How do I save routing information to a configuration file?

If you reboot FreeBSD box, the routing configuration will be lost i.e. the routing information will not persist. You need to edit /etc/rc.conf file to set defaultroute:
# vi /etc/rc.conf

Set default route by editing defaultrouter variable:
defaultrouter="192.168.1.254″

Save and close the file.

Task: Start and Stop FreeBSD Configured Interfaces

To apply changes to a configuration file, you need to stop and restart the corresponding FreeBSD networking interface. The following command will also update routing information:
# /etc/rc.d/netif restart
# /etc/rc.d/routing stop
# /etc/rc.d/routing start