What ports does Alien Swarm use?

Question

I keep on getting disconnected from Alien Swarm (after 10 retries the game auto disconnects) And I remembered that I'm getting very few ports to my computer. What ports should I forward to my computer so that I can play most effectively?

Asked by McKay

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

Answered by Oak

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