Which of the following IPv6 prefixes is used for link-local unicast addresses? (Select the best answer.)
A. 2000::/3
B. FC00::/8
C. FD00::/8
D. FE80::/10
E. FF00::/8
F. ::FFFF:0:0/96
Explanation:
The IPv6 prefix FE80::/10 is used for link-local unicast addresses. IPv6 addresses in the FE80::/10 range begin with the characters FE80 through FEBF. Unicast packets are used for one-to-one 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 neighbor discovery and for environments in which no router is present to provide a routable IPv6 prefix.
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 addresses are not globally routable, but they are routable within an organization.
The IPv6 prefix FF00::/8 is used for multicast addresses, which are used for onetomany communication. IPv6 addresses in theFF00::/8 range begin with the characters FF00 through FFFF. However, certain address ranges are used to indicate the scope of the multicast address. The following IPv6 multicast scopes are defined:
– FF01::/16 – nodelocal
– FF02::/16 – linklocal
-FF05::/16 – sitelocal
– FF08::/16 – organizationlocal
-FF0E::/16 – global
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 Hop 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.
The IPv6 prefix ::FFFF:0:0/96 is used for IPv4mapped IPv6 addresses. IPv6 addresses in this range are typically used for IPv6 over Multiprotocol Label Switching (MPLS). The last 32 bits are used for the IPv4 address and are sometimes written in dotted decimal notation. For example, the IPv4address 192.168.1.1 would be mapped to the IPv6 address ::FFFF:192.168.1.1.