> IPv4 is from the era of local computer networks, which feature clients and servers.
IPv4 on the ARPANET 'went live' in January 1983,[1] but the concept of a firewall didn't really happen until about a decade later (with some protocols having to be altered[2]):
IPv4 on the ARPANET 'went live' in January 1983,[1] but the concept of a firewall didn't really happen until about a decade later (with some protocols having to be altered[2]):
* https://en.wikipedia.org/wiki/Firewalls_and_Internet_Securit...
Some of us still remember open (SMTP) relays and the openness of the early Internet:
* https://en.wikipedia.org/wiki/Open_mail_relay
IPv4 has always not been only about local computer networks: end-to-end connectivity was there at the start and only got choked off later.
[1] https://en.wikipedia.org/wiki/Flag_day_(computing)
[2] https://datatracker.ietf.org/doc/html/rfc1579