HP Serviceguard manual IPv6 Address Prefix, Unicast Addresses, IPv4 and IPv6 Compatibility

IPv6 Address Prefix

IPv6 Address Prefix is similar to CIDR in IPv4 and is written in CIDR notation. An IPv6 address prefix is represented by the notation:

IPv6-address/prefix-lengthwhere ipv6-addressis an IPv6 address in any notation listed above and prefix-lengthis a decimal value representing how many of the leftmost contiguous bits of the address comprise the prefix. Example:

fec0:0:0:1::1234/64

The first 64-bits of the address fec0:0:0:1 forms the address prefix. An address prefix is used in IPv6 addresses to denote how many bits in the IPv6 address represent the subnet.

Unicast Addresses

IPv6 unicast addresses are classified into different types. They are global aggregatable unicast address, site-local address and link-local address. Typically a unicast address is logically divided as follows:

n bits	128-n bits
Subnet prefix	Interface ID

Interface identifiers in a IPv6 unicast address are used to identify the interfaces on a link. Interface identifiers are required to be unique on that link. The link is generally identified by the subnet prefix.

A unicast address is called an unspecified address if all the bits in the address are zero. Textually it is represented as “::”.

The unicast address ::1 or 0:0:0:0:0:0:0:1 is called the loopback address. It is used by a node to send packets to itself.

IPv4 and IPv6 Compatibility

There are a number of techniques for using IPv4 addresses within the framework of IPv6 addressing.

IPv4 Compatible IPv6 Addresses

The IPv6 transition mechanisms use a technique for tunneling IPv6 packets over the existing IPv4 infrastructure. IPv6 nodes that support such mechanisms use a special kind of IPv6 addresses that carry IPv4 addresses in their lower order 32-bits. These addresses are called IPv4 Compatible IPv6 addresses. They are represented as follows:

80 bits	16 bits	32 bits
zeros	0000	IPv4 address

Example:

::192.168.0.1

IPv4 Mapped IPv6 Address

There is a special type of IPv6 address that holds an embedded IPv4 address. This address is used to represent the addresses of IPv4-only nodes as IPv6 addresses. These addresses are used especially by applications that support both IPv6 and IPv4. These addresses are called as IPv4 Mapped IPv6 Addresses. The format of these address is as follows:

80 bits	16 bits	32 bits
zeros	FFFF	IPv4 address

Example:

IPv6 Address Types 379