Iptable for nat assistance

[tleslie]

On Wed, 2007-04-25 at 18:40 +0300, Kihara Muriithi wrote:
> Hi all,
>  I have been attempting to use iptables to NAT internal IPs to an
> external IP without success. I have experience with iptables, but
> mainly on how to close or open specific ports. Nat has proved a little
> challenging and thats why i am seeking assistance. 
>  Lets say I have an internal IPs as 10.0.0.0/24 and need all those IP
> natted to an external IP 192.168.2.1. This is what I have attempted in
> my quest to find a solution. 
> /sbin/iptables -t nat -A POSTROUTING -o eth0 -j SNAT --to 192.168.2.1
> 
> when I check the firewall status, I notice this table insertion
> Chain POSTROUTING (policy ACCEPT)
> target     prot opt source               destination         
> SNAT       all  --  0.0.0.0/0            0.0.0.0/0
> to:192.168.2.1
> 

SNAT means  source address translation, you want DNAT

>  To be frank, I expected 192.168.2.1 to be the destination. The way
> the details are presented is confusing, IMO. Whats however puzzling is
> this command is rejected when I attempt to make it persistant as seen
> below. 
> vi /etec/sysconfig/iptables 
> Just before the line below, I inserted the second command
> REJECT     all  --  0.0.0.0/0            0.0.0.0/0
> reject-with icmp-host-prohibited
> -A POSTROUTING -o eth0 -j SNAT --to 192.168.2.1
> 
> This however don't work as iptable throws an error message and fails
> to come up.
> Now the question is, what is the proper way of doing a nat throw a
> linux box? I have enabled IP forwarding by the way. 
> 
> Thanks in advance
> William

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