Well, if it's TCP/UDP connections, there's only 65k ports available to assign, so it would be all the ports. That's a lot of ports, but I'm not sure why it's supposed to be particularly hard. Off to read the article now...

Edit: As masklin referenced in reply to me[1] that jsnell pointed out, that's the ports for a single IP. So yeah, it's not all the ports, but it is all the ports for a single source IP, unless I'm missing something. You can of course assign multiple source IPs to extend this, but it is a limit to be dealt with.

1: And then deleted it, at least as of now, even though I think it was a good point.