Back in the mid 90's, before NAT was common, we had public IP's everywhere, even with IPv4! Even my home network was on a /24 class C.
A decade later this still seems to be at least partly in place, as I'm able to browse the webserver running on an old colleague's desktop.
I think my sysadmin group would have a collective heart attack if they saw that setup! It's quite incredible to me how independent various parts (and pseudo parts like the national labs) are from each other.
You can be certain that most every packet in, out, or through the place gets captured and inspected by Bro (errr, I guess Zeek now. https://www.zeek.org/ )
I should also mention that not every host had a public IP. I worked with the group that managed midrange compute clusters, which were always behind NAT, with bastion login nodes.