What happens in SLAAC Step 2 — generating the global address?

The host asks the router for the prefix via a Router Solicitation to ff02::2, the Router Advertisement returns the prefix, the host forms a global address from it, and runs DAD again before using it.

1. The host sends a Router Solicitation (RS) to the all-routers multicast address ff02::2 — "any routers here? what's the prefix?"
2. A router replies with a Router Advertisement (RA) containing the network prefix (e.g. 2001:620:0:49::) and the default-router address
3. The host combines the advertised prefix with its interface ID to build a global, routable address
4. It runs DAD again (Neighbor Solicitation) on the new address
5. No conflict → configure the global address, default router, and other parameters (DNS)

Tip: Routers also send RAs periodically and unsolicited, so a host often gets the prefix without even having to ask — the RS just speeds things up at boot.

Go deeper:

• RFC 4862 — IPv6 Stateless Address Autoconfiguration — prefix-from-RA combination and the second DAD before a global address is used.
• RFC 4861 — Neighbor Discovery for IPv6 — the Router Solicitation/Advertisement exchange that delivers the prefix.