Which of the following is true?

You issue the no auto-reg-ephone command on a CME router.
Which of the following is true? (Select the best answer.)

A.
No phones can automatically register with CME.

B.
Phones explicitly listed in the configuration can automatically register with CME.

C.
Phones can be registered in CME only by using the webbased GUI.

D.
The MAC addresses of phones that cannot automatically register will not be recorded.

Explanation:
Only phones that are explicitly listed in the Cisco Unified Communications Manager Express (CME)
configuration can automatically register with CME if you issue the no autoregephone command on a CME
router. When the no autoregephone command is issued in telephonyservice configuration mode, phones that
do not have a Media Access Control (MAC) address explicitly listed in the configuration will be blocked and not
able to automatically register with CME. However, phones with MAC addresses that are explicitly listed in the
configuration will still be able to automatically register.
The autoregephone command, which is issued by default on a CME router, configures a router to automatically
assign an ephone to an IP phone even if the phone’s MAC address is not explicitly listed in the configuration.
When an IP phone registers with a router that is configured with the autoregephone command, the router will
associate the MAC address of the IP phone with the first unassigned ephone on the router. If all the ephones
on the router are associated with IP phones, the router will create a new ephone, provided that the number of
configured ephones does not exceed the value of the max-ephonecommand.
On a Cisco 1700 router that is running IOS 12.4(4)XC, the CME graphical user interface (GUI) will display a
dialog box that includes the words “no new phone to add” and a button labeled OK if you attempt to add a
phone when autoregistration has been disabled on the router. Autoregistration can be disabled by issuing the
no autoregephone command in telephonyservice configuration mode in the router’s commandline interface
(CLI). However, you can register phones in ways other than the CME webbased GUI if auto-registration is
disabled. For example, you can issue the macaddressmacaddresscommand in ephone configuration mode in
the CLI to manually register an IP phone with CME. The only workaround for the CME GUI error is to enable
autoregistration by issuing the autoregephone command in telephonyservice configuration mode in the CLI.
The MAC addresses of phones that cannot automatically register will be recorded by the CME router if the no
autoregephone command has been issued on the CME router. In this scenario, IP phones that are not explicitly
listed in the configuration are blocked by CME when they attempt to automatically register. CME records the
MAC address of each blocked IP phone. You can display a list of blocked IP phones by issuing the show
ephone attemptedregistrations command in privileged EXEC mode. You can erase the record of blocked IP
phone registration attempts by issuing the clear telephonyservice ephoneattemptedregistrations command in
privileged EXEC mode.

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucme/command/reference/cme_cr/
cme_a1ht.html#wp3432972036
https://www.cisco.com/c/en/us/td/docs/ios/12_4/12_4x/release/notes/rn1700xc.html#wp281798