HP 6125XLG R2306-HP 6125XLG Blade Switch Layer 3 - IP Services Configuration G - Page 127
IPv6 address types, Unicast addresses, IPv6 prefix ID
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An IPv6 address consists of an address prefix and an interface ID, which are equivalent to the network ID and the host ID of an IPv4 address. An IPv6 address prefix is written in IPv6-address/prefix-length notation, where the prefix-length is a decimal number indicating how many leftmost bits of the IPv6 address comprises the address prefix. IPv6 address types IPv6 addresses fall into the following types: • Unicast address-An identifier for a single interface, similar to an IPv4 unicast address. A packet sent to a unicast address is delivered to the interface identified by that address. • Multicast address-An identifier for a set of interfaces (typically belonging to different nodes), similar to an IPv4 multicast address. A packet sent to a multicast address is delivered to all interfaces identified by that address. There are no broadcast addresses in IPv6. Their function is replaced by multicast addresses. • Anycast address-An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to an anycast address is delivered to the nearest interface among the interfaces identified by that address. The nearest interface is chosen according to the routing protocol' measure of distance. The type of an IPv6 address is designated by the first several bits, called the format prefix. Table 6 lists the mappings between address types and format prefixes. Table 6 Mappings between address types and format prefixes Type Format prefix (binary) IPv6 prefix ID Unspecified address 00...0 (128 bits) ::/128 Unicast address Loopback address Link-local address 00...1 (128 bits) 1111111010 ::1/128 FE80::/10 Global unicast address Other forms N/A Multicast address 11111111 FF00::/8 Anycast address Anycast addresses use the unicast address space and have the identical structure of unicast addresses. Unicast addresses Unicast addresses comprise global unicast addresses, link-local unicast addresses, the loopback address, and the unspecified address. • Global unicast addresses-Equivalent to public IPv4 addresses, are provided for Internet service providers. This type of address allows for prefix aggregation to restrict the number of global routing entries. • Link-local addresses-Used for communication among link-local nodes for neighbor discovery and stateless autoconfiguration. Packets with link-local source or destination addresses are not forwarded to other links. • A loopback address-0:0:0:0:0:0:0:1 (or ::1). It has the same function as the loopback address in IPv4. It cannot be assigned to any physical interface. A node uses this address to send an IPv6 packet to itself. • An unspecified address-0:0:0:0:0:0:0:0 (or ::). It cannot be assigned to any node. Before acquiring a valid IPv6 address, a node fills this address in the source address field of IPv6 packets. The unspecified address cannot be used as a destination IPv6 address. 119