TRAM                                                            P. Patil
Internet-Draft                                                  T. Reddy
Intended status: Standards Track                                 D. Wing
Expires: January 27, 2017                                          Cisco
                                                           July 26, 2016

                       TURN Server Auto Discovery


   Current Traversal Using Relays around NAT (TURN) server discovery
   mechanisms are relatively static and limited to explicit
   configuration.  These are usually under the administrative control of
   the application or TURN service provider, and not the enterprise,
   ISP, or the network in which the client is located.  Enterprises and
   ISPs wishing to provide their own TURN servers need auto discovery
   mechanisms that a TURN client could use with no or minimal
   configuration.  This document describes three such mechanisms for
   TURN server discovery.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 27, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Discovery Procedure . . . . . . . . . . . . . . . . . . . . .   3
   4.  Discovery using Service Resolution  . . . . . . . . . . . . .   4
     4.1.  Retrieving Domain Name  . . . . . . . . . . . . . . . . .   5
       4.1.1.  DHCP  . . . . . . . . . . . . . . . . . . . . . . . .   5
       4.1.2.  From own Identity . . . . . . . . . . . . . . . . . .   5
     4.2.  Resolution  . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  DNS Service Discovery . . . . . . . . . . . . . . . . . . . .   7
     5.1.  mDNS  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Discovery using Anycast . . . . . . . . . . . . . . . . . . .   8
   7.  Deployment Considerations . . . . . . . . . . . . . . . . . .   9
     7.1.  Mobility and Changing IP addresses  . . . . . . . . . . .   9
     7.2.  Recursively Encapsulated TURN . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Anycast . . . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     9.1.  Service Resolution  . . . . . . . . . . . . . . . . . . .  11
     9.2.  DNS Service Discovery . . . . . . . . . . . . . . . . . .  11
     9.3.  Anycast . . . . . . . . . . . . . . . . . . . . . . . . .  11
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Appendix A.  Change History . . . . . . . . . . . . . . . . . . .  14
     A.1.  Change from draft-patil-tram-serv-disc-00 to -01  . . . .  14
     A.2.  Change from draft-ietf-tram-turn-server-discovery-01 to
           02  . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   TURN [RFC5766] is a protocol that is often used to improve the
   connectivity of Peer-to-Peer (P2P) applications (as defined in
   section 2.7 of [RFC5128]).  TURN allows a connection to be
   established when one or both sides are incapable of a direct P2P
   connection.  It is an important building block for interactive, real-
   time communication using audio, video, collaboration etc.

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   While TURN services are extensively used today, the means to auto
   discover TURN servers do not exist.  TURN clients are usually
   explicitly configured with a well known TURN server.  To allow TURN
   applications to operate seamlessly across different types of networks
   and encourage the use of TURN without the need for manual
   configuration, it is important that there exists an auto discovery
   mechanism for TURN services.  Web Real-Time Communication (WebRTC)
   [I-D.ietf-rtcweb-overview] usages and related extensions, which are
   mostly based on web applications, need this immediately.

   This document describes three discovery mechanisms, so as to maximize
   opportunity for discovery, based on the network in which the TURN
   client finds itself.  The three discovery mechanisms are:

   o  A resolution mechanism based on straightforward Naming Authority
      Pointer (S-NAPTR) resource records in the Domain Name System
      (DNS).  [RFC5928] describes details on retrieving a list of server
      transport addresses from DNS that can be used to create a TURN

   o  DNS Service Discovery

   o  A mechanism based on anycast address for TURN.

   In general, if a client wishes to communicate using one of its
   interfaces using a specific IP address family, it SHOULD query the
   TURN server(s) that has been discovered for that specific interface
   and address family.  How to select an interface and IP address family
   is out of the scope of this document.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in

3.  Discovery Procedure

   TURN clients, by default, discover TURN server(s) by means of local
   or manual TURN configuration i.e., TURN servers configured at the
   system level.  For example, in case of Web Real-Time Communication
   (WebRTC) [I-D.ietf-rtcweb-overview] usages and related extensions,
   which are based on web applications, a Java Script specified TURN
   server MUST be considered as local configuration.  An implementation
   MAY give the user an opportunity (e.g., by means of configuration
   file options or menu items) to specify a TURN server for each address
   family.  A client can choose auto-discovery in the absence of local

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   configuration, if local configuration doesn't work or on top of local
   configuration.  This document does not offer a recommendation on
   server selection.

   A TURN client that implements the auto discovery algorithm, to
   discover TURN servers in the attached network, uses the following
   mechanisms for discovery:

   1.  Service Resolution : The TURN client attempts to perform TURN
       service resolution using the host's DNS domain.

   2.  DNS SD: DNS Service Discovery.

   3.  Anycast : Send TURN allocate request to the assigned TURN anycast
       request for each combination of interface and address family.

   Not all TURN servers may be discovered using NAPTR records or DNS SD;
   Similarly, not all TURN servers may support anycast.  For best
   results, a client SHOULD implement all discovery mechanisms described

   The document does not prescribe a strict order that a client must
   follow for discovery.  An implementation may choose to perform all
   the above steps in parallel for discovery OR choose to follow any
   desired order and stop the discovery procedure if a mechanism

   On hosts with more than one interface or address family (IPv4/v6),
   the TURN server discovery procedure has to be performed for each
   combination of interface and address family.  A client MAY optionally
   choose to perform the discovery procedure only for a desired
   interface/address combination if the client does not wish to discover
   a TURN server for all combinations of interface and address family.

4.  Discovery using Service Resolution

   This mechanism is performed in two steps:

   1.  A DNS domain name is retrieved for each combination of interface
   and address family.

   2.  Retrieved DNS domain names are then used for S-NAPTR lookups as
   per [RFC5928].  Further DNS lookups may be necessary to determine
   TURN server IP address(es).

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4.1.  Retrieving Domain Name

   A client has to determine the domain in which it is located.  The
   following sections provide two possible mechanisms to learn the
   domain name, but other means of retrieving domain names may be used,
   which are outside the scope of this document e.g. local

   Implementations may allow the user to specify a default name that is
   used if no specific name has been configured.

4.1.1.  DHCP

   DHCP can be used to determine the domain name related to an
   interface's point of network attachment.  Network operators may
   provide the domain name to be used for service discovery within an
   access network using DHCP.  Sections 3.2 and 3.3 of [RFC5986] define
   DHCP IPv4 and IPv6 access network domain name options to identify a
   domain name that is suitable for service discovery within the access
   network.  [RFC2132] defines the DHCP IPv4 domain name option; While
   this option is less suitable, it may still be useful if the options
   defined in [RFC5986] are not available.

   For IPv6, the TURN server discovery procedure MUST try to retrieve
   DHCP option 57 (OPTION_V6_ACCESS_DOMAIN).  If no such option can be
   retrieved, the procedure fails for this interface.  For IPv4, the
   TURN server discovery procedure MUST try to retrieve DHCP option 213
   (OPTION_V4_ACCESS_DOMAIN).  If no such option can be retrieved, the
   procedure SHOULD try to retrieve option 15 (Domain Name).  If neither
   option can be retrieved the procedure fails for this interface.  If a
   result can be retrieved it will be used as an input for S-NAPTR

4.1.2.  From own Identity

   For a TURN client with an understanding of the protocol mechanics of
   calling applications, the client may wish to extract the domain name
   from its own identity i.e canonical identifier used to reach the


   SIP   : ''
   JID   : ''
   email : ''

   '' is retrieved from the above examples.

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   The means to extract the domain name may be different based on the
   type of identifier and is outside the scope of this document.

4.2.  Resolution

   Once the TURN discovery procedure has retrieved domain names, the
   resolution mechanism described in [RFC5928] is followed.  An S-NAPTR
   lookup with 'RELAY' application service and the desired protocol tag
   is made to obtain information necessary to connect to the
   authoritative TURN server within the given domain.

   In the example below, for domain '', the resolution
   algorithm will result in IP address, port, and protocol tuples as
      IN NAPTR 100 10 "" RELAY:turn.udp ""
      IN NAPTR 100 10 S RELAY:turn.udp ""
      IN SRV   0 0 3478
      IN A
      IN AAAA     2001:db8:8:4::2

                    | Order | Protocol | IP address       | Port |
                    | 1     | UDP      |        | 3478 |
                    | 2     | UDP      |  2001:db8:8:4::2 | 3478 |

   If no TURN-specific S-NAPTR records can be retrieved, the discovery
   procedure fails for this domain name (and the corresponding interface
   and IP protocol version).  If more domain names are known, the
   discovery procedure may perform the corresponding S-NAPTR lookups
   immediately.  However, before retrying a lookup that has failed, a
   client MUST wait a time period that is appropriate for the
   encountered error (NXDOMAIN, timeout, etc.).

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5.  DNS Service Discovery

   DNS-based Service Discovery (DNS-SD) [RFC6763] and Multicast DNS
   (mDNS) [RFC6762] provide generic solutions for discovering services
   available in a local network.  DNS-SD/ mDNS define a set of naming
   rules for certain DNS record types that they use for advertising and
   discovering services.  PTR records are used to enumerate service
   instances of a given service type.  A service instance name is mapped
   to a host name and a port number using a SRV record.  If a service
   instance has more information to advertise than the host name and
   port number contained in its SRV record, the additional information
   is carried in a TXT record.

   Section 4.1 of [RFC6763] specifies that a service instance name in
   DNS-SD has the following structure:

   <Instance> . <Service> . <Domain>

   The <Domain> portion specifies the DNS sub-domain where the service
   instance is registered.  It may be "local.", indicating the mDNS
   local domain, or it may be a conventional domain name such as
   "".  The <Service> portion of the TURN service instance
   name MUST be "_turnserver._udp", "_turnserver._tcp".

   The <Instance> portion is a DNS label, containing UTF-8-encoded text
   [RFC5198], limited to 63 octets in length.  It is meant to be a user-
   friendly description of the service instance, suitable for a menu-
   like user interface display.  Thus it can contain any characters
   including spaces, punctuation, and non-Latin characters as long as
   they can be encoded in UTF-8.

   For example, TURN server advertises the following DNS records :

      _turnserver._udp.local.  PTR  SRV 0 0 5030 example-turn-

      example-turn-server.local.  A

      example-turn-server.local.  AAAA 2001:db8:8:4::2

   In addition to the service instance name, IP address and the port
   number, DNS-SD provides a way to publish other information pertinent
   to the service being advertised.  The additional data can be stored
   as name/value attributes in a TXT record with the same name as the
   SRV record for the service.  Each name/value pair within the TXT
   record is preceded by a single length byte, thereby limiting the

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   length of the pair to 255 bytes (See Section 6 of [RFC6763] and
   Section 3.3.14 of [RFC1035] for details).

5.1.  mDNS

   A TURN client tries to discover the TURN servers being advertised in
   the site by multicasting a PTR query "_turnserver._udp.local." or
   "_turnserver._tcp.local" or the TURN server can send out gratuitous
   multicast DNS answer packets whenever it starts up, wakes from sleep,
   or detects a chance in network configuration.  TURN clients receive
   these gratuitous packet and cache the information contained in it.

        +------+                                  +-------------+
        | TURN |                                  | TURN Server |
        |Client|                                  |             |
        +------+                                  +-------------+
          |                                              |
          | PTR query "_turnserver._udp.local."          |
          | PTR reply                                    |
          | SRV query                                    |
          | SRV reply                                    |
          | A/AAAA query reply                           |
          | TURN Request                                 |
          | TURN Response                                |

             Figure 1: TURN Server Discovery using mDNS

6.  Discovery using Anycast

   IP anycast can also be used for TURN service discovery.  A packet
   sent to an anycast address is delivered to the "topologically
   nearest" network interface with the anycast address.  Using the TURN
   anycast address, the only two things that need to be deployed in the
   network are the two things that actually use TURN.

   When a client requires TURN services, it sends a TURN allocate
   request to the assigned anycast address.  The TURN anycast server
   responds with a 300 (Try Alternate) error as described in [RFC5766];
   The response contains the TURN unicast address in the ALTERNATE-
   SERVER attribute.  For subsequent communication with the TURN server,
   the client uses the responding server's unicast address.  This has to

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   be done because two packets addressed to an anycast address may reach
   two different anycast servers.  The client, thus, also needs to
   ensure that the initial request fits in a single packet.  An
   implementation may choose to send out every new request to the
   anycast address to learn the closest TURN server each time.

7.  Deployment Considerations

7.1.  Mobility and Changing IP addresses

   A change of IP address on an interface may invalidate the result of
   the TURN server discovery procedure.  For instance, if the IP address
   assigned to a mobile host changes due to host mobility, it may be
   required to re-run the TURN server discovery procedure without
   relying on earlier gained information.  New requests should be made
   to the newly learned TURN servers learned after TURN discovery re-
   run.  However, if an earlier learned TURN server is still accessible
   using the new IP address, procedures described for mobility using
   TURN defined in [I-D.ietf-tram-turn-mobility] can be used for ongoing

7.2.  Recursively Encapsulated TURN

   WebRTC endpoints SHOULD treat any TURN server discovered through the
   mechanims described in this specification as an enterprise/gateway
   server, in accordance with Recursively Encapsulated TURN

8.  IANA Considerations

8.1.  Anycast

   IANA should allocate an IPv4 and an IPv6 well-known TURN anycast
   address. and 2001:0000::/48 are reserved for IETF
   Protocol Assignments, as listed at

   <> and


9.  Security Considerations

   Use of STUN authentication is OPTIONAL for TURN servers provided by
   the local network or by the access network.  A network provided TURN
   server MAY be configured to accept Allocation requests without STUN
   authentication, and a TURN client MAY be configured to accept
   Allocation success responses without STUN authentication from a
   network provided TURN server.  In order to protect against man-in-

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   the-middle attacks when accepting a TURN allocation response without
   STUN authentication, it is RECOMMENDED that the TURN client use one
   of the following techniques with (D)TLS to validate the TURN server:

   o  For certificate-based authentication, a pre-populated trust anchor
      store [RFC6024] allows a TURN client to perform path validation
      for the server certificate obtained during the (D)TLS handshake.
      If the client used a domain name to discover the TURN server, that
      domain name also provides a mechanism for validation of the TURN
      server.  The client MUST use the rules and guidelines given in
      section 6 of [RFC6125] to validate the TURN server identity.

   o  For TURN servers that don't have a certificate trust chain (e.g.,
      because they are on a home network or a corporate network), a
      configured list of TURN servers can contain the Subject Public Key
      Info (SPKI) fingerprint of the TURN servers.  The public key is
      used for the same reasons HTTP pinning [RFC7469] uses the public

   o  Raw public key-based authentication, as defined in [RFC7250],
      could also be used to authenticate a TURN server.

   An auto-discovered TURN server is considered to be only as trusted as
   the path between the client and the TURN server.  In order to safely
   use auto-discovered TURN servers for sessions with 'strict privacy'
   requirements, the user needs to be able to define privacy criteria
   (e.g.  a trusted list of servers, networks, or domains) that are
   considered acceptable for such traffic.  Any discovered TURN server
   outside the criteria is considered untrusted and is not used for
   privacy sensitive communication.

   In some auto-discovery scenarios, it might not be possible for the
   TURN client to use (D)TLS authentication to validate the TURN server.
   However, fall-back to clear text in such cases could leave the TURN
   client open to on-path injection of spoofed TURN messages.  For this
   reason, it is beneficial for the TURN client to make use of
   'opportunistic privacy', analogous to SMTP opportunistic encryption
   [RFC7435], where one does not require privacy but one desires privacy
   when possible.  In this scenario, a TURN client attempts (D)TLS with
   authentication and encryption, falling back to encryption-only if the
   TURN server cannot be authenticated via (D)TLS.  If the TURN server
   does not support unauthenticated (D)TLS, it could fall back to clear
   text, but fallback to clear text is NOT RECOMMENDED because it makes
   the client more susceptible to man-in-the-middle attacks and on-path
   packet injection.  A TURN client SHOULD fall-back to encryption-only
   (D)TLS when (D)TLS authentication is not available in order to
   protect against on-path attackers who might attempt to inject fake
   TURN messages.

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9.1.  Service Resolution

   The primary attack against the methods described in this document is
   one that would lead to impersonation of a TURN server.  An attacker
   could attempt to compromise the S-NAPTR resolution.  Security
   considerations described in [RFC5928] are applicable here as well.

   In addition to considerations related to S-NAPTR, it is important to
   recognize that the output of this is entirely dependent on its input.
   An attacker who can control the domain name can also control the
   final result.  Because more than one method can be used to determine
   the domain name, a host implementation needs to consider attacks
   against each of the methods that are used.

   If DHCP is used, the integrity of DHCP options is limited by the
   security of the channel over which they are provided.  Physical
   security and separation of DHCP messages from other packets are
   commonplace methods that can reduce the possibility of attack within
   an access network; alternatively, DHCP authentication [RFC3188] can
   provide a degree of protection against modification.  When using DHCP
   discovery, clients are encouraged to use unicast DHCP INFORM queries
   instead of broadcast queries which are more easily spoofed in
   insecure networks.

9.2.  DNS Service Discovery

   Since DNS-SD is just a specification for how to name and use records
   in the existing DNS system, it has no specific additional security
   requirements over and above those that already apply to DNS queries
   and DNS updates.  For DNS queries, DNS Security Extensions (DNSSEC)
   [RFC4033] should be used where the authenticity of information is
   important.  For DNS updates, secure updates [RFC2136][RFC3007] should
   generally be used to control which clients have permission to update
   DNS records.

   For mDNS, in addition to what has been described above, a principal
   security threat is a security threat inherent to IP multicast routing
   and any application that runs on it.  A rogue system can advertise
   that it is a TURN server.  Discovery of such rogue systems as TURN
   servers, in itself, is not a security threat if there is a means for
   the TURN client to authenticate and authorize the discovered TURN

9.3.  Anycast

   In a network without any TURN server that is aware of the TURN
   anycast address, outgoing TURN requests could leak out onto the
   external Internet, possibly revealing information.

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   Using an IANA-assigned well-known TURN anycast address enables border
   gateways to block such outgoing packets.  In the default-free zone,
   routers should be configured to drop such packets.  Such
   configuration can occur naturally via BGP messages advertising that
   no route exists to said address.

   Sensitive clients that do not wish to leak information about their
   presence can set an IP TTL on their TURN requests that limits how far
   they can travel into the public Internet.

10.  Acknowledgements

   The authors would like to thank Simon Perrault, Paul Kyzivat, Troy
   Shields, Eduardo Gueiros, Ted Hardie, Bernard Aboba, Karl Stahl and
   Brandon Williams for their review and valuable comments.  Thanks to
   Adam Roach for his detailed review and suggesting DNS Service
   Discovery as an additional discovery mechanism.

11.  References

11.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,

   [RFC2136]  Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, DOI 10.17487/RFC2136, April 1997,

   [RFC3007]  Wellington, B., "Secure Domain Name System (DNS) Dynamic
              Update", RFC 3007, DOI 10.17487/RFC3007, November 2000,

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,

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   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,

   [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)", RFC 5766,
              DOI 10.17487/RFC5766, April 2010,

   [RFC5928]  Petit-Huguenin, M., "Traversal Using Relays around NAT
              (TURN) Resolution Mechanism", RFC 5928,
              DOI 10.17487/RFC5928, August 2010,

   [RFC5986]  Thomson, M. and J. Winterbottom, "Discovering the Local
              Location Information Server (LIS)", RFC 5986,
              DOI 10.17487/RFC5986, September 2010,

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013,

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,

11.2.  Informative References

              Alvestrand, H., "Overview: Real Time Protocols for
              Browser-based Applications", draft-ietf-rtcweb-overview-15
              (work in progress), January 2016.

              Schwartz, B. and J. Uberti, "Recursively Encapsulated TURN
              (RETURN) for Connectivity and Privacy in WebRTC", draft-
              ietf-rtcweb-return-01 (work in progress), January 2016.

              Wing, D., Patil, P., Reddy, T., and P. Martinsen,
              "Mobility with TURN", draft-ietf-tram-turn-mobility-02
              (work in progress), April 2016.

   [RFC3188]  Hakala, J., "Using National Bibliography Numbers as
              Uniform Resource Names", RFC 3188, DOI 10.17487/RFC3188,
              October 2001, <>.

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   [RFC5128]  Srisuresh, P., Ford, B., and D. Kegel, "State of Peer-to-
              Peer (P2P) Communication across Network Address
              Translators (NATs)", RFC 5128, DOI 10.17487/RFC5128, March
              2008, <>.

   [RFC6024]  Reddy, R. and C. Wallace, "Trust Anchor Management
              Requirements", RFC 6024, DOI 10.17487/RFC6024, October
              2010, <>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <>.

   [RFC7250]  Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
              Weiler, S., and T. Kivinen, "Using Raw Public Keys in
              Transport Layer Security (TLS) and Datagram Transport
              Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
              June 2014, <>.

   [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
              Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
              December 2014, <>.

   [RFC7469]  Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
              Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April
              2015, <>.

Appendix A.  Change History

   [Note to RFC Editor: Please remove this section prior to

A.1.  Change from draft-patil-tram-serv-disc-00 to -01

   o  Added IP address (Section 4.1.2) and Own identity (4.1.3) as new
      means to obtain domain names

   o  New Section 4.2.1 SOA (inspired by draft-kist-alto-3pdisc)

   o  300 (Try Alternate) response for Anycast

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A.2.  Change from draft-ietf-tram-turn-server-discovery-01 to 02

   o  Removed sections that describe reverse IP lookup

   o  Added DNS Service Discovery as an additional discovery mechanism

Authors' Addresses

   Prashanth Patil
   Cisco Systems, Inc.


   Tirumaleswar Reddy
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103


   Dan Wing
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, California  95134


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