reverse (PTR) records and CUCM 7.x, 8.x

[aalejo]

In several Cisco documents i have seeing that reverse (PTR) records should be update when CUCM name is change.

Somebody knows the reason of this?. Up to my knowledge CUCM only uses DNS forward A record at boot up for filling the hosts, rhosts, sqlhosts, and services files.

Thanks

[David Hailey]

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.

Hailey

[aalejo]

Hi David

Thanks for your answer.

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.

Regards

[David Hailey]

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.

Link:  http://www.cisco.com/image/gif/paws/13930/cm301_dns.pdf

Hailey

[aalejo]

Hi David

My five points for finding that old and interesting bug. Acording the bug id affects inter cluster communications only.

Alex