krb.realms provides a translation from a hostname to the Kerberos realm name for the services provided by that host.
Each line of the translation file is in one of the following forms:
host_name kerberos_realmdomain_name kerberos_realm
domain_name should be of the form .XXX.YYY, for example, .LCS.MIT.EDU.
If a hostname exactly matches the host_name field in a line of the first form, the corresponding kerberos_realm is used as the realm of the host. If a hostname does not match any host_name in the file, but its domain exactly matches the domain_name field in a line of the second form, the corresponding kerberos_realm is used as the realm of the host.
If no translation entry applies, the host’s realm is considered to be the hostname’s domain portion converted to upper case.
There is no NIS or NIS+ support for this information.