[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07

MMUSIC                                                           D. Wing
Internet-Draft                                                  P. Patil
Intended status: Standards Track                                T. Reddy
Expires: April 9, 2013                                      P. Martinsen
                                                                   Cisco
                                                         October 6, 2012


                        Mobility with ICE (MICE)
                   draft-wing-mmusic-ice-mobility-02

Abstract

   This specification describes how endpoint mobility can be achieved
   using ICE.  Two mechanisms are shown, one where both endpoints
   support ICE and another where only one endpoint supports ICE.

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 April 9, 2013.

Copyright Notice

   Copyright (c) 2012 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
   (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.



Wing, et al.              Expires April 9, 2013                 [Page 1]


Internet-Draft                    MICE                      October 2012


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Notational Conventions . . . . . . . . . . . . . . . . . . . .  4
   3.  Break Before Make  . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Absence of other interfaces in Valid list  . . . . . . . .  5
       3.1.1.  Receiving ICE Mobility event . . . . . . . . . . . . .  6
     3.2.  Presence of other interfaces in Valid list . . . . . . . .  7
       3.2.1.  Receiving ICE Mobility event . . . . . . . . . . . . .  8
     3.3.  Losing an Interface  . . . . . . . . . . . . . . . . . . .  8
       3.3.1.  Keeping unused candidates in the valid list active . .  9
       3.3.2.  Keeping unused relayed candidates active . . . . . . .  9
     3.4.  New STUN Attributes  . . . . . . . . . . . . . . . . . . . 10
   4.  Make Before Break  . . . . . . . . . . . . . . . . . . . . . . 10
   5.  Mobility using TURN  . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Creating an Allocation . . . . . . . . . . . . . . . . . . 12
       5.1.1.  Sending an Allocate Request  . . . . . . . . . . . . . 12
       5.1.2.  Receiving an Allocate Request  . . . . . . . . . . . . 12
       5.1.3.  Receiving an Allocate Success Response . . . . . . . . 13
       5.1.4.  Receiving an Allocate Error Response . . . . . . . . . 13
     5.2.  Refreshing an Allocation . . . . . . . . . . . . . . . . . 13
       5.2.1.  Sending a Refresh Request  . . . . . . . . . . . . . . 13
       5.2.2.  Receiving a Refresh Request  . . . . . . . . . . . . . 13
       5.2.3.  Receiving a Refresh Response . . . . . . . . . . . . . 14
     5.3.  New STUN Attribute MOBILITY-TICKET . . . . . . . . . . . . 14
     5.4.  New STUN Error Response Code . . . . . . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
     7.1.  Considerations for ICE mechanism . . . . . . . . . . . . . 15
     7.2.  Considerations for TURN mechanism  . . . . . . . . . . . . 15
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  Change History . . . . . . . . . . . . . . . . . . . . . . . . 16
     9.1.  Changes from draft-wing-mmusic-ice-mobility-00 to -01  . . 16
     9.2.  Changes from draft-wing-mmusic-ice-mobility-01 to -02  . . 16
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17













Wing, et al.              Expires April 9, 2013                 [Page 2]


Internet-Draft                    MICE                      October 2012


1.  Introduction

   When moving between networks, an endpoint has to change its IP
   address.  This change 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 upper layer
   protocol ambivalent to IP address changes (e.g., SCTP).  The
   mechanisms described in this document are in that last category.

   ICE [RFC5245] ensures two endpoints have a working media path between
   them, and is typically used by Internet-connected interactive media
   systems (e.g., SIP endpoints).  ICE does not expect either the local
   host or the remote host to change their IP addresses.  Although ICE
   does allow an "ICE restart", this is done by sending a re-INVITE
   which goes over the SIP signaling path.  The SIP signaling path is
   often slower than the media path (which needs to be recovered as
   quickly as possible), consumes an extra half round trip, and incurs
   an additional delay if the mobility event forces the endpoint to re-
   connect with its SIP proxy.  When a device changes its IP address, it
   is necessary for it to re-establish connectivity with its SIP proxy,
   which can be performed in parallel with the steps described in this
   document.  This document describes how mobility is performed entirely
   in the media path, without the additional delay of re-establishing
   SIP connectivity, issuing a new offer/answer, or the complications of
   multiple SIP offers.  This document considers re-establishing bi-
   directional media the most critical aspect of a successful mobility
   event, and its efforts are towards meeting that goal.

   A TURN [RFC5766] server relays media packets and is used for a
   variety of purposes, including overcoming NAT and firewall traversal
   issues and IP address privacy.  The existing TURN specification does
   not allow the client address to change, especially if multiple
   clients share the same TURN username (e.g., the same credentials are
   used on multiple devices).

   This document proposes two mechanisms to achieve RTP mobility: a
   mechanism where both endpoints support ICE, and a mechanism where
   only one endpoint supports ICE.  When both endpoints support ICE, ICE
   itself can be used to provide mobility.  When only one endpoint
   supports ICE, a TURN server provides mobility.  Both mobility
   techniques work across and between network types (e.g., between 3G
   and wired Internet access), so long as the client can still access
   the remote ICE peer or TURN server.

   Readers are assumed to be familiar with ICE [RFC5245].





Wing, et al.              Expires April 9, 2013                 [Page 3]


Internet-Draft                    MICE                      October 2012


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 initially selected interface for
      communication may become unavailable (e.g due to loss of coverage
      when moving out of a WiFi hotspot) and new interfaces may become
      available due to administrative action (e.g manual activation of a
      specific connectivity technology) or due to dynamic conditions
      (e.g.  Entering coverage area of a wireless network).

   Make Before Break:  The initially selected interface for
      communication may become deprioritized (e.g new interface becoming
      available and it's per bit cost is cheaper and the connection
      speed is faster than existing interface used for communication).

   Simultaneous Mobility:  If both the endpoints are mobile and roam at
      the same time between networks.


3.  Break Before Make

   When both endpoints support ICE, ICE itself can provide mobility
   functions.  One of the primary aspects of ICE is its address
   gathering, wherein ICE has each endpoint determine all of the IP
   addresses and ports that might be usable for that endpoint and
   communicate that list of addresses and ports to its peer, usually
   over SDP.  That enables the next primary aspect of ICE, which is its
   connectivity checks: each ICE endpoint sends a connectivity check to
   that list of addresses and ports.  A connectivity check may
   unknowingly traverse a NAT, which means the ICE endpoint receiving
   the connectivity check cannot validate the source IP address or port
   of the connectivity against the list of IP addresses and ports
   provided by the ICE peer.  In fact, if the source IP address and port
   is not known to the ICE endpoint, it is added to the list of
   candidates (Section 7.2.1.3 of [RFC5245].  ICE Mobility takes
   advantage of that existent ICE functionality.

   Endpoints that support ICE Mobility perform ICE normally, and MUST
   also include the MOBILITY-SUPPORT attribute in all of their STUN
   requests and their STUN responses.  The inclusion of this attribute
   allows the ICE peer to determine if it can achieve mobility using ICE
   or needs to use TURN.  To force the use of TURN to achieve ICE



Wing, et al.              Expires April 9, 2013                 [Page 4]


Internet-Draft                    MICE                      October 2012


   mobility, the ICE endpoint SHOULD NOT respond to ICE connectivity
   checks that have an IP address and port different from the TURN
   server, unless those connectivity checks contain the MOBILITY-SUPPORT
   attribute.  In this way, the remote peer will think those other
   candidates are invalid (because its connectivity checks did not
   succeed).

   After concluding ICE and moving to the ICE completed state (see
   Section 8 of [RFC5245] either endpoint or both endpoints can initiate
   ICE Mobility, no matter if it was the Controlling Agent or the
   Controlled Agent during normal ICE processing.

3.1.  Absence of other interfaces in Valid list

   When the interface currently being used for communication becomes
   unavailable then ICE agent acquires a list of interfaces that are
   available and based on the locally configured host policy
   preferences, the ICE endpoint performs ICE Mobility using one of the
   available interfaces.  In this case local candidates from the
   selected interface are not present in the valid list.  ICE Mobility
   is performed by :

   1.  The ICE agent remembers the remote host/server-reflexive
       candidates for each component of the media streams previously
       used from the valid list before clearing its ICE check list and
       ICE Valid List.

   2.  The ICE endpoint gathers host candidates on the new interface,
       forms a check list by creating candidate pairs with local host
       candidates and remote host/server-reflexive candidates collected
       in step 1, performs "Computing Pair Priority and Ordering Pairs"
       (Section 5.7.2 of [RFC5245]), "Pruning the Pairs" (Section 5.7.3
       of [RFC5245], "Computing states" (Section 5.7.4 of [RFC5245]).

   3.  The ICE endpoint initiates ICE connectivity checks on those
       candidates from the check list in the previous step, and includes
       the MOBILITY-EVENT attribute in those connectivity checks.

   4.  The ICE endpoint acts as controlling agent and the ICE
       connectivity check from the previous step SHOULD also include the
       USE-CANDIDATE attribute to signal an aggressive nomination (see
       Section 2.6 of [RFC5245]).  An aggressive nomination allows
       sending media immediately after the connectivity check completes,
       without waiting for other connectivity checks to complete.

   5.  The ICE endpoint performs "Discovering Peer Reflexive Candidates"
       (Section 7.1.3.2.1 of [RFC5245]), "Constructing a Valid Pair"
       (Section 7.1.3.2.2 of [RFC5245]), "Updating Pair States" (Section



Wing, et al.              Expires April 9, 2013                 [Page 5]


Internet-Draft                    MICE                      October 2012


       7.1.3.2.3 of [RFC5245]), and "Updating the Nominated Flag"
       (Section 7.1.3.2.4 of [RFC5245]).  When the valid list contains a
       candidate pair for each component then ICE processing is
       considered complete for the media stream and ICE agent can start
       sending media using highest-priority nominated candidate pair.

   6.  Once ICE connectivity checks for all of the media streams are
       completed, the controlling ICE endpoint follows the procedures in
       Section 11.1 of [RFC5245], specifically to send updated offer if
       the candidates in the m and c lines for the media stream (called
       the DEFAULT CANDIDATES) do not match ICE's SELECTED CANDIDATES
       (also see Appendix B.9 of [RFC5245]).

   The ICE endpoint even after Mobility using ICE is successful can
   issue an updated offer indicating ICE restart if connectivity checks
   using higher priority candidate pairs are not successful.

   Mobility using ICE could fail in case of Simultaneous Mobility or if
   the ICE peer is behind NAT that performs Address-Dependent Filtering
   (see Section 5 of [RFC5245]).  Hence the ICE endpoint in parallel
   will re-establish connection with the SIP proxy.  It will then
   determine whether to initiate ICE restart under the following
   conditions :

   1.  After re-establishing connection with the SIP proxy and before
       sending new offer to initiate ICE restart if Mobility using ICE
       is successful then stop sending the new offer.

   2.  After successful negotiation of updated offer/answer to initiate
       ICE restart, proceed with ICE restart and stop Mobility using ICE
       if ICE checks are in the Running/Failed states or ICE is
       partially successful and not yet reached ICE complete state.
       It's not implementation friendly to have to two checks running in
       parallel.  ICE restart can re-use partial successful ICE
       connectivity check results from Mobility using ICE if required as
       optimization.

3.1.1.  Receiving ICE Mobility event

   A STUN Binding Request containing the MOBILITY-EVENT attribute MAY be
   received by an ICE endpoint.  The agent MUST use short-term
   credential to authenticate the STUN request containing the MOBILITY-
   EVENT attribute and perform a message integrity check.  The ICE
   endpoint will generate STUN Binding Response containing the MOBILE-
   SUPPORT attribute and the ICE agent takes role of controlled agent.
   If STUN Request containing the MOBILITY-EVENT attribute is received
   before the endpoint is in the ICE Completed state, it should be
   silently discarded.



Wing, et al.              Expires April 9, 2013                 [Page 6]


Internet-Draft                    MICE                      October 2012


   The agent remembers the highest-priority nominated pairs in the Valid
   list for each component of the media stream, called the previous
   selected pairs before removing all the selected candidate pairs from
   the Valid List .  It continues sending media to that address until it
   finishes with the steps described below.  Because those packets might
   not be received due to the mobility event, it MAY cache a copy of
   those packets.

   1.  The ICE endpoint constructs a pair whose local candidate is equal
       to the transport address on which the STUN request was received
       with MOBILITY-EVENT, USE-CANDIDATE attributes and a remote
       candidate equal to the source transport address where the STUN
       request came from.

   2.  The ICE endpoint will add this pair to the valid list if not
       already present.

   3.  The agent sets the nominated flag for that pair in the valid pair
       to true.  ICE processing is considered complete for a media
       stream if the valid list contains a selected candidate pair for
       each component and ICE agent can start sending media.

   The ICE endpoint will follow Steps 1 to 3 when subsequent STUN
   Binding Requests are received with MOBILITY-EVENT and USE-CANDIDATE
   attributes.

3.2.  Presence of other interfaces in Valid list

   Note : This technique is optional and only relevant if there is a
   host policy to maintain unused candidates on other interfaces using
   the steps in Section 3.3.1.  When the interface currently being used
   for media communication becomes unavailable.  If other interfaces are
   available and local candidates from these interfaces are already
   present in the valid list then ICE endpoint will perform the
   following steps :

   1.  The ICE endpoint based on the locally configured host policy
       preferences, will select a interface whose candidates are already
       present in the valid list.

   2.  The ICE endpoint clears all the pairs in the valid list
       containing the IP addresses from the interface that become
       unavailable.

   3.  The ICE endpoint initiates ICE connectivity checks on the
       selected interface.  The ICE endpoint acts as controlling agent
       and MUST include MOBILITY-EVENT attribute to signal mobility
       event and SHOULD also include the USE-CANDIDATE attribute to



Wing, et al.              Expires April 9, 2013                 [Page 7]


Internet-Draft                    MICE                      October 2012


       signal an aggressive nomination (see Section 2.6 of [RFC5245]).
       When all components have a nominated pair in the valid list,
       media can begin to flow using the highest priority nominated
       pair.

   4.  The ICE endpoint will re-establish connection with the SIP proxy.
       Once ICE connectivity checks for all of the media streams are
       completed, the controlling ICE endpoint follows the procedures in
       Section 11.1 of [RFC5245], specifically to send updated offer if
       the candidates in the m and c lines for the media stream (called
       the DEFAULT CANDIDATES) do not match ICE's SELECTED CANDIDATES
       (also see Appendix B.9 of [RFC5245]).

   The ICE endpoint after Mobility using ICE is successful can issue an
   updated offer indicating ICE restart if higher priority interface
   becomes available.

3.2.1.  Receiving ICE Mobility event

   The ICE endpoint that receives ICE Mobility Event will perform the
   steps in Section 3.1.1.

3.3.  Losing an Interface

   When an interface is lost, the SDP MAY be updated, so that the remote
   ICE host does not waste its efforts with connectivity checks to that
   address, as those checks will fail.  Because it can be argued that
   this is merely an optimization, and that the interface loss might be
   temporary (and soon regained), and that ICE has reasonable
   accommodation for candidates where connectivity checks timeout, this
   specification does not strongly encourage updating the SDP to remove
   a lost interface.

   Likewise, this specification recommends that ICE candidate addresses
   in valid list be maintained actively, subject to the host's policy.
   For example, battery operated hosts have a strong incentive to not
   maintain NAT binding for server reflexive candidates learnt through
   STUN Binding Request, as the maintenance requires sending periodic
   STUN Binding Indication.  As another example, a host that is
   receiving media over IPv6 may not want to persist with keeping a
   NATted IPv4 mapping alive (because that consumes a NAT mapping that
   could be more useful to a host actively utilizing the mapping for
   real traffic).

   Note: this differs from Section 8.3 of [RFC5245], which encourages
   abandoning unused candidates.





Wing, et al.              Expires April 9, 2013                 [Page 8]


Internet-Draft                    MICE                      October 2012


3.3.1.  Keeping unused candidates in the valid list active

   ICE endpoint subject to host policy can continue performing ICE
   connectivity checks using candidates from other interfaces on the
   host even after ICE is complete.  If valid list contains unused
   candidate pairs from other interfaces and one of these interfaces can
   be selected to send to media in case the existing interface used for
   media is unavailable then ICE endpoint can keep the unused candidate
   pairs from other interface{s} alive by sending keepalives every NN
   seconds.  It is recommended to only keep host/server-reflexive
   candidates active in the valid list and not the relayed candidates.

3.3.1.1.  Sending keep alive requests

   Application Mechanism for Keeping Alive the NAT Mappings Associated
   with RTP / RTP Control Protocol (RTCP) Flows [RFC6263] describes
   various reasons for doing keepalives on inactive streams and how to
   keep NAT mapping alive.  However this specification requires some
   additional functionality associated with the keepalives.

   STUN binding requests MUST be used as the keepalive message instead
   of the STUN Binding indication as specified in [RFC5245].  This is to
   ensure positive peer consent from the remote side that the candidate
   pair is still active and in future mobility can be achieved using the
   steps in Section 3.2 .  The request must include the MOBILITY-SUPPORT
   attribute.  If the STUN binding response matches a pair in the
   checklist then that candidate pair should be kept in the list.  If
   the STUN transaction fails then the candidate pair will be removed
   from valid list.

3.3.1.2.  Receiving keep alive requests

   Upon receiving a STUN binding request containing a MOBILITY-SUPPORT
   attribute even when ICE processing is in the Completed state, the ICE
   endpoint will add this pair to the valid list if not already present
   and generate STUN Binding Response containing the MOBILE-SUPPORT
   attribute.

3.3.2.  Keeping unused relayed candidates active

   Discussion : The ICE endpoints can maintain the relayed candidates
   active even when not actively used, so that relayed candidates can be
   tried if ICE connectivity checks using other candidate types fails.
   The ICE agent will have to create permissions in the TURN server for
   the remote relayed candidate IP addresses and perform the following
   steps :





Wing, et al.              Expires April 9, 2013                 [Page 9]


Internet-Draft                    MICE                      October 2012


   1.  The ICE agent will keep the relayed candidates alive using
       Refresh transaction, as described in [RFC5766].

   2.  When the endpoint IP address changes due to mobility, the ICE
       agent will refresh it's allocation with TURN server using
       Section 5.2.

   3.  The ICE agent will pair local and remote relayed candidates for
       connectivity checks when performing the steps in Section 3.1.

   4.  If the ICE connectivity check succeeds only with local and remote
       relayed candidates, it suggests that either other peer is roaming
       at the same time or is behind Address-Dependent Filtering NAT.
       The ICE agent adds the relayed candidate pair to the valid list
       and marks it as selected.  The ICE agent can now send media using
       the newly selected relayed candidate pair.  The Mobile device
       must re-establish connection with SIP proxy, issue an updated
       offer indicating ICE restart so that media can switched to
       higher-priority candidate pairs.

   This approach assists Mobility using ICE to succeed but brings in
   additional overhead of maintaining relayed candidates.

3.4.  New STUN Attributes

   Three new attributes are defined by this section: MOBILITY-EVENT,
   MOBILITY-SUPPORT.

   The MOBILITY-EVENT attribute indicate the sender experienced a
   mobility event.  This attribute has no value, thus the attribute
   length field MUST always be 0.  Rules for sending and interpretation
   of receiving are described above.

   The MOBILITY-SUPPORT attribute indicates the sender supports ICE
   Mobility, as defined in this document.  This attribute has no value,
   thus the attribute length field MUST always be 0.  Rules for sending
   and interpretation of receiving are described above.


4.  Make Before Break

   When a new interface comes up and initially selected interface
   becomes deprioritized (e.g due to a low cost interface becoming
   available).  The ICE endpoint re-connects to the SIP proxy using the
   new interface, gather candidates, exchange updated offer/exchange to
   restart ICE.  Once ICE processing has reached the Completed state
   then the ICE endpoint can successfully switch the media over to the
   new interface.  The interface initially used for communication can



Wing, et al.              Expires April 9, 2013                [Page 10]


Internet-Draft                    MICE                      October 2012


   now be turned off without disrupting communications.


5.  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 also include the 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.  It also ensures that the allocation can
   only be refreshed this way by the same client.  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.























Wing, et al.              Expires April 9, 2013                [Page 11]


Internet-Draft                    MICE                      October 2012


     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                |             |
       |                                    |             |

5.1.  Creating an Allocation

5.1.1.  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.

5.1.2.  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,
   and the TURN session mobility is forbidden by local policy, the
   server MUST reject the request with the new Mobility Forbidden error
   code.  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 create an
   allocation, the server replies with a success response that includes
   a STUN MOBILITY-TICKET attribute.  TURN server stores it's session
   state, such as 5-tuple and NONCE, into a ticket that is encrypted by
   a key known only to the TURN server and sends the ticket in the STUN



Wing, et al.              Expires April 9, 2013                [Page 12]


Internet-Draft                    MICE                      October 2012


   MOBILITY-TICKET attribute as part of Allocate success response.

   The ticket is opaque to the client, so the structure is not subject
   to interoperability concerns, and implementations may diverge from
   this format.  TURN Allocation state information is encrypted using
   128-bit key for Advance Encryption Standard (AES) and 256-bit key for
   HMAC-SHA-256 for integrity protection.

5.1.3.  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.

5.1.4.  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
   client MAY notify the user or operator and SHOULD NOT retry the same
   request with this server until it believes the problem has been
   fixed.

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

5.2.  Refreshing an Allocation

5.2.1.  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 will send a
   Refresh Request as described in Section 7.1 of [RFC5766].  If the
   client wants to retain the existing allocation in case of IP change,
   it will include the MOBILITY-TICKET attribute received in the
   Allocate Success response.  If a Refresh transaction was previously
   made, the MOBILITY-TICKET attribute received in the Refresh Success
   response of the transaction must be used.

5.2.2.  Receiving a Refresh Request

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

   If the STUN MOBILITY-TICKET attribute is included in the Refresh



Wing, et al.              Expires April 9, 2013                [Page 13]


Internet-Draft                    MICE                      October 2012


   Request then the server will not retrieve the 5-tuple from the packet
   to identify an associated allocation.  Instead TURN server will
   decrypt the received ticket, verify the ticket's validity and
   retrieve the 5-tuple allocation from the contents of the ticket.  If
   this 5-tuple obtained from the ticket does not identify an existing
   allocation then the server MUST reject the request with an error.

   If the source IP address and port of the Refresh Request is different
   from the stored 5-tuple allocation, the TURN server proceeds with
   checks to see if NONCE in the Refresh request is the same as the one
   provided in the ticket.  The TURN server also uses MESSAGE-INTEGRITY
   validation to identify the that it is the same user which had
   previously created the TURN allocation.  If the above checks are 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 moved to a new network and acquired a new IP address.  The
   source IP address of the request could either be the host transport
   address or server-reflexive transport address.  The server then
   updates it's 5-tuple with the new client IP address and port.  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.

5.2.3.  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.

5.3.  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 is encrypted and identifies identifies session state such as
   5-tuple and NONCE.  The value of MOBILITY-TICKET is a variable-length
   value.

5.4.  New STUN Error Response Code

   This document defines the following new error response code:

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





Wing, et al.              Expires April 9, 2013                [Page 14]


Internet-Draft                    MICE                      October 2012


6.  IANA Considerations

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

   o  MOBILITY-TICKET (0x802E, in the comprehension-optional range)

   o  MOBILITY-EVENT (0x802, in the comprehension-required range)

   o  MOBILITY-SUPPORT (0x8000, in the comprehension-optional range)

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


7.  Security Considerations

7.1.  Considerations for ICE mechanism

   A mobility event only occurs after both ICE endpoints have exchanged
   their ICE information.  Thus, both username fragments are already
   known to both endpoints.  Each endpoint contributes at least 24 bits
   of randomness to the ice-ufrag (Section 15.4 of [RFC5245]), which
   provides 48 bits of randomness.  An off-path attacker would have to
   guess those 48 bits to cause the endpoints to perform HMAC-SHA1
   validation of the MESSAGE-INTEGRITY attribute.

   An attacker on the path between the ICE endpoints will see both ice-
   ufrags, and can cause the endpoints to perform HMAC-SHA1 validation
   by sending messages from any IP address.

7.2.  Considerations for TURN mechanism

   TURN server MUST use strong encryption and integrity protection for
   the ticket to prevent an attacker from using a brute force mechanism
   to obtain the ticket's contents or refreshing allocations.

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


8.  Acknowledgements

   Thanks to Alfred Heggestad, Lishitao, Sujing Zhou, Martin Thomson,
   Emil Ivov for review and comments.






Wing, et al.              Expires April 9, 2013                [Page 15]


Internet-Draft                    MICE                      October 2012


9.  Change History

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

9.1.  Changes from draft-wing-mmusic-ice-mobility-00 to -01

   o  Updated section 3

9.2.  Changes from draft-wing-mmusic-ice-mobility-01 to -02

   o  Updated Introduction, Notational Conventions, sections 3.1, 3.2.

   o  Updated section 3.5


10.  References

10.1.  Normative References

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

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              April 2010.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 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, April 2010.

10.2.  Informative References

   [RFC6263]  Marjou, X. and A. Sollaud, "Application Mechanism for
              Keeping Alive the NAT Mappings Associated with RTP / RTP
              Control Protocol (RTCP) Flows", RFC 6263, June 2011.

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





Wing, et al.              Expires April 9, 2013                [Page 16]


Internet-Draft                    MICE                      October 2012


Authors' Addresses

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

   Email: dwing@cisco.com


   Prashanth Patil
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marthalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: praspati@cisco.com


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

   Email: tireddy@cisco.com


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

   Email: palmarti@cisco.com













Wing, et al.              Expires April 9, 2013                [Page 17]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/