krb5 "Error Code 52" - UDP packet size - TCP fallback

[Uli]

Hi folks,

I have a problem authenticating my RedHat 9 against Active Directory. 
I'm running the MIT implementation of kerberos.

When I run kinit for my testuser it works fine. The testuser ist just a 
member of the domain with read access to the directory. No other groups 
or permissions. When I try to do a kinit for my own account with all its 
group memberships, etc., I just get the error code 52. I read on the 
internet that this is because the Windows 2000 server switches from UDP 
to TCP if the maximum packet size is exceeded. I think this happens with 
all my "normal" users.

It seems like a lot of people managed to authenticate against AD. 
Maybesomeone can help me with this problem and tell me how he solved it.

Thanks in advance.

Cheers,
Uli