DNS Unreachable Warning – CUCM Version 11.x

Recently upgraded a UC environement from 10.5 to 11.5. After the upgrade was complete, the CUCM Publisher server displayed a “DNS Unreachable” error upon logging into the Administration webpage.


This warning message only appeared on the CUCM Publisher and not the subscriber etc. I confirmed DNS had been configured identically for both the publisher and subscriber. I read that CUCM Version 11.x no does a couple of more network tests that have a direct impact on warning/error messages being displayed on the GUI. One of these tests is against the DNS Reverse Lookup Zone. Pre 11.x versions.. The CUCM server would check to see if a PTR record existed for the hostname, in fact this is required for CUCM installation process to succeed. In version 11.x the CUCM now also continuously checks against the Reverse Lookup Zone for mismatches and displays a warning message on the GUI. In my case, the customer had created an additional A Record for user friendly purposes called myphone.domain.com.au, this automatically created a PTR record. So when CUCM ran checks against the Reverse Lookup Zone, the results displayed a mismatch. Hence the warning was raised and displayed. (Although DNS was functioning perfectly)

Removing this PTR Record resolved the issue with the warning message.

I ran the command “utils diagnose test” to pin point the issue.


This entry was posted in Cisco UC and tagged , by ben. Bookmark the permalink.

2 thoughts on “DNS Unreachable Warning – CUCM Version 11.x

  1. so was this essentially just cosmetic then, since DNS continued to work even before you removed the second record, or was there a functional impact?
    Dealing with this issue now, for the same reasons.

    • Yes, could say cosmetic. The system continues to function as per normal, however as with the other mandatory requirements ie Disk Alignment for VM etc TAC may not support the system until the DNS warning has been resolved.

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