100-890 · Question #49
The Certificate Trust List (CTL) file is an important file that the Cisco IP phone downloads during the bootup process What information is defined in the CTL file?
The correct answer is C. CTL contains a list of Cisco Unified CM and TFTP servers that the IP phone is authorized to connect. See the full explanation below for the reasoning.
Question
The Certificate Trust List (CTL) file is an important file that the Cisco IP phone downloads during the bootup process What information is defined in the CTL file?
Options
- ACTL contains a list of certificates and feature licenses that the IP phone is authorized to use
- BCTL specifies a list of configuration files that the phone can download from the TFTP server
- CCTL contains a list of Cisco Unified CM and TFTP servers that the IP phone is authorized to connect
- DCTL defines how the Cisco IP Phone communicates with Cisco Unified CM and provides a phone with
How the community answered
(30 responses)- A10% (3)
- B7% (2)
- C80% (24)
- D3% (1)
Community Discussion
4
Bao N.May 15, 2026C is the correct answer here. The CTL file is essentially a trust anchor for the phone during its secure boot process, it tells the phone which Unified CM nodes and TFTP servers are legitimate so it will only pull configs and register with servers that have been cryptographically verified. Without a valid CTL, the phone either falls back to non-secure mode or refuses to connect entirely depending on how your cluster is configured. A trips people up because licenses are handled separately through the License Manager, not the CTL, and D looks like it got cut off in the question bank but it is describing something closer to the device config file, not the CTL itself.
Brenda K.May 20, 2026C is the one, and it is worth locking in fast because this is a quick win question. The CTL file is essentially a trust anchor list, so the phone checks it to verify that the Unified CM and TFTP servers it is talking to are authorized, which is the whole point of the security-by-default framework in CUCM.
Samuel O.May 2, 2026I actually read option A first and thought "yeah, certificates and licenses, that makes sense for a trust list," but then I remembered watching our security team set up CTL files years ago and the whole point was controlling which call managers and TFTP servers the phone would even talk to, so C clicked right away. The word "trust" in CTL is really about trusting the servers on the other end, not managing licenses, those live somewhere else entirely.
Brenda K.May 5, 2026The "trust" misdirect in that question is a 10-second trap, so flag it fast and move on, your time is better spent on the weightier configuration questions later in the set.