I've looked around as I too cannot join any coop game or host one.
Normally I would find some sort of ports listing for coop specific gaming, or a guide on how to troubleshoot, but all the forum managers seems to tell us to go through their support.
Problem is; I've been waiting approximately 2 weeks for an answer from ubisoft, and previous to that, I had waited about 1 week without any answer and then my ticket was closed for no reason.
Stop directing your clients to support if the support staff can't and won't help.