STRAW Working Group H. Kaplan
Internet-Draft Oracle
Intended status: Standards Track V. Pascual
Expires: August 14, 2014 Quobis
February 10, 2014
Loop Detection Mechanisms for Session Initiation Protocol (SIP) Back-to-
Back User Agents (B2BUAs)
draft-ietf-straw-b2bua-loop-detection-04
Abstract
SIP Back-to-Back User Agents (B2BUAs) can cause unending SIP request
routing loops because, as User Agent Clients, they can generate SIP
requests with new Max-Forwards values. This document discusses the
difficulties associated with loop detection for B2BUAs, and
requirements for them to prevent infinite loops.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. B2BUA Loop-Detection Behavior . . . . . . . . . . . . . . . . 4
5. B2BUA Max-Forwards Behavior . . . . . . . . . . . . . . . . . 4
6. B2BUA Max-Breadth Behavior . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
SIP provides a means of preventing infinite request forwarding loops
in [RFC3261], and a means of mitigating parallel forking
amplification floods in [RFC5393]. Neither document normatively
defines specific behavior for B2BUAs, however.
Unbounded SIP request loops have actually occurred in SIP
deployments, numerous times. The cause of loops is usually mis-
configuration, but the reason they have been unbounded/unending is
they crossed B2BUAs that reset the Max-Forwards value in the SIP
requests they generated on their UAC side. Although such behavior is
technically legal per [RFC3261] because a B2BUA is a UAC, the
resulting unbounded loops have caused service outages and make
troubleshooting difficult.
Furthermore, [RFC5393] also provides a mechanism to mitigate the
impact of parallel forking amplification issues, through the use of a
"Max-Breadth" header field. If a B2BUA does not pass on this header
field, parallel forking amplification is not mitigated with the
[RFC5393] mechanism.
This document defines normative requirements for Max-Forwards and
Max-Breadth header field behaviors of B2BUAs, in order to mitigate
the effect of loops and parallel forking amplification.
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