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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) -- Looks like a reference, but probably isn't: '16' on line 513 ** Obsolete normative reference: RFC 5077 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 5245 (Obsoleted by RFC 8445, RFC 8839) ** Obsolete normative reference: RFC 5389 (Obsoleted by RFC 8489) ** Obsolete normative reference: RFC 5766 (Obsoleted by RFC 8656) -- Obsolete informational reference (is this intentional?): RFC 6982 (Obsoleted by RFC 7942) Summary: 4 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 TRAM D. Wing 3 Internet-Draft P. Patil 4 Intended status: Standards Track T. Reddy 5 Expires: January 27, 2017 P. Martinsen 6 Cisco 7 July 26, 2016 9 Mobility with TURN 10 draft-ietf-tram-turn-mobility-03 12 Abstract 14 It is desirable to minimize traffic disruption caused by changing IP 15 address during a mobility event. One mechanism to minimize 16 disruption is to expose a shorter network path to the mobility event 17 so only the local network elements are aware of the changed IP 18 address but the remote peer is unaware of the changed IP address. 20 This draft provides such an IP address mobility solution using 21 Traversal Using Relays around NAT (TURN). This is achieved by 22 allowing a client to retain an allocation on the TURN server when the 23 IP address of the client changes. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on January 27, 2017. 42 Copyright Notice 44 Copyright (c) 2016 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 61 3. Mobility using TURN . . . . . . . . . . . . . . . . . . . . . 4 62 3.1. Creating an Allocation . . . . . . . . . . . . . . . . . 5 63 3.1.1. Sending an Allocate Request . . . . . . . . . . . . . 5 64 3.1.2. Receiving an Allocate Request . . . . . . . . . . . . 5 65 3.1.3. Receiving an Allocate Success Response . . . . . . . 6 66 3.1.4. Receiving an Allocate Error Response . . . . . . . . 6 67 3.2. Refreshing an Allocation . . . . . . . . . . . . . . . . 6 68 3.2.1. Sending a Refresh Request . . . . . . . . . . . . . . 6 69 3.2.2. Receiving a Refresh Request . . . . . . . . . . . . . 7 70 3.2.3. Receiving a Refresh Response . . . . . . . . . . . . 8 71 3.3. New STUN Attribute MOBILITY-TICKET . . . . . . . . . . . 8 72 3.4. New STUN Error Response Code . . . . . . . . . . . . . . 8 73 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 74 5. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 75 5.1. open-sys . . . . . . . . . . . . . . . . . . . . . . . . 9 76 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 77 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 78 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 79 8.1. Normative References . . . . . . . . . . . . . . . . . . 10 80 8.2. Informative References . . . . . . . . . . . . . . . . . 11 81 Appendix A. Example ticket construction . . . . . . . . . . . . 12 82 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 84 1. Introduction 86 When moving between networks, the endpoint's IP address can change or 87 (due to NAT) the endpoint's public IP address can change. Such a 88 change of IP address breaks upper layer protocols such as TCP and 89 RTP. Various techniques exist to prevent this breakage, all tied to 90 making the endpoint's IP address static (e.g., Mobile IP, Proxy 91 Mobile IP, LISP). Other techniques exist, which make the change in 92 IP address agnostic to the upper layer protocol (e.g., SCTP). The 93 mechanism described in this document are in that last category. 95 A Traversal Using Relays around NAT (TURN) [RFC5766] server relays 96 media packets and is used for a variety of purposes, including 97 overcoming NAT and firewall traversal issues. The existing TURN 98 specification does not permit a TURN client to reuse an allocation 99 across client IP address changes. Due to this, when the IP address 100 of the client changes, the TURN client has to request for a new 101 allocation, create permissions for the remote peer, create channels 102 etc. In addition the client has to re-establish communication with 103 its signaling server, send an updated offer to the remote peer 104 conveying the new relayed candidate address, remote side has to 105 regather all candidates and signal them to the client and then the 106 endpoints have to perform Interactive Connectivity Establishment 107 (ICE) [RFC5245] connectivity checks. If ICE continuous nomination 108 procedure [I-D.uberti-mmusic-nombis] is used then new relayed 109 candidate address would have to be tricked 110 [I-D.ietf-mmusic-trickle-ice] and ICE connectivity checks have to be 111 performed by the endpoints to nominate pairs that will be selected by 112 ICE. 114 This specification describes a mechanism to seamlessly reuse 115 allocations across client IP address changes without any of the 116 hassles described above. A critical benefit of this technique is 117 that the remote peer does not have to support mobility, or deal with 118 any of the address changes. The client, that is subject to IP 119 address changes, does all the work. The mobility technique works 120 across and between network types (e.g., between 3G and wired Internet 121 access), so long as the client can still access the TURN server. The 122 technique should also work seamlessly when (D)TLS is used as a 123 transport protocol for STUN. When there is a change in IP address, 124 the client uses (D)TLS Session Resumption without Server-Side State 125 as described in [RFC5077] to resume secure communication with the 126 TURN server, using the changed client IP address. 128 2. Notational Conventions 130 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 131 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 132 document are to be interpreted as described in [RFC2119] . 134 This note uses terminology defined in [RFC5245] , and the following 135 additional terminology: 137 Break Before Make: The old communication path is broken ("break") 138 before new communication can be created ("make"). Such changes 139 typically occur because a network is disconnected with a physical 140 cable, turning radio off, or moving out of radio range. 142 Make Before Break: A new communication path is created ("make") 143 before the old communication path is broken ("break"). Such changes 144 typically occur because a network is connected with a physical cable, 145 turning radio on, or moving into radio range. 147 3. Mobility using TURN 149 To achieve mobility, a TURN client should be able to retain an 150 allocation on the TURN server across changes in the client IP address 151 as a consequence of movement to other networks. 153 When the client sends the initial Allocate request to the TURN 154 server, it will include a new STUN attribute MOBILITY-TICKET (with 155 zero length value), which indicates that the client is capable of 156 mobility and desires a ticket. The TURN server provisions a ticket 157 that is sent inside the new STUN attribute MOBILITY-TICKET in the 158 Allocate Success response to the client. The ticket will be used by 159 the client when it wants to refresh the allocation but with a new 160 client IP address and port. This ensures that an allocation can only 161 be refreshed by the same client that allocated relayed transport 162 address. When a client's IP address changes due to mobility, it 163 presents the previously obtained ticket in a Refresh Request to the 164 TURN server. If the ticket is found to be valid, the TURN server 165 will retain the same relayed address/port for the new IP address/port 166 allowing the client to continue using previous channel bindings -- 167 thus, the TURN client does not need to obtain new channel bindings. 168 Any data from external peer will be delivered by the TURN server to 169 this new IP address/port of the client. The TURN client will 170 continue to send application data to its peers using the previously 171 allocated channelBind Requests. 173 TURN TURN Peer 174 client server A 175 |-- Allocate request --------------->| | 176 | + MOBILITY-TICKET (length=0) | | 177 | | | 178 |<--------------- Allocate failure --| | 179 | (401 Unauthorized) | | 180 | | | 181 |-- Allocate request --------------->| | 182 | + MOBILITY-TICKET (length=0) | | 183 | | | 184 |<---------- Allocate success resp --| | 185 | + MOBILITY-TICKET | | 186 ... ... ... 187 (changes IP address) 188 | | | 189 |-- Refresh request ---------------->| | 190 | + MOBILITY-TICKET | | 191 | | | 192 |<----------- Refresh success resp --| | 193 | + MOBILITY-TICKET | | 194 | | | 196 3.1. Creating an Allocation 198 3.1.1. Sending an Allocate Request 200 In addition to the process described in Section 6.1 of [RFC5766] , 201 the client includes the MOBILITY-TICKET attribute with length 0. 202 This indicates the client is a mobile node and wants a ticket. 204 3.1.2. Receiving an Allocate Request 206 In addition to the process described in Section 6.2 of [RFC5766] , 207 the server does the following: 209 If the MOBILITY-TICKET attribute is included, and has length zero, 210 but TURN session mobility is forbidden by local policy, the server 211 MUST reject the request with the new Mobility Forbidden error code. 212 If the MOBILITY-TICKET attribute is included and has non-zero length 213 then the server MUST generate an error response with an error code of 214 400 (Bad Request). Following the rules specified in [RFC5389] , if 215 the server does not understand the MOBILITY-TICKET attribute, it 216 ignores the attribute. 218 If the server can successfully process the request and create an 219 allocation, the server replies with a success response that includes 220 a STUN MOBILITY-TICKET attribute. TURN server can store system 221 internal data into the ticket that is encrypted by a key known only 222 to the TURN server and sends the ticket in the STUN MOBILITY-TICKET 223 attribute as part of Allocate success response. An example for 224 ticket construction is discussed in Appendix A .The ticket is opaque 225 to the client, so the structure is not subject to interoperability 226 concerns, and implementations may diverge from this format. The 227 client could be roaming across networks with different path MTU and 228 from one address family to another (e.g. IPv6 to IPv4). The TURN 229 server to support mobility must assume that the path MTU is unknown 230 and use a ticket length in accordance with published guidance on STUN 231 UDP fragmentation (Section 7.1 of [RFC5389] ). Clients MUST NOT 232 examine the ticket under the assumption that it complies with this 233 document. 235 3.1.3. Receiving an Allocate Success Response 237 In addition to the process described in Section 6.3 of [RFC5766] , 238 the client will store the MOBILITY-TICKET attribute, if present, from 239 the response. This attribute will be presented by the client to the 240 server during a subsequent Refresh request to aid mobility. 242 3.1.4. Receiving an Allocate Error Response 244 If the client receives an Allocate error response with error code TBD 245 (Mobility Forbidden), the error is processed as follows: 247 o TBD (Mobility Forbidden): The request is valid, but the server is 248 refusing to perform it, likely due to administrative restrictions. 249 The client considers the current transaction as having failed. The 250 client MAY notify the user or operator and SHOULD NOT retry the same 251 request with this server until it believes the problem has been 252 fixed. 254 All other error responses must be handled as described in [RFC5766] . 256 3.2. Refreshing an Allocation 258 3.2.1. Sending a Refresh Request 260 If a client wants to refresh an existing allocation and update its 261 time-to-expiry or delete an existing allocation, it will send a 262 Refresh Request as described in Section 7.1 of [RFC5766] . If the 263 client wants to retain the existing allocation in case of IP change, 264 it will include the MOBILITY-TICKET attribute received in the 265 Allocate Success response. If a Refresh transaction was previously 266 made, the MOBILITY-TICKET attribute received in the Refresh Success 267 response of the transaction must be used. 269 3.2.2. Receiving a Refresh Request 271 In addition to the process described in Section 7.2 of [RFC5766] , 272 the server does the following: 274 If the STUN MOBILITY-TICKET attribute is included in the Refresh 275 Request then the server will not retrieve the 5-tuple from the packet 276 to identify an associated allocation. Instead the TURN server will 277 decrypt the received ticket, verify the ticket's validity and 278 retrieve the 5-tuple allocation using the ticket. If this 5-tuple 279 obtained does not identify an existing allocation then the server 280 MUST reject the request with an error. 282 If the source IP address and port of the Refresh Request is different 283 from the stored 5-tuple allocation, the TURN server proceeds with 284 MESSAGE-INTEGRITY validation to identify the that it is the same user 285 which had previously created the TURN allocation. If the above 286 checks are not successful then server MUST reject the request with a 287 441 (Wrong Credentials) error. 289 If all of the above checks pass, the TURN server understands that the 290 client has either moved to a new network and acquired a new IP 291 address (Break Before Make) or is in the process of switching to a 292 new interface (Make Before Break). The source IP address of the 293 request could either be the host transport address or server- 294 reflexive transport address. The server then updates its state data 295 with the new client IP address and port but does not discard the old 296 5-tuple from its state data. TURN server calculates the ticket with 297 the new 5-tuple and sends the new ticket in the STUN MOBILITY-TICKET 298 attribute as part of Refresh Success response. 300 The TURN server MUST continue receiving and processing data on the 301 old 5-tuple and MUST continue transmitting data on the old-5 tuple 302 until it receives an Send Indication or ChannelData message from the 303 client on the new 5-tuple or an message from the client to close the 304 old connection (e.g., a TLS fatal alert, TCP RST). After receiving 305 any of those messages, a TURN server discards the the old ticket and 306 the old 5-tuple associated with the old ticket from its state data. 307 Data sent by the client to the peer is accepted on the new 5-tuple 308 and data received from the peer is forwarded to the new 5-tuple. If 309 the refresh request containing the MOBILITY-TICKET attribute does not 310 succeed (e.g., packet lost if the request is sent over UDP, or the 311 server being unable to fulfill the request) then the client can 312 continue to exchange data on the old 5-tuple until it receives 313 Refresh success response. 315 The old ticket can only be used for the purposes of retransmission. 316 If the client wants to refresh its allocation with a new server- 317 reflexive transport address, it MUST use the new ticket. If the TURN 318 server has not received a Refresh Request with STUN MOBILITY-TICKET 319 attribute but receives Send indications or ChannelData messages from 320 a client, the TURN server may discard or queue those Send indications 321 or ChannelData messages (at its discretion). Thus, it is RECOMMENDED 322 that the client avoid transmitting a Send indication or ChannelData 323 message until it has received an acknowledgement for the Refresh 324 Request with STUN MOBILITY-TICKET attribute. 326 To accommodate for loss of Refresh responses, a server must retain 327 the old STUN MOBILITY-TICKET attribute for a period of at least 30 328 seconds to be able to recognize a retransmission of Refresh request 329 with the old STUN MOBILITY-TICKET attribute from the client. 331 3.2.3. Receiving a Refresh Response 333 In addition to the process described in Section 7.3 of [RFC5766] , 334 the client will store the MOBILITY-TICKET attribute, if present, from 335 the response. This attribute will be presented by the client to the 336 server during a subsequent Refresh Request to aid mobility. 338 3.3. New STUN Attribute MOBILITY-TICKET 340 This attribute is used to retain an Allocation on the TURN server. 341 It is exchanged between the client and server to aid mobility. The 342 value of MOBILITY-TICKET is encrypted and is of variable-length. 344 3.4. New STUN Error Response Code 346 This document defines the following new error response code: 348 Mobility Forbidden: Mobility request was valid but cannot be 349 performed due to administrative or similar restrictions. 351 4. IANA Considerations 353 IANA is requested to add the following attributes to the STUN 354 attribute registry [iana-stun] , 356 o MOBILITY-TICKET (0x8030, in the comprehension-optional range) 358 and to add a new STUN error code "Mobility Forbidden" with the value 359 405 to the STUN Error Codes registry [iana-stun] . 361 5. Implementation Status 363 [Note to RFC Editor: Please remove this section and reference to 364 [RFC6982] prior to publication.] 366 This section records the status of known implementations of the 367 protocol defined by this specification at the time of posting of this 368 Internet-Draft, and is based on a proposal described in [RFC6982] . 369 The description of implementations in this section is intended to 370 assist the IETF in its decision processes in progressing drafts to 371 RFCs. Please note that the listing of any individual implementation 372 here does not imply endorsement by the IETF. Furthermore, no effort 373 has been spent to verify the information presented here that was 374 supplied by IETF contributors. This is not intended as, and must not 375 be construed to be, a catalog of available implementations or their 376 features. Readers are advised to note that other implementations may 377 exist. 379 According to [RFC6982] , "this will allow reviewers and working 380 groups to assign due consideration to documents that have the benefit 381 of running code, which may serve as evidence of valuable 382 experimentation and feedback that have made the implemented protocols 383 more mature. It is up to the individual working groups to use this 384 information as they see fit". 386 5.1. open-sys 388 Organization: This is a public project, the full list of authors 389 and contributors here: http://turnserver.open-sys.org/downloads/ 390 AUTHORS 392 Description: A mature open-source TURN server specs implementation 393 (RFC 5766, RFC 6062, RFC 6156, etc) designed for high-performance 394 applications, especially geared for WebRTC. 396 Implementation: http://code.google.com/p/rfc5766-turn-server/ 398 Level of maturity: The Mobile ICE feature implementation can be 399 qualified as "production" - it is well tested and fully 400 implemented, but not widely used, yet.. 402 Coverage: Fully implements MICE with TURN protocol. 404 Licensing: BSD: http://turnserver.open-sys.org/downloads/LICENSE 406 Implementation experience: MICE implementation is somewhat 407 challenging for a multi-threaded performance-oriented application 408 (because the mobile ticket information must be shared between the 409 threads) but it is doable. 411 Contact: Oleg Moskalenko . 413 6. Security Considerations 415 TURN server MUST use strong encryption and integrity protection for 416 the ticket to prevent an attacker from using a brute force mechanism 417 to obtain the ticket's contents or refreshing allocations. The 418 ticket MUST be constructed such that it has strong entropy to ensure 419 nothing can be gleaned by looking at the ticket alone. 421 An attacker monitoring the traffic between the TURN client and server 422 can impersonate the client and refresh the allocation using the 423 ticket issued to the client with the attackers IP address and port. 424 This attack can be prevented by using STUN long-term credential 425 mechanism or STUN Extension for Third-Party Authorization [RFC7635] 426 or (D)TLS connection between the TURN client and the TURN server. 427 With any of those three mechanisms, when the server receives Refresh 428 Request with STUN MOBILITY-TICKET attribute from the client it 429 identifies that it is indeed the same client but with a new IP 430 address and port using the ticket it had previously issued to refresh 431 the allocation. 433 Security considerations described in [RFC5766] are also applicable to 434 this mechanism. 436 7. Acknowledgements 438 Thanks to Alfred Heggestad, Lishitao, Sujing Zhou, Martin Thomson, 439 Emil Ivov, Oleg Moskalenko and Brandon Williams for review and 440 comments. 442 8. References 444 8.1. Normative References 446 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 447 Requirement Levels", BCP 14, RFC 2119, 448 DOI 10.17487/RFC2119, March 1997, 449 . 451 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, 452 "Transport Layer Security (TLS) Session Resumption without 453 Server-Side State", RFC 5077, DOI 10.17487/RFC5077, 454 January 2008, . 456 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 457 (ICE): A Protocol for Network Address Translator (NAT) 458 Traversal for Offer/Answer Protocols", RFC 5245, 459 DOI 10.17487/RFC5245, April 2010, 460 . 462 [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 463 "Session Traversal Utilities for NAT (STUN)", RFC 5389, 464 DOI 10.17487/RFC5389, October 2008, 465 . 467 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 468 Relays around NAT (TURN): Relay Extensions to Session 469 Traversal Utilities for NAT (STUN)", RFC 5766, 470 DOI 10.17487/RFC5766, April 2010, 471 . 473 8.2. Informative References 475 [I-D.ietf-mmusic-trickle-ice] 476 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 477 Incremental Provisioning of Candidates for the Interactive 478 Connectivity Establishment (ICE) Protocol", draft-ietf- 479 mmusic-trickle-ice-02 (work in progress), January 2015. 481 [I-D.uberti-mmusic-nombis] 482 Uberti, J. and J. Lennox, "Improvements to ICE Candidate 483 Nomination", draft-uberti-mmusic-nombis-00 (work in 484 progress), March 2015. 486 [iana-stun] 487 IANA, , "IANA: STUN Attributes", April 2011, 488 . 491 [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 492 Code: The Implementation Status Section", RFC 6982, 493 DOI 10.17487/RFC6982, July 2013, 494 . 496 [RFC7635] Reddy, T., Patil, P., Ravindranath, R., and J. Uberti, 497 "Session Traversal Utilities for NAT (STUN) Extension for 498 Third-Party Authorization", RFC 7635, 499 DOI 10.17487/RFC7635, August 2015, 500 . 502 Appendix A. Example ticket construction 504 The TURN server uses two different keys: one 128-bit key for Advance 505 Encryption Standard (AES) in Cipher Block Chaining (CBC) mode 506 (AES_128_CBC) and 256-bit key for HMAC-SHA-256-128 for integrity 507 protection. The ticket can be structured as follows: 509 struct { 510 opaque key_name[16]; 511 opaque iv[16]; 512 opaque state<0..2^16-1>; 513 opaque mac[16]; 514 } ticket; 516 Figure 1: Ticket Format 518 Here, key_name serves to identify a particular set of keys used to 519 protect the ticket. It enables the TURN server to easily recognize 520 tickets it has issued. The key_name should be randomly generated to 521 avoid collisions between servers. One possibility is to generate new 522 random keys and key_name every time the server is started. 524 The TURN state information (self-contained or handle) in 525 encrypted_state is encrypted using 128-bit AES in CBC mode with the 526 given IV. The MAC is calculated using HMAC-SHA-256-128 over key_name 527 (16 octets)and IV (16 octets), followed by the length of the 528 encrypted_state field (2 octets) and its contents (variable length). 530 Authors' Addresses 532 Dan Wing 533 Cisco Systems, Inc. 534 170 West Tasman Drive 535 San Jose, California 95134 536 USA 538 Email: dwing@cisco.com 540 Prashanth Patil 541 Cisco Systems, Inc. 542 Bangalore 543 India 545 Email: praspati@cisco.com 546 Tirumaleswar Reddy 547 Cisco Systems, Inc. 548 Cessna Business Park, Varthur Hobli 549 Sarjapur Marathalli Outer Ring Road 550 Bangalore, Karnataka 560103 551 India 553 Email: tireddy@cisco.com 555 Paal-Erik Martinsen 556 Cisco Systems, Inc. 557 Philip Pedersens vei 22 558 Lysaker, Akershus 1325 559 Norway 561 Email: palmarti@cisco.com