Session Traversal Utilities for NAT (STUN) Message Handling for SIP Back-to-Back User Agents (B2BUAs)
RFC 7584
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(July 2015; Errata)
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2018-12-20
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Victor Pascual
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Internet Engineering Task Force (IETF) R. Ravindranath
Request for Comments: 7584 T. Reddy
Category: Standards Track G. Salgueiro
ISSN: 2070-1721 Cisco
July 2015
Session Traversal Utilities for NAT (STUN) Message Handling
for SIP Back-to-Back User Agents (B2BUAs)
Abstract
Session Initiation Protocol (SIP) Back-to-Back User Agents (B2BUAs)
are often designed to be on the media path rather than just
intercepting signaling. This means that B2BUAs often act on the
media path leading to separate media legs that the B2BUA correlates
and bridges together. When acting on the media path, B2BUAs are
likely to receive Session Traversal Utilities for NAT (STUN) packets
as part of Interactive Connectivity Establishment (ICE) processing.
This document defines behavior for a B2BUA performing ICE processing.
The goal of this document is to ensure that B2BUAs properly handle
SIP messages that carry ICE semantics in Session Description Protocol
(SDP) and STUN messages received as part of the ICE procedures for
NAT and Firewall traversal of multimedia sessions.
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/rfc7584.
Ravindranath, et al. Standards Track [Page 1]
RFC 7584 STUN Handling in SIP B2BUAs July 2015
Copyright Notice
Copyright (c) 2015 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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. SDP-Modifying Signaling-only B2BUA . . . . . . . . . . . . . 5
4. Media Plane B2BUAs . . . . . . . . . . . . . . . . . . . . . 5
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Mandatory ICE Termination with B2BUA . . . . . . . . . . 6
4.3. Optional ICE Termination with B2BUA . . . . . . . . . . . 9
4.4. STUN Handling in B2BUA with Forked Signaling . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Normative References . . . . . . . . . . . . . . . . . . 12
6.2. Informative References . . . . . . . . . . . . . . . . . 13
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
In many SIP deployments, SIP entities exist in the SIP signaling and
media path between the originating and final terminating endpoints,
which go beyond the definition of a traditional SIP proxy. These SIP
entities, commonly known as B2BUAs, are described in [RFC7092] and
often perform functions not defined in Standards Track RFCs.
SIP [RFC3261] and other session control protocols that try to use a
direct path for media are typically difficult to use across Network
Address Translators (NATs). These protocols use IP addresses and
transport port numbers encoded in the signaling, such as SDP
[RFC4566] and, in the case of SIP, various header fields. Such
addresses and ports are unreachable if any peers are separated by
NATs.
Ravindranath, et al. Standards Track [Page 2]
RFC 7584 STUN Handling in SIP B2BUAs July 2015
Mechanisms such as STUN [RFC5389], Traversal Using Relays around NAT
(TURN) [RFC5766], and ICE [RFC5245] did not exist when protocols like
SIP began to be deployed. Some mechanisms, such as the early
versions of STUN, started appearing, but they were unreliable and
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