Our local network is connected through cable modem, and D-Link wireless router DI-514. This router has also four RJ-45 ports. Local network could be 10.0.0.0 with mask 255.255.255.0, so up to 254 IP addresses could be assigned from 10.0.0.1 to 10.0.0.254 . It’s getting interesting, how to add another subnetwork to this router.
Router1 (DI-514): WAN port to the cable modem has IP address assigned by ISP (Internet Service Provider). Local network can be 10.0.0.0/25 with mask 255.255.255.128, so 126 IP addresses from range 10.0.0.1 to 10.0.0.126 could be assigned. And there could be another network 10.0.0.128 with mask 255.255.255.128 with another 126 IP addresses from range 10.0.0.129 to 10.0.0.254 . Lets say, that this second network 10.0.0.128 could be used as a connecting network. One port could have IP address 10.0.0.129, port on another device 10.0.0.130, and rest of the address space would be wasted. But in this situation it does not hurt.
Router2 (Linksys): WAN port should be assigned IP address 10.0.0.130, mask 255.255.255.128.
Unfortunately easy available private networks 10.x.x.x (10.0.0.0/8), 172.16.x.x (172.16.0.0/12) and 192.168.x.x (192.168.0.0/16) routers don’t propagate, so it can be challenge to configure it. As a DNS it’s possible to use opendns.org IP addresses 188.8.131.52 or 184.108.40.206 .