Victor,

Because UDP is a connectionless protocol, fragmented UDP packets will be dropped if they arrive at the destination out of order. And most common sense is switch to TCP.

And did you tried add "ip inspect name FOO fragment"?

On 17/02/12 09:04, Victor Sudakov wrote:
Colleagues,

I have searched the cisco-nsp archives and found similar topics but
not much useful for my problem.

Some UDP Kerberos responses arrive fragmented because they don't
fit into the 1500 MTU. You can see a sample packet dump here:
http://zalil.ru/32722730 (the non-initial fragments are in Frames 9
and 22).

As soon as I enable CBAC on the outside interface:

interface Serial0/0
  ip access-group DENY_ALL in
  ip inspect FOO out

those non-initial fragments stop arriving. I think CBAC does not
create dynamic ACL entries for the fragments for some reason.

Other return traffic (non-fragmented) arrives OK. If I permit fragments
in the DENY_ALL access-list, the fragmented packets arrive OK (which
is the workaround I currently use).

Is it a misconfiguration, some known CBAC bug or what? Thank you in
advance for any input.

Cisco 2691, IOS 12.3(26)

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