RE: Snort Rules Help

["Esler, Joel - Contractor" <joel.esler () rcert-s army mil>]

is it coming through on one of the preprocessors?  What alert is it
generating?
 
J

-----Original Message-----
From: snort-users-admin () lists sourceforge net
[mailto:snort-users-admin () lists sourceforge net] On Behalf Of
Cunningham, Andy
Sent: Friday, July 09, 2004 12:26 PM
To: Snort-users () lists sourceforge net
Subject: [Snort-users] Snort Rules Help


Hi there. 
 
Can someone help with a problem I'm having trying to write snort rules.

 
I have a series of rules to either pass legitimate traffic or alert on
certain events.  Finally I have a catch all rule to alert on any packet
not covered by the above.  I've changed the rule order with -o so that
pass rules have the desired effect, and this seems to be working.
 
pass udp $SRC any <> $DEST $PORT (classtype:ignore)
alert ip any any -> any any (msg: "Unexpected unclassified traffic";
classtype: unexpected-traffic; )

 
 
These rules work fine for most of the traffic, but when I get a
fragmented UDP packet come through, the fragment causes the altert to be
generated.  
 
I've tried adding a fragoffset:0 into the rule to only altert if it's
the first fragment, but it doesn't seem to help. 
 
Can anyone suggest what I might be doing wrong?
 
Thanks in advance