What

Allows IPv6 devices to configure their own IPv6 addresses, without needing a DHCPv6 server

StateLess Address AutoConfiguration

Why

Makes the proces simpler, by not needing a central DHCP server
Also means one less point of failure, and one less central bottleneck
Since there is no central state, it also cannot be lost

Concepts

• Router Advertisements (RAs)
  • Routers periodically announce themselves, on the "all nodes" multicast address ff02::1
• Router Solicitation (RS)
  • Devices can request routers to announce themselves, instead of waiting
  • Sent to the "all routers" multicast at ff02::2

How

1. Generate link-local address
   1. Either based on MAC address, or random (more privacy friendly)
2. Do Duplicate Address Detection: "Is anyone using fe80:21a:2bff:fe3c:4d5e?"
   1. If no response, the address is unique and can be used
   2. If there is a response, the address is in use, try again from the start with a newly generated link-local
3. Discover routers: send RS message to all routers multicast
   1. Can also wait for periodic RAs if desired
4. Response/RA will contain router config such as:
   1. Network prefix
   2. Prefix length
   3. Flags
   4. Default gateway info
   5. Prefix valid and preferred lifetimes
5. Generate global scope address
   1. Based on router prefix + MAC/random
   2. E.g. prefix 2001:db8:1::/64 + MAC/random ::21a:2bff:fe3c:4d5e -> 2001:db8:1::21a:2bff:fe3c:4d5e/64
6. Use Duplicate Address Detection again
   1. Only need to check with local devices, since no other devices will use the same prefix
7. Device now has:
   1. Link-local address
   2. Global scope address
   3. Default gateway information