Can anyone tell me why RADIUS uses two UDP port while TACACS+ uses only one ?

[Honey Chaurasia]

I dont know the answer. Someone asked me in an interview.

[Tarik Admani]

You can enable separate servers for authentication/authorization, and use separate servers for accounting.

However that is the way the protocol was designed there isn't a clear explanation what drove that decision.

It would be a great question to ask in your thank you letter.

Thanks