An administrator is attempting to add a new IP phone to the network. The phone does not register and continues to cycle through the registration process. The administrator checks and notices that…

A misconfigured TFTP server would cause the phone to fail during configuration file download after obtaining a correct IP address, not result in an IP address from the wrong network.

The DHCP server is functioning correctly for its scope; the problem is that the phone is on the wrong VLAN and reaches a different DHCP scope than intended.

If CUCM were down, the phone would still obtain a correct IP address and only fail at the SIP or SCCP registration step, not at IP addressing.

Cisco IP phones rely on the switch port's voice VLAN configuration to place their traffic on the correct Layer 2 segment. When the voice VLAN is set incorrectly, the phone sends DHCP requests on the wrong VLAN and receives an IP address from a DHCP scope associated with that wrong VLAN. With an out-of-scope IP address, the phone cannot reach Cisco Unified Communications Manager and loops through the registration process.

The PSTN gateway handles external call routing and plays no role in IP phone DHCP assignment or initial registration.