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Figure 4-9 Link-local Address Format
IPv6 devices must not forward packets that have link-local source or destination addresses to
other links.
Note:
You can configure multiple IPv6 addresses per interface, but only one link-local address.
IPv6 Neighbor Discovery
The IPv6 neighbor discovery process uses ICMP messages and solicited-node multicast
addresses to determine the link-layer address of a neighbor on the same network (local link),
verify the reachability of a neighbor, and track neighboring devices.
1. IPv6 Neighbor Solicitation Message and Neighbor Advertisement Message
A value of 135 in the Type field of the ICMP packet header identifies a neighbor solicitation
(NS) message. Neighbor solicitation messages are sent on the local link when a node wants
to determine the link-layer address of another node on the same local link.
After receiving the neighbor solicitation message, the destination node replies by sending a
neighbor advertisement (NA) message, which has a value of 136 in the Type field of the ICMP
packet header, on the local link. After the source node receives the neighbor advertisement,
the source node and destination node can communicate.
Neighbor advertisement messages are also sent when there is a change in the link-layer
address of a node on a local link.
Address Resolution
The address resolution procedure is as follows:
Node A multicasts an NS message. The source address of the NS message is the IPv6
address of an interface of node A and the destination address is the solicited-node multicast
address of node B. The NS message contains the link-layer address of node A.
After receiving the NS message, node B judges whether the destination address of the
packet corresponds to the solicited-node multicast address. If yes, node B can learn the
link-layer address of node A, and unicasts an NA message containing its link-layer address.
Node A acquires the link-layer address of node B from the NA message.
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