Version 4 of The Internet (the popular one that blew up in the 1990s) is made up of 32 bit numeric addresses attached to physical things to which data has to be

Version 4 of The Internet (the popular one that blew up in the 1990s) is made up of 32 bit numeric addresses attached to physical things to which data has to be routed. In the 80s these would be bunched up by org in nice ways just like how phone numbers that were all in the same place would share an area code. MIT would be 1.1.x.y and you’d route their data to Cambridge MA. IBM would be 2.x.y.z and you’d route to them and let them deal with it internally. Some small outfit in France might’ve gotten 173.4.5.q: you’d send their data into the Atlantic fibre because “173.something” meant “Europe” and let the other end figure it out. In the 90s it all got messy because 32bits wasn’t enough to keep things in a clean hierarchy that reflected how data was routed around the net. Orgs ended up accumulating fragments of IP address space from all over the place for the hosts at their physical site. The hierarchy of the address couldn’t tell you how to route traffic and the rules for routing became highly extensive and dynamic. Enter Autonomous Systems Numbers and BGP. It’s a layer on top of IP addressing that only matters to internet core routers with many choices as to how to your traffic (“multi homed” sites). It helps map IP addresses to actual places — internet peers, aka fellow ISPs — so they can agree with each other how traffic should be routed. BGP lets peers keep these routes updated and let’s you know who owns what. None of this matters if you have a single internet connection. Routing is easy: it’s either “local” or you send it to your ISP. But if you’re an ISP in the centre how do you know who gets what? You use The [Internet] Routing Table as maintained by the BGP system. Some companies have so much traffic they have their own ASN. Because the internet is open, you get to see all the IP addresses which are bundled up inside that ASN, which is what I was linking to. It only works because FB is its own self-serving ISP with its own ASN. (With IPv6 this should all have gone away not because of the number of addresses, but because the address space was 128-bits wide. You could hierarchically route 256 towns in 256 counties in 256 states in 256 countries and still only have used half the hierarchy. ISPs usually get a /32 of this but Facebook announce a bunch of /48s which I don’t understand.)