One of the readiness checklists for enabling DNS in CUCM (installation readiness) is to ensure that a forward and reverse lookup zone are configured and that you create the appropriate records. The reverse PTR is used to provide IP to name lookups. So, if you change the host name of a server but do not update the reverse PTR then IP-based lookups would not resolve properly.
I know the function of the PTR records. I need to know how those records are use on the CUCM 7.x and 8.x. For example, the DNS A records are used for building the IP resolution table when CUCM boots and not for intracluster communication.
I believe the PTR record is used in order to enable proper functionality when CUCM servers are configured within a cluster. The following link pertains to an older version of CCM but also references versions 5.x, 6.x, and 7x. This isn't outlined as much in newer documentation such as the SRND. My opinion would be that, at this point, Cisco just considers it to be best practice. I'll let you know if I come across anything else.
Excerpt: Note: Without this reverse DNS entry, Cisco CallManager clustering does not work.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.