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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 510 ** 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: September 11, 2016 P. Martinsen 6 Cisco 7 March 10, 2016 9 Mobility with TURN 10 draft-ietf-tram-turn-mobility-01 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 September 11, 2016. 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 . . . . . . . 5 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 . . . . . . . . . . . . . 6 70 3.2.3. Receiving a Refresh Response . . . . . . . . . . . . 7 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 . . . . . . . . . . . . . . . . . . . . 8 75 5.1. open-sys . . . . . . . . . . . . . . . . . . . . . . . . 9 76 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 77 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 78 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 79 8.1. Normative References . . . . . . . . . . . . . . . . . . 10 80 8.2. Informative References . . . . . . . . . . . . . . . . . 10 81 Appendix A. Example ticket construction . . . . . . . . . . . . 11 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 SIP server, send an updated offer to the remote peer conveying 104 the new relayed candidate address, remote side has to regather all 105 candidates and signal them to the client and then the endpoints have 106 to perform Interactive Connectivity Establishment (ICE) [RFC5245] 107 connectivity checks. If ICE continuous nomination procedure 108 [I-D.uberti-mmusic-nombis] is used then new relayed candidate address 109 would have to be tricked [I-D.ietf-mmusic-trickle-ice] and ICE 110 connectivity checks have to be performed by the endpoints to nominate 111 pairs that will be selected by ICE. 113 This specification describes a mechanism to seamlessly reuse 114 allocations across client IP address changes without any of the 115 hassles described above. A critical benefit of this technique is 116 that the remote peer does not have to support mobility, or deal with 117 any of the address changes. The client, that is subject to IP 118 address changes, does all the work. The mobility technique works 119 across and between network types (e.g., between 3G and wired Internet 120 access), so long as the client can still access the TURN server. The 121 technique should also work seamlessly when (D)TLS is used as a 122 transport protocol for STUN. When there is a change in IP address, 123 the client uses (D)TLS Session Resumption without Server-Side State 124 as described in [RFC5077] to resume secure communication with the 125 TURN server, using the changed client IP address. 127 2. Notational Conventions 129 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 130 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 131 document are to be interpreted as described in [RFC2119]. 133 This note uses terminology defined in [RFC5245], and the following 134 additional terminology: 136 Break Before Make: The old communication path is broken ("break") 137 before the new communication can be made ("make"). Such changes 138 typically occur because a network is disconnected with a physical 139 cable, turning radio off, or moving out of radio range. 141 Make Before Break: A new communication path is created ("make") 142 before the old communication path is broken ("break"). Such changes 143 typically occur because a network is connected with a physical cable, 144 turning radio on, or moving in of radio range. 146 3. Mobility using TURN 148 To achieve mobility, a TURN client should be able to retain an 149 allocation on the TURN server across changes in the client IP address 150 as a consequence of movement to other networks. 152 When the client sends the initial Allocate request to the TURN 153 server, it will include a new STUN attribute MOBILITY-TICKET (with 154 zero length value), which indicates that the client is capable of 155 mobility and desires a ticket. The TURN server provisions a ticket 156 that is sent inside the new STUN attribute MOBILITY-TICKET in the 157 Allocate Success response to the client. The ticket will be used by 158 the client when it wants to refresh the allocation but with a new 159 client IP address and port. This ensures that an allocation can only 160 be refreshed by the same client that allocated relayed transport 161 address. When a client's IP address changes due to mobility, it 162 presents the previously obtained ticket in a Refresh Request to the 163 TURN server. If the ticket is found to be valid, the TURN server 164 will retain the same relayed address/port for the new IP address/port 165 allowing the client to continue using previous channel bindings -- 166 thus, the TURN client does not need to obtain new channel bindings. 167 Any data from external peer will be delivered by the TURN server to 168 this new IP address/port of the client. The TURN client will 169 continue to send application data to its peers using the previously 170 allocated channelBind Requests. 172 TURN TURN Peer 173 client server A 174 |-- Allocate request --------------->| | 175 | + MOBILITY-TICKET (length=0) | | 176 | | | 177 |<--------------- Allocate failure --| | 178 | (401 Unauthorized) | | 179 | | | 180 |-- Allocate request --------------->| | 181 | + MOBILITY-TICKET (length=0) | | 182 | | | 183 |<---------- Allocate success resp --| | 184 | + MOBILITY-TICKET | | 185 ... ... ... 186 (changes IP address) 187 | | | 188 |-- Refresh request ---------------->| | 189 | + MOBILITY-TICKET | | 190 | | | 191 |<----------- Refresh success resp --| | 192 | + MOBILITY-TICKET | | 193 | | | 195 3.1. Creating an Allocation 197 3.1.1. Sending an Allocate Request 199 In addition to the process described in Section 6.1 of [RFC5766], the 200 client includes the MOBILITY-TICKET attribute with length 0. This 201 indicates the client is a mobile node and wants a ticket. 203 3.1.2. Receiving an Allocate Request 205 In addition to the process described in Section 6.2 of [RFC5766], the 206 server does the following: 208 If the MOBILITY-TICKET attribute is included, and has length zero, 209 but TURN session mobility is forbidden by local policy, the server 210 MUST reject the request with the new Mobility Forbidden error code. 211 If the MOBILITY-TICKET attribute is included and has non-zero length 212 then the server MUST generate an error response with an error code of 213 400 (Bad Request). Following the rules specified in [RFC5389], if 214 the server does not understand the MOBILITY-TICKET attribute, it 215 ignores the attribute. 217 If the server can successfully process the request create an 218 allocation, the server replies with a success response that includes 219 a STUN MOBILITY-TICKET attribute. TURN server can store system 220 internal data into the ticket that is encrypted by a key known only 221 to the TURN server and sends the ticket in the STUN MOBILITY-TICKET 222 attribute as part of Allocate success response. The ticket is opaque 223 to the client, so the structure is not subject to interoperability 224 concerns, and implementations may diverge from this format. An 225 example for ticket construction is discussed in Appendix A. The 226 client could be roaming across networks with different path MTU and 227 from one address family to another (e.g. IPv6 to IPv4). The TURN 228 server to support mobility must assume that the path MTU is unknown 229 and MUST ensure that the ticket length is restricted to avoid UDP 230 fragmentation (Section 7.1 of [RFC5389]). Clients MUST NOT examine 231 the ticket under the assumption that it complies with this document. 233 3.1.3. Receiving an Allocate Success Response 235 In addition to the process described in Section 6.3 of [RFC5766], the 236 client will store the MOBILITY-TICKET attribute, if present, from the 237 response. This attribute will be presented by the client to the 238 server during a subsequent Refresh request to aid mobility. 240 3.1.4. Receiving an Allocate Error Response 242 If the client receives an Allocate error response with error code TBD 243 (Mobility Forbidden), the error is processed as follows: 245 o TBD (Mobility Forbidden): The request is valid, but the server is 246 refusing to perform it, likely due to administrative restrictions. 247 The client considers the current transaction as having failed. The 248 client MAY notify the user or operator and SHOULD NOT retry the same 249 request with this server until it believes the problem has been 250 fixed. 252 All other error responses must be handled as described in [RFC5766]. 254 3.2. Refreshing an Allocation 256 3.2.1. Sending a Refresh Request 258 If a client wants to refresh an existing allocation and update its 259 time-to-expiry or delete an existing allocation, it will send a 260 Refresh Request as described in Section 7.1 of [RFC5766]. If the 261 client wants to retain the existing allocation in case of IP change, 262 it will include the MOBILITY-TICKET attribute received in the 263 Allocate Success response. If a Refresh transaction was previously 264 made, the MOBILITY-TICKET attribute received in the Refresh Success 265 response of the transaction must be used. 267 3.2.2. Receiving a Refresh Request 269 In addition to the process described in Section 7.2 of [RFC5766], the 270 server does the following: 272 If the STUN MOBILITY-TICKET attribute is included in the Refresh 273 Request then the server will not retrieve the 5-tuple from the packet 274 to identify an associated allocation. Instead the TURN server will 275 decrypt the received ticket, verify the ticket's validity and 276 retrieve the 5-tuple allocation using the ticket. If this 5-tuple 277 obtained does not identify an existing allocation then the server 278 MUST reject the request with an error. 280 If the source IP address and port of the Refresh Request is different 281 from the stored 5-tuple allocation, the TURN server proceeds with 282 MESSAGE-INTEGRITY validation to identify the that it is the same user 283 which had previously created the TURN allocation. If the above 284 checks are not successful then server MUST reject the request with a 285 441 (Wrong Credentials) error. 287 If all of the above checks pass, the TURN server understands that the 288 client has either moved to a new network and acquired a new IP 289 address (Break Before Make) or is in the process of switching to a 290 new interface (Make Before Break). The source IP address of the 291 request could either be the host transport address or server- 292 reflexive transport address. The server then updates it's state data 293 with the new client IP address and port but does not discard the old 294 5-tuple from it's state data. TURN server calculates the ticket with 295 the new 5-tuple and sends the new ticket in the STUN MOBILITY-TICKET 296 attribute as part of Refresh Success response. 298 The TURN server MUST continue receiving and processing data on the 299 old 5-tuple and MUST continue transmitting data on the old-5 tuple 300 until it receives an Send Indication or ChannelData message from the 301 client on the new 5-tuple or an message from the client to close the 302 old connection (e.g., a TLS fatal alert, TCP RST). After receiving 303 any of those messages, TURN server updates its 5-tuple with the new 304 client IP address and port. Data sent by the client to the peer is 305 accepted on the new 5-tuple and data received from the peer is 306 forwarded to the new 5-tuple. If the refresh request containing the 307 MOBILITY-TICKET attribute does not succeed (e.g., packet lost if the 308 request is sent over UDP, or the server being unable to fulfill the 309 request) then the client can continue to exchange data on the old 310 5-tuple until it receives Refresh success response. 312 The old ticket can only be used for the purposes of retransmission. 313 If the client wants to refresh its allocation with a new server- 314 reflexive transport address, it MUST use the new ticket. If the TURN 315 server has not received a Refresh Request with STUN MOBILITY-TICKET 316 attribute but receives Send indications or ChannelData messages from 317 a client, the TURN server may discard or queue those Send indications 318 or ChannelData messages (at its discretion). Thus, it is RECOMMENDED 319 that the client avoid transmitting a Send indication or ChannelData 320 message until it has received an acknowledgement for the Refresh 321 Request with STUN MOBILITY-TICKET attribute. 323 To accommodate for loss of Refresh responses, a server must retain 324 the old STUN MOBILITY-TICKET attribute for a period of at least 30 325 seconds to be able recognize a retransmission of Refresh request with 326 the old STUN MOBILITY-TICKET attribute from the client. 328 3.2.3. Receiving a Refresh Response 330 In addition to the process described in Section 7.3 of [RFC5766], the 331 client will store the MOBILITY-TICKET attribute, if present, from the 332 response. This attribute will be presented by the client to the 333 server during a subsequent Refresh Request to aid mobility. 335 3.3. New STUN Attribute MOBILITY-TICKET 337 This attribute is used to retain an Allocation on the TURN server. 338 It is exchanged between the client and server to aid mobility. The 339 value of MOBILITY-TICKET is encrypted and is of variable-length. 341 3.4. New STUN Error Response Code 343 This document defines the following new error response code: 345 Mobility Forbidden: Mobility request was valid but cannot be 346 performed due to administrative or similar restrictions. 348 4. IANA Considerations 350 IANA is requested to add the following attributes to the STUN 351 attribute registry [iana-stun], 353 o MOBILITY-TICKET (0x8030, in the comprehension-optional range) 355 and to add a new STUN error code "Mobility Forbidden" with the value 356 405 to the STUN Error Codes registry [iana-stun]. 358 5. Implementation Status 360 [Note to RFC Editor: Please remove this section and reference to 361 [RFC6982] prior to publication.] 363 This section records the status of known implementations of the 364 protocol defined by this specification at the time of posting of this 365 Internet-Draft, and is based on a proposal described in [RFC6982]. 366 The description of implementations in this section is intended to 367 assist the IETF in its decision processes in progressing drafts to 368 RFCs. Please note that the listing of any individual implementation 369 here does not imply endorsement by the IETF. Furthermore, no effort 370 has been spent to verify the information presented here that was 371 supplied by IETF contributors. This is not intended as, and must not 372 be construed to be, a catalog of available implementations or their 373 features. Readers are advised to note that other implementations may 374 exist. 376 According to [RFC6982], "this will allow reviewers and working groups 377 to assign due consideration to documents that have the benefit of 378 running code, which may serve as evidence of valuable experimentation 379 and feedback that have made the implemented protocols more mature. 380 It is up to the individual working groups to use this information as 381 they see fit". 383 5.1. open-sys 385 Organization: This is a public project, the full list of authors 386 and contributors here: http://turnserver.open-sys.org/downloads/ 387 AUTHORS 389 Description: A mature open-source TURN server specs implementation 390 (RFC 5766, RFC 6062, RFC 6156, etc) designed for high-performance 391 applications, especially geared for WebRTC. 393 Implementation: http://code.google.com/p/rfc5766-turn-server/ 395 Level of maturity: The Mobile ICE feature implementation can be 396 qualified as "production" - it is well tested and fully 397 implemented, but not widely used, yet.. 399 Coverage: Fully implements MICE with TURN protocol. 401 Licensing: BSD: http://turnserver.open-sys.org/downloads/LICENSE 403 Implementation experience: MICE implementation is somewhat 404 challenging for a multi-threaded performance-oriented application 405 (because the mobile ticket information must be shared between the 406 threads) but it is doable. 408 Contact: Oleg Moskalenko . 410 6. Security Considerations 412 TURN server MUST use strong encryption and integrity protection for 413 the ticket to prevent an attacker from using a brute force mechanism 414 to obtain the ticket's contents or refreshing allocations. The 415 ticket MUST be constructed such that it has strong entropy to ensure 416 nothing can be gleaned by looking at the ticket alone. 418 An attacker monitoring the traffic between the TURN client and server 419 can impersonate the client and refresh the allocation using the 420 ticket issued to the client with the attackers IP address and port. 421 This attack can be prevented by using STUN long-term credential 422 mechanism or STUN Extension for Third-Party Authorization [RFC7635] 423 or (D)TLS connection between the TURN client and the TURN server. 424 With any of those three mechanisms, when the server receives Refresh 425 Request with STUN MOBILITY-TICKET attribute from the client it 426 identifies that it is indeed the same client but with a new IP 427 address and port using the ticket it had previously issued to refresh 428 the allocation. 430 Security considerations described in [RFC5766] are also applicable to 431 this mechanism. 433 7. Acknowledgements 435 Thanks to Alfred Heggestad, Lishitao, Sujing Zhou, Martin Thomson, 436 Emil Ivov, Oleg Moskalenko and Brandon Williams for review and 437 comments. 439 8. References 441 8.1. Normative References 443 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 444 Requirement Levels", BCP 14, RFC 2119, 445 DOI 10.17487/RFC2119, March 1997, 446 . 448 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, 449 "Transport Layer Security (TLS) Session Resumption without 450 Server-Side State", RFC 5077, DOI 10.17487/RFC5077, 451 January 2008, . 453 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 454 (ICE): A Protocol for Network Address Translator (NAT) 455 Traversal for Offer/Answer Protocols", RFC 5245, 456 DOI 10.17487/RFC5245, April 2010, 457 . 459 [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 460 "Session Traversal Utilities for NAT (STUN)", RFC 5389, 461 DOI 10.17487/RFC5389, October 2008, 462 . 464 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 465 Relays around NAT (TURN): Relay Extensions to Session 466 Traversal Utilities for NAT (STUN)", RFC 5766, 467 DOI 10.17487/RFC5766, April 2010, 468 . 470 8.2. Informative References 472 [I-D.ietf-mmusic-trickle-ice] 473 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 474 Incremental Provisioning of Candidates for the Interactive 475 Connectivity Establishment (ICE) Protocol", draft-ietf- 476 mmusic-trickle-ice-02 (work in progress), January 2015. 478 [I-D.uberti-mmusic-nombis] 479 Uberti, J. and J. Lennox, "Improvements to ICE Candidate 480 Nomination", draft-uberti-mmusic-nombis-00 (work in 481 progress), March 2015. 483 [iana-stun] 484 IANA, , "IANA: STUN Attributes", April 2011, 485 . 488 [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 489 Code: The Implementation Status Section", RFC 6982, 490 DOI 10.17487/RFC6982, July 2013, 491 . 493 [RFC7635] Reddy, T., Patil, P., Ravindranath, R., and J. Uberti, 494 "Session Traversal Utilities for NAT (STUN) Extension for 495 Third-Party Authorization", RFC 7635, 496 DOI 10.17487/RFC7635, August 2015, 497 . 499 Appendix A. Example ticket construction 501 The TURN server uses two different keys: one 128-bit key for Advance 502 Encryption Standard (AES) in Cipher Block Chaining (CBC) mode 503 (AES_128_CBC) and 256-bit key for HMAC-SHA-256-128 for integrity 504 protection. The ticket can be structured as follows: 506 struct { 507 opaque key_name[16]; 508 opaque iv[16]; 509 opaque state<0..2^16-1>; 510 opaque mac[16]; 511 } ticket; 513 Figure 1: Ticket Format 515 Here, key_name serves to identify a particular set of keys used to 516 protect the ticket. It enables the TURN server to easily recognize 517 tickets it has issued. The key_name should be randomly generated to 518 avoid collisions between servers. One possibility is to generate new 519 random keys and key_name every time the server is started. 521 The TURN state information (self-contained or handle) in 522 encrypted_state is encrypted using 128-bit AES in CBC mode with the 523 given IV. The MAC is calculated using HMAC-SHA-256-128 over key_name 524 (16 octets)and IV (16 octets), followed by the length of the 525 encrypted_state field (2 octets) and its contents (variable length). 527 Authors' Addresses 529 Dan Wing 530 Cisco Systems, Inc. 531 170 West Tasman Drive 532 San Jose, California 95134 533 USA 535 Email: dwing@cisco.com 537 Prashanth Patil 538 Cisco Systems, Inc. 539 Bangalore 540 India 542 Email: praspati@cisco.com 544 Tirumaleswar Reddy 545 Cisco Systems, Inc. 546 Cessna Business Park, Varthur Hobli 547 Sarjapur Marathalli Outer Ring Road 548 Bangalore, Karnataka 560103 549 India 551 Email: tireddy@cisco.com 553 Paal-Erik Martinsen 554 Cisco Systems, Inc. 555 Philip Pedersens vei 22 556 Lysaker, Akershus 1325 557 Norway 559 Email: palmarti@cisco.com