Configure CA Support on a Cisco Router
Step 3 – add a CA server entry to the router host table

The host name and IP domain name of the router must be configured if this has not already been done. This is required because the router assigns a fully qualified domain name (FQDN) to the keys and certificates used by IPSec, and the FQDN is based on the host name and IP domain name assigned to the router. For example, a certificate named "router20.example.com" is based on a router host name of "router20" and a router IP domain name of "example.com".

To specify or modify the hostname for the network server, use the hostname global configuration command . The setup command facility also prompts for a hostname at startup.

To define a default domain name that the Cisco IOS software uses to complete unqualified hostnames use the ip domain-name global configuration command. Unqualified names are names without a dotted-decimal domain name. To disable use of the DNS, use the no form of this command.

Use the ip host global configuration command to define a static hostname-to-address mapping in the host cache . To remove the name-to-address mapping, use the no form of this command.