using NAT to prevent overlapping IP's

[salmans]

Cisco says you can use NAT to prevent overlapping IP's in the following scenario: You have a company that is using the entire 192.168.0.0/16 range. Your company buys a new company whos internal network uses a portion of the 192.168.0.0/16 range. If you plug the new network into your exhisting network there will be an overlap of IP's. Cisco says you can use NAT on the new network so that when the IP's leave the new network coming into your old network NAT gives them a 172.16.10.0/24 IP (example). All is fine and I understand this, however the problem is how can a host (192.168.x.x) on the old network, initiate comms with a host (192.168.x.x)on the new network? Simply because the old network is using the entire 192.168.0.0/16 range so the destination address of the packet from the old host will be to a 192.168.x.x on the new network, but that address is already in use on the old network. I know that if a host on the new network initiates the communications there is no problem, but what if a host on the old network initiates the comms to a host on the new network? Would the host on the new network need a public IP and then on the old network put a DNS entry in? I know that should work but is there another way? Any ideas????? This has me stumped !!!!

Do it right the first time, and there won't be a second time!

 

[watchguardmonkey]

hosts on the old network have to target hosts on the new network by using one of the NAT pool IP's, ie one of the 172.16.10.0 IP's.

you would create static nat mappings for servers, printers etc on the new network that need to be accessed from the old network, eg server on new network 192.168.1.100, would be broadcast on the old network as 172.16.10.100, there is no other way of doing it using NAT.

 

[salmans]

Thank you so much. This haunted me all night long!

Do it right the first time, and there won't be a second time!