route

See your system's routing table

netstat -nr

Add a route

sudo route -n add 192.168.200.0/24 192.168.2.1

The example above is one I ran into when I was using OpenVPN and by default it was sending all traffic (even local) to through the VPN. Basically anytime I tried to get to my 192.168.200.x subnet on my local network, it would come back as unavailable. The command above forces my Mac to use my default gateway of 192.168.2.1 to get to the 192.168.200.x network.