• When Alice requests a TGT or a ticket to Bob, the KDC puts her 4-octet IPv4 address
inside the ticket. Bob, when presented with a ticket, will check to make sure that the
network layer source address on the connect request is the same as the one specified
inside the ticket.
• Likewise, when the KDC receives a ticket request, it checks that the request is coming
from the network layer address specified in the TGT.
• There are two reasons for putting Alice's network layer address in the ticket.
• The first reason is to prevent Alice from giving the ticket and session key to some
third party, so that the third party can impersonate Alice.
• The second reason is to prevent some third party from intercepting the ticket and
authenticator on the wire and using it from Trudy's network layer address.
• Putting the network layer address in the ticket instead of the authenticator is done to
specifically disallow delegation. Kerberos V5 does allow delegation, but only with the
mediation of the KDC and only if the originally acquired ticket explicitly permits it.