Source note · SIP 503 and trunk out-of-service failures
An INVITE or OPTIONS to the Direct Routing SIP proxy whose Contact header uses an IP address instead of the SBC FQDN is refused with 403 Forbidden.
Checked 2026-09-25
- Vendor
- Microsoft
- Product
- Teams Phone Direct Routing
- Subsystem
- OPTIONS
- Deployment
- multi-tenant
- Region
- not restricted
- Release range
- current as of 2026-09-25
- Checked
- 2026-09-25
Sources
- Teams Phone System Direct Routing: SIP protocol — Microsoft · tier 2 current vendor documentation · Section 'Detailed requirements for Contact header and Request-URI' > Contact header
Cite this note
APA
WarmTransfer. (2026, September 25). SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-contact-ip-403. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-contact-ip-403
BibTeX
@misc{warmtransfer-claim-sip-503-trunk-failures-dr-contact-ip-403,
title = {SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-contact-ip-403},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-contact-ip-403},
note = {Source note sip-503-trunk-failures-dr-contact-ip-403, checked 2026-09-25}
}