RFC 3261 explains the 200-byte margin below path MTU as allowance for SIP responses being larger than requests, for example because Record-Route values are added to responses to INVITE.
Checked 2026-10-02
- Vendor
- not restricted
- Product
- not restricted
- Subsystem
- SIP transport selection
- Deployment
- on-premises, multi-tenant
- Region
- not restricted
- Release range
- RFC 3261 as published
- Checked
- 2026-10-02
Sources
- RFC 3261 — SIP: Session Initiation Protocol — IETF / RFC Editor · tier 1 standards and regulators · Section 18.1.1 Sending Requests, rationale paragraph following the 1300-byte rule
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting failed calls caused by large SIP messages over UDP: source note sip-fragmentation-troubleshooting-rfc3261-200-byte-buffer. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-fragmentation-troubleshooting-rfc3261-200-byte-buffer
BibTeX
@misc{warmtransfer-claim-sip-fragmentation-troubleshooting-rfc3261-200-byte-buffer,
title = {Troubleshooting failed calls caused by large SIP messages over UDP: source note sip-fragmentation-troubleshooting-rfc3261-200-byte-buffer},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-fragmentation-troubleshooting-rfc3261-200-byte-buffer},
note = {Source note sip-fragmentation-troubleshooting-rfc3261-200-byte-buffer, checked 2026-10-02}
}