Network Address Translation (NAT) or firewall). Refer to 121 [RFC6887]. 123 3. IP Address Selection: PCP Server with Multiple IP Addresses 125 This section describes the behavior a PCP client follows to contact 126 its PCP server when the PCP client has multiple IP addresses for a 127 single PCP server. 129 1. A PCP client should construct a set of candidate source addresses 130 (Section 4 of [RFC6724]), based on application input and PCP 131 [RFC6887] constraints. For example, when sending a PEER or a MAP 132 with FILTER request for an existing TCP connection, the only 133 candidate source address is the source address used for the 134 existing TCP connection. But when sending a MAP request for a 135 service that will accept incoming connections, the candidate 136 source addresses may be all of the node's IP addresses, or some 137 subset of IP addresses on which the service is configured to 138 listen. 140 2. The PCP client then sorts the PCP server IP addresses as per 141 Section 6 of [RFC6724] using the candidate source addresses 142 selected in the previous step as input to the destination address 143 selection algorithm. 145 3. The PCP client initializes its Maximum Retransmission Count (MRC) 146 to 4. 148 4. The PCP client sends its PCP messages following the 149 retransmission procedure specified in Section 8.1.1 of [RFC6887]. 150 If no response is received after MRC attempts, the PCP client re- 151 tries the procedure with the next IP address in the sorted list. 153 The PCP client may receive a response from an IP address after 154 exhausting MRC attempts for that particular IP address. The PCP 155 client SHOULD ignore such response because receiving a delayed 156 response after exhausting 4 retransmissions sent with 157 exponentially increasing intervals is an indication that problems 158 are to be encountered in the corresponding forwarding path and/or 159 when processing subsequent requests by that PCP server instance. 161 If, when sending PCP requests, the PCP client receives a hard 162 ICMP error [RFC1122] it MUST immediately try the next IP address 163 from the list of PCP server IP addresses. 165 5. If the PCP client has exhausted all IP addresses configured for a 166 given PCP server, the procedure SHOULD be repeated every fifteen 167 (15) minutes until the PCP request is successfully answered. 169 6. Once the PCP client has successfully received a response from a 170 PCP server's IP address, all subsequent PCP requests to that PCP 171 server are sent on the same IP address until that IP address 172 becomes unresponsive. In case the IP address becomes 173 unresponsive, the PCP client clears the cache of sorted 174 destination addresses and follows the steps described above to 175 contact the PCP server again. 177 For efficiency, the PCP client SHOULD use the same Mapping Nonce for 178 requests sent to all IP addresses belonging to the same PCP server. 179 As a reminder, nonce validation checks are performed when operating 180 in the Simple Threat Model (Section 18.1 of [RFC6887]) to defend 181 against some off-path attacks. 183 4. IP Address Selection: Multiple PCP Servers 185 This section describes the behavior a PCP client follows to contact 186 multiple PCP servers, with each PCP server reachable on a list of IP 187 addresses. There is no requirement that these multiple PCP servers 188 have the same capabilities. 190 Note, how PCP clients are configured to separate lists of IP 191 addresses of each PCP server is implementation-specific and 192 deployment-specific. For example, a PCP client can be configured 193 using DHCP with multiple lists of PCP server IP addresses; each 194 list is referring to a distinct PCP server [RFC7291]. 196 If several PCP servers are configured, each with multiple IP 197 addresses, the PCP client contacts all PCP servers using the 198 procedure described in Section 3. 200 As specified in Section 11.2 and Section 12.2 of [RFC6887], the PCP 201 client must use a different Mapping Nonce for each PCP server it 202 communicates with. 204 If the PCP client is configured, using some means, with the 205 capabilities of each PCP server, a PCP client may choose to contact 206 all PCP servers simultaneously or iterate through them with a delay. 208 This procedure may result in a PCP client instantiating multiple 209 mappings maintained by distinct PCP servers. The decision to use all 210 these mappings or delete some of them depends on the purpose of the 211 PCP request. For example, if the PCP servers are configuring 212 firewall (not NAT) functionality then the client would by default 213 (i.e., unless it knows that they all replicate state among them) need 214 to use all the PCP servers. 216 5. Example: Multiple PCP Servers on a Single Interface 218 Figure 1 depicts an example that is used to illustrate the server 219 selection procedure specified in Section 3 and Section 4. In this 220 example, PCP servers (A and B) are co-located with edge routers 221 (rtr1, rtr2) with each PCP server controlling its own device. 223 ISP Network 224 | | 225 ......................................................... 226 | | Subscriber Network 227 +----------+-----+ +-----+----------+ 228 | PCP-Server-A | | PCP-Server-B | 229 | (rtr1) | | (rtr2) | 230 +-------+--------+ +--+-------------+ 231 192.0.2.1 | | 198.51.100.1 232 2001:db8:1111::1 | | 2001:db8:2222::1 233 | | 234 | | 235 -------+-------+------+----------- 236 | 237 | 203.0.113.0 238 | 2001:db8:3333::1 239 +---+---+ 240 | Host | 241 +-------+ 243 Edge Routers (rtr1, rtr2) 245 Figure 1 247 The example describes behavior when a single IP address for one PCP 248 server is not responsive. The PCP client is configured with two PCP 249 servers for the same interface, PCP-Server-A and PCP-Server-B each 250 having two IP addresses, an IPv4 address and an IPv6 address. The 251 PCP client wants an IPv4 mapping so it orders the addresses as 252 follows: 254 o PCP-Server-A: 256 * 192.0.2.1 258 * 2001:db8:1111::1 260 o PCP-Server-B: 262 * 198.51.100.1 264 * 2001:db8:2222::1 266 Suppose that: 268 o The path to reach 192.0.2.1 is broken 270 o The path to reach 2001:db8:1111::1 is working 271 o The path to reach 198.51.100.1 is working 273 o The path to reach 2001:db8:2222::1 is working 275 It sends two PCP requests at the same time, the first to 192.0.2.1 276 (corresponding to PCP-Server-A) and the second to 198.51.100.1 277 (corresponding to PCP-Server-B). The path to 198.51.100.1 is working 278 so a PCP response is received. Because the path to 192.0.2.1 is 279 broken, no PCP response is received. The PCP client retries 4 times 280 to elicit a response from 192.0.2.1 and finally gives up on that 281 address and sends a PCP message to 2001::db8:1111:1. That path is 282 working, and a response is received. Thereafter, the PCP client 283 should continue using that responsive IP address for PCP-Server-A 284 (2001:db8:1111::1). In this particular case, it will have to use 285 THIRD_PARTY option for IPv4 mappings. 287 6. Security Considerations 289 PCP related security considerations are discussed in [RFC6887]. 291 This document does not specify how PCP server addresses are 292 provisioned on the PCP client. It is the responsibility of PCP 293 server provisioning document(s) to elaborate on security 294 considerations to discover legitimate PCP servers. 296 7. IANA Considerations 298 This document does not request any action from IANA. 300 8. Acknowledgements 302 Many thanks to Dave Thaler, Simon Perreault, Hassnaa Moustafa, Ted 303 Lemon, Chris Inacio, and Brian Haberman for their reviews and 304 comments. 306 9. References 308 9.1. Normative References 310 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 311 Requirement Levels", BCP 14, RFC 2119, March 1997. 313 [RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown, 314 "Default Address Selection for Internet Protocol Version 6 315 (IPv6)", RFC 6724, September 2012. 317 [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. 318 Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 319 2013. 321 9.2. Informative References 323 [RFC1122] Braden, R., "Requirements for Internet Hosts - 324 Communication Layers", STD 3, RFC 1122, October 1989. 326 [RFC4116] Abley, J., Lindqvist, K., Davies, E., Black, B., and V. 327 Gill, "IPv4 Multihoming Practices and Limitations", RFC 328 4116, July 2005. 330 [RFC7291] Boucadair, M., Penno, R., and D. Wing, "DHCP Options for 331 the Port Control Protocol (PCP)", RFC 7291, July 2014. 333 Appendix A. Multi-homing 335 The main problem of a PCP multi-homing situation can be succinctly 336 described as 'one PCP client, multiple PCP servers'. As described in 337 Section 3, if a PCP client discovers multiple PCP servers, it should 338 send requests to all of them with assumptions described in Section 1. 340 The following sub-sections describe multi-homing examples to 341 illustrate the PCP client behavior. 343 A.1. IPv6 Multi-homing 345 In this example of an IPv6 multi-homed network, two or more routers 346 co-located with firewalls are present on a single link shared with 347 the host(s). Each router is in turn connected to a different service 348 provider network and the host in this environment would be offered 349 multiple prefixes and advertised multiple DNS servers. Consider a 350 scenario in which firewalls within an IPv6 multi-homing environment 351 also implement a PCP server. The PCP client learns the available PCP 352 servers using DHCP [RFC7291] or any other provisioning mechanism. In 353 reference to Figure 2, a typical model is to embed DHCP servers in 354 rtr1 and rtr2. A host located behind rtr1 and rtr2 can contact these 355 two DHCP servers and retrieve from each server the IP address(es) of 356 the corresponding PCP server. 358 The PCP client will send PCP requests in parallel to each of the PCP 359 servers. 361 ================== 362 | Internet | 363 ================== 364 | | 365 | | 366 +----+-+ +-+----+ 367 | ISP1 | | ISP2 | 368 +----+-+ +-+----+ ISP Network 369 | | 370 ......................................................... 371 | | 372 | | Subscriber Network 373 +-------+---+ +----+------+ 374 | rtr1 with | | rtr2 with | 375 | FW1 | | FW2 | 376 +-------+---+ +----+------+ 377 | | 378 | | 379 -------+----------+------ 380 | 381 +---+---+ 382 | Host | 383 +-------+ 385 Figure 2: IPv6 Multihoming 387 A.2. IPv4 Multi-homing 389 In this example an IPv4 multi-homed network described in 'NAT- or 390 RFC2260-based multi-homing' (Section 3.3 of [RFC4116]), the gateway 391 router is connected to different service provider networks. This 392 method uses Provider-Aggregatable (PA) addresses assigned by each 393 transit provider to which the site is connected. The site uses NAT 394 to translate the various provider addresses into a single set of 395 private-use addresses within the site. In such a case, two PCP 396 servers might have to be present to configure NAT to each of the 397 transit providers. The PCP client learns the available PCP servers 398 using DHCP [RFC7291] or any other provisioning mechanism. In 399 reference to Figure 3, a typical model is to embed the DHCP server 400 and the PCP servers in rtr1. A host located behind rtr1 can contact 401 the DHCP server to obtain IP addresses of the PCP servers. The PCP 402 client will send PCP requests in parallel to each of the PCP servers. 404 ===================== 405 | Internet | 406 ===================== 407 | | 408 | | 409 +----+--------+ +-+------------+ 410 | ISP1 | | ISP2 | 411 | | | | 412 +----+--------+ +-+------------+ ISP Network 413 | | 414 | | 415 .............................................................. 416 | | 417 | Port1 | Port2 Subscriber Network 418 | | 419 +----+--------------+----+ 420 |rtr1: NAT & PCP servers | 421 | GW Router | 422 +----+-------------------+ 423 | 424 | 425 | 426 -----+-------------- 427 | 428 +-+-----+ 429 | Host | (private address space) 430 +-------+ 432 Figure 3: IPv4 Multihoming 434 Authors' Addresses 436 Mohamed Boucadair 437 France Telecom 438 Rennes 35000 439 France 441 EMail: mohamed.boucadair@orange.com 443 Reinaldo Penno 444 Cisco 445 USA 447 EMail: repenno@cisco.com 448 Dan Wing 449 Cisco Systems, Inc. 450 170 West Tasman Drive 451 San Jose, California 95134 452 USA 454 EMail: dwing@cisco.com 456 Prashanth Patil 457 Cisco Systems, Inc. 458 Bangalore 459 India 461 EMail: praspati@cisco.com 463 Tirumaleswar Reddy 464 Cisco Systems, Inc. 465 Cessna Business Park, Varthur Hobli 466 Sarjapur Marathalli Outer Ring Road 467 Bangalore, Karnataka 560103 468 India 470 EMail: tireddy@cisco.com