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Updated:October 14, 2016
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This document describes how to configure Network Address Translation (NAT) to enable communication between server and client which are on different network segments with overlapping IP space.
There are no specific requirements for this document.
This document is not restricted to specific software and hardware versions.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
Note: This document applies to all Cisco routers and switches that run Cisco IOS.
Enable communication between a Server and clients on two separated network segments with overlapping IP Space (usually seen when a network merger happens).
Two networks with same IP space are connected across Router A and Router B, (here we are using loopbacks to simulate the connected network).
NAT router between Router A and Router B enables the communication between overlapping IP network space.
When the Clients initiate traffic to the global IP of Server, the traffic hits the NAT router and the traffic is forwarded to the Server, but when the traffic is returned back to NAT router, the Router fails to forward the traffic as the Server 192.168.1.1 is attached/known on inside interface.
To fix this, Mask (NAT) the outside Source traffic as it traverses across the NAT router.
Enable NAT on inside and outside interfaces.
interface Ethernet0/0 description Connection to Server ip address 10.1.0.2 255.255.255.252 ip nat inside end
interface Ethernet0/1 description Connection to Clients ip address 10.2.0.2 255.255.255.252 ip nat outside end
Configure NAT to translate inside local to inside Global Address.
ip nat inside source static 192.168.1.1 10.100.1.1 extendable
Now, configure NAT statements to translate the source of the clients as they hit the NAT outside interface.
ip nat outside source static network 192.168.1.0 10.100.2.0 /24
Route for the Server. Note that the a specific route for the server is configured pointing towards LAN ( Ethernet 0/0)
ip route 192.168.1.1 255.255.255.255 Ethernet0/0 10.1.0.1
Route for the Client Network:
ip route 192.168.1.0 255.255.255.0 Ethernet0/1 10.2.0.1
Use this section in order to confirm that your configuration works properly.