Ask HN: What does each part of an IP Address represent?

[thisismyhnuser]

What does each component of an IP Address represent? Take "215.54.87.2". According to https://www.iplocation.net/ this IP address is located in Columbus, Ohio. (I made up those numbers....it is just some random Jerry.)

Does "215." essentially say the IP address is located in the US, "215.54." say it is in Ohio and "215.54.87." say it is a company in Columbus? Further, a single company would own the block of "215.54.87.*", no? And that company may or may not be an ISP, right?

The above is for an IPv4 address...how does the breakdown work for IPv6 addresses?

I feel like these are stupid beginner questions but I can't seem to find a good tutorial on IP addresses for dummies.

[detaro]

The dots are just for human readability, showing the address byte-by-byte, and don't have any "meaning" anymore. Geographic structure is also only accidental.

Subdivisions nowadays happen nearly everywhere and noted with a a slash and a number after the IP address (e.g. 215.54.87.0/24 is the network containing all addresses where the first 24 bits are the same as in 215.54.87.0, 215.54.87.0/28 would be all the addresses where the first 28 bits are the same etc).

The rules differ a bit between the regions, but if I remember correctly a /24 is the smallest that can be officially assigned to an entity and announced in the global routing tables. They are free to slice smaller inside their networks though, and e.g. give a customer a /28 or /30 to use.

I hope that is somewhat understandable, I'm having a hard time putting it in words...

EDIT: IPv6 is same principle (although the notation for the address itself is now different). One important size there is /64, which is the subnet size for which automatic address assignment works, and the default size for subnets containing end devices. If you get IPv6 internet, you get at least a /64 (although a /56 is recommended), so you don't need NAT because you have more than enough addresses for everything.

[Spoom]

You used to be able to buy blocks of public addresses from ARIN (and I guess you still can[0] but only under special circumstances[1]) but the IPv4 public assignment table is essentially full. You could buy blocks in class A (i.e you would own X.<all>.<all>.<all>), class B (X.Y.<all>.<all>), or class C (X.Y.Z.<all>).

The class assignments themselves are now either a result of an RFP (for special class IP blocks like multicast) or historical significance (basically, who grabbed it when it was available). XKCD had a comic in 2006 mapping the IPv4 assignment table[2].

I don't know much about IPv6 other than that its address space is so large that you essentially don't need to use NAT anymore, so I doubt we'll ever deplete it.

0. https://www.arin.net/fees/fee_schedule.html

1. https://www.arin.net/resources/request/ipv4_countdown.html

2. https://xkcd.com/195/

[thisismyhnuser]

I can't even read the arin.net pages...does something screwy to my browser...both Chrome and Firefox in Linux.

[herbst]

Works for me on chrome on ubuntu.