Source note · SIP registration failures
Without RFC 3581, SIP returns UDP responses to the request's source address but to the port written in the top Via, and behind a NAT that port is not the one the NAT binding opened.
Checked 2026-09-25
- Vendor
- not restricted
- Product
- SIP
- Subsystem
- nat-traversal
- Deployment
- any
- Region
- not restricted
- Release range
- RFC 3581
- Checked
- 2026-09-25
Sources
- RFC 3581: An Extension to the Session Initiation Protocol (SIP) for Symmetric Response Routing — IETF / RFC Editor · tier 1 standards and regulators · Introduction (problem statement sentence beginning 'responses to requests are returned to the source address')
Cite this note
APA
WarmTransfer. (2026, September 25). SIP registration failures: source note sip-registration-failures-via-port-nat-problem. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-registration-failures-via-port-nat-problem
BibTeX
@misc{warmtransfer-claim-sip-registration-failures-via-port-nat-problem,
title = {SIP registration failures: source note sip-registration-failures-via-port-nat-problem},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-registration-failures-via-port-nat-problem},
note = {Source note sip-registration-failures-via-port-nat-problem, checked 2026-09-25}
}