The Key Distribution Centers (KDCs) issue Kerberos tickets. Each KDC
contains a copy of the Kerberos database. The master KDC contains the
master copy of the database, which it propagates to the slave KDCs at
regular intervals. All database changes (such as password changes) are
made on the master KDC.
Slave KDCs provide Kerberos ticket-granting services, but not database
administration. This allows clients to continue to obtain tickets when
the master KDC is unavailable.
MIT recommends that you install all of your KDCs to be able
to function as either the master or one of the slaves. This will enable
you to easily switch your master KDC with one of the slaves if
necessary. (See Switching Master and Slave KDCs.) This installation
procedure is based on that recommendation.