What ports does Alien Swarm use

alien-swarmnetworking

I keep on getting disconnected from Alien Swarm (after 10 retries the game auto disconnects) and I remembered that I have very few ports forwarded to my computer.

What ports should I forward to my computer so that I can play most effectively?

Best Answer

I believe 27015 is the port you should be forwarding for client connection. A server can be hosted on any port, but this appears to be the default one.

If you want to host a dedicated server, you would need to forward 27005 as well.

Alternatively, this post on Steam forums suggests enabling

  • UDP 27000 to 27020 inclusive
  • TCP 27020 to 27050 inclusive
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