VoIP IP phone registration issues

When an IP phone is connected to a network, it goes through a registration process. When an IP phone cannot register, the following troubleshooting steps and checks should be performed.

1. Make sure the voice VLAN configuration on the port of the switch to which the phone is connected is configured correctly.
2. Ensure that the DHCP server is reachable on the voice VLAN and is configured correctly.
3. Confirm that option 150 is configured correctly on the DHCP server and is pointing to an active TFTP server.
4. Make sure the TFTP server is reachable from the voice VLAN.

Links:

https://forum.networklessons.com/t/voice-vlan/783/26?u=lagapides

https://networklessons.com/cisco/ccna-routing-switching-icnd1-100-105/voice-vlan/

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_55_se/configuration/guide/scg3750/swvoip.html