Steam P2P session failed.

[Smol Eldritch Princess]

So I'm trying to host a game with a friend and they keep getting a message about steam p2p session failed. They also had this pop up for them "Exception of type 'yIRC.NotConnectedExceptuon' was thrown.". I know others have mentioned this stuff before but i'm not very great with technical stuff.

Edit: had them run /debug on it and this is what she got.
https://cdn.discordapp.com/attachments/321362953033089028/527920796971040779/20181227134608_1.jpg

[SaltyO]

P2P Errors can be lots of different things. So many that people will hestitate to trouble shoot it hehe.

Most common problems are: Your friend is behind a firewall or AV software that is blocking the p2p. Try connecting with firewall off and AV off to be sure.
It could also be a proxy or controlled connection. In a college dorm or something? Parents locking or filtering the connection?
It could also be an issue with your router, and ports need to be open. Ports might need to be opened or forwarded on the firewall as well.

Port forwarding is kind of tough to explain, so hopefully it isn't that. If it is, it really isn't that hard.

[Smol Eldritch Princess]

I understand port forwarding somewhat. what ports would need to be opened?

[SaltyO]

TTS uses Steam's p2p services.
I've been told you only need to worry about UDP 4380 or the Steamworks p2p ports. It's been a while since tweaking this stuff, but that worked for me.

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)

[Classic Kiriyama]

In case this helps anyone, had this issue today. Turned out that when I was joining games, it was downloading the assets to a folder that is uploaded to onedrive. Pausing the onedrive sync for 8 hours caused the issue to go away, and onedrive just synced later.

[CornMaized!!!]

so if im in a dorm am i just screwed