NATting using the same interface ?

[cjdoidge]

hi there,

I was wondering, is it possible to set up NAT/PAT for packets arriving/leaving (after being routed) the same interface , e.g. not going "through" the router ?

I think that this is not possible but I need to be sure... Any help ?

Thanks,

Alex

[pkhatri]

Hi Alex,

That is certainly possible, using an intermediary loopback interface. The feature is called NAT on a stick and described here:

http://www.cisco.com/warp/public/556/nat-on-stick.html

Hope that helps - pls do rate the post if it does.

Paresh

[cjdoidge]

I've had a look, but I need something like this (attached). Both examples in that article not quite what I need.

[tdrais]

That is called nat on a stick.

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094430.shtml

Once you understand how to do this NAT will never confuse you again.

There may be a newer method with the new NAI interfaces in the latest IOS but I have not had time to test this and have not seen any documentation on using these new nat features for this purpose.

[cjdoidge]

Hi there,

Just following that article suggestions, I wonder, if I add ip policy route-map to the interface, will it affect the routing for the other IPs, not specified in that route-map ? in other words, if I add "ip policy route-map" command to the interface - will it affect any existing NAT/non-NAT configuration ?

thanks,

Alex

[sundar.palaniappan]

Alex,

If PBR (policy routing) doesn't match any traffic then that traffic isn't routed normally i.e based on your routing table and configuration setup.

Hence, when you do NAT-on-a-stick you would want to only match the traffic, that's to be NATted out the same interface, with a route map and force the traffic to go through loopback (nat outside) interface.

Hope that helps!

Regards,

Sundar