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Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols
RFC 5245

Internet Engineering Task Force (IETF)                      J. Rosenberg
Request for Comments: 5245                                   jdrosen.net
Obsoletes: 4091, 4092                                         April 2010
Category: Standards Track
ISSN: 2070-1721

             Interactive Connectivity Establishment (ICE):
     A Protocol for Network Address Translator (NAT) Traversal for
                         Offer/Answer Protocols

Abstract

   This document describes a protocol for Network Address Translator
   (NAT) traversal for UDP-based multimedia sessions established with
   the offer/answer model.  This protocol is called Interactive
   Connectivity Establishment (ICE).  ICE makes use of the Session
   Traversal Utilities for NAT (STUN) protocol and its extension,
   Traversal Using Relay NAT (TURN).  ICE can be used by any protocol
   utilizing the offer/answer model, such as the Session Initiation
   Protocol (SIP).

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5245.

Rosenberg                    Standards Track                    [Page 1]
RFC 5245                           ICE                        April 2010

Copyright Notice

   Copyright (c) 2010 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   6
   2.  Overview of ICE . . . . . . . . . . . . . . . . . . . . . . .   7
     2.1.  Gathering Candidate Addresses . . . . . . . . . . . . . .   9
     2.2.  Connectivity Checks . . . . . . . . . . . . . . . . . . .  11
     2.3.  Sorting Candidates  . . . . . . . . . . . . . . . . . . .  12
     2.4.  Frozen Candidates . . . . . . . . . . . . . . . . . . . .  13
     2.5.  Security for Checks . . . . . . . . . . . . . . . . . . .  14
     2.6.  Concluding ICE  . . . . . . . . . . . . . . . . . . . . .  14
     2.7.  Lite Implementations  . . . . . . . . . . . . . . . . . .  16
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .  16
   4.  Sending the Initial Offer . . . . . . . . . . . . . . . . . .  19
     4.1.  Full Implementation Requirements  . . . . . . . . . . . .  19
       4.1.1.  Gathering Candidates  . . . . . . . . . . . . . . . .  19
         4.1.1.1.  Host Candidates . . . . . . . . . . . . . . . . .  20
         4.1.1.2.  Server Reflexive and Relayed Candidates . . . . .  20
         4.1.1.3.  Computing Foundations . . . . . . . . . . . . . .  22
         4.1.1.4.  Keeping Candidates Alive  . . . . . . . . . . . .  22
       4.1.2.  Prioritizing Candidates . . . . . . . . . . . . . . .  22
         4.1.2.1.  Recommended Formula . . . . . . . . . . . . . . .  23
         4.1.2.2.  Guidelines for Choosing Type and Local
                   Preferences . . . . . . . . . . . . . . . . . . .  23
       4.1.3.  Eliminating Redundant Candidates  . . . . . . . . . .  25
       4.1.4.  Choosing Default Candidates . . . . . . . . . . . . .  25
     4.2.  Lite Implementation Requirements  . . . . . . . . . . . .  25
     4.3.  Encoding the SDP  . . . . . . . . . . . . . . . . . . . .  26
   5.  Receiving the Initial Offer . . . . . . . . . . . . . . . . .  28
     5.1.  Verifying ICE Support . . . . . . . . . . . . . . . . . .  28
     5.2.  Determining Role  . . . . . . . . . . . . . . . . . . . .  29
     5.3.  Gathering Candidates  . . . . . . . . . . . . . . . . . .  30
     5.4.  Prioritizing Candidates . . . . . . . . . . . . . . . . .  30
     5.5.  Choosing Default Candidates . . . . . . . . . . . . . . .  31

Rosenberg                    Standards Track                    [Page 2]
RFC 5245                           ICE                        April 2010

     5.6.  Encoding the SDP  . . . . . . . . . . . . . . . . . . . .  31

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