Static NAT based on destination subnet

Unanswered Question
Sep 15th, 2008

I need a Cisco 1841 router to perform Static NAT only for a given remote destination.

For example, we have

Site A

Site B

Site C

Site A <==> Site B <==> Site C

When Site A talks to Site B I don't need a NAT translation. But when Site A talks to Site C, I need the router at Site B to NAT to When Site C talks to I need it to NAT to

I've been able to get it to work using route-maps and dynamic NAT pools, but it's not the way I need it. For example, is being NATTED to instead of and the return traffic isn't making it back.

I sure hope this makes sense.


I have this problem too.
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Marwan ALshawi Mon, 09/15/2008 - 17:09

try this on router B:

access-list 100 permit

route-map nat1 permit 10

match ip address 100

ip nat inside source static route-map nat1

and apply ip nat inside on the interface facing site A and ip nat outside on the interface faceing site C

and have a look at the following link as well:

good luck

if helpful Rate

dennylester Tue, 09/16/2008 - 07:56

This kind of worked. The IP Nat inside source static only did a one to one translation.

I need

ip nat inside source static network /24

but it won't let me reference a route-map. I suppose I can manually create 254 one to one translations.



jpoplawski Tue, 09/16/2008 - 14:35

Can I ask why the need for NAT? It seems like you should just be able to turn on ospf or eigrp and route the traffic accordingly? I don't want to oversimplify, however doing a one to one nat for 254 hosts, sounds pretty cumbersome.

dennylester Tue, 09/16/2008 - 14:52

Overlapping subnets.

Site C bought us out and assigned us a block of private addresses. We haven't renumbered Site A yet but need the connectivity right away. Somewhere on the Site C network they have an overlap and mandated we change our end.

Since Site B was ours to begin with, all their hosts are currently configured to access Site A resources on the old subnet.

The good news is the one to one configuration went pretty quick using Excel and notepad and pasting the configuration into the router.


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