define what to nat

Nicolás Velásquez O. gnicolax at
Tue Apr 26 20:17:28 CEST 2005

Hello there, 

I've done some research, and yet I couldn't find any information.

I want to define what is natted, not only filter what is natted.

An example where it could be needed:
Let's say that I have openswan and 2.6 native ipsec. That means no 
virtual ipsec iface. I want to connect various site LANs to my hq LAN 
through VPN, so no nat should be done between those LAN-LAN 

An example of one site-hq lan-lan connection:
LAN A <---> FW A / VPN A <---> INTERNET <---> FW B / VPN B <---> LAN B

segment A: (HQ)
segment B: (site)

I could use:
On FW A:
iptables -t nat -A POSTROUTING -o eth0 -d ! -j MASQUERADE

On FW B:
iptables -t nat -A POSTROUTING -o eth0 -d ! -j MASQUERADE

That would work, yet if the number of site-hq lan-lan connections grows, 
it becomes either not useful and/or difficult to maintain.

So I was wondering if there is a way to do something like:
iptables -t nat -A POSTROUTING -o eth0 -d -j "DO NOT NAT"
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

This way even if the number of sites to connect using VPN grows, it will 
be easy to maintain.

Is there a way to achieve what I want??

Ps: I tried the mangle table too.
Ps2: Sorry for my english.


Nicolás Velásquez O.
Bogotá, Colombia

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