The IPv6 address prefixes FE80::/10 and FF02::/16 are not routable. The IPv6 prefix FE80::/10 is used for linklocal unicast addresses. IPv6 addresses in the FE80::/10 range begin with the characters FE80 through FEBF. Unicast packets are used for onetoone communication. Linklocal addresses are unique only on the local segment. Therefore, linklocal addresses are not routable. An IPv6capable host typically creates a linklocal unicast address automatically at startup. Linklocal unicast addresses are used for nexthop neighbor discovery and for environments in which no router is present to provide a routable IPv6 prefix.

The IPv6 prefix FF02::/16 is used for linklocal multicast addresses. Like linklocal unicast addresses, linklocal multicast addresses are not routable.

The IPv6 prefix 2000::/3 is used for global aggregatable unicast addresses. IPv6 addresses in the 2000::/3 range begin with the characters 2000 through 3FFF.

Global aggregatable unicast address prefixes are distributed by the Internet Assigned Numbers Authority (IANA) and are globally routable over the Internet.

The IPv6 prefixes FC00::/8 and FD00::/8 are used for uniquelocal unicast addresses? together, these prefixes can be summarized as FC00::/7. IPv6 addresses in these ranges begin with the characters FC00 through FDFF. Uniquelocal unicast addresses are not globally routable, but they are routable within an organization.

Al IPv6 addresses beginning with FF are multicast addresses, which are used for onetomany communication. The following IPv6 multicast scopes are defined:
- FF01::/16 - nodelocal
- FF02::/16 - linklocal
- FF05::/16 - sitelocal
- FF08::/16 - organizationlocal
- FF0E::/16 – global

The FF01::/16 prefix is used for nodelocal multicast addresses. These addresses are used only on the interface itself, much like a loopback address. Therefore, they are not routable.

The FF05::/16 prefix is used for sitelocal multicast addresses, and the FF08::/16 prefix is used for organization local multicast addresses. Like uniquelocal unicast addresses, sitelocal multicast and organization local multicast addresses are not globally routable, but they are routable within an organization. The FF0E::/16 prefix is used for globally routable multicast addresses.

IPv6 hosts use the multicasting capabilities of the Neighbor Discovery (ND) protocol to discover the link layer addresses of neighbor hosts. The Hop Limit field is typically set to 255 in ND packets that are sent to neighbors. Routers decrement the Hop Limit value as a packet is forwarded from hop to hop. Therefore, a router that receives an ND packet with a Ho Limit value of 255 considers the source of the ND packet to be a neighbor. If a router receives an ND packet with a Hop Limit that is less than 255, the packet is ignored, thereby protecting the router from threats that could result from the ND protocol's lack of neighbor authentication.