We are trying to plan a site-site vpn connecting our corporate network to a vendor's network. Both firewalls are Cisco ASA 5510s. The problem is, their private network ID matches a network ID that exists on our private WAN, which is 192.168.100.0/24. This network id is what actually connects interfaces of our remote site routers via fiber. But, I digress. How is the tunnel going to be established with the remote network given that the destination network matches a network id on our own WAN? Will I have to use NAT?
Thanks for any insight. We have successfully set up site-sites with this firewall, but I have never run into a problem where the destination network happens to match one of our internal ids on the WAN.