Hello,

You or your friend have either a moderator or strict NAT type. In the lobby go to your settings you will see your nat type.

Strict can only play with open Nat types.

If your moderate you should be able to play with open and other moderates but it often is a problem joining other moderates as well, basically only open nat types serve any consistency in this game. All in all this NAT type issue is one of the biggest problems with rainbow six, but it never gets brought up and it's embarrassing for NAT types to be an issue in this age of gaming.


I didn't find the right solution from the internet.
References:
http://forums.ubi.com/showthread.php/1726584-I-can-t-play-Rainbow-six-siege-online-with-my-friends
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