Re: IPTables and different types of NAT

[Grant Taylor <gtaylor@riverviewtech.net>]

Pedro Gonçalves wrote:
> I want to know if it is possible to use IPTables to implement
> -Full Cone NAT
> -Restricted Cone NAT
> -Port Restricted Cone NAT
> -Symmetric NAT

I see no reason why it would not be possible.  However, such 
distinctions are usually not made.  The ""default (if you will) NAT that 
is used on most SOHO Linux routers would be considered "Restricted Cone 
NAT" in such as external hosts can not connect to internal hosts unless 
the internal host has contacted the external host first.

"Full Cone Nat" could easily be implemented with inbound redirection to 
the internal system.

"Port Restricted Cone NAT" is nothing more than "Restricted Cone NAT" 
with port filtering.  This is what is usually done if you have a server 
behind a NATing router / firewall.  In this case, you only port forward 
the ports that you need.

I'm not sure if there is inherent support for "Symmetric NAT" or not. 
I'm sure that support could be added for this if it does not exist.

> If  so, where can I find information about how to implement each type of
> NAT?

I just did a quick Google for what the various types of NAT mean and ran 
across this:  http://en.wikipedia.org/wiki/Network_address_translation

As far as information on how to do it, all but "Symmetric NAT" can be 
very simply done with basic IPTables SOHO style NATing.



Grant. . . .