The format prefix is the first field of the IP address. In IPv6, addressing is controlled by the format prefix that operates as a kind of address type. These, in turn, can have their own types of addresses.Ī unicast address is used for a packet that is sent to a single destination.Ī anycast address is used for a packet that can be sent to more than one destination.Ī multicast address is used to broadcast a packet to a range of destinations. There are three basic kinds of IPv6 addresses: unicast, multi-cast, and anycast. In this case, the IPv4 address (32 bits) can be used to represent the last two segments of an IPv6 address, and can be written using IPv4 notation. To ease the transition from IPv4 addressing to IPv6, a form of addressing incorporating IPv4 addresses is also supported. The loopback address 0000000000000001 can be reduced to just the following. There can be only one use of the :: symbol per address. IPv6 supports a shorthand symbol for representing a sequence of several zeros in adjacent fields. Many addresses will have sequences of zeros. The loopback address used for locahost addressing can be written with seven preceding zeros and a 1. Segments with all zeros can be reduced to a single zero. You can cut any preceding zeros, but not trailing zeros in any given segment. In the following example, the first four segments represent the network part of the IPv6 address, and the following four segments represent the interface (host) address. These are 0 through 9, continuing with the characters A through F. Hexadecimal numbers use 16 unique numbers, instead of the 8 used in octal numbering. To more easily represent 16 bit binary numbers, hexadecimal numbers are used. The number of bits used for sub-netting can be adjusted with a CIDR mask, much like that in IPv4 CIDR addressing (see previous section).Īn IPv6 address is written as 8 segments representing 16 bits each (128 bits total). The last 64 bits are used for the interface address, known as the interface identifier field. The first 64 bits are used for network addressing, of which the first few bits are reserved for indicating the address type. An IPv6 address consists of 128 bits, up from the 32 bits used in IPv4 addresses.
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