[LARTC] Re: RFC1918 blocking and DNAT

[LARTC] Re: RFC1918 blocking and DNAT

[Antonio Paulo Salgado Forster]

Not much related to this, but is there any way to make CBQ match packets
with no firewall mark set (default) when using Firewall mark classifier?

Thanks!

Forster




"Alexander W . Janssen" <yalla@ynfonatic.de>@lists.samba.org on 11/04/2001
18:34:57

Please respond to "Alexander W . Janssen" <yalla@ynfonatic.de>

Sent by:  netfilter-admin@lists.samba.org


To:   Urs Thuermann <urs@isnogud.escape.de>
cc:   Netfilter Mailinglist <netfilter@lists.samba.org>
Subject:  Re: RFC1918 blocking and DNAT



Hello Urs,

On Sun, Apr 01, 2001 at 11:03:42AM +0200, Urs Thuermann wrote:
[...]
>     iptables -t mangle -A PREROUTING -s 10.0.0.0/8     -j MARK --set-mark
1
>     iptables -t mangle -A PREROUTING -d 10.0.0.0/8     -j MARK --set-mark
1
>     iptables -t mangle -A PREROUTING -s 172.16.0.0/12  -j MARK --set-mark
1
>     iptables -t mangle -A PREROUTING -d 172.16.0.0/12  -j MARK --set-mark
1
>     iptables -t mangle -A PREROUTING -s 192.168.0.0/16 -j MARK --set-mark
1
>     iptables -t mangle -A PREROUTING -d 192.168.0.0/16 -j MARK --set-mark
1
>
>     iptables -A extin -m mark --mark 1 -j DROP
>
> Would this work?  And is there another way to do it, using only the
> filter tables?

yes, this would work. Another way to restrict so called "martians"
(packets with source-ip equal to private assigend ones which come from
the internet) is setting the kernel-option "reverse path filtering" to
the value of 2 for your external interface. Example:

   echo 2 > /proc/sys/net/ipv4/conf/ippp0

   if ippp0 is your external interface.

Turning on these options drops all packets with obvisiously "bogus"
packets, that means: If you have a network 172.16.0.0/12 behind your
firewall, then no one with one of these IP's would be allowed to be
routed through your Linux-Box. You might want to read the "Advanced
Routing HOWTO", especially section 12.1 "Reverse Path Filtering"
(http://www.linuxdoc.org/HOWTO/Adv-Routing-HOWTO-12.html).

Anyway, but the best would be to block martian on the router. Just add
the crap to the DENY-list of the router. Possible at least on Cisco.
Call your provider if you can't administrate your router by yourself.

> BTW, the man page does not tell what the default value of a packets
> netfilter mark is when it is not changed in the mangle table.  I
> assume this is 0, right?

There is no implicit mark, you allways have to give a --set-mark.

Cheers, Alex.


--
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