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The figure below shows the structure of a global unicast address.
Figure 4-7 Global Unicast Address Format
Link-local address
A link-local address is an IPv6 unicast address that can be automatically configured on any
interface using the link-local prefix FE80::/10 (1111 1110 10) and the interface identifier in the
modified EUI-64 format. Link-local addresses are used in the neighbor discovery protocol and
the stateless autoconfiguration process. Nodes on a local link can use link-local addresses to
communicate. The figure below shows the structure of a link-local address.
Figure 4-8 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