Just to add a datapoint to the previous comment, my large public US university hands out public IPs to every device on WiFi. If there is a firewall, it doesn't block 8080 or 22.

The point is that, if printing works for those people, then we know they have this port open, at least on the university network. So even if it's not exploitable over the internet, it's definitely exploitable from the whole university network, which is almost as good as from the internet.

Yes. It's rather sad that so many people equate NAT with a firewall. Two totally different things. A firewall is good, NAT is annoying. We need to push IPv6 harder.

Great opportunity to expand the Sci-Hub effort /s