At a high level in NTLM, a communication takes place between the client and server, then the server checks with the authority to authenticate the client. But in Kerberos, the client first checks in with the authority, obtains a ticket, and uses that to prove identity. Kerberos supports caching tickets, so an entire communication could occur with but a single interaction with the authority. NTLM doesn't support caching, so every request from the client results in another request to the authority. And the differences go on.
Different protocols can require different routes to authentication.
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