Refer to the exhibit. An administrator is attempting to register a SIP phone to a Cisco UCM but the registration is failing. The IP address of the SIP Phone is 10.117.34 222 and the IP 1 address of…

While certificate issues can cause SIP registration failures, especially for secure SIP (TLS on port 5061), a blocked port 5060 for standard SIP is a more fundamental and common cause when basic IP connectivity is confirmed by pings.

The problem statement indicates successful pings to the UCM's IP address, suggesting that basic network path resolution to the UCM is functioning. If the phone is configured with the UCM's IP address, DNS lookup for an FQDN is not necessarily the immediate issue preventing TCP connection establishment.

NTP mismatches can lead to various communication issues, including certificate validation failures, but they are less likely to prevent the initial TCP session from being established on the correct port than a direct port block.

Successful pings confirm basic network connectivity between the SIP phone and Cisco UCM at the IP layer. However, SIP registration relies on specific transport ports, commonly TCP port 5060 (or 5061 for SIP over TLS). If a network device, such as a firewall or ACL, is blocking TCP port 5060 between the SIP phone and the Cisco UCM, the SIP registration messages cannot reach the UCM, causing the registration to fail. Resolving this requires opening the necessary TCP port.