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PASSEDserver / sip_trunk_failure
SIP Trunk Registration Failure — All Outbound Calls Dead
The SIP trunk between the on-premises PBX and the ITSP loses registration after the provider changes their SBC IP without notice. All outbound and inbound PSTN calls fail. Internal extension-to-extension calls still work.
Pattern
VOIP_QUALITY
Severity
CRITICAL
Confidence
85%
Remediation
Remote Hands
Test Results
| Metric | Expected | Actual | Result |
|---|---|---|---|
| Pattern Recognition | VOIP_QUALITY | VOIP_QUALITY | |
| Severity Assessment | CRITICAL | CRITICAL | |
| Incident Correlation | Yes | 18 linked | |
| Cascade Escalation | N/A | No | |
| Remediation | — | Remote Hands — Corax contacts on-site support via call, email, or API |
Scenario Conditions
3CX PBX v20. SIP trunk to provider (Lumen). Provider changed SBC IP from 204.15.80.10 to 204.15.80.50 without notification. Registration timeout after 5 retries. 200 desk phones. 50 concurrent call capacity.
Injected Error Messages (2)
SIP trunk registration failure — 3CX PBX trunk 'Lumen-SIP-Primary' status: UNREGISTERED, SIP 408 Request Timeout to 204.15.80.10:5060, 5 consecutive registration failures, all PSTN calls routing to voicemail, outbound calls returning SIP 503 Service Unavailable
All outbound PSTN calls failing — SIP INVITE receiving no response from ITSP, SIP trunk down, call routing table has no backup trunk, 200 users unable to make external calls, SIP ALG on firewall verified disabled
Neural Engine Root Cause Analysis
The 3CX PBX server is experiencing SIP trunk registration failures with the primary Lumen carrier, receiving SIP 408 Request Timeout errors when attempting to register with 204.15.80.10:5060. This indicates either network connectivity issues between the PBX and the SIP provider, firewall/NAT traversal problems blocking SIP traffic, or the carrier's SIP server being unavailable. The 5 consecutive failures and correlation with 10 other incidents suggests a broader network or infrastructure issue affecting external connectivity from this location.
Remediation Plan
1. Verify network connectivity by testing ping and traceroute to 204.15.80.10 from the PBX server. 2. Check firewall rules and NAT configuration for UDP port 5060 and RTP port ranges. 3. Test SIP registration manually using SIP diagnostic tools. 4. Contact Lumen to verify SIP trunk status and any reported outages. 5. If network connectivity is confirmed working, restart the 3CX Phone System service. 6. Consider failing over to backup SIP trunk if available. 7. Monitor SIP registration status and call quality after remediation.
Tested: 2026-03-30Monitors: 2 | Incidents: 2Test ID: cmncjjqhz020iobqer28u8dd4