An Internet Control Message Protocol version 6 (ICMPv6) router solicitation message is sent by an IPv6capable host at startup. When IPv6 is enabled on a router interface, a linklocal address is created. Before the address is assigned to the interface, duplicate address detection (DAD) is performed to determine whether the IPv6 address is unique on the link. If DAD determines that the address is unique, the linklocal address is assigned to the interface and the router solicitation message is sent to the allrouters multicast address FF02::2. Hosts use router solicitation messages to request an immediate router advertisement.
A router advertisement that is sent in response to a router solicitation message is sent directly to the host that sent the router solicitation. Routers also send unsolicited router advertisements periodically to the allnodes multicast address FF02::1. Router advertisements contain the following information:
- The IPv6 address of the router interface attached to the link
- One or more IPv6 prefixes for the local link
- The lifetime for each prefix
- Flags that specify whether stateless or stateful autoconfiguration can be used
- The hop limit and maximum transmission unit (MTU) that the host should use
- Whether the router is a default router
- The amount of time that the router can be used as a default router
When a host receives a router advertisement, the IPv6 link-local prefix is added to the host's interface identifier to create the host's full IPv6 address. The first three octets of the interface identifier are set to the Organizationally Unique Identifier (OUI) of the Media Access Control (MAC) address of the interface. The fourth and fifth octets are set to FFFE. The sixth, seventh, and eighth octets are equal to the last three octets of the MAC address.
A host will send a neighbor solicitation message to determine the link-layer address of another host on the local link. Neighbor solicitation messages are sent with the sender's own link-layer address to the solicited-node multicast address. The solicited-node multicast address is created by adding the FF02::1:FF00/104 prefix to the last 24 bits of the destination host's IPv6 address. After a destination host's link-layer address is discovered, neighbor solicitations can be used to verify thereachability of a destination host.
When a host receives a neighbor solicitation message, it will reply with a neighbor advertisement message that contains the link-layer address of the host. The neighbor advertisement is sent directly to the host that sent the neighbor solicitation. A host will send an unsolicited neighbor advertisement whenever its address changes. Unsolicited neighbor advertisements are sent to the allnodes link-local multicast address FF02::1.