A lot of players including me experience heavy lag issues.
Played with some friends together. All of us live max. 30km away from each other. When it comes to us, we were also experiencing heavy network issues. We all had different ISP.
BTW: Any other service crashed when the game session began beside the lags, including Teamspeak and Steam Services e.g. friendslist were not available. Maybe your data amount is too big when playing. Or you block all essential http and internet ports when playing...
Please check this or publish a port list if the last mentioned thing is the issue.
Thx in advance and cheers