> IP addresses aren't just numbers assigned to machines. They must also — effectively — encode the route to that machine; you can sort of imagine it as a tree,

> IP addresses aren't just numbers assigned to machines. They must also — effectively — encode the route to that machine; you can sort of imagine it as a tree, with each bit giving you successively more local directions on the Internet. Now, of course, that's not exactly how it works, but the point is that some parts of that tree are going to be sparsely populated. Having a wider address space means you can make bigger, but not necessarily full, allocations in the address space, allowing you to keep whole networks together in a common prefixes, which results in simpler routing tables. (At least, that's the idea as I understand it.) Exactly, and the huge address space allows the standard to right out set some structure to it, with 48 bits for global routing, 16 bits for subnet addressing, plus 64 bits for link-local, interface identifier. Routing is only concerned about the first 64 bits (which has all the fast operations you could dream of) and global routing only the first 48 even. Obviously doing some work to match the topology to the address space in a smart way by leveraging CIDR to reduce the size of routing tables is always going to be useful. https://en.wikipedia.org/wiki/IPv6_address#Unicast_and_anycast_address_format https://en.wikipedia.org/wiki/IPv6_address#Unicast_and_anyca...