Re: [SLUG] iptables packet drop logging

From: billt (billt@ifelse.org)
Date: Mon Jul 02 2001 - 06:40:03 EDT


On Fri, Jun 29, 2001 at 08:29:27PM -0400, Brian S. Armstrong wrote:
> Is there any way to get iptables to log the DROP packets to
> /var/log/messages the same way iptables does with the DENY packets?

There isn't a specific switch to turn on logging in iptables.
Instead, you can either insert a matching rule to match the same type
of packet you want to drop, but make the target LOG instead of DROP
(there are options like --log-prefix and --log-level for the LOG
target) like:

iptables -A FORWARD -p tcp --dport 23 \
         -j LOG --log-prefix "TELNET "
iptables -A FORWARD -p tcp --dport 23 \
         -j DROP

...or set up a chain called something like LOGDROP with the rules:

iptables -N LOGDROP
iptables -A LOGDROP -j LOG --log-prefix "LOGDROP "
iptables -A LOGDROP -j DROP

then any packet that should be dropped and be sent to LOGDROP (-j
LOGDROP) which will log the packet then drop it. So there's no need
for a bunch of duplicate matching rules.

Either way, log messages from the LOG target will go to the 'kern'
 syslog facility.



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