Re: iptables configuration help

[Jason Opperisano <opie@817west.com>]

On Fri, Nov 05, 2004 at 09:11:24PM +0530, Vijay Kumar wrote:
> Hello,
> 
> I have a firewall with three nic ( external ip, DMZ ip, LAN ip ) 
> I have added a subinterface on the external interface ( public ip with a public ip address ) 
> 
> There is 1 machine on the internal LAN and I want it to go out using the IP of the sub interface,
> i.e access the internet using the exteral sub interface IP which I have added. 
> 
> I have done the following : 
> 
> iptables -t nat -I POSTROUTING -s 172.16.0.119 -o eth1:0 -j SNAT --to-source <external_ip> 

i really wish this question would come up more often...

add your secondary IP address to eth1 like so:

  ip addr add <external_ip> dev eth1

and write your NAT rule like so:

  iptables -t nat -I POSTROUTING -s 172.16.0.119 -o eth1 \
    -j SNAT --to-source <external_ip>

> After adding this I also added the below mentioned rules : 
> 
> iptables -A INPUT -s 172.16.0.119 -d 0.0.0.0/0.0.0.0 -j ACCEPT 

INPUT is only for packets who's destination IP is local to the firewall
itself--so this will allow you to access the firewall machine from
172.16.0.119.

> iptables -I FORWARD -s 172.16.0.119 -j ACCEPT 

ok.  make sure you've also enabled IP forwarding:

  sysctl -w net.ipv4.ip_forward=1

and make sure you're allowing reply packets back through your FORWARD
chain:

  iptables -I FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

<snip>

if only there were a way to search the archives of this mailing list to
see how people have solved this riddle of the sphinx in the past...oh
wait...

  http://marc.theaimsgroup.com/?l=netfilter&r=1&w=2

-j

--
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 that girls should stick to girls sports, such as hot oil wrestling
 and foxy boxing and such and such."
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