Would you use a single NAT for a whole country? I always assumed ISP network infrastructures were regional. Not the least because if you put 10 millions IPs behind a single public IP, you will quickly run out of your 65000 ports.
You can use more connections than 65k, since connections are identified by srchost, srcport, desthost, and destport. You are restricted to 65k NATted connections to a single server's* web site, though.
Good point, but still, there aren’t that many google, instagram or windows update IPs. I can easily imagine more than 1% of the 10 millions people connecting to google simultaneously.
I can't recall, does TCP require that src:srcport->dest:destport pairs be unique, or is there another way to distinguish connections (sequence numberd maybe?)? I guess there are other IP protocols like UDP though...
