For quite some time, Microsoft’s operating systems have been set by default to register a machine’s IP addresses to the assigned DNS zone by default:

 
While this can be very convenient, it can also lead to some big problems particularly with some of the Office Communications Server roles.  It will likely lead to all manner of problems and it’s not easy to find the cause!

The problems show up on the Office Communications Server roles that use more than one IP address: the Mediation Server and the Edge Server.  The Best Practice on the Mediation server is to install two network interface boards with individual IP addresses on each one.  It also specifies that these addresses should be on separate subnets.  For the Edge, the Best Practice is to install 4 network interface cards with individual IPs.  OK, before you start letting me have it, this is Best Practice and I’m not getting into a discussion about straying from Best Practice regarding network cards and IP addresses etc. on these boxes.  The bottom line is when using more than 1 IP address on either of these roles the DNS autoregistration will register all the IP addresses.  You will end up with several (1 for each IP on the box)  “A” records in the DNS zone with the same hostname but different IP addresses.   

As an analogy, think of this as being a dynamic rather than static DNS address.  Would you ever give a server device a dynamic TCP/IP address?  Not likely!  I use the same reasoning when I am installing OCS servers.   I always disable the autoregistration on the Mediation and Edge servers and usually do so on the other OCS roles as well.  I like my servers to have static IP addresses and static DNS entries! 
Remember; once you disable the autoregistration you must manually create the “A” record for the IP or IPs.  Typically, I will create the “A” record for the IP representing the network interface card facing the OCS Pool on the Mediation Server and not create a record for the gateway facing interface.  For the Edge server, I create “A” records for the network cards/IP addresses facing the public side within the external DNS zone and create an “A” record for the internal interface in the appropriate internal zone.  Again, this is just an example, I’m not saying its right or wrong for every install of Mediation or Edge servers.  Let’s keep our eye on the prize!

The moral of the story, and some of my Best Practices:

1. Don’t let Office Communications Server hardware autoregister themselves to DNS.  Sidebar: Don’t let servers in general autoregister themselves to DNS, especially those with multiple IP addresses.

2. All Office Communications Servers have “A” records manually/statically created for them within DNS.  Do not create “A” records with identical host names and different IP addresses in the same DNS zone.

3. At several points during an installation, double check the Office Communications Server DNS records.

4. If needed, the “hosts”  file on a machine is your friend!