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The UPLINX CTL Report wizard generates a report that contains the CTL signatures of Cisco phones. It also compares the phones' CTL signatures to the desired values present on CUCM.
With the CTL signature report you can pinpoint CTL signature mismatches between the CUCM cluster and the phones, enabling targeted resolution of the underlying issues.
The report is generated in HTML and CSV format. It is required that the web page of Cisco phones is reachable, and the phones must be registered with CUCM. If the web server is not enabled, the wizard will ask you if you wish to enable the web page. Afterwards, it can be disabled again.
For detailed steps of the UPLINX CTL Report wizard, please see How to generate an ITL report.
View sample report in HTML
What is CTL (Certificate Trust List)?
CTL (Certificate Trust List) is a Cisco security feature on Cisco phones and secures communication between phones and from phones to the CUCM and gateways. CTL is only in use when the CUCM Cluster is in secure or mixed security mode. The mode is defined in the Enterprise Parameter cluster security mode.
You can only run the CTL Report wizard of the UPLINX Phone Control Tool, if the CUCM Cluster is in secure or mixed security mode.
Why is it important to check the CTL (Certificate Trust List) signature is correct?
Maintaining consistent and matching CTL signatures between the CUCM cluster and the phones is crucial for ensuring secure communications and the proper functioning of the Cisco Unified Communications Manager infrastructure.
The CTL itself is a list of certificates (for CUCM servers and services) that are considered trusted within the CUCM environment. The CTL signature is a cryptographic hash and is generated as MD5 or SHA1. The generated CTL report will contain the CTL signature of each phone.
When the phone's CTL signature does not match the CTL signature of the CUCM cluster, several consequences can occur:
•Impact on Secure Communications: The phone might not be able to establish secure communications with the CUCM or other devices within the network that require the trusted certificates listed in the CTL.
•Limited Functionality: In a secure or mixed security mode environment, the phone's access to certain secure services or features might be restricted until the CTL mismatch issue is resolved.
•Security Implications: If there's a mismatch in the CTL signature, it could indicate a potential security risk or a compromise in the integrity of the trust relationship between the phone and the CUCM cluster.
The mismatch between the CTL (Certificate Trust List) signatures on a phone and the CUCM (Cisco Unified Communications Manager) cluster can occur for various reasons, such as failed CTL updates, network connectivity issues, mis-configured settings, expired or revoked certificates, software bugs, or unauthorized tampering.
Resolving this mismatch involves troubleshooting network connectivity, verifying configuration settings, triggering CTL updates on the phone, checking logs for errors, and seeking assistance from Cisco support if needed. Maintaining matching CTL signatures is critical for ensuring secure communication and proper functionality within the Cisco Unified Communications Manager environment.
Read more about CTL on the Cisco guides
•IP Phone Security and CTL (Certificate Trust List)
•Understand CUCM Security By Default and ITL Operation and Troubleshooting
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The CTL report generator retrieves the CTL signature from the phones' web server. The web server must be reachable, the CTL Signature must be present in the phones web page at
http(s)://<IP of Phone>/NetworkConfigurationX
Please note that some phones might not support this web page and the CTL signature is then not obtainable.
The report can be generated during office hours.
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