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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: October 20, 2016 Cisco 6 April 18, 2016 8 TURN Server Auto Discovery 9 draft-ietf-tram-turn-server-discovery-07 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, 17 ISP, or 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 three such mechanisms for 21 TURN 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 October 20, 2016. 40 Copyright Notice 42 Copyright (c) 2016 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 . . . . . . . . . . . . . . . . . . . . . . . . 5 63 4.1.2. From own Identity . . . . . . . . . . . . . . . . . . 5 64 4.2. Resolution . . . . . . . . . . . . . . . . . . . . . . . 5 65 5. DNS Service Discovery . . . . . . . . . . . . . . . . . . . . 6 66 5.1. mDNS . . . . . . . . . . . . . . . . . . . . . . . . . . 7 67 6. Discovery using Anycast . . . . . . . . . . . . . . . . . . . 8 68 7. Deployment Considerations . . . . . . . . . . . . . . . . . . 9 69 7.1. Mobility and Changing IP addresses . . . . . . . . . . . 9 70 7.2. Recursively Encapsulated TURN . . . . . . . . . . . . . . 9 71 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 72 8.1. Anycast . . . . . . . . . . . . . . . . . . . . . . . . . 9 73 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 74 9.1. Service Resolution . . . . . . . . . . . . . . . . . . . 10 75 9.2. DNS Service Discovery . . . . . . . . . . . . . . . . . . 11 76 9.3. Anycast . . . . . . . . . . . . . . . . . . . . . . . . . 11 77 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 78 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 79 11.1. Normative References . . . . . . . . . . . . . . . . . . 12 80 11.2. Informative References . . . . . . . . . . . . . . . . . 13 81 Appendix A. Change History . . . . . . . . . . . . . . . . . . . 14 82 A.1. Change from draft-patil-tram-serv-disc-00 to -01 . . . . 14 83 A.2. Change from draft-ietf-tram-turn-server-discovery-01 to 84 02 . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 87 1. Introduction 89 TURN [RFC5766] is a protocol that is often used to improve the 90 connectivity of Peer-to-Peer (P2P) applications (as defined in 91 section 2.7 of [RFC5128]). TURN allows a connection to be 92 established when one or both sides are incapable of a direct P2P 93 connection. It is an important building block for interactive, real- 94 time communication using audio, video, collaboration etc. 96 While TURN services are extensively used today, the means to auto 97 discover TURN servers do not exist. TURN clients are usually 98 explicitly configured with a well known TURN server. To allow TURN 99 applications to operate seamlessly across different types of networks 100 and encourage the use of TURN without the need for manual 101 configuration, it is important that there exists an auto discovery 102 mechanism for TURN services. Web Real-Time Communication (WebRTC) 103 [I-D.ietf-rtcweb-overview] usages and related extensions, which are 104 mostly based on web applications, need this immediately. 106 This document describes three discovery mechanisms, so as to maximize 107 opportunity for discovery, based on the network in which the TURN 108 client finds itself. The three discovery mechanisms are: 110 o A resolution mechanism based on straightforward Naming Authority 111 Pointer (S-NAPTR) resource records in the Domain Name System 112 (DNS). [RFC5928] describes details on retrieving a list of server 113 transport addresses from DNS that can be used to create a TURN 114 allocation. 116 o DNS Service Discovery 118 o A mechanism based on anycast address for TURN. 120 In general, if a client wishes to communicate using one of its 121 interfaces using a specific IP address family, it SHOULD query the 122 TURN server(s) that has been discovered for that specific interface 123 and address family. How to select an interface and IP address family 124 is out of the scope of this document. 126 2. Terminology 128 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 129 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 130 "OPTIONAL" in this document are to be interpreted as described in 131 [RFC2119]. 133 3. Discovery Procedure 135 A TURN client that implements the auto discovery algorithm uses the 136 following mechanisms for discovery: 138 1. Local Configuration : Local or manual TURN configuration i.e., 139 TURN servers configured at the system level. For example, in 140 case of Web Real-Time Communication (WebRTC) 141 [I-D.ietf-rtcweb-overview] usages and related extensions, which 142 are based on web applications, a Java Script specified TURN 143 server MUST be considered as local configuration. An 144 implementation MAY give the user an opportunity (e.g., by means 145 of configuration file options or menu items) to specify a TURN 146 server for each address family. 148 2. Service Resolution : The TURN client attempts to perform TURN 149 service resolution using the host's DNS domain. 151 3. DNS SD: DNS Service Discovery. 153 4. Anycast : Send TURN allocate request to the assigned TURN anycast 154 request for each combination of interface and address family. 156 Not all TURN servers may be discovered using NAPTR records or DNS SD; 157 Similarly, not all TURN servers may support anycast. For best 158 results, a client SHOULD implement all discovery mechanisms described 159 above. 161 The document does not prescribe a strict order that a client must 162 follow for discovery. An implementation may choose to perform all 163 the above steps in parallel for discovery OR choose to follow any 164 desired order and stop the discovery procedure if a mechanism 165 succeeds. 167 On hosts with more than one interface or address family (IPv4/v6), 168 the TURN server discovery procedure has to be performed for each 169 combination of interface and address family. A client MAY optionaly 170 choose to perform the discovery procedure only for a desired 171 interface/address combination if the client does not wish to discover 172 a TURN server for all combinations of interface and address family. 174 4. Discovery using Service Resolution 176 This mechanism is performed in two steps: 178 1. A DNS domain name is retrieved for each combination of interface 179 and address family. 181 2. Retrieved DNS domain names are then used for S-NAPTR lookups as 182 per [RFC5928]. Further DNS lookups may be necessary to determine 183 TURN server IP address(es). 185 4.1. Retrieving Domain Name 187 A client has to determine the domain in which it is located. The 188 following sections provide two possible mechanisms to learn the 189 domain name, but other means of retrieving domain names may be used, 190 which are outside the scope of this document e.g. local 191 configuration. 193 Implementations may allow the user to specify a default name that is 194 used if no specific name has been configured. 196 4.1.1. DHCP 198 DHCP can be used to determine the domain name related to an 199 interface's point of network attachment. Network operators may 200 provide the domain name to be used for service discovery within an 201 access network using DHCP. Sections 3.2 and 3.3 of [RFC5986] define 202 DHCP IPv4 and IPv6 access network domain name options to identify a 203 domain name that is suitable for service discovery within the access 204 network. [RFC2132] defines the DHCP IPv4 domain name option; While 205 this option is less suitable, it may still be useful if the options 206 defined in [RFC5986] are not available. 208 For IPv6, the TURN server discovery procedure MUST try to retrieve 209 DHCP option 57 (OPTION_V6_ACCESS_DOMAIN). If no such option can be 210 retrieved, the procedure fails for this interface. For IPv4, the 211 TURN server discovery procedure MUST try to retrieve DHCP option 213 212 (OPTION_V4_ACCESS_DOMAIN). If no such option can be retrieved, the 213 procedure SHOULD try to retrieve option 15 (Domain Name). If neither 214 option can be retrieved the procedure fails for this interface. If a 215 result can be retrieved it will be used as an input for S-NAPTR 216 resolution. 218 4.1.2. From own Identity 220 For a TURN client with an understanding of the protocol mechanics of 221 calling applications, the client may wish to extract the domain name 222 from its own identity i.e canonical identifier used to reach the 223 user. 225 Example 227 SIP : 'sip:alice@example.com' 228 JID : 'alice@example.com' 229 email : 'alice@example.com' 231 'example.com' is retrieved from the above examples. 233 The means to extract the domain name may be different based on the 234 type of identifier and is outside the scope of this document. 236 4.2. Resolution 238 Once the TURN discovery procedure has retrieved domain names, the 239 resolution mechanism described in [RFC5928] is followed. An S-NAPTR 240 lookup with 'RELAY' application service and the desired protocol tag 241 is made to obtain information necessary to connect to the 242 authoritative TURN server within the given domain. 244 In the example below, for domain 'example.net', the resolution 245 algorithm will result in IP address, port, and protocol tuples as 246 follows: 248 example.net. 249 IN NAPTR 100 10 "" RELAY:turn.udp "" example.net. 251 example.net. 252 IN NAPTR 100 10 S RELAY:turn.udp "" _turn._udp.example.net. 254 _turn._udp.example.net. 255 IN SRV 0 0 3478 a.example.net. 257 a.example.net. 258 IN A 192.0.2.1 259 IN AAAA 2001:db8:8:4::2 261 +-------+----------+------------------+------+ 262 | Order | Protocol | IP address | Port | 263 +-------+----------+------------------+------+ 264 | 1 | UDP | 192.0.2.1 | 3478 | 265 +-------+----------+------------------+------+ 266 | 2 | UDP | 2001:db8:8:4::2 | 3478 | 267 +-------+----------+------------------+------+ 269 If no TURN-specific S-NAPTR records can be retrieved, the discovery 270 procedure fails for this domain name (and the corresponding interface 271 and IP protocol version). If more domain names are known, the 272 discovery procedure may perform the corresponding S-NAPTR lookups 273 immediately. However, before retrying a lookup that has failed, a 274 client MUST wait a time period that is appropriate for the 275 encountered error (NXDOMAIN, timeout, etc.). 277 5. DNS Service Discovery 279 DNS-based Service Discovery (DNS-SD) [RFC6763] and Multicast DNS 280 (mDNS) [RFC6762] provide generic solutions for discovering services 281 available in a local network. DNS-SD/ mDNS define a set of naming 282 rules for certain DNS record types that they use for advertising and 283 discovering services. PTR records are used to enumerate service 284 instances of a given service type. A service instance name is mapped 285 to a host name and a port number using a SRV record. If a service 286 instance has more information to advertise than the host name and 287 port number contained in its SRV record, the additional information 288 is carried in a TXT record. 290 Section 4.1 of [RFC6763] specifies that a service instance name in 291 DNS-SD has the following structure: 293 . . 295 The portion specifies the DNS sub-domain where the service 296 instance is registered. It may be "local.", indicating the mDNS 297 local domain, or it may be a conventional domain name such as 298 "example.com.". The portion of the TURN service instance 299 name MUST be "_turnserver._udp", "_turnserver._tcp". 301 The portion is a DNS label, containing UTF-8-encoded text 302 [RFC5198], limited to 63 octets in length. It is meant to be a user- 303 friendly description of the service instance, suitable for a menu- 304 like user interface display. Thus it can contain any characters 305 including spaces, punctuation, and non-Latin characters as long as 306 they can be encoded in UTF-8. 308 For example, TURN server advertises the following DNS records : 310 _turnserver._udp.local. PTR example.com._turnserver._udp.local. 312 example.com._turnserver._udp.local. SRV 0 0 5030 example-turn- 313 server.local. 315 example-turn-server.local. A 198.51.100.2 317 example-turn-server.local. AAAA 2001:db8:8:4::2 319 In addition to the service instance name, IP address and the port 320 number, DNS-SD provides a way to publish other information pertinent 321 to the service being advertised. The additional data can be stored 322 as name/value attributes in a TXT record with the same name as the 323 SRV record for the service. Each name/value pair within the TXT 324 record is preceded by a single length byte, thereby limiting the 325 length of the pair to 255 bytes (See Section 6 of [RFC6763] and 326 Section 3.3.14 of [RFC1035] for details). 328 5.1. mDNS 330 A TURN client tries to discover the TURN servers being advertised in 331 the site by multicasting a PTR query "_turnserver._udp.local." or 332 "_turnserver._tcp.local" or the TURN server can send out gratuitous 333 multicast DNS answer packets whenever it starts up, wakes from sleep, 334 or detects a chance in network configuration. TURN clients receive 335 these gratuitous packet and cache the information contained in it. 337 +------+ +-------------+ 338 | TURN | | TURN Server | 339 |Client| | | 340 +------+ +-------------+ 341 | | 342 | PTR query "_turnserver._udp.local." | 343 |--------------------------------------------->| 344 | PTR reply | 345 |<---------------------------------------------| 346 | SRV query | 347 |--------------------------------------------->| 348 | SRV reply | 349 |<---------------------------------------------| 350 | A/AAAA query reply | 351 |--------------------------------------------->| 352 | TURN Request | 353 |--------------------------------------------->| 354 | TURN Response | 355 |<---------------------------------------------| 357 Figure 1: TURN Server Discovery using mDNS 359 6. Discovery using Anycast 361 IP anycast can also be used for TURN service discovery. A packet 362 sent to an anycast address is delivered to the "topologically 363 nearest" network interface with the anycast address. Using the TURN 364 anycast address, the only two things that need to be deployed in the 365 network are the two things that actually use TURN. 367 When a client requires TURN services, it sends a TURN allocate 368 request to the assigned anycast address. The TURN anycast server 369 responds with a 300 (Try Alternate) error as described in [RFC5766]; 370 The response contains the TURN unicast address in the ALTERNATE- 371 SERVER attribute. For subsequent communication with the TURN server, 372 the client uses the responding server's unicast address. This has to 373 be done because two packets addressed to an anycast address may reach 374 two different anycast servers. The client, thus, also needs to 375 ensure that the initial request fits in a single packet. An 376 implementation may choose to send out every new request to the 377 anycast address to learn the closest TURN server each time. 379 7. Deployment Considerations 381 7.1. Mobility and Changing IP addresses 383 A change of IP address on an interface may invalidate the result of 384 the TURN server discovery procedure. For instance, if the IP address 385 assigned to a mobile host changes due to host mobility, it may be 386 required to re-run the TURN server discovery procedure without 387 relying on earlier gained information. New requests should be made 388 to the newly learned TURN servers learned after TURN discovery re- 389 run. However, if an earlier learned TURN server is still accessible 390 using the new IP address, procedures described for mobility using 391 TURN defined in [I-D.ietf-tram-turn-mobility] can be used for ongoing 392 streams. 394 7.2. Recursively Encapsulated TURN 396 WebRTC endpoints SHOULD treat any TURN server discovered through the 397 mechanims described in this specification as an enterprise/gateway 398 server, in accordance with Recursively Encapsulated TURN 399 [I-D.ietf-rtcweb-return]. 401 8. IANA Considerations 403 8.1. Anycast 405 IANA should allocate an IPv4 and an IPv6 well-known TURN anycast 406 address. 192.0.0.0/24 and 2001:0000::/48 are reserved for IETF 407 Protocol Assignments, as listed at 409 and 411 413 9. Security Considerations 415 Use of STUN authentication is OPTIONAL for TURN servers provided by 416 the local network or by the access network. A network provided TURN 417 server MAY be configured to accept Allocation requests without STUN 418 authentication, and a TURN client MAY be configured to accept 419 Allocation success responses without STUN authentication from a 420 network provided TURN server. In order to protect against man-in- 421 the-middle attacks when accepting a TURN allocation response without 422 STUN authentication, it is RECOMMENDED that the TURN client use one 423 of the following techniques with (D)TLS to validate the TURN server: 425 o For certificate-based authentication, a pre-populated trust anchor 426 store [RFC6024] allows a TURN client to perform path validation 427 for the server certificate obtained during the (D)TLS handshake. 428 If the client used a domain name to discover the TURN server, that 429 domain name also provides a mechanism for validation of the TURN 430 server. The client MUST use the rules and guidelines given in 431 section 6 of [RFC6125] to validate the TURN server identity. 433 o For TURN servers that don't have a certificate trust chain (e.g., 434 because they are on a home network or a corporate network), a 435 configured list of TURN servers can contain the Subject Public Key 436 Info (SPKI) fingerprint of the TURN servers. The public key is 437 used for the same reasons HTTP pinning [RFC7469] uses the public 438 key. 440 o Raw public key-based authentication, as defined in [RFC7250], 441 could also be used to authenticate a TURN server. 443 An auto-discovered TURN server is considered to be only as trusted as 444 the path between the client and the TURN server. In order to safely 445 use auto-discovered TURN servers for sessions with 'strict privacy' 446 requirements, the user needs to be able to define privacy criteria 447 (e.g. a trusted list of servers, networks, or domains) that are 448 considered acceptable for such traffic. Any discovered TURN server 449 outside the criteria is considered untrusted and is not used for 450 privacy sensitive communication. 452 In some auto-discovery scenarios, it might not be possible for the 453 TURN client to use (D)TLS authentication to validate the TURN server. 454 However, fall-back to clear text in such cases could leave the TURN 455 client open to on-path injection of spoofed TURN messages. For this 456 reason, it is beneficial for the TURN client to make use of 457 'opportunistic privacy', analogous to SMTP opportunistic encryption 458 [RFC7435], where one does not require privacy but one desires privacy 459 when possible. In this scenario, a TURN client attempts (D)TLS with 460 authentication and encryption, falling back to encryption-only if the 461 TURN server cannot be authenticated via (D)TLS. If the TURN server 462 does not support unauthenticated (D)TLS, then the client falls back 463 to clear text. Fallback to clear text is NOT RECOMMENDED because it 464 makes the client more susceptible to man-in-the-middle attacks and 465 on-path packet injection. A TURN client SHOULD fall-back to 466 encryption-only (D)TLS when (D)TLS authentication is not available in 467 order to protect against on-path attackers who might attempt to 468 inject fake TURN messages. 470 9.1. Service Resolution 472 The primary attack against the methods described in this document is 473 one that would lead to impersonation of a TURN server. An attacker 474 could attempt to compromise the S-NAPTR resolution. Security 475 considerations described in [RFC5928] are applicable here as well. 477 In addition to considerations related to S-NAPTR, it is important to 478 recognize that the output of this is entirely dependent on its input. 479 An attacker who can control the domain name can also control the 480 final result. Because more than one method can be used to determine 481 the domain name, a host implementation needs to consider attacks 482 against each of the methods that are used. 484 If DHCP is used, the integrity of DHCP options is limited by the 485 security of the channel over which they are provided. Physical 486 security and separation of DHCP messages from other packets are 487 commonplace methods that can reduce the possibility of attack within 488 an access network; alternatively, DHCP authentication [RFC3188] can 489 provide a degree of protection against modification. When using DHCP 490 discovery, clients are encouraged to use unicast DHCP INFORM queries 491 instead of broadcast queries which are more easily spoofed in 492 insecure networks. 494 9.2. DNS Service Discovery 496 Since DNS-SD is just a specification for how to name and use records 497 in the existing DNS system, it has no specific additional security 498 requirements over and above those that already apply to DNS queries 499 and DNS updates. For DNS queries, DNS Security Extensions (DNSSEC) 500 [RFC4033] should be used where the authenticity of information is 501 important. For DNS updates, secure updates [RFC2136][RFC3007] should 502 generally be used to control which clients have permission to update 503 DNS records. 505 For mDNS, in addition to what has been described above, a principal 506 security threat is a security threat inherent to IP multicast routing 507 and any application that runs on it. A rogue system can advertise 508 that it is a TURN server. Discovery of such rogue systems as TURN 509 servers, in itself, is not a security threat if there is a means for 510 the TURN client to authenticate and authorize the discovered TURN 511 servers. 513 9.3. Anycast 515 In a network without any TURN server that is aware of the TURN 516 anycast address, outgoing TURN requests could leak out onto the 517 external Internet, possibly revealing information. 519 Using an IANA-assigned well-known TURN anycast address enables border 520 gateways to block such outgoing packets. In the default-free zone, 521 routers should be configured to drop such packets. Such 522 configuration can occur naturally via BGP messages advertising that 523 no route exists to said address. 525 Sensitive clients that do not wish to leak information about their 526 presence can set an IP TTL on their TURN requests that limits how far 527 they can travel into the public Internet. 529 10. Acknowledgements 531 The authors would like to thank Simon Perrault, Paul Kyzivat, Troy 532 Shields, Eduardo Gueiros, Ted Hardie, Bernard Aboba, Karl Stahl and 533 Brandon Williams for their review and valuable comments. Thanks to 534 Adam Roach for his detailed review and suggesting DNS Service 535 Discovery as an additional discovery mechanism. 537 11. References 539 11.1. Normative References 541 [RFC1035] Mockapetris, P., "Domain names - implementation and 542 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 543 November 1987, . 545 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 546 Requirement Levels", BCP 14, RFC 2119, 547 DOI 10.17487/RFC2119, March 1997, 548 . 550 [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor 551 Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997, 552 . 554 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 555 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 556 RFC 2136, DOI 10.17487/RFC2136, April 1997, 557 . 559 [RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic 560 Update", RFC 3007, DOI 10.17487/RFC3007, November 2000, 561 . 563 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 564 Rose, "DNS Security Introduction and Requirements", 565 RFC 4033, DOI 10.17487/RFC4033, March 2005, 566 . 568 [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network 569 Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008, 570 . 572 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 573 Relays around NAT (TURN): Relay Extensions to Session 574 Traversal Utilities for NAT (STUN)", RFC 5766, 575 DOI 10.17487/RFC5766, April 2010, 576 . 578 [RFC5928] Petit-Huguenin, M., "Traversal Using Relays around NAT 579 (TURN) Resolution Mechanism", RFC 5928, 580 DOI 10.17487/RFC5928, August 2010, 581 . 583 [RFC5986] Thomson, M. and J. Winterbottom, "Discovering the Local 584 Location Information Server (LIS)", RFC 5986, 585 DOI 10.17487/RFC5986, September 2010, 586 . 588 [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, 589 DOI 10.17487/RFC6762, February 2013, 590 . 592 [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service 593 Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, 594 . 596 11.2. Informative References 598 [I-D.ietf-rtcweb-overview] 599 Alvestrand, H., "Overview: Real Time Protocols for 600 Browser-based Applications", draft-ietf-rtcweb-overview-15 601 (work in progress), January 2016. 603 [I-D.ietf-rtcweb-return] 604 Schwartz, B. and J. Uberti, "Recursively Encapsulated TURN 605 (RETURN) for Connectivity and Privacy in WebRTC", draft- 606 ietf-rtcweb-return-01 (work in progress), January 2016. 608 [I-D.ietf-tram-turn-mobility] 609 Wing, D., Patil, P., Reddy, T., and P. Martinsen, 610 "Mobility with TURN", draft-ietf-tram-turn-mobility-02 611 (work in progress), April 2016. 613 [RFC3188] Hakala, J., "Using National Bibliography Numbers as 614 Uniform Resource Names", RFC 3188, DOI 10.17487/RFC3188, 615 October 2001, . 617 [RFC5128] Srisuresh, P., Ford, B., and D. Kegel, "State of Peer-to- 618 Peer (P2P) Communication across Network Address 619 Translators (NATs)", RFC 5128, DOI 10.17487/RFC5128, March 620 2008, . 622 [RFC6024] Reddy, R. and C. Wallace, "Trust Anchor Management 623 Requirements", RFC 6024, DOI 10.17487/RFC6024, October 624 2010, . 626 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and 627 Verification of Domain-Based Application Service Identity 628 within Internet Public Key Infrastructure Using X.509 629 (PKIX) Certificates in the Context of Transport Layer 630 Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March 631 2011, . 633 [RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J., 634 Weiler, S., and T. Kivinen, "Using Raw Public Keys in 635 Transport Layer Security (TLS) and Datagram Transport 636 Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, 637 June 2014, . 639 [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection 640 Most of the Time", RFC 7435, DOI 10.17487/RFC7435, 641 December 2014, . 643 [RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning 644 Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April 645 2015, . 647 Appendix A. Change History 649 [Note to RFC Editor: Please remove this section prior to 650 publication.] 652 A.1. Change from draft-patil-tram-serv-disc-00 to -01 654 o Added IP address (Section 4.1.2) and Own identity (4.1.3) as new 655 means to obtain domain names 657 o New Section 4.2.1 SOA (inspired by draft-kist-alto-3pdisc) 659 o 300 (Try Alternate) response for Anycast 661 A.2. Change from draft-ietf-tram-turn-server-discovery-01 to 02 663 o Removed sections that describe reverse IP lookup 665 o Added DNS Service Discovery as an additional discovery mechanism 667 Authors' Addresses 669 Prashanth Patil 670 Cisco Systems, Inc. 671 Bangalore 672 India 674 Email: praspati@cisco.com 676 Tirumaleswar Reddy 677 Cisco Systems, Inc. 678 Cessna Business Park, Varthur Hobli 679 Sarjapur Marathalli Outer Ring Road 680 Bangalore, Karnataka 560103 681 India 683 Email: tireddy@cisco.com 685 Dan Wing 686 Cisco Systems, Inc. 687 170 West Tasman Drive 688 San Jose, California 95134 689 USA 691 Email: dwing@cisco.com