I needed to add a default route to my SCO Openserver 5.05 box. I used the following command
route add default 192.168.4.3 (192.168.4.3 is the main router on my network)
To make this persistent I then edited /etc/tcp, searched for the word “ifconfig” and added the line after the ifconfig statements.
/etc/route add default 192.168.4.3
This will not however, survive an upgrade. (This is an old box, so I don’t expect I will be upgrading)
There is an article here that gives a much more detailed description and further options.