IPv6 Addressing Configuration

Neighbor Discovery (ND)

Neighbor Discovery (ND)

Neighbor Discovery (ND) is the IPv6 equivalent of the IPv4 ARP for layer 2 address resolution, and uses IPv6 ICMP messages to do the following:

■Determine the link-layer address of neighbors on the same VLAN inter­ face.

■Verify that a neighbor is reachable.

■Track neighbor (local) routers.

Neighbor Discovery enables functions such as the following:

■router and neighbor solicitation and discovery

■detecting address changes for devices on a VLAN

■identifying a replacement for a router or router path that has become unavailable

■duplicate address detection (DAD)

■router advertisement processing

■neighbor reachability

■autoconfiguration of unicast addresses

■resolution of destination addresses

■changes to link-layer addresses

■anycast address operation

An instance of Neighbor Discovery is triggered on a device when a new (tentative) or changed IPv6 address is detected. (This includes stateless, stateful, and static address configuration.) ND operates in a per-VLAN scope; that is, within the VLAN on which the device running the ND instance is a member. Neighbor discovery actually occurs when there is communication between devices on a VLAN. That is, a device needing to determine the link- layer address of another device on the VLAN initiates a (multicast) neighbor solicitation message (containing a solicited-node multicast address that corre­ sponds to the IPv6 address of the destination device) on the VLAN. When the destination device receives the neighbor solicitation, it responds with a neighbor advertisement message identifying its link-layer address. When the initiating device receives this advertisement, the two devices are ready to exchange traffic on the VLAN interface. Also, when an IPv6 interface becomes operational, it transmits a router solicitation on the interface and listens for a router advertisement.

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