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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 TRAM P. Patil 3 Internet-Draft T. Reddy 4 Intended status: Standards Track D. Wing 5 Expires: January 25, 2015 Cisco 6 July 24, 2014 8 TURN Server Auto Discovery 9 draft-ietf-tram-turn-server-discovery-00 11 Abstract 13 Current Traversal Using Relays around NAT (TURN) server discovery 14 mechanisms are relatively static and limited to explicit 15 configuration. These are usually under the administrative control of 16 the application or TURN service provider, and not the enterprise or 17 the ISP, the network in which the client is located. Enterprises and 18 ISPs wishing to provide their own TURN servers need auto discovery 19 mechanisms that a TURN client could use with no or minimal 20 configuration. This document describes two such mechanisms for TURN 21 server discovery. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on January 25, 2015. 40 Copyright Notice 42 Copyright (c) 2014 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Discovery Procedure . . . . . . . . . . . . . . . . . . . . . 3 60 4. Discovery using Service Resolution . . . . . . . . . . . . . 4 61 4.1. Retrieving Domain Name . . . . . . . . . . . . . . . . . 4 62 4.1.1. DHCP . . . . . . . . . . . . . . . . . . . . . . . . 4 63 4.1.2. IP Address . . . . . . . . . . . . . . . . . . . . . 5 64 4.1.3. From own Identity . . . . . . . . . . . . . . . . . . 5 65 4.2. Resolution . . . . . . . . . . . . . . . . . . . . . . . 5 66 4.2.1. SOA . . . . . . . . . . . . . . . . . . . . . . . . . 6 67 5. Discovery using Anycast . . . . . . . . . . . . . . . . . . . 7 68 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 7 69 6.1. Mobility and Changing IP addresses . . . . . . . . . . . 7 70 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 71 7.1. Anycast . . . . . . . . . . . . . . . . . . . . . . . . . 8 72 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 73 8.1. Service Resolution . . . . . . . . . . . . . . . . . . . 8 74 8.2. Anycast . . . . . . . . . . . . . . . . . . . . . . . . . 8 75 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 76 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 77 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 78 10.2. Informative References . . . . . . . . . . . . . . . . . 10 79 Appendix A. Change History . . . . . . . . . . . . . . . . . . . 10 80 A.1. Change from draft-patil-tram-serv-disc-00 to -01 . . . . 10 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 83 1. Introduction 85 TURN [RFC5766] is a protocol that is often used to improve the 86 connectivity of P2P applications. By providing a relay service, TURN 87 ensures that a connection can be established even when one or both 88 sides is incapable of a direct P2P connection. It is an important 89 building block for interactive, real-time communication using audio, 90 video, collaboration etc. While TURN services are extensively used 91 today, the means to auto discover TURN servers do not exist. TURN 92 clients are usually explicitly configured with a well known TURN 93 server. To allow TURN applications operate seamlessly across 94 different types of networks and encourage the use of TURN without the 95 need for manual configuration, it is important that there exists an 96 auto discovery mechanism for TURN services. WebRTC usages and 97 related extensions, which are mostly based on web applications, need 98 this immediately. 100 This document describes two discovery mechanisms. The reason for 101 providing two mechanisms is to maximize the opportunity for 102 discovery, based on the network in the which the TURN client sees 103 itself. 105 o A resolution mechanism based on straightforward Naming Authority 106 Pointer (S-NAPTR) resource records in the Domain Name System 107 (DNS). [RFC5928] describes details on retrieving a list of server 108 transport addresses from DNS that can be used to create a TURN 109 allocation. 111 o A mechanism based on anycast address for TURN. 113 In general, if a client wishes to communicate using one of its 114 interfaces using a specific IP address family, it SHOULD query the 115 TURN server(s) that has been discovered for that specific interface 116 and address family. How to select an interface and IP address 117 family, is out of the scope of this document. 119 2. Terminology 121 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 122 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 123 document are to be interpreted as described in [RFC2119]. 125 3. Discovery Procedure 127 A TURN client that implements the auto discovery algorithm MUST 128 proceed with discovery in the following order: 130 1. Local Configuration : Local or manual configuration should be 131 tried first, as it may be an explicit preferred choice of a user. 132 An implementation MAY give the user an opportunity (e.g., by 133 means of configuration file options or menu items) to specify a 134 TURN server for every address family. 136 2. Service Resolution : The TURN client attempts to perform TURN 137 service resolution using the DNS domain name that the host 138 belongs to OR the hosts' global IP address. The TURN client will 139 attempt to do this for each combination of interface and address 140 family. The retrieved DNS domain names OR IP addresses are then 141 used for NAPTR lookups. 143 3. Anycast : Send TURN allocate request to the assigned TURN anycast 144 request for each combination of interface and address family. 146 While it is expected that Step-3 be performed if Step-2 fails, an 147 implementation may choose to perform steps 2 and 3 in parallel. 149 4. Discovery using Service Resolution 151 This mechanism is performed in two steps: 153 1. A DNS domain name is retrieved for each combination of interface 154 and address family. 156 2. Retrieved DNS domain names are then used for S-NAPTR lookups as 157 per [RFC5928]. Further DNS lookups may be necessary to determine 158 TURN server IP address(es). 160 On hosts with more than one interface or address family (IPv4/v6), 161 the TURN server discovery procedure has to be run for each 162 combination of interface and address family. 164 4.1. Retrieving Domain Name 166 The domain, in which the client is located, can be determined using 167 one of the techniques provided below. An implementation can choose 168 to use any or all techniques. 170 Implementations may allow the user to specify a default name that is 171 used if no specific name has been configured. Other means of 172 retrieving domain names may be used, which are outside the scope of 173 this document e.g. local configuration. 175 4.1.1. DHCP 177 DHCP can be used to determine the domain name related to an 178 interface's point of network attachment. Network operators may 179 provide the domain name to be used for service discovery within an 180 access network using DHCP. [RFC5986] defines DHCP IPv4 and IPv6 181 access network domain name options to identify a domain name that is 182 suitable for service discovery within the access network. [RFC2132] 183 defines the DHCP IPv4 domain name option. While this option is less 184 suitable, it still may be useful if the option defined in [RFC5986] 185 is not available. 187 For IPv6, the TURN server discovery procedure MUST try to retrieve 188 DHCP option 57 (OPTION_V6_ACCESS_DOMAIN). If no such option can be 189 retrieved, the procedure fails for this interface. For IPv4, the 190 TURN server discovery procedure MUST try to retrieve DHCP option 213 191 (OPTION_V4_ACCESS_DOMAIN). If no such option can be retrieved, the 192 procedure SHOULD try to retrieve option 15 (Domain Name). If neither 193 option can be retrieved the procedure fails for this interface. If a 194 result can be retrieved it will be used as an input for S-NAPTR 195 resolution. 197 4.1.2. IP Address 199 Typically, but not necessarily, the DNS domain name is the domain 200 name in which the client is located, i.e., a PTR lookup on the 201 client's IP address (according to [RFC1035], Section 3.5 for IPv4 or 202 [RFC3596], Section 2.5 for IPv6) would yield a similar name. 203 However, due to the widespread use of Network Address Translation 204 (NAT), the client MAY need to determine its public IP address using 205 mechanisms described in [RFC7216]. 207 4.1.3. From own Identity 209 A TURN client could also wish to extract the domain name from its own 210 identity i.e canonical identifier used to reach the user. 212 Example 214 SIP : 'sip:alice@example.com' 215 JID : 'alice@example.com' 216 email : 'alice@example.com' 218 'example.com' is retrieved from the above examples. 220 The means to extract the domain name may be different based on the 221 type of identifier and is outside the scope of this document. 223 4.2. Resolution 225 Once the TURN discovery procedure has retrieved domain names, the 226 resolution mechanism described in [RFC5928] is followed. An S-NAPTR 227 lookup with 'RELAY' application service and the desired protocol tag 228 is made to obtain information necessary to connect to the 229 authoritative TURN server within the given domain. 231 In the example below, for domain 'example.net', the resolution 232 algorithm will result in IP address, port, and protocol tuples as 233 follows: 235 example.net. 236 IN NAPTR 100 10 "" RELAY:turn.udp "" example.net. 238 example.net. 239 IN NAPTR 100 10 S RELAY:turn.udp "" _turn._udp.example.net. 241 _turn._udp.example.net. 242 IN SRV 0 0 3478 a.example.net. 244 a.example.net. 245 IN A 192.0.2.1 247 +-------+----------+------------+------+ 248 | Order | Protocol | IP address | Port | 249 +-------+----------+------------+------+ 250 | 1 | UDP | 192.0.2.1 | 3478 | 251 +-------+----------+------------+------+ 253 If no TURN-specific S-NAPTR records can be retrieved, the discovery 254 procedure fails for this domain name (and the corresponding interface 255 and IP protocol version). If more domain names are known, the 256 discovery procedure may perform the corresponding S-NAPTR lookups 257 immediately. However, before retrying a lookup that has failed, a 258 client MUST wait a time period that is appropriate for the 259 encountered error (NXDOMAIN, timeout, etc.). 261 4.2.1. SOA 263 If no TURN-specific S-NAPTR records can be retrieved using the 264 previous step, additional steps described in this section have to be 265 followed. First, an SOA record for the "reverse zone" i.e., the zone 266 in the in-addr.arpa. or ip6.arpa. domain that contains the IP 267 address(s) in question, has to be retrieved. IP addresses can be 268 determined, if not done already, as described in Section 4.1.2. 270 A sample SOA record could be: 272 100.51.198.in-addr.arpa 273 IN SOA dns1.isp.example.net. hostmaster.isp.example.net. ( 274 1 ; Serial 275 604800 ; Refresh 276 86400 ; Retry 277 2419200 ; Expire 278 604800 ) ; Negative Cache TTL 280 If this lookup fails, the discovery procedure is aborted without a 281 result. 283 Once the SOA record is available, the discovery procedure extracts 284 the MNAME field, i.e., the responsible master name server from the 285 SOA record. An example MNAME could be: dns1.isp.example.net. Then, 286 an S-NAPTR lookup as specified in the previous step Section 4.2 is 287 performed on this MNAME to discover the TURN service. If no TURN- 288 specific S-NAPTR records can be retrieved, the discovery procedure 289 fails for this domain name (and the corresponding interface and IP 290 protocol version). 292 5. Discovery using Anycast 294 IP anycast is an elegant solution for TURN service discovery. A 295 packet sent to an anycast address is delivered to the "topologically 296 nearest" network interface with the anycast address. Using the TURN 297 anycast address, the only two things that need to be deployed in the 298 network are the two things that actually use TURN. 300 When a client requires TURN services, it sends a TURN allocate 301 request to the assigned anycast address. The TURN anycast server 302 responds with a 300 (Try Alternate) error as described in [RFC5766]; 303 The response contains the TURN unicast address in the ALTERNATE- 304 SERVER attribute. For subsequent communication with the TURN server, 305 the client uses the responding server's unicast address. This has to 306 be done because two packets addressed to an anycast address may reach 307 two different anycast servers. The client, thus, also needs to 308 ensure that the initial request fits in a single packet. An 309 implementation may choose to send out every new request to the 310 anycast address to learn the closest TURN server each time. 312 6. Deployment Considerations 314 6.1. Mobility and Changing IP addresses 316 A change of IP address on an interface may invalidate the result of 317 the TURN server discovery procedure. For instance, if the IP address 318 assigned to a mobile host changes due to host mobility, it may be 319 required to re-run the TURN server discovery procedure without 320 relying on earlier gained information. New requests should be made 321 to the newly learned TURN servers learned after TURN discovery re- 322 run. However, if an earlier learned TURN server is still accessible 323 using the new IP address, procedures described for mobility using 324 TURN defined in [I-D.wing-mmusic-ice-mobility] can be used for 325 ongoing streams. 327 7. IANA Considerations 329 7.1. Anycast 331 IANA should allocate an IPv4 and an IPv6 well-known TURN anycast 332 address. 192.0.0.0/24 and 2001:0000::/48 are reserved for IETF 333 Protocol Assignments, as listed at 335 and 337 339 8. Security Considerations 341 In general, it is recommended that a TURN client authenticate with 342 the TURN server to identify a rouge server. 343 [I-D.petithuguenin-tram-turn-dtls] can be potentially used by a 344 client to validate a previously unknown server. 346 8.1. Service Resolution 348 The primary attack against the methods described in this document is 349 one that would lead to impersonation of a TURN server. An attacker 350 could attempt to compromise the S-NAPTR resolution. Security 351 considerations described in [RFC5928] are applicable here as well. 353 In addition to considerations related to S-NAPTR, it is important to 354 recognize that the output of this is entirely dependent on its input. 355 An attacker who can control the domain name can also control the 356 final result. Because more than one method can be used to determine 357 the domain name, a host implementation needs to consider attacks 358 against each of the methods that are used. 360 If DHCP is used, the integrity of DHCP options is limited by the 361 security of the channel over which they are provided. Physical 362 security and separation of DHCP messages from other packets are 363 commonplace methods that can reduce the possibility of attack within 364 an access network; alternatively, DHCP authentication [RFC3188] can 365 provide a degree of protection against modification. When using DHCP 366 discovery, clients are encouraged to use unicast DHCP INFORM queries 367 instead of broadcast queries which are more easily spoofed in 368 insecure networks. 370 8.2. Anycast 372 In a network without any TURN server that is aware of the TURN 373 anycast address, outgoing TURN requests could leak out onto the 374 external Internet, possibly revealing information. 376 Using an IANA-assigned well-known TURN anycast address enables border 377 gateways to block such outgoing packets. In the default-free zone, 378 routers should be configured to drop such packets. Such 379 configuration can occur naturally via BGP messages advertising that 380 no route exists to said address. 382 Sensitive clients that do not wish to leak information about their 383 presence can set an IP TTL on their TURN requests that limits how far 384 they can travel into the public Internet. 386 9. Acknowledgements 388 Discovery using Service Resolution described in Section 4 of this 389 document was derived from similar techniques described in ALTO Server 390 Discovery [I-D.ietf-alto-server-discovery] and 391 [I-D.kist-alto-3pdisc]. 393 10. References 395 10.1. Normative References 397 [I-D.petithuguenin-tram-turn-dtls] 398 Petit-Huguenin, M. and G. Salgueiro, "Datagram Transport 399 Layer Security (DTLS) as Transport for Traversal Using 400 Relays around NAT (TURN)", draft-petithuguenin-tram-turn- 401 dtls-00 (work in progress), January 2014. 403 [I-D.wing-mmusic-ice-mobility] 404 Wing, D., Reddy, T., Patil, P., and P. Martinsen, 405 "Mobility with ICE (MICE)", draft-wing-mmusic-ice- 406 mobility-07 (work in progress), June 2014. 408 [RFC1035] Mockapetris, P., "Domain names - implementation and 409 specification", STD 13, RFC 1035, November 1987. 411 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 412 Requirement Levels", BCP 14, RFC 2119, March 1997. 414 [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor 415 Extensions", RFC 2132, March 1997. 417 [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, 418 "DNS Extensions to Support IP Version 6", RFC 3596, 419 October 2003. 421 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 422 Relays around NAT (TURN): Relay Extensions to Session 423 Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. 425 [RFC5928] Petit-Huguenin, M., "Traversal Using Relays around NAT 426 (TURN) Resolution Mechanism", RFC 5928, August 2010. 428 [RFC5986] Thomson, M. and J. Winterbottom, "Discovering the Local 429 Location Information Server (LIS)", RFC 5986, September 430 2010. 432 [RFC7216] Thomson, M. and R. Bellis, "Location Information Server 433 (LIS) Discovery Using IP Addresses and Reverse DNS", RFC 434 7216, April 2014. 436 10.2. Informative References 438 [I-D.ietf-alto-server-discovery] 439 Kiesel, S., Stiemerling, M., Schwan, N., Scharf, M., and 440 S. Yongchao, "ALTO Server Discovery", draft-ietf-alto- 441 server-discovery-10 (work in progress), September 2013. 443 [I-D.kist-alto-3pdisc] 444 Kiesel, S., Krause, K., and M. Stiemerling, "Third-Party 445 ALTO Server Discovery (3pdisc)", draft-kist-alto-3pdisc-05 446 (work in progress), January 2014. 448 [RFC3188] Hakala, J., "Using National Bibliography Numbers as 449 Uniform Resource Names", RFC 3188, October 2001. 451 Appendix A. Change History 453 [Note to RFC Editor: Please remove this section prior to 454 publication.] 456 A.1. Change from draft-patil-tram-serv-disc-00 to -01 458 o Added IP address (Section 4.1.2) and Own identity (4.1.3) as new 459 means to obtain domain names 461 o New Section 4.2.1 SOA (inspired by draft-kist-alto-3pdisc) 463 o 300 (Try Alternate) response for Anycast 465 Authors' Addresses 467 Prashanth Patil 468 Cisco Systems, Inc. 469 Bangalore 470 India 472 Email: praspati@cisco.com 473 Tirumaleswar Reddy 474 Cisco Systems, Inc. 475 Cessna Business Park, Varthur Hobli 476 Sarjapur Marathalli Outer Ring Road 477 Bangalore, Karnataka 560103 478 India 480 Email: tireddy@cisco.com 482 Dan Wing 483 Cisco Systems, Inc. 484 170 West Tasman Drive 485 San Jose, California 95134 486 USA 488 Email: dwing@cisco.com