### What is it for? An IP Address is supposed to be a unique sequence number what can idenitfy a computer across the whole internet The number is 32 bits and it looks like this ``` 255.255.255.255 ``` This number represent a fractal idex into the IP space, where we try and preserve some locality via the top bits. ![[IP Addressing with Lebesgue indexing.png]] This pic was produced by one of my favorite techniques, Lebesgue Indexing! https://blog.benjojo.co.uk/post/scan-ping-the-internet-hilbert-curve ### CIDR blocks Sometimes, you'll see things that look like this ``` 255.255.255.123/24 ``` The stuff behind the slash is just a number from 0-32 that tells you how many of those bits are used to talk about indexing into the network, versus which are used to index into the subnet. This helps router algorithms to be a little bit smarter because they have more information about which bits might be common prefixes. And when there are common prefixes, they can do somethin called Route Aggregation ### What's the deal with `192.168.x.x`? This is just an implementation detail Some people [decided that this number is for private networks](https://www.rfc-editor.org/rfc/rfc1918) and everyone's agreed.