Source note · SIP call forwarding and routing loops
If an SBC or PBX acting as a B2BUA starts each outgoing leg at a fresh Max-Forwards value instead of copying and decrementing the received value, a call looping between that device and a carrier never runs Max-Forwards down to zero and is not stopped by a 483.
inferred · Checked 2026-09-25
- Vendor
- IETF
- Product
- SIP
- Subsystem
- B2BUA loop detection
- Deployment
- any
- Region
- not restricted
- Release range
- general
- Status
- inferred
- Checked
- 2026-09-25
Sources
- RFC 7332: Loop Detection Mechanisms for Session Initiation Protocol (SIP) Back-to-Back User Agents (B2BUAs) — IETF / RFC Editor · tier 1 standards and regulators · Section 3 B2BUA Behavior (reasoning from the copy-and-decrement requirement)
Cite this note
APA
WarmTransfer. (2026, September 25). SIP call forwarding and routing loops: source note sip-forwarding-loops-b2bua-reset-defeats. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-forwarding-loops-b2bua-reset-defeats
BibTeX
@misc{warmtransfer-claim-sip-forwarding-loops-b2bua-reset-defeats,
title = {SIP call forwarding and routing loops: source note sip-forwarding-loops-b2bua-reset-defeats},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-forwarding-loops-b2bua-reset-defeats},
note = {Source note sip-forwarding-loops-b2bua-reset-defeats, checked 2026-09-25}
}