The first command is for TCP, and the second is for UDP.

This says anything on the ports between 2705 is allowed. Iptables -I INPUT -p udp -dport 27005:27015 -j ACCEPT Next, we need to specifically allow all the ports required for Garry’s Mod (27005 - 27015 inclusive) with these commands: iptables -I INPUT -p tcp -dport 27005:27015 -j ACCEPT The second line tells the firewall to block all outgoing ICMP packets, this is much less important, but just double ensures there won’t be any ICMP communication happening. This also means if someone tries to ping your server, they will get no response. This basically tells the firewall to ignore every ICMP packet it receives, and take absolutely no action on it. Iptables -A OUTPUT -p icmp -icmp-type echo-reply -j DROP To block all non-required ports, the following commands are required: iptables -A INPUT -p icmp -icmp-type echo-request -j DROP ICMP is not required for the operation of the server, and blocking it completely will not have any negative effects on Garry's Mod, however, it will help reduce the attack vectors of a DDoS attack. Assuming this server will be dedicated to Garry’s Mod, it’s safe to block absolutely all incoming ports (including ICMP) besides the ones required for Garry's Mod. This tutorial will teach you how to make a Garry's Mod game server.įirstly, we need to make sure the firewall is secure to reduce the chances of a security issue. The instructions are designed for Ubuntu 14.04 32 bit, but should work on all versions of Ubuntu.

Garrys mod server