RFC 3261 states the 1300-byte figure for unknown path MTU is based on assuming a 1500-byte Ethernet MTU.
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
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting failed calls caused by large SIP messages over UDP: source note sip-fragmentation-troubleshooting-rfc3261-1300-assumes-1500. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-fragmentation-troubleshooting-rfc3261-1300-assumes-1500
BibTeX
@misc{warmtransfer-claim-sip-fragmentation-troubleshooting-rfc3261-1300-assumes-1500,
title = {Troubleshooting failed calls caused by large SIP messages over UDP: source note sip-fragmentation-troubleshooting-rfc3261-1300-assumes-1500},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-fragmentation-troubleshooting-rfc3261-1300-assumes-1500},
note = {Source note sip-fragmentation-troubleshooting-rfc3261-1300-assumes-1500, checked 2026-10-02}
}