| Abstract
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The Session Initiation Protocol (SIP) operates over UDP and TCP. 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 where the request came from.
Table of Contents
1 Introduction ........................................ 3
2 Terminology ......................................... 3
3 Client Behavior ..................................... 3
4 Server Behavior ..................................... 4
5 Syntax .............................................. 5
6 Example ............................................. 5
7 Security Considerations ............................. 6
8 IANA Considerations ................................. 7
9 IAB Considerations .................................. 7
9.1 Problem Definition .................................. 8
9.2 Exit Strategy ....................................... 8
9.3 Brittleness Introduced by this Specification ........ 8
9.4 Requirements for a Long Term Solution ............... 9
9.5 Issues with Existing NAPT Boxes ..................... 10
10 Acknowledgements .................................... 10
11 Author's Addresses .................................. 11
12 Normative References ................................ 11
13 Informative References .............................. 12
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