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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) -- Obsolete informational reference (is this intentional?): RFC 5389 (Obsoleted by RFC 8489) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIMPLE Working Group C. Holmberg 3 Internet-Draft Ericsson 4 Intended status: Standards Track S. Blau 5 Expires: October 22, 2010 Ericsson AB 6 April 20, 2010 8 An Alternative Connection Model for the Message Session Relay Protocol 9 (MSRP) 10 draft-ietf-simple-msrp-acm-08.txt 12 Abstract 14 This document defines an alternative connection model for Message 15 Session Relay Protocol (MSRP) User Agents (UAs), which uses the 16 connection-oriented media (COMEDIA) mechanism in order to create the 17 MSRP transport connection. The model allows MSRP UAs behind Network 18 Address Translators (NATs) to negotiate which endpoint initiates the 19 establishment of the TCP connection, in order for MSRP messages to 20 traverse the NAT. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on October 22, 2010. 39 Copyright Notice 41 Copyright (c) 2010 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. Applicability statement . . . . . . . . . . . . . . . . . . . . 3 59 4. COMEDIA for MSRP . . . . . . . . . . . . . . . . . . . . . . . 4 60 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 4.2. a=setup . . . . . . . . . . . . . . . . . . . . . . . . . . 4 62 4.3. TLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 63 4.4. a=connection . . . . . . . . . . . . . . . . . . . . . . . 6 64 4.5. MSRP relay connection . . . . . . . . . . . . . . . . . . . 6 65 5. Interoperability with connection model defined in RFC 4975 . . 6 66 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 67 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 68 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 69 9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 7 70 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 71 10.1. Normative References . . . . . . . . . . . . . . . . . . . 8 72 10.2. Informative References . . . . . . . . . . . . . . . . . . 8 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 75 1. Introduction 77 The Message Session Relay Protocol (MSRP) core specification 78 [RFC4975] defines that the MSRP UA which sends the SDP offer is 79 "active", and it is responsible for creating the MSRP transport 80 connection towards the remote UA if a new connection is required. 81 The core specification also allows, but does not define, alternate 82 mechanisms for MSRP UAs to create MSRP transport connections. 84 [RFC4145] defines a connection-oriended media mechanism, COMEDIA, 85 that endpoints can use to negotiate the endpoint which initiates the 86 creation of media transport connection. 88 COMEDIA is especially useful when an endpoint is located behind a 89 NAT. The endpoint can use the mechanism to indicate that it will 90 create the media transport connection, in order for the media to 91 traverse the NAT without the usage of relays. 93 An example is the Open Mobile Alliance (OMA) defined "Instant Message 94 using SIMPLE" [OMA-TS-SIMPLE_IM-V1_0-20090901-D], where one MSRP UA 95 of every MSRP transport connection represents a media server, which 96 is always located in the carrier network. The media server has a 97 global IP address and handles application specific policy control as 98 well as NAT traversal. The OMA IM (Instant Messenger) uses COMEDIA 99 for NAT traversal, and all OMA IM MSRP clients support COMEDIA. 101 This document defines how an MSRP UA uses COMEDIA in order to 102 negotiate which UA will create the MSRP transport TCP connection 103 towards the other UA. The document also defines how an MSRP UA which 104 uses COMEDIA can establish an MSRP transport connection with a remote 105 UA that does not support COMEDIA. 107 2. Terminology 109 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 110 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 111 document are to be interpreted as described in RFC 2119 [RFC2119]. 113 3. Applicability statement 115 Support of this specification is optional for MSRP user agents in 116 general. User Agents that are likely to be deployed in networks 117 where User Agents need to establish the TCP connections in order to 118 traverse NATs SHOULD support this specification in order to improve 119 the odds of being able to communicate across NATs. 121 4. COMEDIA for MSRP 123 4.1. General 125 This section defines how an MSRP UA that supports this specification 126 uses the COMEDIA SDP attributes defined in [RFC4145]. 128 4.2. a=setup 130 An MSRP UA MUST support the SDP a=setup attribute [RFC4145], in order 131 to negotiate which endpoint will create the MSRP transport connection 132 towards the other UA. 134 The a=setup attribute is particularly useful when one MSRP UA 135 represents a network media server, or any other entity that is not 136 located behind a NAT. The a=setup attribute allows the media server 137 to ensure that MSRP UAs create the MSRP transport connections towards 138 the server, so that NATs at user's premises will not interfere with 139 the connection creation. 141 An MSRP UA MUST always include an explicit a=setup attribute in its 142 SDP offers and answers, since it is sometimes useful for the other 143 endpoint, or for entities in the network, to know whether the UA 144 supports COMEDIA or not. 146 An MSRP UA MUST support the a=setup "active", "actpass" and "passive" 147 attribute values. 149 When the a=setup attribute value is "actpass" or "passive", the IP 150 address and port values in the MSRP URI of the SDP a=path attribute 151 MUST contain the actual address and port values on which the UA can 152 receive a TCP Open request for the MSRP transport connection. 154 In accordance with [RFC4145], if the a=setup attribute value is 155 "active", the port number value SHOULD be 9. 157 If an MSRP UA can provide a global IP address that the other endpoint 158 can use as destination for a TCP Open request, the UA MUST use the 159 a=setup "actpass" attribute value in SDP offers. This is in order to 160 allow the remote UA to send an SDP answer with an a=setup "active" 161 attribute value if the UA is located behind NAT, and in order to be 162 compatible with MSRP UAs that do not support COMEDIA and thus always 163 will act as passive endpoints. If an MSRP UA cannot provide the 164 actual transport address, the UA MUST use the a=setup "active" 165 attribute value. 167 The UA MUST NOT use the a=setup "passive" attribute value in an SDP 168 offer. 170 The MSRP UA can determine that it provides a global IP address in the 171 following scenarios: 173 - the UA can determine that it is not located behind a NAT; 175 - the UA relays its MSRP transport connections via a relay (e.g. 176 MSRP relay or TURN server); or 178 - the UA has used Session Traversal Utilities for NAT (STUN) 179 [RFC5389] signaling to retrieve NAT address and port through the 180 local port to be used for the eventual transport connection, while 181 also having determined that the NAT is not address restricted. 183 Some UAs can determine whether the SIP [RFC3261] signaling has 184 traversed a NAT by inspecting the SIP Via header field in the 200 185 (OK) response to the initial SIP REGISTER request, and comparing the 186 IP addresses in the Via sent-by and the received header field 187 parameters. If the IP addresses are not the same then the UA can 188 determine that there is a NAT in the path. Even though the media 189 transport might not traverse the NAT, it is safe to assume that it 190 will, and set the a=setup attribute accordingly. This comparing 191 mechanism does not work in all scenarios, though. For example, if 192 SIP a requests crosses a SIP proxy before crossing a NAT, the UA will 193 not be able to detect the NAT by comparing the IP addresses. 195 If an SDP offer includes an a=setup "actpass" attribute value, the 196 SDP answer MAY include an a=setup "active" attribute value, but 197 SHOULD include a=setup "passive" attribute value if the SDP answerer 198 knows that it is not located behind a NAT. 200 Once the active UA has established the MSRP transport connection, the 201 UA MUST immediately send an MSRP SEND request, as defined in 202 [RFC4975]. 204 NOTE: According to [RFC4975] the initiating UA is always active, but 205 when COMEDIA is used the a=setup attribute is used to negotiate which 206 UA becomes active. 208 4.3. TLS 210 If an MSRP UA conformant to this document uses TLS, it MUST use the 211 TLS mechanisms defined in [RFC4975] and [RFC4976]. 213 According to [RFC4975], the connection can be established with or 214 without TLS mutual authentication. In case mutual authentication is 215 not used, the listening device waits until it receives a request on 216 the connection, at which time it infers the identity of the 217 connecting device from the associated session description. From TLS 218 authentication point of view it is thus irrelevant whether an 219 endpoint takes the active or passive role. 221 If an MSRP UA uses a self-signed TLS certificate to authenticate 222 itself to MSRP peers it also includes its certificate fingerprint in 223 the SDP. 225 Note that fingerprints can only be exchanged in peer-to-peer 226 communication, as MSRP relays [RFC4976] will not receive the SDP 227 payloads containing the fingerprint attributes. 229 4.4. a=connection 231 MSRP UAs MUST NOT use the SDP a=connection attribute. [RFC4975] 232 defines connection reuse procedures for MSRP, and this document does 233 not modify those procedures. 235 If an MSRP UA receives an a=connection attribute, the UA MUST ignore 236 it. 238 4.5. MSRP relay connection 240 If an MSRP UA is located behind an MSRP relay [RFC4976], the UA MUST 241 always initiate a transport connection towards the relay, no matter 242 what value the client has provided in the a=setup attribute. 244 NOTE: Even if an MSRP UA initiates the TCP connection towards its 245 relay, the UA will only send a SEND request if the UA is active, 246 based on the COMEDIA negotiation. 248 5. Interoperability with connection model defined in RFC 4975 250 An MSRP UA conformant to this document can interoperate with a UA 251 that follows the connection model defined in [RFC4975]. However, if 252 an MSRP UA conformant to this document is located behind NAT, and 253 does not proxy its MSRP communication via an MSRP relay, and the UA 254 receives an SDP offer from a remote UA that follows the connection 255 model defined in [RFC4975], NAT traversal can only be achieved if the 256 MSRP UA supports ICE [I.D.ietf-mmusic-ice-tcp] and the network 257 provides TURN servers, or if the network supports SBC assisted NAT 258 traversal for TCP. 260 6. Security Considerations 262 According to the connection model defined in [RFC4975], the MSRP UA 263 that sends the SDP offer becomes the active party, and it is 264 responsible for creating the MSRP transport connection towards the 265 remote UA if a new connection is required. 267 When COMEDIA is used, either the sender or the receiver of the SDP 268 offer can become the active party. [RFC4975] requires that the 269 active party immediately issues an MSRP SEND request once the 270 connection has been established. This allows the passive party to 271 bind the inbound TCP connection to the message session identified by 272 the session id part of its MSRP URI. The use of COMEDIA does not 273 change this requirement, but the sender of the SDP offer is no longer 274 assumed to always become the active party. 276 The active party also takes the role as TLS client, if TLS is used to 277 protect the MSRP messages. However, there are no procedures in 278 [RFC4975] that would break in case the receiver of the SDP offer 279 takes the role as TLS client, and the level of security provided by 280 TLS is not affected. 282 7. IANA Considerations 284 This document has no actions for IANA. 286 8. Acknowledgements 288 Thanks to Ben Campbell, Remi Denis-Courmont, Nancy Greene, Hadriel 289 Kaplan, Adam Roach, Robert Sparks, Salvatore Loreto and Shida 290 Schubert for their guidance and input in order to produce this 291 document. 293 9. Change Log 295 [RFC EDITOR NOTE: Please remove this section when publishing] 297 Changes from draft-ietf-simple-msrp-acm-07 298 o WGLC editorial changes. 300 Changes from draft-ietf-simple-msrp-acm-06 301 o WGLC changes. 303 Changes from draft-ietf-simple-msrp-acm-05 304 o TLS section modified. 306 Changes from draft-ietf-simple-msrp-acm-04 307 o TLS section modified. 308 o Security considerations section modified. 310 Changes from draft-ietf-simple-msrp-acm-03 311 o Changes based on WGLC comments from Adam Roach and Ben Campbell. 312 o New section added related to interoperability with connection 313 model defined in RFC 4975. 314 o Text related to a=setup "holdconn" attribute value removed. 315 o NAT keepalive section removed. 316 o Usage of COMEDIA-TLS removed. 318 Changes from draft-ietf-simple-mscp-acm-02 319 o Changes based on WGLC comments from Salvatore Loreto and Shida 320 Schubert. 322 Changes from draft-ietf-simple-msrp-acm-01 323 o Procedures for using SDP c/m for routing of MSRP messages removed. 324 o Procedures related to modification of MSRP address information by 325 intermediates moved to separate document. 326 o Solution to open issue on usage of the SDP a=connection 327 implemented. 329 10. References 331 10.1. Normative References 333 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 334 Requirement Levels", BCP 14, RFC 2119, March 1997. 336 [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in 337 the Session Description Protocol (SDP)", RFC 4145, 338 September 2005. 340 [RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message 341 Session Relay Protocol (MSRP)", RFC 4975, September 2007. 343 [RFC4976] Jennings, C., Mahy, R., and A. Roach, "Relay Extensions 344 for the Message Sessions Relay Protocol (MSRP)", RFC 4976, 345 September 2007. 347 10.2. Informative References 349 [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 350 "Session Traversal Utilities for NAT (STUN)", RFC 5389, 351 October 2008. 353 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 354 A., Peterson, J., Sparks, R., Handley, M., and E. 355 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 356 June 2002. 358 Authors' Addresses 360 Christer Holmberg 361 Ericsson 362 Hirsalantie 11 363 Jorvas 02420 364 Finland 366 Email: christer.holmberg@ericsson.com 368 Staffan Blau 369 Ericsson AB 370 P.O Box 407 371 Sweden 373 Email: staffan.blau@ericsson.com