What is "steam P2P session failed" ?

[Andy]

Because of this , I can not play anything with my friend. He live in same area.
2 days ago, It doesn't happen, I dont know Why ...

[SaltyO]

Please search the forums and read the FAQ. This is a common issue with many possible causes and solutions. Most common is firewall is blocking the ports Steam needs for its p2p service.

[ChizBallz]

What ports need to be open/forwarded? I usually get this error when people disconnect from my game or when I shutdown my game.

[SaltyO]

Really all you need is 1 of the outgoing UDP p2p ports for voice but your needs may vary.




Required Ports for Steam
Which ports do I need to open on my router or firewall for Steam?

To log into Steam and download content:
• HTTP (TCP port 80) and HTTPS (443)
• UDP 27015 through 27030
• TCP 27015 through 27030

Steam Client
• UDP 27000 to 27015 inclusive (Game client traffic)
• UDP 27015 to 27030 inclusive (Typically Matchmaking and HLTV)
• UDP 27031 and 27036 (incoming, for In-Home Streaming)
• TCP 27036 and 27037 (incoming, for In-Home Streaming)
• UDP 4380

Dedicated or Listen Servers
• TCP 27015 (SRCDS Rcon port)

Steamworks P2P Networking and Steam Voice Chat
• UDP 3478 (Outbound)
• UDP 4379 (Outbound)
• UDP 4380 (Outbound)

You can launch the game with the -log flag or type "/debug" in this chat window and it will help troubleshoot connection issues.

Your network must be configured to allow Steam access to the following ports (in order from highest to lowest priority for QoS users):

Steam Client
UDP 27000 to 27015 inclusive (Game client traffic)
UDP 27015 to 27030 inclusive (Typically Matchmaking and HLTV)
TCP 27014 to 27050 inclusive (Steam downloads)
UDP 4380

Dedicated or Listen Servers
TCP 27015 (SRCDS Rcon port)

Steamworks P2P Networking and Steam Voice Chat
UDP 3478 (Outbound)
UDP 4379 (Outbound)
UDP 4380 (Outbound)