IPv6

IPv4 no much internet for everybody :O. IPv6 much mooore internet for everybody!

Addresses

These have a length of 128 bit, which is split into eight hexadecimal blocks separated by a colon containing 16 bits each.

Structure:

Global routing prefix (48 bit assinged by isp)
Subnet ID (16 bit local subnet)
Interface ID (64 bit host ID -- often mac address)

You are allowed to simplify IPv6 addresses by collapsing subsequent blocks of zeros (once) and eliding leading zeros: 2030:DE:22::33AF:0:1234 There is also this mixed IPv4/IPv6 notation used in some environments: xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:ddd.ddd.ddd.ddd IPv6 uses ::1 as loopback address (localhost)

Unicast, Multicast, and Anycast

Unicast: Used for point to point communication and therefore must be unique.
Multicast: Used for broadcasting to all users that share the same multicast address, which can be in different networks
Anycast: Used to send packet to only one, typically the nearest, interface in a network

An application for anycast would be a service provided by multiple server, i.e., any server would be a valid target for the request, so the request should be sent to whoever is the nearest.

Scopes

Nodes often have multiple addresses. These are categorized by scope:

Node local: On your machine, i.e., basically localhost (::1)
Link local: All interfaces connected to the same node
Site local: All interfaces in the same closed network, think company network
Global: The World Wide Web :O

Automatic Address Configuration

IPv6 enables automatic address configuration similar to Dynamic Host Configuration Protocol. Small networks (without a router) use the link local address, larger ones, on the other side, must use unique local unicast or global unicast addresses

Stateless Address Auto Configuration (SLAAC)

A node generates its own interface ID. To ensure it's unique it often uses its MAC address, timestamp, or some other random number.