[dsukhin]

I can speak using MIT as an example and I assume Harvard is the same way for the same reasons.

Big research institutions that were present when IP addresses were being allocated got A LOT of IPs by simply asking for them. Apple has the entire 17.0.0.0/8 range. Ford Motor Company has one, the US Gov has a lot [0]. Up until recently MIT had all of 18. (they sold something like half to AWS for a hefty sum not too long ago).

As a student (or visitor), when you joined the network (wired or Wi-Fi) you weren’t allocated some internal IP behind a router but a PUBLIC 18.something that was in the global address space because they had so many IPs available. This meant you could literally host something on the public internet from your dorm room because every device on the network was publicly routable by a unique public IP address.

[0] https://en.m.wikipedia.org/wiki/List_of_assigned_/8_IPv4_add... (see the last section on the original allocation)

[jjav]

> As a student (or visitor), when you joined the network (wired or Wi-Fi) you weren’t allocated some internal IP behind a router but a PUBLIC

As an interesting detail, which seems alien today, is that this was also true at my various employers throughout the 90s. My desktops at work all had public IP addresses and were directly on the Internet, no firewall or anything.

I ran mail and web servers, fully internet accessible, on my work desktops (and lab machines). It was a natural thing to do.

[jiggunjer]

so the modem was just connected to a switch?

[EvanAnderson]

The router on the OP's network was probably just being a router. No fancy NAT junk, and probably no ACLs / fireballing. It was pretty common to have something like a T1 circuit, a CSU/DSU that connected to the T1 and presented a serial connection, and a PPP or SDLC connection to your upstream ISP over that serial connection. The router's Ethernet interface is connected to your switch (or hub) and all the hosts have IP addresses in the subnet your ISP assigned. Fancier shops might have a proxy server or dedicated firewall box between the LAN and the router.

[jiggunjer]

I see. An ISP subnet isn't really the same as a public IP though?

[EvanAnderson]

Back in the 90s your ISP would have given you a subnet of public IPs to use. I have a Customer w/ a T1 that they've had since the late 90s with the same /26 of public addresses on it the whole time.

[jjav]

> so the modem was just connected to a switch?

What EvanAnderson said.

The office ethernet network just contained a router, which would be hooked up to the upstream (via multiple T1 lines, IIRC). So everything on the office network had a public IP and was directly on the internet.

[WarOnPrivacy]

I had a biz customer who had an early cable internet connection. ISP plugged their dumb modem directly into the hub and every PC had a public IP.

This was awesome for about 3 hours until the worms showed up - because Win98 didn't come with a firewall.

[zengargoyle]

USC would disable any residential port trying to host a real server like that (i.e. not a game server or something). It's a research and education network, not your free ISP. If you have legitimate reasons, get a teacher's note and we'll let you. We watched the connection counts, we'll investigate the weird and probably disable your port and account and send you to Student Conduct. You have to fly under the radar, too many connections to other machines on inside (you're up to something), or too much traffic (you're up to something else). Then again, we were better at network than most other universities.

[beamatronic]

We had this in 1992 at my university