Okay, you have a router whose internal IP address is 192.168.1.1 and another whose internal IP address is 192.168.2.1. This implies that your two networks are 192.168.1.0/255.255.255.0 and 192.168.2.0/255.255.255.0, respectively. (Actually, it doesn't imply the netmask, but you already told us those.) On the 192.168.1.1 router, the remote network and netmask are 192.168.2.0 and 255.255.255.0. On the 192.168.2.1 router, the remote network and netmask are 192.168.1.0 and 255.255.255.0. Each router wants to know what network it's supposed to be expecting on the remote side.