Source note · SIP ALG problems on firewalls and routers
Teams Direct Routing refuses an incoming INVITE or OPTIONS whose Contact hostname is an IP address rather than an FQDN, with a 403 Forbidden.
Checked 2026-09-25
- Vendor
- Microsoft
- Product
- Teams Phone Direct Routing
- Subsystem
- SIP signaling
- Deployment
- multi-tenant, hybrid
- 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 · Detailed requirements for Contact header and Request-URI > Contact header last paragraph
Cite this note
APA
WarmTransfer. (2026, September 25). SIP ALG problems on firewalls and routers: source note sip-alg-problems-teams-dr-ip-contact-403. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-alg-problems-teams-dr-ip-contact-403
BibTeX
@misc{warmtransfer-claim-sip-alg-problems-teams-dr-ip-contact-403,
title = {SIP ALG problems on firewalls and routers: source note sip-alg-problems-teams-dr-ip-contact-403},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-alg-problems-teams-dr-ip-contact-403},
note = {Source note sip-alg-problems-teams-dr-ip-contact-403, checked 2026-09-25}
}