Distinguish between user-id and machine-id

[Ashutosh Malegaonkar]

Folks,

Newbie Question:
I am writing a simple application whose end-goal is to create a user table
after looking at kerberos packets in my network.

I am currently looking TGS_REP only. Inside TGS, I am looking at
"Principal-name". Now the question is, I see both machine name and used-id
in subsequent packets.

How do I distinguish between used-id VS machine name? Is there any other
message I need to look at so that I can get only user-ids.

Thanks!
ashutosh