Found a solution on Halo CE Co-op "connection interrupted"

[P-Slayer]

Both players launch the SAME MISSION on single player first with the SAME DIFFICULTY and SAME SKULLS turned on. After that, both players exit the single player mission and join co-op. Make sure you wait for a bit before that player joins otherwise there will be a message saying that you can't join a game. Take turns hosting the game if possible. Restart your PC as a last resort. It worked for us so hopefully it should for work all of you guys. I do not know why but that is the way to fix the problem. Let me know if it works for you guys.

[Varaosa]

Originally posted by Onii-chan!:

Both players launch the SAME MISSION on single player first with the SAME DIFFICULTY and SAME SKULLS turned on. After that, exit the single player mission and join co-op. It worked for us so hopefully it should for work all of you guys. I do not know why but that is the way to fix the problem. Let me know if it works for you guys.

-No, it's not working for me & i still got the issue there. I just try normal way when usual co-op was working but, try this guide, my friend say then he can't join the game. So, you can't join the another game when game is already running or we can't with friend.

[P-Slayer]

Originally posted by Varaosa:

Originally posted by Onii-chan!:

Both players launch the SAME MISSION on single player first with the SAME DIFFICULTY and SAME SKULLS turned on. After that, exit the single player mission and join co-op. It worked for us so hopefully it should for work all of you guys. I do not know why but that is the way to fix the problem. Let me know if it works for you guys.

-No, it's not working for me & i still got the issue there. I just try normal way when usual co-op was working but, try this guide, my friend say then he can't join the game. So, you can't join the another game when game is already running or we can't with friend.

I think both of you guys were suppose to exit the single player mission and wait for a bit first to join co-op. Sometimes if that player joins too early, then there will be a message saying that you can't join because that person is in game. Also try taking turns hosting the game if possible. Also make sure you join manually on steam friend instead of the steam invite link. Trying restarting PC if possible. If that's not the issue then good luck. So far this method works me. 343 really needs to fix this issue. I had troubled trying to find a way to make co-op work until I found this method. I can't find any other ways to fix.

[BabySealClubber]

I have contacted halo support about this and according to them they say its because my NAT settings were not set to open. Even though they already were open I reset all of them but it still did not work for me. Maybe it will work for you guys.

[Varaosa]

I have no issue with firewall because, im already played co-op with my friend until i got this issue suddenly & after this i din't get or can get this co-op any more working so, it can't be that then my NAT setup was get into closed suddenly & because im already restart my pc multiple time when i was try this multiple days, i still din't get this work for me.

[Varaosa]

Originally posted by Onii-chan!:

Originally posted by Varaosa:

-No, it's not working for me & i still got the issue there. I just try normal way when usual co-op was working but, try this guide, my friend say then he can't join the game. So, you can't join the another game when game is already running or we can't with friend.

I think both of you guys were suppose to exit the single player mission and wait for a bit first to join co-op. Sometimes if that player joins too early, then there will be a message saying that you can't join because that person is in game...

-We just try this but, this still not work us. Also those message "you can't join because that person is in game..." happend only us when if you are in singleplayer game not when you are in main menu. Everyting else solutions are already tested & do but, those not working for us at all.

[tCapt]

https://steamcommunity.com/app/976730/discussions/0/1751276296706976610/?ctp=3#c1752402450225726683
One of us showed "Teredo is unable to qualify" on the xbox live settings, we pressed 'fix it' and restarted.

[BRT Cobra]

lol its a nat thing. go to windows settings then gaming then network, run the test. then click fix then run test again to show nat open.

may need to do this every time you start windows though if you have nat issues

[Varaosa]

Originally posted by John Oliver:

lol its a nat thing. go to windows settings then gaming then network, run the test. then click fix then run test again to show nat open.

may need to do this every time you start windows though if you have nat issues

-It's open & connected in those setup so, NAT is not my issue.

[Dealman]

It's most likely something on your end, since it's worked flawlessly for me and my friend.

What router do you have? Have you tried opening the necessary ports? Have you tried DMZ mode?

Restarting your computer has nothing to do with it, it won't affect how strict your NAT setup is.

[Varaosa]

Originally posted by Dealman:

It's most likely something on your end, since it's worked flawlessly for me and my friend.

What router do you have? Have you tried opening the necessary ports? Have you tried DMZ mode?

Restarting your computer has nothing to do with it, it won't affect how strict your NAT setup is.

-There is many other try to solute this issue, using more solutions that me & they not also not get this game working jet with using those solutions so, i don't think then i can't get this working neither if i try. Some others are try to do thease & still not get this get this game working jet:

- Power cycled modem
- Already attempted Relays fix
- Already created at least 6 Port Forwards
- Performed file verify (in Steam), all green;
- Disabled Win10 Pub/Private firewalls
- Added EasyAntiCheat and Halo MCC applications to firewall whitelisting

-I was used & do most of thease & any previous solution & still don't get this game working in co-op & also every of those is still solution that any normal user or players not should or need to do if they want or start playing co-op or multiplayer if game & multiplayer working normally.

All my previous setuping in couple first run was setup when last time co-op working just fine with out do anyting this or setup manipulate or fixsing.

[Define Brackish Water]

Have you installed every part of Halo CE? Check the properties for MCC in your Steam library and look at what DLC is installed. Do you have both singleplayer and multiplayer for CEA & H1?


Don't forget about sending bug reports to 343i.
https://support.halowaypoint.com/hc/en-us/articles/360036218972-How-to-Submit-a-Ticket

[Magicktech]

Originally posted by John Oliver:

lol its a nat thing. go to windows settings then gaming then network, run the test. then click fix then run test again to show nat open.

may need to do this every time you start windows though if you have nat issues

If people have that issue they should use static ip on their network... might help. And looking up Xbox Live ports that should be open and opening those also... or maybe enabling uPnP if its disabled in the router.

[Varaosa]

Originally posted by Define Brackish Water:

Have you installed every part of Halo CE? Check the properties for MCC in your Steam library and look at what DLC is installed. Do you have both singleplayer and multiplayer for CEA & H1?


Don't forget about sending bug reports to 343i.
https://support.halowaypoint.com/hc/en-us/articles/360036218972-How-to-Submit-a-Ticket

-Yes, every part was separely select "on" in sinlgeplayer/multiplayer mode & those was should be "on" if we are already played Halo CE, before.

[Define Brackish Water]

Originally posted by Varaosa:

Originally posted by Define Brackish Water:

Have you installed every part of Halo CE? Check the properties for MCC in your Steam library and look at what DLC is installed. Do you have both singleplayer and multiplayer for CEA & H1?


Don't forget about sending bug reports to 343i.
https://support.halowaypoint.com/hc/en-us/articles/360036218972-How-to-Submit-a-Ticket

-Yes, every part was separely select "on" in sinlgeplayer/multiplayer mode & those was should be "on" if we are already played Halo CE, before.

Darn, someone in another thread said that they had the same issue because they lacked the multiplayer portion. Thanks for confirming.

[Leirel]

These articles helped me fix the issue:

This one helped me find the Xbox live settings and fix check a couple things. It did not fix my issue but got me looking in the right direction.

https://www.pcworld.com/article/3568681/master-chief-collection-campaign-co-op-not-working-heres-how-to-fix-it.html

These helped me fix it:
https://support.xbox.com/help/hardware-network/connect-network/server-connectivity-xbox-app-displays-blocked
https://support.xbox.com/help/Hardware-Network/connect-network/troubleshoot-party-chat

I searched for hours to find this fix. I hope this helps someone else. GOOD LUCK!