The domain of a Kerberos installation is called a realm and is identified by a name, such as FOOBAR.COM or simply ACCOUNTING. Kerberos is case-sensitive, so foobar.com is actually a different realm than FOOBAR.COM. Use the case you prefer. It is common practice, however, to use uppercase realm names.

It is also a good idea to use your DNS domain name (or a subdomain, such as ACCOUNTING.FOOBAR.COM). As shown below, your life as an administrator can be much easier if you configure your Kerberos clients to locate the KDC and other Kerberos services via DNS. To do so, it is helpful if your realm name is a subdomain of your DNS domain name.

Unlike the DNS name space, Kerberos is not hierarchical. You cannot set up a realm named FOOBAR.COM, have two “subrealms” named DEVELOPMENT and ACCOUNTING underneath it, and expect the two subordinate realms to somehow inherit principals from FOOBAR.COM. Instead, you would have three separate realms for which you would have to configure crossrealm authentication for users from one realm to interact with servers or other users from another realm.

For the sake of simplicity, assume you are setting up just one realm for your entire organization. For the remainder of this section, the realm name EXAMPLE.COM is used in all examples.