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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) == Missing Reference: 'Initiate-Tag' is mentioned on line 446, but not defined == Missing Reference: 'RFCXXXX' is mentioned on line 1691, but not defined ** Obsolete normative reference: RFC 4960 (Obsoleted by RFC 9260) ** Obsolete normative reference: RFC 6096 (Obsoleted by RFC 9260) -- Obsolete informational reference (is this intentional?): RFC 793 (Obsoleted by RFC 9293) Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Stewart 3 Internet-Draft Netflix, Inc. 4 Intended status: Standards Track M. Tuexen 5 Expires: January 3, 2019 I. Ruengeler 6 Muenster Univ. of Appl. Sciences 7 July 2, 2018 9 Stream Control Transmission Protocol (SCTP) Network Address Translation 10 Support 11 draft-ietf-tsvwg-natsupp-12.txt 13 Abstract 15 The Stream Control Transmission Protocol (SCTP) provides a reliable 16 communications channel between two end-hosts in many ways similar to 17 the Transmission Control Protocol (TCP). With the widespread 18 deployment of Network Address Translators (NAT), specialized code has 19 been added to NAT for TCP that allows multiple hosts to reside behind 20 a NAT and yet use only a single globally unique IPv4 address, even 21 when two hosts (behind a NAT) choose the same port numbers for their 22 connection. This additional code is sometimes classified as Network 23 Address and Port Translation (NAPT). 25 This document describes the protocol extensions required for the SCTP 26 endpoints and the mechanisms for NATs necessary to provide similar 27 features of NAPT in the single-point and multi-point traversal 28 scenario. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on January 3, 2019. 47 Copyright Notice 49 Copyright (c) 2018 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 67 4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 4.1. SCTP NAT Traversal Scenarios . . . . . . . . . . . . . . 6 69 4.1.1. Single Point Traversal . . . . . . . . . . . . . . . 6 70 4.1.2. Multi Point Traversal . . . . . . . . . . . . . . . . 7 71 4.2. Limitations of Classical NAPT for SCTP . . . . . . . . . 8 72 4.3. The SCTP Specific Variant of NAT . . . . . . . . . . . . 8 73 5. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . 12 74 5.1. Modified Chunks . . . . . . . . . . . . . . . . . . . . . 12 75 5.1.1. Extended ABORT Chunk . . . . . . . . . . . . . . . . 12 76 5.1.2. Extended ERROR Chunk . . . . . . . . . . . . . . . . 13 77 5.2. New Error Causes . . . . . . . . . . . . . . . . . . . . 13 78 5.2.1. VTag and Port Number Collision Error Cause . . . . . 13 79 5.2.2. Missing State Error Cause . . . . . . . . . . . . . . 14 80 5.2.3. Port Number Collision Error Cause . . . . . . . . . . 15 81 5.3. New Parameters . . . . . . . . . . . . . . . . . . . . . 15 82 5.3.1. Disable Restart Parameter . . . . . . . . . . . . . . 16 83 5.3.2. VTags Parameter . . . . . . . . . . . . . . . . . . . 16 84 6. Procedures for SCTP End Points and NATs . . . . . . . . . . . 17 85 6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 17 86 6.2. Association Setup Considerations . . . . . . . . . . . . 18 87 6.3. Handling of Internal Port Number and Verification Tag 88 Collisions . . . . . . . . . . . . . . . . . . . . . . . 18 89 6.4. Handling of Internal Port Number Collisions . . . . . . . 19 90 6.5. Handling of Missing State . . . . . . . . . . . . . . . . 20 91 6.6. Handling of Fragmented SCTP Packets . . . . . . . . . . . 22 92 6.7. Multi-Point Traversal Considerations . . . . . . . . . . 22 93 7. Various Examples of NAT Traversals . . . . . . . . . . . . . 23 94 7.1. Single-homed Client to Single-homed Server . . . . . . . 23 95 7.2. Single-homed Client to Multi-homed Server . . . . . . . . 25 96 7.3. Multihomed Client and Server . . . . . . . . . . . . . . 28 97 7.4. NAT Loses Its State . . . . . . . . . . . . . . . . . . . 32 98 7.5. Peer-to-Peer Communication . . . . . . . . . . . . . . . 34 99 8. Socket API Considerations . . . . . . . . . . . . . . . . . . 39 100 8.1. Get or Set the NAT Friendliness 101 (SCTP_NAT_FRIENDLY) . . . . . . . . . . . . . . . . . . . 40 102 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40 103 9.1. New Chunk Flags for Two Existing Chunk Types . . . . . . 40 104 9.2. Three New Error Causes . . . . . . . . . . . . . . . . . 41 105 9.3. Two New Chunk Parameter Types . . . . . . . . . . . . . . 42 106 10. Security Considerations . . . . . . . . . . . . . . . . . . . 42 107 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 42 108 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 43 109 12.1. Normative References . . . . . . . . . . . . . . . . . . 43 110 12.2. Informative References . . . . . . . . . . . . . . . . . 43 111 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44 113 1. Introduction 115 Stream Control Transmission Protocol [RFC4960] provides a reliable 116 communications channel between two end-hosts in many ways similar to 117 TCP [RFC0793]. With the widespread deployment of Network Address 118 Translators (NAT), specialized code has been added to NAT for TCP 119 that allows multiple hosts to reside behind a NAT using private 120 addresses (see [RFC6890]) and yet use only a single globally unique 121 IPv4 address, even when two hosts (behind a NAT) choose the same port 122 numbers for their connection. This additional code is sometimes 123 classified as Network Address and Port Translation (NAPT). Please 124 note that this document focuses on the case where the NAT maps 125 multiple private addresses to a single public address. To date, 126 specialized code for SCTP has not yet been added to most NATs so that 127 only true NAT is available. The end result of this is that only one 128 SCTP capable host can be behind a NAT and this host can only be 129 single-homed. The only alternative for supporting legacy NATs is to 130 use UDP encapsulation as specified in [RFC6951]. 132 This document describes an SCTP specific variant NAT and specific 133 packets and procedures to help NATs provide similar features of NAPT 134 in the single-point and multi-point traversal scenario. An SCTP 135 implementation supporting this extension will follow these procedures 136 to assure that in both single-homed and multi-homed cases a NAT will 137 maintain the proper state without needing to change port numbers. 139 It is possible and desirable to make these changes for a number of 140 reasons: 142 o It is desirable for SCTP internal end-hosts on multiple platforms 143 to be able to share a NAT's public IP address in the same way that 144 a TCP session can use a NAT. 146 o If a NAT does not need to change any data within an SCTP packet it 147 will reduce the processing burden of NAT'ing SCTP by NOT needing 148 to execute the CRC32c checksum required by SCTP. 150 o Not having to touch the IP payload makes the processing of ICMP 151 messages in NATs easier. 153 An SCTP-aware NAT will need to follow these procedures for generating 154 appropriate SCTP packet formats. 156 When considering this feature it is possible to have multiple levels 157 of support. At each level, the Internal Host, External Host and NAT 158 may or may not support the features described in this document. The 159 following table illustrates the results of the various combinations 160 of support and if communications can occur between two endpoints. 162 +---------------+------------+---------------+---------------+ 163 | Internal Host | NAT | External Host | Communication | 164 +---------------+------------+---------------+---------------+ 165 | Support | Support | Support | Yes | 166 | Support | Support | No Support | Limited | 167 | Support | No Support | Support | None | 168 | Support | No Support | No Support | None | 169 | No Support | Support | Support | Limited | 170 | No Support | Support | No Support | Limited | 171 | No Support | No Support | Support | None | 172 | No Support | No Support | No Support | None | 173 +---------------+------------+---------------+---------------+ 175 Table 1: Communication possibilities 177 From the table we can see that when a NAT does not support the 178 extension no communication can occur. This is because for the most 179 part of the current situation i.e. SCTP packets sent externally from 180 behind a NAT are discarded by the NAT. In some cases, where the NAT 181 supports the feature but one of the two external hosts does not 182 support the feature, communication may occur but in a limited way. 183 For example only one host may be able to have a connection when a 184 collision case occurs. 186 2. Conventions 188 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 189 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 190 document are to be interpreted as described in [RFC2119]. 192 3. Terminology 194 This document uses the following terms, which are depicted in 195 Figure 1. Familiarity with the terminology used in [RFC4960] and 196 [RFC5061] is assumed. 198 Private-Address (Priv-Addr): The private address that is known to 199 the internal host. 201 Internal-Port (Int-Port): The port number that is in use by the host 202 holding the Private-Address. 204 Internal-VTag (Int-VTag): The SCTP Verification Tag (VTag) that the 205 internal host has chosen for its communication. The VTag is a 206 unique 32-bit tag that must accompany any incoming SCTP packet for 207 this association to the Private-Address. 209 External-Address (Ext-Addr): The address that an internal host is 210 attempting to contact. 212 External-Port (Ext-Port): The port number of the peer process at the 213 External-Address. 215 External-VTag (Ext-VTag): The Verification Tag that the host holding 216 the External-Address has chosen for its communication. The VTag 217 is a unique 32-bit tag that must accompany any incoming SCTP 218 packet for this association to the External-Address. 220 Public-Address (Pub-Addr): The public address assigned to the NAT 221 box which it uses as a source address when sending packets towards 222 the External-Address. 224 Internal Network | External Network 225 | 226 Private | Public External 227 +---------+ Address | Address /--\/--\ Address +---------+ 228 | SCTP | +-----+ / \ | SCTP | 229 |end point|=========| NAT |=======| Internet |==========|end point| 230 | A | +-----+ \ / | B | 231 +---------+ Internal | \--/\--/ External+---------+ 232 Internal Port | Port External 233 VTag | VTag 235 Figure 1: Basic network setup 237 4. Motivation 239 4.1. SCTP NAT Traversal Scenarios 241 This section defines the notion of single and multi-point NAT 242 traversal. 244 4.1.1. Single Point Traversal 246 In this case, all packets in the SCTP association go through a single 247 NAT, as shown below: 249 Internal Network | External Network 250 | 251 +---------+ | /--\/--\ +---------+ 252 | SCTP | +-----+ / \ | SCTP | 253 |end point|=========| NAT |========= | Internet | ========|end point| 254 | A | +-----+ \ / | B | 255 +---------+ | \--/\--/ +---------+ 256 | 258 Single NAT scenario 260 A variation of this case is shown below, i.e., multiple NATs in a 261 single path: 263 Internal | External : Internal | External 264 | : | 265 +---------+ | : | /--\/--\ +---------+ 266 | SCTP | +-----+ : +-----+ / \ | SCTP | 267 |end point|==| NAT |=======:=======| NAT |==| Internet |==|end point| 268 | A | +-----+ : +-----+ \ / | B | 269 +---------+ | : | \--/\--/ +---------+ 270 | : | 272 Serial NATs scenario 274 In this single point traversal scenario, we must acknowledge that 275 while one of the main benefits of SCTP multi-homing is redundant 276 paths, the NAT function represents a single point of failure in the 277 path of the SCTP multi-home association. However, the rest of the 278 path may still benefit from path diversity provided by SCTP multi- 279 homing. 281 The two SCTP endpoints in this case can be either single-homed or 282 multi-homed. However, the important thing is that the NAT (or NATs) 283 in this case sees all the packets of the SCTP association. 285 4.1.2. Multi Point Traversal 287 This case involves multiple NATs and each NAT only sees some of the 288 packets in the SCTP association. An example is shown below: 290 Internal | External 291 +------+ /---\/---\ 292 +---------+ /=======|NAT A |=========\ / \ +---------+ 293 | SCTP | / +------+ \/ \ | SCTP | 294 |end point|/ ... | Internet |===|end point| 295 | A |\ \ / | B | 296 +---------+ \ +------+ / \ / +---------+ 297 \=======|NAT B |=========/ \---\/---/ 298 +------+ 299 | 301 Parallel NATs scenario 303 This case does NOT apply to a single-homed SCTP association (i.e., 304 BOTH endpoints in the association use only one IP address). The 305 advantage here is that the existence of multiple NAT traversal points 306 can preserve the path diversity of a multi-homed association for the 307 entire path. This in turn can improve the robustness of the 308 communication. 310 4.2. Limitations of Classical NAPT for SCTP 312 Using classical NAPT may result in changing one of the SCTP port 313 numbers during the processing which requires the recomputation of the 314 transport layer checksum. Whereas for UDP and TCP this can be done 315 very efficiently, for SCTP the checksum (CRC32c) over the entire 316 packet needs to be recomputed. This would considerably add to the 317 NAT computational burden, however hardware support may mitigate this 318 in some implementations. 320 An SCTP endpoint may have multiple addresses but only has a single 321 port number. To make multipoint traversal work, all the NATs 322 involved must recognize the packets they see as belonging to the same 323 SCTP association and perform port number translation in a consistent 324 way. One possible way of doing this is to use pre-defined table of 325 ports and addresses configured within each NAT. Other mechanisms 326 could make use of NAT to NAT communication. Such mechanisms are not 327 to be deployable on a wide scale base and thus not a recommended 328 solution. Therefore the SCTP variant of NAT has been developed. 330 4.3. The SCTP Specific Variant of NAT 332 In this section we assume that we have multiple SCTP capable hosts 333 behind a NAT which has one Public-Address. Furthermore we are 334 focusing in this section on the single point traversal scenario. 336 The modification of SCTP packets sent to the public Internet is easy. 337 The source address of the packet has to be replaced with the Public- 338 Address. It may also be necessary to establish some state in the NAT 339 box to handle incoming packets, which is discussed later. 341 For SCTP packets coming from the public Internet the destination 342 address of the packets has to be replaced with the Private-Address of 343 the host the packet has to be delivered to. The lookup of the 344 Private-Address is based on the External-VTag, External-Port, 345 Internal-VTag and the Internal-Port. 347 For the SCTP NAT processing the NAT box has to maintain a table of 348 Internal-VTag, Internal-Port, External-VTag, External-Port, Private- 349 Address, and whether the restart procedure is disabled or not. An 350 entry in that table is called a NAT state control block. The 351 function Create() obtains the just mentioned parameters and returns a 352 NAT-State control block. 354 The entries in this table fulfill some uniqueness conditions. There 355 must not be more than one entry with the same pair of Internal-Port 356 and External-Port. This rule can be relaxed, if all entries with the 357 same Internal-Port and External-Port have the support for the restart 358 procedure enabled. In this case there must be no more than one entry 359 with the same Internal-Port, External-Port and Ext-VTag and no more 360 than one entry with the same Internal-Port, External-Port and Int- 361 VTag. 363 The processing of outgoing SCTP packets containing an INIT-chunk is 364 described in the following figure. The scenario shown is valid for 365 all message flows in this section. 367 /--\/--\ 368 +--------+ +-----+ / \ +--------+ 369 | Host A | <------> | NAT | <------> | Internet | <------> | Host B | 370 +--------+ +-----+ \ / +--------+ 371 \--/\---/ 373 INIT[Initiate-Tag] 374 Priv-Addr:Int-Port ------> Ext-Addr:Ext-Port 375 Ext-VTag=0 377 Create(Initiate-Tag, Int-Port, 0, Ext-Port, Priv-Addr, 378 RestartSupported) 379 Returns(NAT-State control block) 381 Translate To: 383 INIT[Initiate-Tag] 384 Pub-Addr:Int-Port ------> Ext-Addr:Ext-Port 385 Ext-VTag=0 387 Normally a NAT control block will be created. However, it is 388 possible that there is already a NAT control block with the same 389 External-Address, External-Port, Internal-Port, and Internal-VTag but 390 different Private-Address. In this case the INIT MUST be dropped by 391 the NAT and an ABORT MUST be sent back to the SCTP host with the 392 M-Bit set and an appropriate error cause (see Section 5.1.1 for the 393 format). The source address of the packet containing the ABORT chunk 394 MUST be the destination address of the packet containing the INIT 395 chunk. 397 It is also possible that a connection to External-Address and 398 External-Port exists without an Internal-VTag conflict but the 399 External-Address does not support the DISABLE_RESTART feature (noted 400 in the NAT control block when the prior connection was established). 401 In such a case the INIT SHOULD be dropped by the NAT and an ABORT 402 SHOULD be sent back to the SCTP host with the M-Bit set and an 403 appropriate error cause (see Section 5.1.1 for the format). 405 The processing of outgoing SCTP packets containing no INIT-chunk is 406 described in the following figure. 408 /--\/--\ 409 +--------+ +-----+ / \ +--------+ 410 | Host A | <------> | NAT | <------> | Internet | <------> | Host B | 411 +--------+ +-----+ \ / +--------+ 412 \--/\---/ 414 Priv-Addr:Int-Port ------> Ext-Addr:Ext-Port 415 Ext-VTag 417 Translate To: 419 Pub-Addr:Int-Port ------> Ext-Addr:Ext-Port 420 Ext-VTag 422 The processing of incoming SCTP packets containing INIT-ACK chunks is 423 described in the following figure. The Lookup() function getting as 424 input the Internal-VTag, Internal-Port, External-VTag, and External- 425 Port, returns the corresponding entry of the NAT table and updates 426 the External-VTag by substituting it with the value of the Initiate- 427 Tag of the INIT-ACK chunk. The wildcard character signifies that the 428 parameter's value is not considered in the Lookup() function or 429 changed in the Update() function, respectively. 431 /--\/--\ 432 +--------+ +-----+ / \ +--------+ 433 | Host A | <------> | NAT | <------> | Internet | <------> | Host B | 434 +--------+ +-----+ \ / +--------+ 435 \--/\---/ 437 INIT-ACK[Initiate-Tag] 438 Pub-Addr:Int-Port <---- Ext-Addr:Ext-Port 439 Int-VTag 441 Lookup(Int-VTag, Int-Port, *, Ext-Port) 442 Update(*, *, Initiate-Tag, *) 444 Returns(NAT-State control block containing Priv-Addr) 446 INIT-ACK[Initiate-Tag] 447 Priv-Addr:Int-Port <------ Ext-Addr:Ext-Port 448 Int-VTag 450 In the case Lookup fails, the SCTP packet is dropped. The Update 451 routine inserts the External-VTag (the Initiate-Tag of the INIT-ACK 452 chunk) in the NAT state control block. 454 The processing of incoming SCTP packets containing an ABORT or 455 SHUTDOWN-COMPLETE chunk with the T-Bit set is described in the 456 following figure. 458 /--\/--\ 459 +--------+ +-----+ / \ +--------+ 460 | Host A | <------> | NAT | <------> | Internet | <------> | Host B | 461 +--------+ +-----+ \ / +--------+ 462 \--/\---/ 464 Pub-Addr:Int-Port <------ Ext-Addr:Ext-Port 465 Ext-VTag 467 Lookup(*, Int-Port, Ext-VTag, Ext-Port) 469 Returns(NAT-State control block containing Priv-Addr) 471 Priv-Addr:Int-Port <------ Ext-Addr:Ext-Port 472 Ext-VTag 474 The processing of other incoming SCTP packets is described in the 475 following figure. 477 /--\/--\ 478 +--------+ +-----+ / \ +--------+ 479 | Host A | <------> | NAT | <------> | Internet | <------> | Host B | 480 +--------+ +-----+ \ / +--------+ 481 \--/\---/ 483 Pub-Addr:Int-Port <------ Ext-Addr:Ext-Port 484 Int-VTag 486 Lookup(Int-VTag, Int-Port, *, Ext-Port) 488 Returns(NAT-State control block containing Local-Address) 490 Priv-Addr:Int-Port <------ Ext-Addr:Ext-Port 491 Int-VTag 493 For an incoming packet containing an INIT-chunk a table lookup is 494 made only based on the addresses and port numbers. If an entry with 495 an External-VTag of zero is found, it is considered a match and the 496 External-VTag is updated. 498 This allows the handling of INIT-collision through NAT. 500 5. Data Formats 502 This section defines the formats used to support NAT traversal. 503 Section 5.1 and Section 5.2 describe chunks and error causes sent by 504 NATs and received by SCTP end points. Section 5.3 describes 505 parameters sent by SCTP end points and used by NATs and SCTP end 506 points. 508 5.1. Modified Chunks 510 This section presents existing chunks defined in [RFC4960] that are 511 modified by this document. 513 5.1.1. Extended ABORT Chunk 515 0 1 2 3 516 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 1 517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 518 | Type = 6 | Reserved |M|T| Length | 519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 520 \ \ 521 / zero or more Error Causes / 522 \ \ 523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 524 The ABORT chunk is extended to add the new 'M-bit'. The M-bit 525 indicates to the receiver of the ABORT chunk that the chunk was not 526 generated by the peer SCTP endpoint, but instead by a middle box. 528 [NOTE: 530 ASSIGNMENT OF M-BIT TO BE CONFIRMED BY IANA. 532 ] 534 5.1.2. Extended ERROR Chunk 536 0 1 2 3 537 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 1 538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 539 | Type = 9 | Reserved |M|T| Length | 540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 541 \ \ 542 / zero or more Error Causes / 543 \ \ 544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 546 The ERROR chunk defined in [RFC4960] is extended to add the new 547 'M-bit'. The M-bit indicates to the receiver of the ERROR chunk that 548 the chunk was not generated by the peer SCTP endpoint, but instead by 549 a middle box. 551 [NOTE: 553 ASSIGNMENT OF M-BIT TO BE CONFIRMED BY IANA. 555 ] 557 5.2. New Error Causes 559 This section defines the new error causes added by this document. 561 5.2.1. VTag and Port Number Collision Error Cause 563 0 1 2 3 564 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 1 565 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 566 | Cause Code = 0x00B0 | Cause Length = Variable | 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 \ Chunk / 569 / \ 570 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 571 Cause Code: 2 bytes (unsigned integer) 572 This field holds the IANA defined cause code for the 'VTag and 573 Port Number Collision' Error Cause. The suggested value of this 574 field for IANA is 0x00B0. 576 Cause Length: 2 bytes (unsigned integer) 577 This field holds the length in bytes of the error cause. The 578 value MUST be the length of the Cause-Specific Information plus 4. 580 Chunk: variable length 581 The Cause-Specific Information is filled with the chunk that 582 caused this error. This can be an INIT, INIT-ACK, or ASCONF 583 chunk. Note that if the entire chunk will not fit in the ERROR 584 chunk or ABORT chunk being sent then the bytes that do not fit are 585 truncated. 587 [NOTE: 589 ASSIGNMENT OF CAUSE-CODE TO BE CONFIRMED BY IANA. 591 ] 593 5.2.2. Missing State Error Cause 595 0 1 2 3 596 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 1 597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 | Cause Code = 0x00B1 | Cause Length = Variable | 599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 600 \ Incoming Packet / 601 / \ 602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 Cause Code: 2 bytes (unsigned integer) 605 This field holds the IANA defined cause code for the 'Missing 606 State' Error Cause. The suggested value of this field for IANA is 607 0x00B1. 609 Cause Length: 2 bytes (unsigned integer) 610 This field holds the length in bytes of the error cause. The 611 value MUST be the length of the Cause-Specific Information plus 4. 613 Incoming Packet: variable length 614 The Cause-Specific Information is filled with the IPv4 or IPv6 615 packet that caused this error. The IPv4 or IPv6 header MUST be 616 included. Note that if the packet will not fit in the ERROR chunk 617 or ABORT chunk being sent then the bytes that do not fit are 618 truncated. 620 [NOTE: 622 ASSIGNMENT OF CAUSE-CODE TO BE CONFIRMED BY IANA. 624 ] 626 5.2.3. Port Number Collision Error Cause 628 0 1 2 3 629 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 1 630 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 631 | Cause Code = 0x00B2 | Cause Length = Variable | 632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 633 \ Chunk / 634 / \ 635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 637 Cause Code: 2 bytes (unsigned integer) 638 This field holds the IANA defined cause code for the 'Port Number 639 Collision' Error Cause. The suggested value of this field for 640 IANA is 0x00B2. 642 Cause Length: 2 bytes (unsigned integer) 643 This field holds the length in bytes of the error cause. The 644 value MUST be the length of the Cause-Specific Information plus 4. 646 Chunk: variable length 647 The Cause-Specific Information is filled with the chunk that 648 caused this error. This can be an INIT, INIT-ACK, or ASCONF 649 chunk. Note that if the entire chunk will not fit in the ERROR 650 chunk or ABORT chunk being sent then the bytes that do not fit are 651 truncated. 653 [NOTE: 655 ASSIGNMENT OF CAUSE-CODE TO BE CONFIRMED BY IANA. 657 ] 659 5.3. New Parameters 661 This section defines new parameters and their valid appearance 662 defined by this document. 664 5.3.1. Disable Restart Parameter 666 This parameter is used to indicate that the RESTART procedure is 667 requested to be disabled. Both endpoints of an association MUST 668 include this parameter in the INIT chunk and INIT-ACK chunk when 669 establishing an association and MUST include it in the ASCONF chunk 670 when adding an address to successfully disable the restart procedure. 672 0 1 2 3 673 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 1 674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 675 | Type = 0xC007 | Length = 4 | 676 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 678 Parameter Type: 2 bytes (unsigned integer) 679 This field holds the IANA defined parameter type for the Disable 680 Restart Parameter. The suggested value of this field for IANA is 681 0xC007. 683 Parameter Length: 2 bytes (unsigned integer) 684 This field holds the length in bytes of the parameter. The value 685 MUST be 4. 687 [NOTE: 689 ASSIGNMENT OF PARAMETER TYPE TO BE CONFIRMED BY IANA. 691 ] 693 This parameter MAY appear in INIT, INIT-ACK and ASCONF chunks and 694 MUST NOT appear in any other chunk. 696 5.3.2. VTags Parameter 698 This parameter is used to help a NAT recover from state loss. 700 0 1 2 3 701 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 1 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 | Parameter Type = 0xC008 | Parameter Length = 16 | 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 705 | ASCONF-Request Correlation ID | 706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 707 | Internal Verification Tag | 708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 709 | External Verification Tag | 710 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 711 Parameter Type: 2 bytes (unsigned integer) 712 This field holds the IANA defined parameter type for the VTags 713 Parameter. The suggested value of this field for IANA is 0xC008. 715 Parameter Length: 2 bytes (unsigned integer) 716 This field holds the length in bytes of the parameter. The value 717 MUST be 16. 719 ASCONF-Request Correlation ID: 4 bytes (unsigned integer) 720 This is an opaque integer assigned by the sender to identify each 721 request parameter. The receiver of the ASCONF Chunk will copy 722 this 32-bit value into the ASCONF Response Correlation ID field of 723 the ASCONF-ACK response parameter. The sender of the ASCONF can 724 use this same value in the ASCONF-ACK to find which request the 725 response is for. Note that the receiver MUST NOT change this 726 32-bit value. 728 Internal Verification Tag: 4 bytes (unsigned integer) 729 The Verification Tag that the internal host has chosen for its 730 communication. The Verification Tag is a unique 32-bit tag that 731 must accompany any incoming SCTP packet for this association to 732 the Private-Address. 734 External Verification Tag: 4 bytes (unsigned integer) The 735 Verification Tag that the host holding the External-Address has 736 chosen for its communication. The VTag is a unique 32-bit tag 737 that must accompany any incoming SCTP packet for this association 738 to the External-Address. 740 [NOTE: 742 ASSIGNMENT OF PARAMETER TYPE TO BE CONFIRMED BY IANA. 744 ] 746 This parameter MAY appear in ASCONF chunks and MUST NOT appear in any 747 other chunk. 749 6. Procedures for SCTP End Points and NATs 751 6.1. Overview 753 When an SCTP endpoint is behind an SCTP-aware NAT a number of 754 problems may arise as it tries to communicate with its peer: 756 o IP addresses can not not be included in the SCTP packet. This is 757 discussed in Section 6.2. 759 o More than one host behind a NAT may pick the same VTag and source 760 port when talking to the same peer server. This creates a 761 situation where the NAT will not be able to tell the two 762 associations apart. This situation is discussed in Section 6.3. 764 o When an SCTP endpoint is a server communicating with multiple 765 peers and the peers are behind the same NAT, then the two 766 endpoints cannot be distinguished by the server. This case is 767 discussed in Section 6.4. 769 o A restart of a NAT during a conversation could cause a loss of its 770 state. This problem and its solution is discussed in Section 6.5. 772 o NAT boxes need to deal with SCTP packets being fragmented at the 773 IP layer. This is discussed in Section 6.6. 775 o An SCTP endpoint may be behind two NATs providing redundancy. The 776 method to set up this scenario is discussed in Section 6.7. 778 Each of these mechanisms requires additional chunks and parameters, 779 defined in this document, and possibly modified handling procedures 780 from those specified in [RFC4960]. 782 6.2. Association Setup Considerations 784 The association setup procedure defined in [RFC4960] allows multi- 785 homed SCTP end points to exchange its IP-addresses by using IPv4 or 786 IPv6 address parameters in the INIT and INIT-ACK chunks. However, 787 this can't be used when NATs are present. 789 Every association MUST initially be set up single-homed. There MUST 790 NOT be any IPv4 Address parameter, IPv6 Address parameter, or 791 Supported Address Types parameter in the INIT-chunk. The INIT-ACK 792 chunk MUST NOT contain any IPv4 Address parameter or IPv6 Address 793 parameter. 795 If the association should finally be multi-homed, the procedure in 796 Section 6.7 MUST be used. 798 The INIT and INIT-ACK chunk SHOULD contain the Disable Restart 799 parameter defined in Section 5.3.1. 801 6.3. Handling of Internal Port Number and Verification Tag Collisions 803 Consider the case where two hosts in the Private-Address space want 804 to set up an SCTP association with the same service provided by some 805 hosts in the Internet. This means that the External-Port is the 806 same. If they both choose the same Internal-Port and Internal-VTag, 807 the NAT box cannot distinguish between incoming packets anymore. But 808 this is very unlikely. The Internal-VTags are chosen at random and 809 if the Internal-Ports are also chosen from the ephemeral port range 810 at random this gives a 46-bit random number which has to match. In 811 the TCP-like NAPT case the NAT box can control the 16-bit Natted Port 812 and therefore avoid collisions deterministically. 814 The same can happen with the External-VTag when an INIT-ACK chunk or 815 an ASCONF chunk is processed by the NAT. 817 However, in this unlikely event the NAT box MUST send an ABORT chunk 818 with the M-bit set if the collision is triggered by an INIT or INIT- 819 ACK chunk or send an ERROR chunk with the M-bit set if the collision 820 is triggered by an ASCONF chunk. The M-bit is a new bit defined by 821 this document to express to SCTP that the source of this packet is a 822 "middle" box, not the peer SCTP endpoint (see Section 5.1.1). If a 823 packet containing an INIT-ACK chunk triggers the collision, the 824 corresponding packet containing the ABORT chunk MUST contain the same 825 source and destination address and port numbers as the packet 826 containing the INIT-ACK chunk. In the other two cases, the source 827 and destination address and port numbers MUST be swapped. 829 The sender of the packet containing the INIT chunk or the receiver of 830 the INIT-ACK chunk, upon reception of an ABORT chunk with M-bit set 831 and the appropriate error cause code for colliding NAT table state is 832 included, MUST reinitiate the association setup procedure after 833 choosing a new initiate tag, if the association is in COOKIE-WAIT 834 state. In any other state, the SCTP endpoint MUST NOT respond. 836 The sender of the ASCONF chunk, upon reception of an ERROR chunk with 837 M-bit set, MUST stop adding the path to the association. 839 The sender of the ERROR or ABORT chunk MUST include the error cause 840 with cause code 'VTag and Port Number Collision' (see Section 5.2.1). 842 6.4. Handling of Internal Port Number Collisions 844 When two SCTP hosts are behind an SCTP-aware NAT it is possible that 845 two SCTP hosts in the Private-Address space will want to set up an 846 SCTP association with the same server running on the same host in the 847 Internet. For the NAT, appropriate tracking may be performed by 848 assuring that the VTags are unique between the two hosts. 850 But for the external SCTP server on the Internet this means that the 851 External-Port and the External-Address are the same. If they both 852 have chosen the same Internal-Port the server cannot distinguish 853 between both associations based on the address and port numbers. For 854 the server it looks like the association is being restarted. To 855 overcome this limitation the client sends a Disable Restart parameter 856 in the INIT-chunk. 858 When the server receives this parameter it MUST do the following: 860 o Include a Disable Restart parameter in the INIT-ACK to inform the 861 client that it will support the feature. 863 o Disable the restart procedures defined in [RFC4960] for this 864 association. 866 Servers that support this feature will need to be capable of 867 maintaining multiple connections to what appears to be the same peer 868 (behind the NAT) differentiated only by the VTags. 870 The NAT, when processing the INIT-ACK, should note in its internal 871 table that the association supports the Disable Restart extension. 872 This note is used when establishing future associations (i.e. when 873 processing an INIT from an internal host) to decide if the connection 874 should be allowed. The NAT MUST do the following when processing an 875 INIT: 877 o If the INIT is destined to an external address and port for which 878 the NAT has no outbound connection, allow the INIT creating an 879 internal mapping table. 881 o If the INIT matches the external address and port of an already 882 existing connection, validate that the external server supports 883 the Disable Restart feature, if it does allow the INIT to be 884 forwarded. 886 o If the external server does not support the Disable Restart 887 extension the NAT MUST send an ABORT with the M-bit set. 889 The 'Port Number Collision' error cause (see Section 5.2.3) MUST be 890 included in the ABORT chunk. 892 If the collision is triggered by an ASCONF chunk, a packet containing 893 an ERROR chunk with the 'Port Number Collision' error cause MUST be 894 sent back. 896 6.5. Handling of Missing State 898 If the NAT box receives a packet from the internal network for which 899 the lookup procedure does not find an entry in the NAT table, a 900 packet containing an ERROR chunk is sent back with the M-bit set. 901 The source address of the packet containing the ERROR chunk MUST be 902 the destination address of the incoming SCTP packet. The 903 verification tag is reflected and the T-bit is set. Please note that 904 such a packet containing an ERROR chunk SHOULD NOT be sent if the 905 received packet contains an ABORT, SHUTDOWN-COMPLETE or INIT-ACK 906 chunk. An ERROR chunk MUST NOT be sent if the received packet 907 contains an ERROR chunk with the M-bit set. 909 When sending the ERROR chunk, the new error cause 'Missing State' 910 (see Section 5.2.2) MUST be included and the new M-bit of the ERROR 911 chunk MUST be set (see Section 5.1.2). 913 Upon reception of this ERROR chunk by an SCTP endpoint the receiver 914 SHOULD take the following actions: 916 o Validate that the verification tag is reflected by looking at the 917 VTag that would have been included in the outgoing packet. 919 o Validate that the peer of the SCTP association supports the 920 dynamic address extension, if it does not discard the incoming 921 ERROR chunk. 923 o Generate a new ASCONF chunk containing the VTags parameter (see 924 Section 5.3.2) and the Disable Restart parameter if the 925 association is using the disabled restart feature. By processing 926 this packet the NAT can recover the appropriate state. The 927 procedures for generating an ASCONF chunk can be found in 928 [RFC5061]. 930 If the NAT box receives a packet for which it has no NAT table entry 931 and the packet contains an ASCONF chunk with the VTags parameter, the 932 NAT box MUST update its NAT table according to the verification tags 933 in the VTags parameter and the optional Disable Restart parameter. 935 The peer SCTP endpoint receiving such an ASCONF chunk SHOULD either 936 add the address and respond with an acknowledgment, if the address is 937 new to the association (following all procedures defined in 938 [RFC5061]). Or, if the address is already part of the association, 939 the SCTP endpoint MUST NOT respond with an error, but instead should 940 respond with an ASCONF-ACK chunk acknowledging the address but take 941 no action (since the address is already in the association). 943 Note that it is possible that upon receiving an ASCONF chunk 944 containing the VTags parameter the NAT will realize that it has an 945 'Internal Port Number and Verification Tag collision'. In such a 946 case the NAT MUST send an ERROR chunk with the error cause code set 947 to 'VTag and Port Number Collision' (see Section 5.2.1). 949 If an SCTP endpoint receives an ERROR with 'Internal Port Number and 950 Verification Tag collision' as the error cause and the packet in the 951 Error Chunk contains an ASCONF with the VTags parameter, careful 952 examination of the association is required. The endpoint MUST do the 953 following: 955 o Validate that the verification tag is reflected by looking at the 956 VTag that would have been included in the outgoing packet. 958 o Validate that the peer of the SCTP association supports the 959 dynamic address extension, if it does not discard the incoming 960 ERROR chunk. 962 o If the association is attempting to add an address (i.e. following 963 the procedures in Section 6.7) then the endpoint MUST-NOT consider 964 the address part of the association and SHOULD make no further 965 attempt to add the address (i.e. cancel any ASCONF timers and 966 remove any record of the path), since the NAT has a VTag collision 967 and the association cannot easily create a new VTag (as it would 968 if the error occurred when sending an INIT). 970 o If the endpoint has no other path, i. e. the procedure was 971 executed due to missing a state in the NAT, then the endpoint MUST 972 abort the association. This would occur only if the local NAT 973 restarted and accepted a new association before attempting to 974 repair the missing state (Note that this is no different than what 975 happens to all TCP connections when a NAT looses its state). 977 6.6. Handling of Fragmented SCTP Packets 979 A NAT box MUST support IP reassembly of received fragmented SCTP 980 packets. The fragments may arrive in any order. 982 When an SCTP packet has to be fragmented by the NAT box and the IP 983 header forbids fragmentation a corresponding ICMP packet SHOULD be 984 sent. 986 6.7. Multi-Point Traversal Considerations 988 If a multi-homed SCTP endpoint behind a NAT connects to a peer, it 989 SHOULD first set up the association single-homed with only one 990 address causing the first NAT to populate its state. Then it SHOULD 991 add each IP address using ASCONF chunks sent via their respective 992 NATs. The address to add is the wildcard address and the lookup 993 address SHOULD also contain the VTags parameter and optionally the 994 Disable Restart parameter as illustrated above. 996 7. Various Examples of NAT Traversals 998 Please note that this section is informational only. 1000 The addresses being used in the following examples are IPv4 addresses 1001 for private-use networks and for documentation as specified in 1002 [RFC6890]. However, the method described here is not limited to this 1003 NAT44 case. 1005 7.1. Single-homed Client to Single-homed Server 1007 The internal client starts the association with the external server 1008 via a four-way-handshake. Host A starts by sending an INIT chunk. 1010 /--\/--\ 1011 +--------+ +-----+ / \ +--------+ 1012 | Host A | <------> | NAT | <------> | Internet | <------> | Host B | 1013 +--------+ +-----+ \ / +--------+ 1014 \--/\---/ 1015 +---------+--------+----------+--------+-----------+ 1016 NAT | Int | Int | Ext | Ext | Priv | 1017 | VTag | Port | VTag | Port | Addr | 1018 +---------+--------+----------+--------+-----------+ 1020 INIT[Initiate-Tag = 1234] 1021 10.0.0.1:1 ------> 203.0.113.1:2 1022 Ext-VTtag = 0 1024 A NAT entry is created, the source address is substituted and the 1025 packet is sent on: 1027 NAT creates entry: 1028 +---------+--------+----------+--------+-----------+ 1029 NAT | Int | Int | Ext | Ext | Priv | 1030 | VTag | Port | VTag | Port | Addr | 1031 +---------+--------+----------+--------+-----------+ 1032 | 1234 | 1 | 0 | 2 | 10.0.0.1 | 1033 +---------+--------+----------+--------+-----------+ 1035 INIT[Initiate-Tag = 1234] 1036 192.0.2.1:1 ------------------------> 203.0.113.1:2 1037 Ext-VTtag = 0 1039 Host B receives the INIT and sends an INIT-ACK with the NAT's 1040 external address as destination address. 1042 /--\/--\ 1043 +--------+ +-----+ / \ +--------+ 1044 | Host A | <------> | NAT | <------> | Internet | <------> | Host B | 1045 +--------+ +-----+ \ / +--------+ 1046 \--/\---/ 1048 INIT-ACK[Initiate-Tag = 5678] 1049 192.0.2.1:1 <----------------------- 203.0.113.1:2 1050 Int-VTag = 1234 1052 NAT updates entry: 1053 +---------+--------+----------+--------+-----------+ 1054 NAT | Int | Int | Ext | Ext | Priv | 1055 | VTag | Port | VTag | Port | Addr | 1056 +---------+--------+----------+--------+-----------+ 1057 | 1234 | 1 | 5678 | 2 | 10.0.0.1 | 1058 +---------+--------+----------+--------+-----------+ 1060 INIT-ACK[Initiate-Tag = 5678] 1061 10.0.0.1:1 <------ 203.0.113.1:2 1062 Int-VTag = 1234 1064 The handshake finishes with a COOKIE-ECHO acknowledged by a COOKIE- 1065 ACK. 1067 /--\/--\ 1068 +--------+ +-----+ / \ +--------+ 1069 | Host A | <------> | NAT | <------> | Internet | <------> | Host B | 1070 +--------+ +-----+ \ / +--------+ 1071 \--/\---/ 1073 COOKIE-ECHO 1074 10.0.0.1:1 ------> 203.0.113.1:2 1075 Ext-VTag = 5678 1077 COOKIE-ECHO 1078 192.0.2.1:1 -----------------------> 203.0.113.1:2 1079 Ext-VTag = 5678 1081 COOKIE-ACK 1082 192.0.2.1:1 <----------------------- 203.0.113.1:2 1083 Int-VTag = 1234 1085 COOKIE-ACK 1086 10.0.0.1:1 <------ 203.0.113.1:2 1087 Int-VTag = 1234 1089 7.2. Single-homed Client to Multi-homed Server 1091 The internal client is single-homed whereas the external server is 1092 multi-homed. The client (Host A) sends an INIT like in the single- 1093 homed case. 1095 +--------+ 1096 /--\/--\ /-|Router 1| \ 1097 +------+ +-----+ / \ / +--------+ \ +------+ 1098 | Host | <-----> | NAT | <-> | Internet | == =| Host | 1099 | A | +-----+ \ / \ +--------+ / | B | 1100 +------+ \--/\--/ \-|Router 2|-/ +------+ 1101 +--------+ 1103 +---------+--------+----------+--------+-----------+ 1104 NAT | Int | Int | Ext | Ext | Priv | 1105 | VTag | Port | VTag | Port | Addr | 1106 +---------+--------+----------+--------+-----------+ 1108 INIT[Initiate-Tag = 1234] 1109 10.0.0.1:1 ---> 203.0.113.1:2 1110 Ext-VTag = 0 1112 NAT creates entry: 1114 +---------+--------+----------+--------+-----------+ 1115 NAT | Int | Int | Ext | Ext | Priv | 1116 | VTag | Port | VTag | Port | Addr | 1117 +---------+--------+----------+--------+-----------+ 1118 | 1234 | 1 | 0 | 2 | 10.0.0.1 | 1119 +---------+--------+----------+--------+-----------+ 1121 INIT[Initiate-Tag = 1234] 1122 192.0.2.1:1 --------------------------> 203.0.113.1:2 1123 Ext-VTag = 0 1125 The server (Host B) includes its two addresses in the INIT-ACK chunk, 1126 which results in two NAT entries. 1128 +--------+ 1129 /--\/--\ /-|Router 1| \ 1130 +------+ +-----+ / \ / +--------+ \ +------+ 1131 | Host | <-----> | NAT | <-> | Internet | == =| Host | 1132 | A | +-----+ \ / \ +--------+ / | B | 1133 +------+ \--/\--/ \-|Router 2|-/ +------+ 1134 +--------+ 1136 INIT-ACK[Initiate-tag = 5678, IP-Addr = 203.0.113.129] 1137 192.0.2.1:1 <-------------------------- 203.0.113.1:2 1138 Int-VTag = 1234 1140 NAT does need to change the table for second address: 1142 +---------+--------+----------+--------+-----------+ 1143 NAT | Int | Int | Ext | Ext | Priv | 1144 | VTag | Port | VTag | Port | Addr | 1145 +---------+--------+----------+--------+-----------+ 1146 | 1234 | 1 | 5678 | 2 | 10.0.0.1 | 1147 +---------+--------+----------+--------+-----------+ 1149 INIT-ACK[Initiate-Tag = 5678] 1150 10.0.0.1:1 <--- 203.0.113.1:2 1151 Int-VTag = 1234 1153 The handshake finishes with a COOKIE-ECHO acknowledged by a COOKIE- 1154 ACK. 1156 +--------+ 1157 /--\/--\ /-|Router 1| \ 1158 +------+ +-----+ / \ / +--------+ \ +------+ 1159 | Host | <-----> | NAT | <-> | Internet | == =| Host | 1160 | A | +-----+ \ / \ +--------+ / | B | 1161 +------+ \--/\--/ \-|Router 2|-/ +------+ 1162 +--------+ 1164 COOKIE-ECHO 1165 10.0.0.1:1 ---> 203.0.113.1:2 1166 ExtVTag = 5678 1168 COOKIE-ECHO 1169 192.0.2.1:1 --------------------------> 203.0.113.1:2 1170 Ext-VTag = 5678 1172 COOKIE-ACK 1173 192.0.2.1:1 <-------------------------- 203.0.113.1:2 1174 Int-VTag = 1234 1176 COOKIE-ACK 1177 10.0.0.1:1 <--- 203.0.113.1:2 1178 Int-VTag = 1234 1180 7.3. Multihomed Client and Server 1182 The client (Host A) sends an INIT to the server (Host B), but does 1183 not include the second address. 1185 +-------+ 1186 /--| NAT 1 |--\ /--\/--\ 1187 +------+ / +-------+ \ / \ +--------+ 1188 | Host |=== ====| Internet |====| Host B | 1189 | A | \ +-------+ / \ / +--------+ 1190 +------+ \--| NAT 2 |--/ \--/\--/ 1191 +-------+ 1193 +---------+--------+----------+--------+-----------+ 1194 NAT 1 | Int | Int | Ext | Ext | Priv | 1195 | VTag | Port | VTag | Port | Addr | 1196 +---------+--------+----------+--------+-----------+ 1198 INIT[Initiate-Tag = 1234] 1199 10.0.0.1:1 --------> 203.0.113.1:2 1200 Ext-VTag = 0 1202 NAT 1 creates entry: 1204 +---------+--------+----------+--------+-----------+ 1205 NAT 1 | Int | Int | Ext | Ext | Priv | 1206 | VTag | Port | VTag | Port | Addr | 1207 +---------+--------+----------+--------+-----------+ 1208 | 1234 | 1 | 0 | 2 | 10.0.0.1 | 1209 +---------+--------+----------+--------+-----------+ 1211 INIT[Initiate-Tag = 1234] 1212 192.0.2.1:1 ---------------------> 203.0.113.1:2 1213 ExtVTag = 0 1215 Host B includes its second address in the INIT-ACK, which results in 1216 two NAT entries in NAT 1. 1218 +-------+ 1219 /--------| NAT 1 |--------\ /--\/--\ 1220 +------+ / +-------+ \ / \ +--------+ 1221 | Host |=== ====| Internet |===| Host B | 1222 | A | \ +-------+ / \ / +--------+ 1223 +------+ \--------| NAT 2 |--------/ \--/\--/ 1224 +-------+ 1226 INIT-ACK[Initiate-Tag = 5678, IP-Addr = 203.0.113.129] 1227 192.0.2.1:1 <----------------------- 203.0.113.1:2 1228 Int-VTag = 1234 1230 NAT 1 does not need to update the table for second address: 1232 +---------+--------+----------+--------+-----------+ 1233 NAT 1 | Int | Int | Ext | Ext | Priv | 1234 | VTag | Port | VTag | Port | Addr | 1235 +---------+--------+----------+--------+-----------+ 1236 | 1234 | 1 | 5678 | 2 | 10.0.0.1 | 1237 +---------+--------+----------+--------+-----------+ 1239 INIT-ACK[Initiate-Tag = 5678] 1240 10.0.0.1:1 <-------- 203.0.113.1:2 1241 Int-VTag = 1234 1243 The handshake finishes with a COOKIE-ECHO acknowledged by a COOKIE- 1244 ACK. 1246 +-------+ 1247 /--------| NAT 1 |--------\ /--\/--\ 1248 +------+ / +-------+ \ / \ +--------+ 1249 | Host |=== ====| Internet |===| Host B | 1250 | A | \ +-------+ / \ / +--------+ 1251 +------+ \--------| NAT 2 |--------/ \--/\--/ 1252 +-------+ 1254 COOKIE-ECHO 1255 10.0.0.1:1 --------> 203.0.113.1:2 1256 Ext-VTag = 5678 1258 COOKIE-ECHO 1259 192.0.2.1:1 ------------------> 203.0.113.1:2 1260 Ext-VTag = 5678 1262 COOKIE-ACK 1263 192.0.2.1:1 <------------------ 203.0.113.1:2 1264 Int-VTag = 1234 1266 COOKIE-ACK 1267 10.0.0.1:1 <------- 203.0.113.1:2 1268 Int-VTag = 1234 1270 Host A announces its second address in an ASCONF chunk. The address 1271 parameter contains an undefined address (0) to indicate that the 1272 source address should be added. The lookup address parameter within 1273 the ASCONF chunk will also contain the pair of VTags (external and 1274 internal) so that the NAT may populate its table completely with this 1275 single packet. 1277 +-------+ 1278 /--------| NAT 1 |--------\ /--\/--\ 1279 +------+ / +-------+ \ / \ +--------+ 1280 | Host |=== ====| Internet |===| Host B | 1281 | A | \ +-------+ / \ / +--------+ 1282 +------+ \--------| NAT 2 |--------/ \--/\--/ 1283 +-------+ 1285 ASCONF [ADD-IP=0.0.0.0, INT-VTag=1234, Ext-VTag = 5678] 1286 10.1.0.1:1 --------> 203.0.113.129:2 1287 Ext-VTag = 5678 1289 NAT 2 creates complete entry: 1291 +---------+--------+----------+--------+-----------+ 1292 NAT 2 | Int | Int | Ext | Ext | Priv | 1293 | VTag | Port | VTag | Port | Addr | 1294 +---------+--------+----------+--------+-----------+ 1295 | 1234 | 1 | 5678 | 2 | 10.1.0.1 | 1296 +---------+--------+----------+--------+-----------+ 1298 ASCONF [ADD-IP,Int-VTag=1234, Ext-VTag = 5678] 1299 192.0.2.129:1 ---------------------> 203.0.113.129:2 1300 Ext-VTag = 5678 1302 ASCONF-ACK 1303 192.0.2.129:1 <--------------------- 203.0.113.129:2 1304 Int-VTag = 1234 1306 ASCONF-ACK 1307 10.1.0.1:1 <----- 203.0.113.129:2 1308 Int-VTag = 1234 1310 7.4. NAT Loses Its State 1312 Association is already established between Host A and Host B, when 1313 the NAT loses its state and obtains a new public address. Host A 1314 sends a DATA chunk to Host B. 1316 /--\/--\ 1317 +--------+ +-----+ / \ +--------+ 1318 | Host A | <----------> | NAT | <----> | Internet | <----> | Host B | 1319 +--------+ +-----+ \ / +--------+ 1320 \--/\--/ 1322 +---------+--------+----------+--------+-----------+ 1323 NAT | Int | Int | Ext | Ext | Priv | 1324 | VTag | Port | VTag | Port | Addr | 1325 +---------+--------+----------+--------+-----------+ 1326 | 1234 | 1 | 5678 | 2 | 10.0.0.1 | 1327 +---------+--------+----------+--------+-----------+ 1329 DATA 1330 10.0.0.1:1 ----------> 203.0.113.1:2 1331 Ext-VTag = 5678 1333 The NAT box cannot find entry for the association. It sends ERROR 1334 message with the M-Bit set and the cause "NAT state missing". 1336 /--\/--\ 1337 +--------+ +-----+ / \ +--------+ 1338 | Host A | <----------> | NAT | <----> | Internet | <----> | Host B | 1339 +--------+ +-----+ \ / +--------+ 1340 \--/\--/ 1342 ERROR [M-Bit, NAT state missing] 1343 10.0.0.1:1 <---------- 203.0.113.1:2 1344 Ext-VTag = 5678 1346 On reception of the ERROR message, Host A sends an ASCONF chunk 1347 indicating that the former information has to be deleted and the 1348 source address of the actual packet added. 1350 /--\/--\ 1351 +--------+ +-----+ / \ +--------+ 1352 | Host A | <----------> | NAT | <----> | Internet | <----> | Host B | 1353 +--------+ +-----+ \ / +--------+ 1354 \--/\--/ 1356 ASCONF [ADD-IP,DELETE-IP,Int-VTag=1234, Ext-VTag = 5678] 1357 10.0.0.1:1 ----------> 203.0.113.129:2 1358 Ext-VTag = 5678 1360 +---------+--------+----------+--------+-----------+ 1361 NAT | Int | Int | Ext | Ext | Priv | 1362 | VTag | Port | VTag | Port | Addr | 1363 +---------+--------+----------+--------+-----------+ 1364 | 1234 | 1 | 5678 | 2 | 10.0.0.1 | 1365 +---------+--------+----------+--------+-----------+ 1367 ASCONF [ADD-IP,DELETE-IP,Int-VTag=1234, Ext-VTag = 5678] 1368 192.0.2.2:1 -------------------> 203.0.113.129:2 1369 Ext-VTag = 5678 1371 Host B adds the new source address and deletes all former entries. 1373 /--\/--\ 1374 +--------+ +-----+ / \ +--------+ 1375 | Host A | <----------> | NAT | <----> | Internet | <----> | Host B | 1376 +--------+ +-----+ \ / +--------+ 1377 \--/\--/ 1379 ASCONF-ACK 1380 192.0.2.2:1 <------------------- 203.0.113.129:2 1381 Int-VTag = 1234 1383 ASCONF-ACK 1384 10.1.0.1:1 <---------- 203.0.113.129:2 1385 Int-VTag = 1234 1387 DATA 1388 10.0.0.1:1 ----------> 203.0.113.1:2 1389 Ext-VTag = 5678 1390 DATA 1391 192.0.2.2:1 -------------------> 203.0.113.129:2 1392 Ext-VTag = 5678 1394 7.5. Peer-to-Peer Communication 1396 If two hosts are behind NATs, they have to get knowledge of the 1397 peer's public address. This can be achieved with a so-called 1398 rendezvous server. Afterwards the destination addresses are public, 1399 and the association is set up with the help of the INIT collision. 1400 The NAT boxes create their entries according to their internal peer's 1401 point of view. Therefore, NAT A's Internal-VTag and Internal-Port 1402 are NAT B's External-VTag and External-Port, respectively. The 1403 naming of the verification tag in the packet flow is done from the 1404 sending peer's point of view. 1406 Internal | External External | Internal 1407 | | 1408 | /--\/---\ | 1409 +--------+ +-------+ / \ +-------+ +--------+ 1410 | Host A |<--->| NAT A |<-->| Internet |<-->| NAT B |<--->| Host B | 1411 +--------+ +-------+ \ / +-------+ +--------+ 1412 | \--/\---/ | 1414 NAT-Tables 1415 +---------+--------+----------+--------+-----------+ 1416 NAT A | Int | Int | Ext | Ext | Priv | 1417 | VTag | Port | VTag | Port | Addr | 1418 +---------+--------+----------+--------+-----------+ 1420 +---------+--------+----------+--------+-----------+ 1421 NAT B | Int | Int | Ext | Ext | Priv | 1422 | v-tag | port | v-tag | port | Addr | 1423 +---------+--------+----------+--------+-----------+ 1425 INIT[Initiate-Tag = 1234] 1426 10.0.0.1:1 --> 203.0.113.1:2 1427 Ext-VTag = 0 1429 NAT A creates entry: 1431 +---------+--------+----------+--------+-----------+ 1432 NAT A | Int | Int | Ext | Ext | Priv | 1433 | VTag | Port | VTag | Port | Addr | 1434 +---------+--------+----------+--------+-----------+ 1435 | 1234 | 1 | 0 | 2 | 10.0.0.1 | 1436 +---------+--------+----------+--------+-----------+ 1438 INIT[Initiate-Tag = 1234] 1439 192.0.2.1:1 ----------------> 203.0.113.1:2 1440 Ext-VTag = 0 1442 NAT B processes INIT, but cannot find an entry. The SCTP packet is 1443 silently discarded and leaves the NAT table of NAT B unchanged. 1445 +---------+--------+----------+--------+-----------+ 1446 NAT B | Int | Int | Ext | Ext | Priv | 1447 | VTag | Port | VTag | Port | Addr | 1448 +---------+--------+----------+--------+-----------+ 1450 Now Host B sends INIT, which is processed by NAT B. Its parameters 1451 are used to create an entry. 1453 Internal | External External | Internal 1454 | | 1455 | /--\/---\ | 1456 +--------+ +-------+ / \ +-------+ +--------+ 1457 | Host A |<--->| NAT A |<-->| Internet |<-->| NAT B |<--->| Host B | 1458 +--------+ +-------+ \ / +-------+ +--------+ 1459 | \--/\---/ | 1461 INIT[Initiate-Tag = 5678] 1462 192.0.2.1:1 <-- 10.1.0.1:2 1463 Ext-VTag = 0 1465 +---------+--------+-----------+----------+--------+ 1466 NAT B | Int | Int | Priv | Ext | Ext | 1467 | VTag | Port | Addr | VTag | Port | 1468 +---------+--------+-----------+----------+--------+ 1469 | 5678 | 2 | 10.1.0.1 | 0 | 1 | 1470 +---------+--------+-----------+----------+--------+ 1472 INIT[Initiate-Tag = 5678] 1473 192.0.2.1:1 <--------------- 203.0.113.1:2 1474 Ext-VTag = 0 1476 NAT A processes INIT. As the outgoing INIT of Host A has already 1477 created an entry, the entry is found and updated: 1479 Internal | External External | Internal 1480 | | 1481 | /--\/---\ | 1482 +--------+ +-------+ / \ +-------+ +--------+ 1483 | Host A |<--->| NAT A |<-->| Internet |<-->| NAT B |<--->| Host B | 1484 +--------+ +-------+ \ / +-------+ +--------+ 1485 | \--/\---/ | 1487 VTag != Int-VTag, but Ext-VTag == 0, find entry. 1488 +---------+--------+----------+--------+-----------+ 1489 NAT A | Int | Int | Ext | Ext | Priv | 1490 | VTag | Port | VTag | Port | Addr | 1491 +---------+--------+----------+--------+-----------+ 1492 | 1234 | 1 | 5678 | 2 | 10.0.0.1 | 1493 +---------+--------+----------+--------+-----------+ 1495 INIT[Initiate-tag = 5678] 1496 10.0.0.1:1 <-- 203.0.113.1:2 1497 Ext-VTag = 0 1499 Host A send INIT-ACK, which can pass through NAT B: 1501 Internal | External External | Internal 1502 | | 1503 | /--\/---\ | 1504 +--------+ +-------+ / \ +-------+ +--------+ 1505 | Host A |<--->| NAT A |<-->| Internet |<-->| NAT B |<--->| Host B | 1506 +--------+ +-------+ \ / +-------+ +--------+ 1507 | \--/\---/ | 1509 INIT-ACK[Initiate-Tag = 1234] 1510 10.0.0.1:1 --> 203.0.113.1:2 1511 Ext-VTag = 5678 1513 INIT-ACK[Initiate-Tag = 1234] 1514 192.0.2.1:1 ----------------> 203.0.113.1:2 1515 Ext-VTag = 5678 1517 NAT B updates entry: 1519 +---------+--------+----------+--------+-----------+ 1520 NAT B | Int | Int | Ext | Ext | Priv | 1521 | VTag | Port | VTag | Port | Addr | 1522 +---------+--------+----------+--------+-----------+ 1523 | 5678 | 2 | 1234 | 1 | 10.1.0.1 | 1524 +---------+--------+----------+--------+-----------+ 1526 INIT-ACK[Initiate-Tag = 1234] 1527 192.0.2.1:1 --> 10.1.0.1:2 1528 Ext-VTag = 5678 1530 The lookup for COOKIE-ECHO and COOKIE-ACK is successful. 1532 Internal | External External | Internal 1533 | | 1534 | /--\/---\ | 1535 +--------+ +-------+ / \ +-------+ +--------+ 1536 | Host A |<--->| NAT A |<-->| Internet |<-->| NAT B |<--->| Host B | 1537 +--------+ +-------+ \ / +-------+ +--------+ 1538 | \--/\---/ | 1540 COOKIE-ECHO 1541 192.0.2.1:1 <-- 10.1.0.1:2 1542 Ext-VTag = 1234 1544 COOKIE-ECHO 1545 192.0.2.1:1 <------------- 203.0.113.1:2 1546 Ext-VTag = 1234 1548 COOKIE-ECHO 1549 10.0.0.1:1 <-- 203.0.113.1:2 1550 Ext-VTag = 1234 1552 COOKIE-ACK 1553 10.0.0.1:1 --> 203.0.113.1:2 1554 Ext-VTag = 5678 1556 COOKIE-ACK 1557 192.0.2.1:1 ----------------> 203.0.113.1:2 1558 Ext-VTag = 5678 1560 COOKIE-ACK 1561 192.0.2.1:1 --> 10.1.0.1:2 1562 Ext-VTag = 5678 1564 8. Socket API Considerations 1566 This section describes how the socket API defined in [RFC6458] is 1567 extended to provide a way for the application to control NAT 1568 friendliness. 1570 Please note that this section is informational only. 1572 A socket API implementation based on [RFC6458] is extended by 1573 supporting one new read/write socket option. 1575 8.1. Get or Set the NAT Friendliness (SCTP_NAT_FRIENDLY) 1577 This socket option uses the option_level IPPROTO_SCTP and the 1578 option_name SCTP_NAT_FRIENDLY. It can be used to enable/disable the 1579 NAT friendliness for future associations and retrieve the value for 1580 future and specific ones. 1582 struct sctp_assoc_value { 1583 sctp_assoc_t assoc_id; 1584 uint32_t assoc_value; 1585 }; 1587 assoc_id: This parameter is ignored for one-to-one style sockets. 1588 For one-to-many style sockets the application may fill in an 1589 association identifier or SCTP_FUTURE_ASSOC for this query. It is 1590 an error to use SCTP_{CURRENT|ALL}_ASSOC in assoc_id. 1592 assoc_value: A non-zero value indicates a NAT-friendly mode. 1594 9. IANA Considerations 1596 [NOTE to RFC-Editor: 1598 "RFCXXXX" is to be replaced by the RFC number you assign this 1599 document. 1601 ] 1603 [NOTE to RFC-Editor: 1605 The suggested values for the chunk type and the chunk parameter 1606 types are tentative and to be confirmed by IANA. 1608 ] 1610 This document (RFCXXXX) is the reference for all registrations 1611 described in this section. The suggested changes are described 1612 below. 1614 9.1. New Chunk Flags for Two Existing Chunk Types 1616 As defined in [RFC6096] two chunk flags have to be assigned by IANA 1617 for the ERROR chunk. The suggested value for the T bit is 0x01 and 1618 for the M bit is 0x02. 1620 This requires an update of the "ERROR Chunk Flags" registry for SCTP: 1622 ERROR Chunk Flags 1624 +------------------+-----------------+-----------+ 1625 | Chunk Flag Value | Chunk Flag Name | Reference | 1626 +------------------+-----------------+-----------+ 1627 | 0x01 | T bit | [RFCXXXX] | 1628 | 0x02 | M bit | [RFCXXXX] | 1629 | 0x04 | Unassigned | | 1630 | 0x08 | Unassigned | | 1631 | 0x10 | Unassigned | | 1632 | 0x20 | Unassigned | | 1633 | 0x40 | Unassigned | | 1634 | 0x80 | Unassigned | | 1635 +------------------+-----------------+-----------+ 1637 As defined in [RFC6096] one chunk flag has to be assigned by IANA for 1638 the ABORT chunk. The suggested value of the M bit is 0x02. 1640 This requires an update of the "ABORT Chunk Flags" registry for SCTP: 1642 ABORT Chunk Flags 1644 +------------------+-----------------+-----------+ 1645 | Chunk Flag Value | Chunk Flag Name | Reference | 1646 +------------------+-----------------+-----------+ 1647 | 0x01 | T bit | [RFC4960] | 1648 | 0x02 | M bit | [RFCXXXX] | 1649 | 0x04 | Unassigned | | 1650 | 0x08 | Unassigned | | 1651 | 0x10 | Unassigned | | 1652 | 0x20 | Unassigned | | 1653 | 0x40 | Unassigned | | 1654 | 0x80 | Unassigned | | 1655 +------------------+-----------------+-----------+ 1657 9.2. Three New Error Causes 1659 Three error causes have to be assigned by IANA. It is suggested to 1660 use the values given below. 1662 This requires three additional lines in the "Error Cause Codes" 1663 registry for SCTP: 1665 Error Cause Codes 1667 +-------+--------------------------------+-----------+ 1668 | Value | Cause Code | Reference | 1669 +-------+--------------------------------+-----------+ 1670 | 176 | VTag and Port Number Collision | [RFCXXXX] | 1671 | 177 | Missing State | [RFCXXXX] | 1672 | 178 | Port Number Collision | [RFCXXXX] | 1673 +-------+--------------------------------+-----------+ 1675 9.3. Two New Chunk Parameter Types 1677 Two chunk parameter types have to be assigned by IANA. It is 1678 suggested to use the values given below. IANA should assign these 1679 values from the pool of parameters with the upper two bits set to 1680 '11'. 1682 This requires two additional lines in the "Chunk Parameter Types" 1683 registry for SCTP: 1685 Chunk Parameter Types 1687 +----------+--------------------------+-----------+ 1688 | ID Value | Chunk Parameter Type | Reference | 1689 +----------+--------------------------+-----------+ 1690 | 49159 | Disable Restart (0xC007) | [RFCXXXX] | 1691 | 49160 | VTags (0xC008) | [RFCXXXX] | 1692 +----------+--------------------------+-----------+ 1694 10. Security Considerations 1696 State maintenance within a NAT is always a subject of possible Denial 1697 Of Service attacks. This document recommends that at a minimum a NAT 1698 runs a timer on any SCTP state so that old association state can be 1699 cleaned up. 1701 For SCTP end points, this document does not add any additional 1702 security considerations to the ones given in [RFC4960], [RFC4895], 1703 and [RFC5061]. In particular, SCTP is protected by the verification 1704 tags and the usage of [RFC4895] against off-path attackers. 1706 11. Acknowledgments 1708 The authors wish to thank Gorry Fairhurst, Bryan Ford, David Hayes, 1709 Alfred Hines, Karen E. E. Nielsen, Henning Peters, Timo Voelker, 1710 Dan Wing, and Qiaobing Xie for their invaluable comments. 1712 In addition, the authors wish to thank David Hayes, Jason But, and 1713 Grenville Armitage, the authors of [DOI_10.1145_1496091.1496095], for 1714 their suggestions. 1716 12. References 1718 12.1. Normative References 1720 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1721 Requirement Levels", BCP 14, RFC 2119, 1722 DOI 10.17487/RFC2119, March 1997, 1723 . 1725 [RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla, 1726 "Authenticated Chunks for the Stream Control Transmission 1727 Protocol (SCTP)", RFC 4895, DOI 10.17487/RFC4895, August 1728 2007, . 1730 [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", 1731 RFC 4960, DOI 10.17487/RFC4960, September 2007, 1732 . 1734 [RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. 1735 Kozuka, "Stream Control Transmission Protocol (SCTP) 1736 Dynamic Address Reconfiguration", RFC 5061, 1737 DOI 10.17487/RFC5061, September 2007, 1738 . 1740 [RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission 1741 Protocol (SCTP) Chunk Flags Registration", RFC 6096, 1742 DOI 10.17487/RFC6096, January 2011, 1743 . 1745 12.2. Informative References 1747 [DOI_10.1145_1496091.1496095] 1748 Hayes, D., But, J., and G. Armitage, "Issues with network 1749 address translation for SCTP", ACM SIGCOMM Computer 1750 Communication Review Vol. 39, pp. 23, 1751 DOI 10.1145/1496091.1496095, December 2008. 1753 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 1754 RFC 793, DOI 10.17487/RFC0793, September 1981, 1755 . 1757 [RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V. 1758 Yasevich, "Sockets API Extensions for the Stream Control 1759 Transmission Protocol (SCTP)", RFC 6458, 1760 DOI 10.17487/RFC6458, December 2011, 1761 . 1763 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 1764 "Special-Purpose IP Address Registries", BCP 153, 1765 RFC 6890, DOI 10.17487/RFC6890, April 2013, 1766 . 1768 [RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream 1769 Control Transmission Protocol (SCTP) Packets for End-Host 1770 to End-Host Communication", RFC 6951, 1771 DOI 10.17487/RFC6951, May 2013, 1772 . 1774 Authors' Addresses 1776 Randall R. Stewart 1777 Netflix, Inc. 1778 Chapin, SC 29036 1779 US 1781 Email: randall@lakerest.net 1783 Michael Tuexen 1784 Muenster University of Applied Sciences 1785 Stegerwaldstrasse 39 1786 48565 Steinfurt 1787 DE 1789 Email: tuexen@fh-muenster.de 1791 Irene Ruengeler 1792 Muenster University of Applied Sciences 1793 Stegerwaldstrasse 39 1794 48565 Steinfurt 1795 DE 1797 Email: i.ruengeler@fh-muenster.de