The depleting IPv4 addresses is one of the main reasons for a new IP version, IPv6. The size of an address in IPv4 address is 32-bit (4-bytes). This is increased much larger and the size of an address in IPv6 is 128 bits, which is four times longer than the 32-bit IPv4 address. The number of possible addresses in IPv4 is 2^32 (4,294,967,296) but in IPv6 it is 2^128 (3.4x10^38) addresses. Such a large amount of available IPv6 addresses ensure that we will never again run out of IPv6 addresses and it also allows multiple levels of hierarchy and flexibility in designing hierarchical unicast addressing and routing.
IPv4 addresses are 32-bit binary addresses, divided into 4-Octets (Bytes). This 32-bit large number is difficult to represent in binary format and therefore IPv4 addresses are represented in decimals, separated by a dot. An example of IPv4 address is 192.168.100.10. However, IPv6 addresses are so much larger than IPv4 addresses and even representing them in decimals is difficult. Hence the IPv6 addresses are represented in hexadecimal numbers, separated by a colon. An example of IPv6 address is 2001:0DB8:0000:0002:0022:2217:FF3B:118C.
- IPv6 Address Representation
IPv6 Address Representation
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Zero compression
IPv4-compatible IPv6 addresses
IPv6 Address Structure
- An IPv6 prefix indicates the block of address space or a network. The IPv6 prefix follows the general IPv6 addressing rules and is represented as: IPv6 address/prefix length.Where IPv6 address represents the hexadecimal 128-bit address, and prefix length is a decimal value that indicates the number of contiguous, higher-order bits of the address that make up the network portion of the address. For example, '21DA:D3::/48' and '21DA:D3:0:2F3B::/64' are IPv6 address prefixes.
- IPv6 Interface ID indicates the specific interface which is unique to the IPv6 prefix of the IPv6 address.
Types of IPv6 Addresses
- An unicast address identifies a single interface within the scope of the type of unicast address. A packet sent to a unicast address is delivered to the interface identified by that address. For the Unicast IPv6 Addresses, there are many types: Global unicast addresses, Link local addresses etc. Global unicast addresses are globally routable and reachable on the IPv6 portion of the Internet.A prefix for link local addresses is always FE80::/64 with the interface ID be 64-bit length.
- A multicast address identifies multiple interfaces (typically belonging to different nodes). A packet sent to an anycast address is delivered to one of the interfaces identified by that address.
- An anycast address identifies a set of interfaces (typically belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces identified by that address.