| 单词 | IPv6 address (Internet Protocol version 6 address) |
| 释义 | IPv6 address (Internet Protocol version 6 address) A binary number that uniquely identifies a host computer connected to the Internet and running the IPv6 protocol suite.The IP packet header provides an originating address field so that a host can identify itself as the originator of a packet.The IP packet header also provides a destination address field so that an originating host can identity the target host for which a packet is intended. Based on that information, the Internet routers can act to deliver the packet to the target host, which can respond to the originating host, as appropriate.The IPv6 address field size is 128 bits, which yields the theoretical potential for 2128 or 340,282,366,920,938,463,463,374,607,431,768,211,456 unique addresses. At this level, the dotted decimal notation convention employed in IPv4 becomes cumbersome, so an IPv6 address comprises 8 sections separated by colons and expressed as x:x:x:x:x:x:x:x where each x represents 16 bits defined in hexadecimal notation. Following are example IPv6 addresses: FEDC:BA98:7654:3210:FEDC:BA98:7654:3210 1080:0000:0000:0000:0008:0800:200C:417A with each field given a value in decimal notation of 0–65,535, the range expressed by two octets in binary notation (216 = 65,536, or 0–65,535). Leading zeros can be suppressed, which simplifies the latter above address to the following: 1080:0:0:0:8:800:200C:417A If one or more groups (sections) of 16 zeros appear in an address, they can be compressed through the use of a :: (double colon) code.This compresses the above address to the following: 1080::8:800:200C:417A Technically speaking, IPv6 addresses are assigned to interfaces, rather than nodes. The IPv6 addressing architecture provides for unicast, multicast, and anycast addresses. • Unicast: A unicast address is associated with a single interface that is associated with a single node, and can, in effect, identify the node. A unicast address can be of several types and here are also special-purpose unicast subtypes, including IPv6 addresses with embedded IPv4 addresses. A global unicast address is a conventional, publicly routable address that can be used in the Internet or any public domain. A link-local address is similar to an IPv4 private IP address, as it is not meant to be routed, but confined to a single segment. A site–local address is used by an organization that has not yet connected to the Internet. A loopback address is used when a host needs to send a packet back to itself. • Multicast: A multicast address identifies a group of nodes, each of which can belong to multiple groups. A packet sent to a multicast group is delivered to every interface in the group. Multicast addresses begin with the binary prefix 11111111. A multicast address essentially is a targeted version of an IPv4 broadcast address. • Anycast: An anycast address is assigned to multiple interfaces, typically on multiple nodes. A packet with an anycast address is delivered to the closest interface with that address, as determined by the routing protocols measure of distance. Anycast addresses are allocated from the unicast address space. IPv6 address types are defined in RFC 3513.The Internet Protocol version 4 (IPv4) addressing scheme is quite different. See also anycast address, binary, binary notation, broadcast, compression, computer, dotted decimal notation, hexadecimal notation, global unicast address, header, hexadecimal notation, host, interface, Internet, IPv4 address, link-local address, loopback address, multicast address, node, packet, protocol suite, router, site–local address, suppression, and unicast address. 74570c09.qxd 9/11/07 12:22 PM Page 258 |
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