combine two customer networks with over lapping IP address range

Unanswered Question


I have to integrte two customers networks

after a take over, but both networks are with overlapping IP address range, both

networks like to talk to each other for resource sharing while maintaining same IP addressing for some time.

And they need to use exinting arranements for Internet access also.

Any advice will be appreciated.


I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3.5 (4 ratings)
greensubmarine2009 Mon, 05/03/2010 - 23:16

Hi,try this:

network A——network B

A uses

B uses

A PC in A using wants to access in B.


Make a nat static entry in A:(arrow means the nat) ——>

and another nat static entry in B:——>

When A accesses B,A accesses the B using ,instead of

The nat  process in A will convert A'addresses to "network C"( ,for example),and when B applys A,B will  use a destination address.

Have a try!

rajatsetia Mon, 05/03/2010 - 23:52

End solution is change IP Addressing of one of network.

In this kind of environment, NAT will work out well (both in terms of manageability & load on your device) if number of NAT entries are not huge. But if every end point has communicate with each other then IP Address migration is recommended.

As for servers you have to do static NAT and endpoints can be PATed. Just start with NAT entries which are absolute necessity and in parallel work out a uniform IP Addressing plan for both locations.

** Will recommend you to kindly go through NAT operational details. Check for applications in your environment& how it works along with NAT

Ganesh Hariharan Tue, 05/04/2010 - 00:31

Thanks rajatsetia,

That is the exact plan, but your recommendation about application compatibility with NATing is a highlighted point.

Did anyone find a good example in Cisco docs, with a router combining two networks, any thoughts about size of the router for a 10Mbps WAN Ethernet link between two sites.



Check out the below link in NAT in Overlapping Networks,Hope to Help !!


rajatsetia Tue, 05/04/2010 - 03:09

Not very up to date with router models available, but ISR 2800 series will suffice your requirement,decision about specific model depends on number of ports or slots you need depending on current/future requirement.

In my opinion approach should be - target a application and check application doc for NAT support.

Another aspect is - check how NAT works, then you analyse how your application works and check for any compatibility or operational glitch.

Input that you should look out in NAT operational guide -

- number of connections your device support

- any general NAT level limitation which is not related to specific protocol

But more important is to check application documentation and look out NAT support or any operational issue.



This Discussion