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Re: is it possible to block ip packets that contains experimental tcp op

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Subject: Re: is it possible to block ip packets that contains experimental tcp options ?
From: Pascal Hambourg <pascal.mail@plouf.fr.eu.org>
Date: Mon, 21 May 2007 20:27:15 +0200
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Hello,

Glenn Terjesen a écrit :
What i meant with "experimental tcp options" is that my ids (snort)
keept logging these "experimental tcp options"

#
code 76
length 8
data 01019DEDBEF00005

I know this aint a snort list, but my servers don't serve any services
that require this kind of traffic.

So i was wondering if iptables has any way of blocking these.

If you have a black list of options you want to drop (or a white list of allowed options), what about the "--tcp-option" option of the "tcp" match ?

These to magic lines fixed it all
iptables -A FORWARD -p tcp --tcp-flags ALL ALL -j DROP
iptables -A FORWARD -p tcp --tcp-flags ALL NONE -j DROP

I wonder how these rules could drop packets according to TCP options. TCP flag combinations are not TCP options.


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