Part 2 : The Firewall configuration

Here we will go briefly over how to configure iptables to use with Left 4 Dead 2 (and other Steam games in general).  This is a short and basic guide


This is part 2 of a 4 part series on how to set up and config a Left 4 Dead 2 dedicated server on CentOS Linux.

Part 1 : Setting up the environment and installing the server

Part 2 : Firewall configuration

Part 3 : Monitoring the dedicated server.

Part 4 : Extras.  Host and MOTD banners, Exclusive servers and lobby.


If you’re linux box is on the internet you most likely have a firewall on it.  If not, then you should really put a firewall on it.  Steam uses alot of ports ( https://support.steampowered.com/kb_article.php?ref=8571-GLVN-8711 ), so you need to add exceptions to your firewall for these ports.  For Example here is how you would go about doing it for iptables. Open “/etc/sysconfig/iptables” in an editor of your choice and put these lines somewhere in there.

 #####
 # Steam Ports
 #####
 # Game Client Traffic + Matchmaking and HLTV
 -A INPUT -p udp -m udp --dport 27000:27030 -j ACCEPT
 # Steam Downloads
 -A INPUT -p tcp -m tcp --dport 27014:27050 -j ACCEPT
 # Other ports for Steam
 -A INPUT -p udp -m udp --dport 4380 -j ACCEPT
 -A INPUT -p udp -m udp --dport 3478 -j ACCEPT
 -A INPUT -p udp -m udp --dport 4379 -j ACCEPT
 -A INPUT -p udp -m udp --dport 4380 -j ACCEPT

This should enable the use of all Steam features (steam download, voice and matchmaking).  I’m sure some of these are not used by dedicated servers but I haven’t had time to look into this further.  It’s a good rule of thumb to sort the rules in iptables in the order of their use on the machine,  if your machine is primarily a web server then putting port 80 early in the list of rules is a good way to save few CPU cycles,  and if your machine is a dedicated Steam server then putting the steam ports as early as possible will save CPU cycles.  It’s also a good idea to begin the iptables with this :

 # Accept everything fromt he loopback device
 -A INPUT -i lo -j ACCEPT
 # Accept stuff that has already been established or is related
 -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

Having the Related, established this early ensures that connections that are related to other connections or already established to your machine won’t have to travel a long list of rules before they are accepted.

this is it for Part 2,  make sure to check out Part 3.

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2 Responses to Left 4 Dead 2 Dedicated Server on Linux : Part 2

  1. Armando says:

    Thanks.
    Gracias.