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Versions: (draft-wing-tram-turn-mobility) 00 01 02 03 04 05 06 07 08 09 RFC 8016

TRAM                                                            T. Reddy
Internet-Draft                                                   D. Wing
Intended status: Standards Track                                P. Patil
Expires: March 13, 2017                                     P. Martinsen
                                                                   Cisco
                                                       September 9, 2016


                           Mobility with TURN
                    draft-ietf-tram-turn-mobility-09

Abstract

   It is desirable to minimize traffic disruption caused by changing IP
   address during a mobility event.  One mechanism to minimize
   disruption is to expose a shorter network path to the mobility event
   so only the local network elements are aware of the changed IP
   address but the remote peer is unaware of the changed IP address.

   This draft provides such an IP address mobility solution using
   Traversal Using Relays around NAT (TURN).  This is achieved by
   allowing a client to retain an allocation on the TURN server when the
   IP address of the client changes.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 March 13, 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



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   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.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   3
   3.  Mobility using TURN . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Creating an Allocation  . . . . . . . . . . . . . . . . .   5
       3.1.1.  Sending an Allocate Request . . . . . . . . . . . . .   5
       3.1.2.  Receiving an Allocate Request . . . . . . . . . . . .   6
       3.1.3.  Receiving an Allocate Success Response  . . . . . . .   6
       3.1.4.  Receiving an Allocate Error Response  . . . . . . . .   6
     3.2.  Refreshing an Allocation  . . . . . . . . . . . . . . . .   7
       3.2.1.  Sending a Refresh Request . . . . . . . . . . . . . .   7
       3.2.2.  Receiving a Refresh Request . . . . . . . . . . . . .   7
       3.2.3.  Receiving a Refresh Response  . . . . . . . . . . . .   9
     3.3.  New STUN Attribute MOBILITY-TICKET  . . . . . . . . . . .   9
     3.4.  New STUN Error Response Code  . . . . . . . . . . . . . .   9
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Implementation Status . . . . . . . . . . . . . . . . . . . .   9
     5.1.  open-sys  . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Example ticket construction  . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   When moving between networks, the endpoint's IP address can change or
   (due to NAT) the endpoint's public IP address can change.  Such a
   change of IP address breaks upper layer protocols such as TCP and
   RTP.  Various techniques exist to prevent this breakage, all tied to
   making the endpoint's IP address static (e.g., Mobile IP, Proxy
   Mobile IP, LISP).  Other techniques exist, which make the change in
   IP address agnostic to the upper layer protocol (e.g., SCTP).  The
   mechanism described in this document are in that last category.

   A Traversal Using Relays around NAT (TURN) [RFC5766] server relays
   media packets and is used for a variety of purposes, including



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   overcoming NAT and firewall traversal issues.  The existing TURN
   specification does not permit a TURN client to reuse an allocation
   across client IP address changes.  Due to this, when the IP address
   of the client changes, the TURN client has to request a new
   allocation, create permissions for the remote peer, create channels
   etc.  In addition the client has to re-establish communication with
   its signaling server, send an updated offer to the remote peer
   conveying the new relayed candidate address, remote side has to
   regather all candidates and signal them to the client and then the
   endpoints have to perform Interactive Connectivity Establishment
   (ICE) [RFC5245] connectivity checks.  If ICE continuous nomination
   procedure [I-D.uberti-mmusic-nombis] is used then new relayed
   candidate address would have to be trickled
   [I-D.ietf-mmusic-trickle-ice] and ICE connectivity checks have to be
   performed by the endpoints to nominate pairs that will be selected by
   ICE.

   This specification describes a mechanism to seamlessly reuse
   allocations across client IP address changes without any of the
   hassles described above.  A critical benefit of this technique is
   that the remote peer does not have to support mobility, or deal with
   any of the address changes.  The client, that is subject to IP
   address changes, does all the work.  The mobility technique works
   across and between network types (e.g., between 3G and wired Internet
   access), so long as the client can still access the TURN server.  The
   technique should also work seamlessly when (D)TLS is used as a
   transport protocol for Session Traversal Utilities for NAT (STUN)
   [RFC5389].  When there is a change in IP address, the client uses
   (D)TLS Session Resumption without Server-Side State as described in
   [RFC5077] to resume secure communication with the TURN server, using
   the changed client IP address.

2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This note uses terminology defined in [RFC5245], and the following
   additional terminology:

   Break Before Make: The old communication path is broken ("break")
   before new communication can be created ("make").  Such changes
   typically occur because a network is disconnected with a physical
   cable, turning radio off, or moving out of radio range.

   Make Before Break: A new communication path is created ("make")
   before the old communication path is broken ("break").  Such changes



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   typically occur because a network is connected with a physical cable,
   turning radio on, or moving into radio range.

3.  Mobility using TURN

   To achieve mobility, a TURN client should be able to retain an
   allocation on the TURN server across changes in the client IP address
   as a consequence of movement to other networks.

   When the client sends the initial Allocate request to the TURN
   server, it will include a new STUN attribute MOBILITY-TICKET (with
   zero length value), which indicates that the client is capable of
   mobility and desires a ticket.  The TURN server provisions a ticket
   that is sent inside the new STUN attribute MOBILITY-TICKET in the
   Allocate Success response to the client.  The ticket will be used by
   the client when it wants to refresh the allocation but with a new
   client IP address and port.  This ensures that an allocation can only
   be refreshed by the same client that allocated relayed transport
   address.  When a client's IP address changes due to mobility, it
   presents the previously obtained ticket in a Refresh Request to the
   TURN server.  If the ticket is found to be valid, the TURN server
   will retain the same relayed address/port for the new IP address/port
   allowing the client to continue using previous channel bindings --
   thus, the TURN client does not need to obtain new channel bindings.
   Any data from external peer will be delivered by the TURN server to
   this new IP address/port of the client.  The TURN client will
   continue to send application data to its peers using the previously
   allocated channelBind Requests.























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          TURN                                 TURN           Peer
          client                               server          A
            |-- Allocate request --------------->|             |
            |   + MOBILITY-TICKET (length=0)     |             |
            |                                    |             |
            |<--------------- Allocate failure --|             |
            |                 (401 Unauthorized) |             |
            |                                    |             |
            |-- Allocate request --------------->|             |
            |   + MOBILITY-TICKET (length=0)     |             |
            |                                    |             |
            |<---------- Allocate success resp --|             |
            |            + MOBILITY-TICKET       |             |
           ...                                  ...           ...
        (changes IP address)
            |                                    |             |
            |-- Refresh request ---------------->|             |
            |   + MOBILITY-TICKET                |             |
            |                                    |             |
            |<----------- Refresh success resp --|             |
            |   + MOBILITY-TICKET                |             |
            |                                    |             |

                       Figure 1: Mobility using TURN

   In Figure 1, the client sends an Allocate request with an MOBILITY-
   TICKET attribute to the server without credentials.  Since the server
   requires that all requests be authenticated using STUN's long-term
   credential mechanism, the server rejects the request with a 401
   (Unauthorized) error code.  The client then tries again, this time
   including credentials (not shown).  This time, the server accepts the
   Allocate request and returns an Allocate success response and a
   ticket inside the MOBILITY-TICKET attribute.  Sometime later, the
   client IP address changes and decides to refresh the allocation and
   thus sends a Refresh request to the server with MOBILITY-TICKET
   attribute containing the ticket it had received from the server.  The
   refresh is accepted and the server replies with a Refresh success
   response and a new ticket inside the MOBILITY-TICKET attribute.

3.1.  Creating an Allocation

3.1.1.  Sending an Allocate Request

   In addition to the process described in Section 6.1 of [RFC5766], the
   client includes the MOBILITY-TICKET attribute with length 0.  This
   indicates the client is a mobile node and wants a ticket.





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3.1.2.  Receiving an Allocate Request

   In addition to the process described in Section 6.2 of [RFC5766], the
   server does the following:

   If the MOBILITY-TICKET attribute is included, and has length zero,
   but TURN session mobility is forbidden by local policy, the server
   will reject the request with the new Mobility Forbidden error code.
   If the MOBILITY-TICKET attribute is included and has non-zero length
   then the server will generate an error response with an error code of
   400 (Bad Request).  Following the rules specified in [RFC5389], if
   the server does not understand the MOBILITY-TICKET attribute, it
   ignores the attribute.

   If the server can successfully process the request and create an
   allocation, the server replies with a success response that includes
   a STUN MOBILITY-TICKET attribute.  TURN server can store system
   internal data into the ticket that is encrypted by a key known only
   to the TURN server and sends the ticket in the STUN MOBILITY-TICKET
   attribute as part of Allocate success response.  An example for
   ticket construction is discussed in Appendix A .The ticket is opaque
   to the client, so the structure is not subject to interoperability
   concerns, and implementations may diverge from this format.  The
   client could be roaming across networks with different path MTU and
   from one address family to another (e.g.  IPv6 to IPv4).  The TURN
   server to support mobility must assume that the path MTU is unknown
   and use a ticket length in accordance with published guidance on STUN
   UDP fragmentation (Section 7.1 of [RFC5389]).

   Note: There is no guarantee that the fields in the ticket are going
   to be decodable to a client, and therefore attempts by a client to
   examine the ticket are unlikely to be useful.

3.1.3.  Receiving an Allocate Success Response

   In addition to the process described in Section 6.3 of [RFC5766], the
   client will store the MOBILITY-TICKET attribute, if present, from the
   response.  This attribute will be presented by the client to the
   server during a subsequent Refresh request to aid mobility.

3.1.4.  Receiving an Allocate Error Response

   If the client receives an Allocate error response with error code TBD
   (Mobility Forbidden), the error is processed as follows:

   o TBD (Mobility Forbidden): The request is valid, but the server is
   refusing to perform it, likely due to administrative restrictions.
   The client considers the current transaction as having failed.  The



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   client can notify the user or operator.  The client SHOULD NOT retry
   to send Allocate request containing MOBILITY-TICKET with this server
   until it believes the problem has been fixed.

   All other error responses must be handled as described in [RFC5766].

3.2.  Refreshing an Allocation

3.2.1.  Sending a Refresh Request

   If a client wants to refresh an existing allocation and update its
   time-to-expiry or delete an existing allocation, it sends a Refresh
   Request as described in Section 7.1 of [RFC5766].  If IP address or
   source port number of the client has changed and the client wants to
   retain the existing allocation, the client includes the MOBILITY-
   TICKET attribute received in the Allocate Success response in the
   Refresh Request.  If there has been no IP address or source port
   number change, the client MUST NOT include a MOBILITY-TICKET
   attribute, as this will be rejected by the server and the client
   would need to retransmit the Refresh Request without the MOBILITY-
   TICKET attribute.

3.2.2.  Receiving a Refresh Request

   In addition to the process described in Section 7.2 of [RFC5766], the
   server does the following:

   If the STUN MOBILITY-TICKET attribute is included in the Refresh
   Request and the server configuration changed to forbid mobility or
   the server transparently fails-over to another server instance that
   forbids mobility then the server rejects the Refresh request with a
   Mobility Forbidden error code and the client starts afresh with a new
   allocation.

   If the STUN MOBILITY-TICKET attribute is included in the Refresh
   Request then the server will not retrieve the 5-tuple from the packet
   to identify an associated allocation.  Instead the TURN server will
   decrypt the received ticket, verify the ticket's validity and
   retrieve the 5-tuple allocation using the ticket.  If this 5-tuple
   obtained does not identify an existing allocation then the server
   MUST reject the request with a 437 (Allocation Mismatch) error.  If
   the ticket is invalid then the server MUST reject the request with a
   400 (Bad Request) error.

   If the source IP address and port of the Refresh Request with STUN
   MOBILITY-TICKET attribute is same as the stored 5-tuple allocation
   then the TURN server rejects the request with 400 (Bad Request)
   error.  If the source IP address and port of the Refresh Request is



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   different from the stored 5-tuple allocation, the TURN server
   proceeds with MESSAGE-INTEGRITY validation to identify the that it is
   the same user which had previously created the TURN allocation.  If
   the above check is not successful then server MUST reject the request
   with a 441 (Wrong Credentials) error.

   If all of the above checks pass, the TURN server understands that the
   client has either moved to a new network and acquired a new IP
   address (Break Before Make) or is in the process of switching to a
   new interface (Make Before Break).  The source IP address of the
   request could either be the host transport address or server-
   reflexive transport address.  The server then updates its state data
   with the new client IP address and port but does not discard the old
   5-tuple from its state data.  TURN server calculates the ticket with
   the new 5-tuple and sends the new ticket in the STUN MOBILITY-TICKET
   attribute as part of Refresh Success response.  The new ticket sent
   in the refresh response MUST be different from the old ticket.

   The TURN server MUST continue receiving and processing data on the
   old 5-tuple and MUST continue transmitting data on the old-5 tuple
   until it receives an Send Indication or ChannelData message from the
   client on the new 5-tuple or an message from the client to close the
   old connection (e.g., a TLS fatal alert, TCP RST).  After receiving
   any of those messages, a TURN server discards the the old ticket and
   the old 5-tuple associated with the old ticket from its state data.
   Data sent by the client to the peer is accepted on the new 5-tuple
   and data received from the peer is forwarded to the new 5-tuple.  If
   the refresh request containing the MOBILITY-TICKET attribute does not
   succeed (e.g., packet lost if the request is sent over UDP, or the
   server being unable to fulfill the request) then the client can
   continue to exchange data on the old 5-tuple until it receives
   Refresh success response.

   The old ticket can only be used for the purposes of retransmission.
   If the client wants to refresh its allocation with a new server-
   reflexive transport address, it MUST use the new ticket.  If the TURN
   server has not received a Refresh Request with STUN MOBILITY-TICKET
   attribute but receives Send indications or ChannelData messages from
   a client, the TURN server MAY discard or queue those Send indications
   or ChannelData messages (at its discretion).  Thus, it is RECOMMENDED
   that the client avoid transmitting a Send indication or ChannelData
   message until it has received an acknowledgement for the Refresh
   Request with STUN MOBILITY-TICKET attribute.

   To accommodate for loss of Refresh responses, a server must retain
   the old STUN MOBILITY-TICKET attribute for a period of at least 30
   seconds to be able to recognize a retransmission of Refresh request
   with the old STUN MOBILITY-TICKET attribute from the client.



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3.2.3.  Receiving a Refresh Response

   In addition to the process described in Section 7.3 of [RFC5766], the
   client will store the MOBILITY-TICKET attribute, if present, from the
   response.  This attribute will be presented by the client to the
   server during a subsequent Refresh Request to aid mobility.

3.3.  New STUN Attribute MOBILITY-TICKET

   This attribute is used to retain an Allocation on the TURN server.
   It is exchanged between the client and server to aid mobility.  The
   value of MOBILITY-TICKET is encrypted and is of variable-length.

3.4.  New STUN Error Response Code

   This document defines the following new error response code:

      TBD Mobility Forbidden: Mobility request was valid but cannot be
      performed due to administrative or similar restrictions.

4.  IANA Considerations

   [Note to RFC editor: Please update sections 3.1.4 and 3.4 with the
   error number.]

   IANA is requested to add the following attributes to the STUN
   attribute registry [iana-stun],

   o  MOBILITY-TICKET (0x8030, in the comprehension-optional range)

   and to add a new STUN error code "Mobility Forbidden" with the value
   405 to the STUN Error Codes registry [iana-stun].

5.  Implementation Status

   [Note to RFC Editor: Please remove this section and reference to
   [RFC6982] prior to publication.]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC6982].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their



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   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC6982], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

5.1.  open-sys

   Organization:   This is a public project, the full list of authors
      and contributors here: http://turnserver.open-sys.org/downloads/
      AUTHORS

   Description:   A mature open-source TURN server specs implementation
      (RFC 5766, RFC 6062, RFC 6156, etc) designed for high-performance
      applications, especially geared for WebRTC.

   Implementation:   http://code.google.com/p/rfc5766-turn-server/

   Level of maturity:   The Mobile ICE feature implementation can be
      qualified as "production" - it is well tested and fully
      implemented, but not widely used, yet..

   Coverage:   Fully implements Mobility with TURN.

   Licensing:   BSD: http://turnserver.open-sys.org/downloads/LICENSE

   Implementation experience:   Mobility with TURN implementation is
      somewhat challenging for a multi-threaded performance-oriented
      application (because the mobile ticket information must be shared
      between the threads) but it is doable.

   Contact:   Oleg Moskalenko <mom040267@gmail.com>.

6.  Security Considerations

   TURN server MUST always ensure that the ticket is authenticated and
   encrypted using strong cryptographic algorithms to prevent
   modification or eavesdropping by an attacker.  The ticket MUST be
   constructed such that it has strong entropy to ensure nothing can be
   gleaned by looking at the ticket alone.

   An attacker monitoring the traffic between the TURN client and server
   can impersonate the client and refresh the allocation using the
   ticket issued to the client with the attackers IP address and port.



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   TURN client and server MUST use STUN long-term credential mechanism
   [RFC5389] or STUN Extension for Third-Party Authorization
   [RFC7635][RFC7635] or (D)TLS connection to avoid malicious users
   trying to impersonate the client.  With any of those three
   mechanisms, when the server receives Refresh Request with STUN
   MOBILITY-TICKET attribute from the client it identifies that it is
   indeed the same client but with a new IP address and port using the
   ticket it had previously issued to refresh the allocation.  If (D)TLS
   is not used or (D)TLS handshake fails, and authentication also fails
   then TURN client and server MUST fail, and not proceed with TURN
   mobility.

   Security considerations described in [RFC5766] are also applicable to
   this mechanism.

7.  Acknowledgements

   Thanks to Alfred Heggestad, Lishitao, Sujing Zhou, Martin Thomson,
   Emil Ivov, Oleg Moskalenko, Dave Waltermire, Pete Resnick, Antoni
   Przygienda, Alissa Cooper, Ben Campbell, Suresh Krishnan, Mirja
   Kuehlewind, Jonathan Lennox and Brandon Williams for review and
   comments.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC5077]  Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
              "Transport Layer Security (TLS) Session Resumption without
              Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
              January 2008, <http://www.rfc-editor.org/info/rfc5077>.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              DOI 10.17487/RFC5245, April 2010,
              <http://www.rfc-editor.org/info/rfc5245>.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              DOI 10.17487/RFC5389, October 2008,
              <http://www.rfc-editor.org/info/rfc5389>.




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   [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,
              <http://www.rfc-editor.org/info/rfc5766>.

8.2.  Informative References

   [I-D.ietf-mmusic-trickle-ice]
              Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE:
              Incremental Provisioning of Candidates for the Interactive
              Connectivity Establishment (ICE) Protocol", draft-ietf-
              mmusic-trickle-ice-02 (work in progress), January 2015.

   [I-D.uberti-mmusic-nombis]
              Uberti, J. and J. Lennox, "Improvements to ICE Candidate
              Nomination", draft-uberti-mmusic-nombis-00 (work in
              progress), March 2015.

   [iana-stun]
              IANA, , "IANA: STUN Attributes", April 2011,
              <http://www.iana.org/assignments/stun-parameters/stun-pa
              rameters.xml>.

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982,
              DOI 10.17487/RFC6982, July 2013,
              <http://www.rfc-editor.org/info/rfc6982>.

   [RFC7635]  Reddy, T., Patil, P., Ravindranath, R., and J. Uberti,
              "Session Traversal Utilities for NAT (STUN) Extension for
              Third-Party Authorization", RFC 7635,
              DOI 10.17487/RFC7635, August 2015,
              <http://www.rfc-editor.org/info/rfc7635>.

Appendix A.  Example ticket construction

   The TURN server uses two different keys: one 128-bit key for Advance
   Encryption Standard (AES) in Cipher Block Chaining (CBC) mode
   (AES_128_CBC) and 256-bit key for HMAC-SHA-256-128 for integrity
   protection.  The ticket can be structured as follows:










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         struct {
             opaque key_name[16];
             opaque iv[16];
             opaque encrypted_state<0..2^16-1>;
             opaque mac[16];
         } ticket;

                          Figure 2: Ticket Format

   Here, key_name serves to identify a particular set of keys used to
   protect the ticket.  It enables the TURN server to easily recognize
   tickets it has issued.  The key_name should be randomly generated to
   avoid collisions between servers.  One possibility is to generate new
   random keys and key_name every time the server is started.

   The TURN state information (self-contained or handle) in
   encrypted_state is encrypted using 128-bit AES in CBC mode with the
   given IV.  The MAC is calculated using HMAC-SHA-256-128 over key_name
   (16 octets)and IV (16 octets), followed by the length of the
   encrypted_state field (2 octets) and its contents (variable length).

Authors' Addresses

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

   Email: tireddy@cisco.com


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

   Email: dwing@cisco.com


   Prashanth Patil
   Cisco Systems, Inc.
   Bangalore
   India

   Email: praspati@cisco.com



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   Paal-Erik Martinsen
   Cisco Systems, Inc.
   Philip Pedersens vei 22
   Lysaker, Akershus  1325
   Norway

   Email: palmarti@cisco.com












































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