UDP/TCP problem in cross-realm authentication

Bjoern Tore Sund bjorn.sund at it.uib.no
Fri May 22 05:43:40 EDT 2009

miguel.sanders at arcelormittal.com wrote:
> Moreover, do you even see the KRB5KRB_ERR_RESPONSE_TOO_BIG reply from the KDC?

The MIT KDC doesn't seem to see the fragmented UDP packets at all, only 
when the occasional non-fragmented packet arrives does anything happen. 
 From the client side the connection (I'm testing with a web page on 
apache) just seems to hang for 20-30 seconds before the connection falls 
back to username/password authentication.


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> -----Oorspronkelijk bericht-----
> Van: kerberos-bounces at mit.edu [mailto:kerberos-bounces at mit.edu] Namens Bjoern Tore Sund
> Verzonden: vrijdag 22 mei 2009 11:05
> Aan: kerberos at mit.edu
> Onderwerp: UDP/TCP problem in cross-realm authentication
> We have linux clients in an MIT Kerberos realm (1.6.3), Windows XP SP3 clients in AD and  two-way trust configured.  Accessing AD resources from Linux clients work perfectly.
> Accessing resources in the MIT Kerberos realm from Windows fails more often than not.  Lots of packet sniffing shows fragmented UDP packets which the unix server isn't able to reassemble.  So, in accordance with
> http://support.microsoft.com/kb/244474 we've set HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Lsa\
> Kerberos\Parameters\MaxPacketSize to 1 on the XP clients.  Still no go, they never try TCP (again sniffing both on the XP client and the unix kerberos server) but go straight for TCP.  TCP is working on the unix kerberos server, the linux clients are happily using it.  Have anyone seen MaxPacketSize fail to have effect before?  Any ideas on how to trace this further?
> -BT

Bjørn Tore Sund       Phone: 555-84894   Email:   bjorn.sund at it.uib.no
IT department         VIP:   81724       Support: http://bs.uib.no
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