route add default <Gateway IP>
Example: route add default 192.168.1.1
Verify that route is added using 'netstat -r' command
Check the route info in FreeBSD
[root@bsd84 ~]# netstat -r
Routing tables
Internet:
Destination Gateway Flags Refs Use Netif Expire
default 10.102.33.1 UGS 0 0 xn0
10.0.0.0 link#4 U 0 3157101 xn0
localhost link#3 UH 0 1291 lo0
Internet6:
Destination Gateway Flags Netif Expire
:: localhost UGRS lo0
localhost link#3 UH lo0
::ffff:0.0.0.0 localhost UGRS lo0
fe80::%lo0 link#3 U lo0
fe80::1%lo0 link#3 UHS lo0
ff01::%lo0 fe80::1%lo0 U lo0
ff02::%lo0 fe80::1%lo0 U lo0
Useful link : https://www.cyberciti.biz/faq/freebsd-setup-default-routing-with-route-command/
https://www.freebsd.org/cgi/man.cgi?query=route