Calendar Server requires a few things on your network before you can start using it:
If a firewall is between Calendar Server and your users, it must be configured to allow traffic on TCP port 8008 (or 8443 for Secure Sockets Layer [SSL] encryption).
Calendar Server needs directory service. (See the next section.)
Calendar Server can work better with a DNS system with full reverse lookups running on the network in midsize to large networks.
Here are some more specifics about directory service and optional DNS.
Directory service for Calendar service
Calendar Server must be connected to a directory server of some type on the network. This could be Open Directory running on the same server as Calendar Server, accessible from the Open Directory pane in the Server app. (See Part II for more on directory services.)
Open Directory could be located on the same Mac server or on another server computer (Mac OS X 10.5 Server or later), or the directory could be another non-Apple LDAP server such as Microsoft’s Active Directory. You don’t need to modify the directory service.
Optional: Setting up DNS for calendar service
Although it’s not a requirement, you can add a service record ...