From mboxrd@z Thu Jan  1 00:00:00 1970
From: Patrick McHardy <kaber@trash.net>
Subject: Re: checking rule specifications in a match
Date: Tue, 20 Jun 2006 15:23:23 +0200
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To: =?ISO-8859-15?Q?Bj=F6rn_Lindstr=F6m?= <bjorn.mailinglist@gmail.com>
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Bj=F6rn Lindstr=F6m wrote:
> Hi.
> I am writing an iptables match to match the IEC-60870-5-104 protocol.
> I only want this match to be used on tcp packets and therefore I want
> iptables to reject rules if does not specify tcp as the protocol (-p
> tcp). I am currently doing this check in the checkentry function in the
> kernel module. This works but the error message only say "iptables:
> Unknown error 4294967295" if -p tcp is left out. Is it possible to do
> this check any other way to get a more comprehensible error message?

This is probably because you're using a broken version of iptables
userspace. Current kernels allow you to enforce a specific protocol
by setting the .proto field in struct xt_match, which will also handle
inversion correctly and logs a message to the ringbuffer on error.