While trying to register to Cisco UCM, a Cisco IP phone reports TFTP authorization failure. Which cause of this issue is true?
A. DHCP option 150 has the incorrect TFTP address configured.
B. The phone has a cabling issue.
C. The TFTP address for the phone is not in the CTL file.
D. A firewall in the network is blocking access.
I think both can be correct A and C. Depends whether you see it as a problem of the DHCP pointing the phone to wrong CUCM (A) or problem of CTL not containing proper CUCM address if DHCP points the phone to correct CUCM.
The answer is C, it’s authorization failure, the TFTP address is not exist in the CTL file of the phone.
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cuipph/7832/english/adminguide/cs78_b_conference-7832-admin-guide-cucm/cs78_b_conference-7832-admin-guide-cucm_chapter_01001.html#CUIP_RF_T808A2C2_00