Preferably, you should connect Router B with Router A via LAN,
for a better link speed. However, with the following assumptions:
1. Only a single serial port for Router B is available
2. Router A has another serial port available
3. You are using V.35 cables for the serial ports
4. You have a V.35 DCE cable
connect Router A and Router B via back-to-back serial cable connection.
Configure clocking on the router where the DCE cable is attached,
configure IP addresses, configure routing. If you don't have enough
global IP addresses, you can use NAT.
It would be better if you could specify which routers do you have and
what ports are already used.
Hope this helps.
