AS_REQ represents the client request within the AS Exchange

AS_REQ is the initial authentication request, the Kerberos client (kinit) asks the KDC (more specifically the Kerberos Authentication Service) for a Ticket Granting Ticket. The request is completely Plaintext and looks like this:

AS_REQ = ( PrincipalClient , PrincipalService , IP_list , Lifetime )

IP_list may also be null. In this case the corresponding ticket can be used by any machine. This resolves the problem of those Kerberos clients under NAT, since their request would arrive at the service with a source address different from that of the requesting user, but the same as the router making the NAT. Instead, in the case of machines with more than one network card, IP_list should contain the IP addresses of all the cards: in fact it would be difficult to predict beforehand with which connection the server which provides the service would be contacted.

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