All of your department’s IP phones are connected to a switch that does not support PoE. A DHCP server has
been configured for the voice VLAN on the switch. Another administrator power cycles the switch without
warning. No calls are in progress.
Which of the following is most likely to occur? (Select the best answer.)

A.
The IP phones will power down until the switch restarts.

B.
The IP phones will not be affected by the power cycle.

C.
The IP phones will disappear from the UCM configuration.

D.
The IP phones will reset and lose IP configuration information.

Explanation:
Most likely, the IP phones will reset and lose IP configuration information when the administrator power cycles
the switch because, in this scenario, the IP addressing information is automatically assigned to each IP phone
by a Dynamic Host Configuration Protocol (DHCP) server. When an IP phone is disconnected from Cisco
Unified Communications Manager (UCM), the phone will automatically reset in an attempt to re-establish
communication. Therefore, if an IP phone suddenly resets or is continuously attempting to register with UCM, it
is important to first verify the phone’s connectivity to the network switch.IP phones can be manually configured with IP addressing information. In that case, the IP phones would reset.
Similarly, the IP phones will not be able to download configuration files from the Trivial File Transfer Protocol
(TFTP) server until connectivity to the switch is restored.
The IP phones will not disappear from the UCM configuration. You can verify that an IP phone exists in the
UCM by clicking Device > Phone > Find in UCM Administration and searching for the particular IP phone’s
Media Access Control (MAC) address. The IP phone will no longer be registered with UCM when it loses
connectivity. However, the IP phone’s record in the UCM configuration will remain there.
The IP phones will not power down until the switch restarts, because the switch in this scenario does not
support Power over Ethernet (PoE). Therefore, the IP phones in this scenario must be connected to individual
power supplies in order to obtain power. In addition to registration problems, IP configuration problems, and
TFTP configuration problems, IP phones that are powered directly from a switch by using PoE will not be able
to receive power until the switch has restarted.
The IP phones will be affected by the power cycle. In addition to registration problems, IP configuration
problems, and TFTP configuration problems, IP phones that are powered directly from a switch by using PoE
will not be able to receive power until the switch has restarted.

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cuipph/7905g_7912g/5_0/sip/english/administration/
guide/5_0/LowPtrb.html#wp1092158