connect two networks

Dear fellow network architects :wink:

Im plannig to connect two physical networks that both have very similar characteristics.
Each network has its own internet gateway (NAT router) and its own dhcp server.

Network A’s router is my trusty openSuse 10.3 box with two network interfaces (one facing the web, the other facing my lan). obiously it has routing between the two interfaces enabled, with masquerading.
Ip range is

Network B’s router is an ordinary router w/ a bunch of local ports and wireless access point functionality (linksys i think). the linksys router also is the dhcp.
Ip range is

machines from network A are not allowed to use network B’s internet gateway and vice versa.

what i want is: be able to connect from a machine in network A to a machine in network B (not over the internet) and vice versa.
What physical (wiring) and non-physical (software config.) changes do i need to make?
I was thinking that i’d need to place a router without NAT between the two networks, and maybe tell the internet gateways not to route any traffic directed to the other lan into the depths of the internet.
or would it be sufficient to get a third ethernet interface, add it to network A’s openSuse router and configure a bridge between it’s current local eth. interface and the to be added 3rd eth. interface?

thanks a lot in advance.

I can answer that small part. Routers will never route packages for any address to the internet because these are private addresses.

However when one of the systems in network A uses the Internet IP address (the “outside” one) of network B, it will be routed over the internet. This can be avoided by resolving the hostnames of B in A (and B) with the internal IP addresses. And of course, on the systems in A, beside the default route (which will most probably point to the internet router of A), there must be a route for B telling to go to your internal router (to be created).