Server A eth0 has the IP 192.168.1.91 (will be later internet).
Server A eth1 has the IP 192.168.1.92 (local network).

Server B eth0 has the IP 192.168.1.93 (will be later internet).
Server B eth1 has the IP 192.168.1.94 (local network).

Server C eth0 has the IP 192.168.1.95 (will be later internet).
Server C eth1 has the IP 192.168.1.96 (local network).

route add -net 192.168.1.94 netmask 255.255.255.255 dev eth1
route add -net 192.168.1.96 netmask 255.255.255.255 dev eth1

192.168.1.94 dev eth1  src 192.168.1.91

192.168.1.96 dev eth1  src 192.168.1.91