Add Route Between Two Systems

Type ifconfig in terminal (command Prompt) to know IP
Type route -n in terminal (command Prompt) to know GateWay

First System IP : 203.41.55.23
Second System IP : 23.41.67.89

First System Gateway : 203.41.55.1
Second System Gateway : 23.41.67.1

You can add route in any One System is Enough for example

Add route in First System

route add -host 23.41.67.89 gw 203.41.55.1

Or

Add route in Second System

route add -host 203.41.55.23 gw 23.41.67.1