
Description
We have configured the HA feature with two UCM630X successfully. We also configure a SIP Peer trunk with an Avaya PBX. However, when the phones are registered with HA Cluster IP address, the outbound calls fail with an error: The call is rejected by the server. The outbound call works if the phones are registered with Primary UCM A Local IP address or Peer IP.
Setup
Primary UCM A: 10.91.0.90
Secondary UCM B: 10.91.0.92
HA Cluster IP: 10.91.0.91
Analysis & Troubleshooting
From the UCM’s packet capture, it is found that the Avaya CM sends 403 Forbidden (Invalid domain in From header) to UCM when the call is made

Primary UCM A sends INVITE with From header <sip:10101@10.91.0.90>
To resolve this error, navigate to UCM A > VOIP Peer Trunk Setting > From Domain > enter HA Cluster IP (for eg. 10.91.0.91 in this case).