From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Taylor, Grant" <gtaylor@riverviewtech.net>
Subject: Re: Prevent traceroutes
Date: Fri, 20 May 2005 02:44:14 -0500
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> iptables -t filter -A DROP_TRACE -o eth0 -p udp -m recent --name Drop_Traceroute --update --seconds 200 --rdest -j DROP
> iptables -t filter -A DROP_TRACE -o eth0 -p udp -m recent --name Drop_Traceroute --set --rdest -m ttl --ttl-eq 1 -j DROP
> iptables -t filter -A DROP_TRACE -o eth0 -p icmp -m recent --name Drop_Traceroute --update --seconds 200 --rdest -j DROP
> iptables -t filter -A DROP_TRACE -o eth0 -p icmp -m recent --name Drop_Traceroute --set --rdest -m ttl --ttl-eq 1 -j DROP
> 
> The only thing that I have not figured out as of yet how to do is DROP 
> the first packet that the firewall sees as every attempt that I made, 
> even a DROP policy on the FORWARD and OUTPUT chain, did not block the 
> first "TTL Time Exceeded" response.

I just figured it out and have tested it.  I *think* the reason that my first script did not work for the first router is b/c the raw routing code will send the ICMP TTL time exceeded message before any of the chains in the filter table have a chance to process the packet.  Hens my using the nat:PREROUTING chain.  I have also made the filtering process easier too as you do not have to filter in the filter:INPUT and filter:FORWARD chains, just the nat:PREROUTING now.

iptables -t nat -A PREROUTING -i $LAN -p udp -m recent --name Drop_Traceroute --update --seconds 200 --rdest -j DROP
iptables -t nat -A PREROUTING -i $LAN -p udp -m recent --name Drop_Traceroute --set --rdest -m ttl --ttl-eq 1 -j DROP
iptables -t nat -A PREROUTING -i $LAN -p icmp -m recent --name Drop_Traceroute --update --seconds 200 --rdest -j DROP
iptables -t nat -A PREROUTING -i $LAN -p icmp -m recent --name Drop_Traceroute --set --rdest -m ttl --ttl-eq 1 -j DROP

This will prevent any traceroutes via the methods mentioned before from any computer coming in on interface $LAN.



Grant. . . .