[TriLUG] IP Tables rule to block all non-local traffic

[Ron Kelley via TriLUG]

Greetings all.

My IP Tables skills are very lacking, and I don’t want to break anything in the process.  Thus, I am reaching out…

I need the right iptables command to do the following:
----------------------------------------------
* Allow any connection to any ip on the local subnet
* Allow any connection to any ip on an adjacent subnet
* Block all other traffic

server_ip:  192.168.100.21/24
adjacent_subnet: 172.16.0.0/16


iptables -A OUTPUT —dport=<any> -s 192.168.100.0/24 -j ACCEPT
iptables -A OUTPUT —dport=<any> -s 172.16.0.0/16 -j ACCEPT
iptables -A OUTPUT -dport=<any> -j REJECT


Thanks for any pointers.

-Ron