        • Instances: are used for service principals and special
administrative principals.    • Realms: the unique realm of
control provided by the Kerberos installation. Usually the DNS
domain converted to uppercase (EXAMPLE.COM).    • Key
Distribution Center: (KDC) consist of three parts, a database of
all principals, the authentication server, and the ticket
granting server. For each realm there must be at least one KDC.
• Ticket Granting Ticket: issued by the Authentication Server
(AS), the Ticket Granting Ticket (TGT) is encrypted in the
user's password which is known only to the user and the KDC.
• Keytab Files: are files extracted from the KDC principal
database and contain the encryption key for a service or host.
To put the pieces together, a Realm has at least one KDC,
preferably two for redundancy, which contains a database of
Principals. When a user principal logs into a workstation,
configured for Kerberos authentication, the KDC issues a Ticket
Granting Ticket (TGT). If the user suppli