Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)
RFC 8656

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Internet Engineering Task Force (IETF)                     T. Reddy, Ed.
Request for Comments: 8656                                        McAfee
Obsoletes: 5766, 6156                                   A. Johnston, Ed.
Category: Standards Track                           Villanova University
ISSN: 2070-1721                                              P. Matthews
                                                          Alcatel-Lucent
                                                            J. Rosenberg
                                                             jdrosen.net
                                                           February 2020

 Traversal Using Relays around NAT (TURN): Relay Extensions to Session
                   Traversal Utilities for NAT (STUN)

Abstract

   If a host is located behind a NAT, it can be impossible for that host
   to communicate directly with other hosts (peers) in certain
   situations.  In these situations, it is necessary for the host to use
   the services of an intermediate node that acts as a communication
   relay.  This specification defines a protocol, called "Traversal
   Using Relays around NAT" (TURN), that allows the host to control the
   operation of the relay and to exchange packets with its peers using
   the relay.  TURN differs from other relay control protocols in that
   it allows a client to communicate with multiple peers using a single
   relay address.

   The TURN protocol was designed to be used as part of the Interactive
   Connectivity Establishment (ICE) approach to NAT traversal, though it
   can also be used without ICE.

   This document obsoletes RFCs 5766 and 6156.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8656.

Copyright Notice

   Copyright (c) 2020 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
   (https://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.  Terminology
   3.  Overview of Operation
     3.1.  Transports
     3.2.  Allocations
     3.3.  Permissions
     3.4.  Send Mechanism
     3.5.  Channels
     3.6.  Unprivileged TURN Servers
     3.7.  Avoiding IP Fragmentation
     3.8.  RTP Support
     3.9.  Happy Eyeballs for TURN
   4.  Discovery of TURN Server
     4.1.  TURN URI Scheme Semantics
   5.  General Behavior
   6.  Allocations
   7.  Creating an Allocation
     7.1.  Sending an Allocate Request
     7.2.  Receiving an Allocate Request
     7.3.  Receiving an Allocate Success Response
     7.4.  Receiving an Allocate Error Response
   8.  Refreshing an Allocation
     8.1.  Sending a Refresh Request
     8.2.  Receiving a Refresh Request
     8.3.  Receiving a Refresh Response
   9.  Permissions
   10. CreatePermission
     10.1.  Forming a CreatePermission Request
     10.2.  Receiving a CreatePermission Request
     10.3.  Receiving a CreatePermission Response
   11. Send and Data Methods
     11.1.  Forming a Send Indication
     11.2.  Receiving a Send Indication
     11.3.  Receiving a UDP Datagram
     11.4.  Receiving a Data Indication
     11.5.  Receiving an ICMP Packet
     11.6.  Receiving a Data Indication with an ICMP Attribute
   12. Channels
     12.1.  Sending a ChannelBind Request
     12.2.  Receiving a ChannelBind Request
     12.3.  Receiving a ChannelBind Response
     12.4.  The ChannelData Message
     12.5.  Sending a ChannelData Message
     12.6.  Receiving a ChannelData Message
     12.7.  Relaying Data from the Peer
   13. Packet Translations
     13.1.  IPv4-to-IPv6 Translations
     13.2.  IPv6-to-IPv6 Translations
     13.3.  IPv6-to-IPv4 Translations
   14. UDP-to-UDP Relay
   15. TCP-to-UDP Relay
   16. UDP-to-TCP Relay
   17. STUN Methods
   18. STUN Attributes
     18.1.  CHANNEL-NUMBER
     18.2.  LIFETIME
     18.3.  XOR-PEER-ADDRESS
     18.4.  DATA
     18.5.  XOR-RELAYED-ADDRESS
     18.6.  REQUESTED-ADDRESS-FAMILY
     18.7.  EVEN-PORT
     18.8.  REQUESTED-TRANSPORT