Hi Gary,

The recommendation is actually to use IP Addresses instead of Hostnames in CCM installs;

Domain Name System (DNS)

DNS enables the mapping of host names and network services to IP addresses within a network or networks. DNS server(s) deployed within a network provide a database that maps network services to hostnames and, in turn, hostnames to IP addresses. Devices on the network can query the DNS server and receive IP addresses for other devices in the network, thereby facilitating communication between network devices.

Complete reliance on a single network service such as DNS can introduce an element of risk when a critical IP Communications system is deployed. If the DNS server becomes unavailable and a network device is relying on that server to provide a hostname-to-IP-address mapping, communication can and

will fail. For this reason, Cisco highly recommends that you do not rely on DNS name resolution for any communications between Unified CM and the IP Communications endpoints. The use of DNS to provide

simplified system management and Server (SRV) records is supported, and Cisco recommends defining each Unified CM cluster as a member of a valid sub-domain within the larger organizational DNS domain whenever possible.

Configure Unified CM(s), gateways, and endpoint devices to use IP addresses rather than hostnames. Cisco does not recommend configuration of DNS parameters such as DNS server addresses, hostnames, and domain names in endpoint device configurations. During the initial installation of the publisher in a Unified CM cluster, the publisher will be referenced in the server table by the hostname you provided for the system. Before installation and configuration of any subsequent subscribers or the definition of any endpoints, you should change this server entry to the IP address of the publisher rather than the

hostname. Each subscriber added to the cluster should be defined in this same server table via IP address initially and not by hostname. Each subscriber should be added to this server table one device at a time, and there should be no definitions for non-existent subscribers at any time other than the new subscriber being installed.

During installation of the publisher and subscriber, Cisco recommend that you do not select the option to enable DNS unless DNS is specifically required for system management purposes. If DNS is enabled,

Cisco still highly recommend that you do not use DNS names in the configuration of the IP

Communications endpoints, gateways, and Unified CM servers. Even if DNS is enabled on the servers in the cluster, it is never used for any intra-cluster server-to-server communications and is used only for

communications to devices external to the cluster itself.

From this good SRND;

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/5x/50nstrct.pdf

Hope this helps!

Rob