IP forwarding

[Mike Burger]

On Mon, 13 Sep 2004 menonrr at adelphia.net wrote:

> 
> Hello,
> 
> The mailing list friends helped me to enable IP forwarding on my Redhat 9 gateway with the rule:
> 
> "iptables -t nat -A POSTROUTING -o eth1 -j SNAT --to-source 172.16.3.10"
> 
> This rule forwards the traffic from the internal network (172.16.4.0/24) to the outside.
> 
> Problem:
> 
> But I feel that the internal IPs are being forwarded with the IP address of the external NIC of the gateway.
> 
> It would be helpful if I could have a way to keep the internal IP address (172.16.4.0)as it is without being substituted with the gateways IP address(172.16.3.10). This is because I want the external users to see the internal machines(172.16.4.0 network) as it is.

Does your gateway have the address you want attached to it?

At a command prompt, type "ip addr"  If the output does not include a line 
that starts like:

inet 172.16.3.10

Then it can't and won't forward out that way.

If not, add this line to your rc.local file:

ip addr add 172.16.3.10 dev eth1

And, while you're at it, run it, as root, from your command line, to add 
that IP address to your external interface.


-- 
Mike Burger
http://www.bubbanfriends.org

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