Skip to main content

An Extension to the Session Initiation Protocol (SIP) for Symmetric Response Routing

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 3581.
Authors Henning Schulzrinne , Jonathan Rosenberg
Last updated 2015-10-14 (Latest revision 2003-07-03)
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state (None)
Document shepherd (None)
IESG IESG state RFC 3581 (Proposed Standard)
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Allison J. Mankin
IESG note
Send notices to <>
A new Request for Comments is now available in online RFC libraries.

        RFC 3581

        Title:      An Extension to the Session Initiation Protocol
                    (SIP) for Symmetric Response Routing
        Author(s):  J. Rosenberg, H. Schulzrinne
        Status:     Standards Track
        Date:       August 2003
        Pages:      13
        Characters: 66133
        Updates/Obsoletes/SeeAlso:    None

        I-D Tag:    draft-ietf-sip-symmetric-response-01.txt


The Session Initiation Protocol (SIP) operates over UDP and TCP, among
others.  When used with UDP, responses to requests are returned to the
source address the request came from, and to the port written into the
topmost Via header field value of the request.  This behavior is not
desirable in many cases, most notably, when the client is behind a
Network Address Translator (NAT).  This extension defines a new
parameter for the Via header field, called "rport", that allows a
client to request that the server send the response back to the
source IP address and port from which the request originated.

This document is a product of the Session Initiation Protocol Working
Group of the IETF.

This is now a Proposed Standard Protocol.

This document specifies an Internet standards track protocol for
the Internet community, and requests discussion and suggestions
for improvements.  Please refer to the current edition of the
"Internet Official Protocol Standards" (STD 1) for the
standardization state and status of this protocol.  Distribution
of this memo is unlimited.

This announcement is sent to the IETF list and the RFC-DIST list.
Requests to be added to or deleted from the IETF distribution list
should be sent to IETF-REQUEST@IETF.ORG.  Requests to be
added to or deleted from the RFC-DIST distribution list should

Details on obtaining RFCs via FTP or EMAIL may be obtained by sending
an EMAIL message to rfc-info@RFC-EDITOR.ORG with the message body 
help: ways_to_get_rfcs.  For example:

        To: rfc-info@RFC-EDITOR.ORG
        Subject: getting rfcs

        help: ways_to_get_rfcs

Requests for special distribution should be addressed to either the
author of the RFC in question, or to RFC-Manager@RFC-EDITOR.ORG.  Unless
specifically noted otherwise on the RFC itself, all RFCs are for
unlimited distribution.echo 
Submissions for Requests for Comments should be sent to
RFC-EDITOR@RFC-EDITOR.ORG.  Please consult RFC 2223, Instructions to RFC
Authors, for further information.