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IPv6 Support

IPv6 is version 6 of the Internet Protocol that was formally adopted for general use. It was initially called IP Next Generation (IPng). IPv6 is intended to replace the previous standard IPv4.

IPv4 the existing Internet Protocol only supports 4 billion (4 109) addresses. IPv6 supports up to 3.4 x 1038 (340 undecillion) addresses. It is expected that IPv4 will be supported until at least 2025, to allow time for bugs and system errors to be corrected in IPv6.

IPv6 addressing


The most dramatic change from IPv4 to IPv6 is the length of network addresses. IPv6 addresses, as defined by IETF's RFC 2373 and RFC 2374, are 128 bits long. This corresponds to 32 hexadecimal digits, which are normally used to write IPv6 addresses.

In many cases, IPv6 addresses are composed of two logical parts: a 64-bit network prefix, and a 64-bit host-addressing part, which is often automatically generated from the interface MAC address.

IPv6 and the Domain Name System

IPv6 addresses are represented in the Domain Name System by AAAA records (so-called quad-A records) for forward lookups (by analogy A records for IPv4). Reverse lookups take place under ip6.arpa domain where address space is delegated on nibble boundaries. This scheme is defined in RFC 3596.

The AAAA scheme was incorporated at the time IPv6 architecture was designed and is a simple generalization of the IPv4 DNS. The AAAA scheme was effectively standardized in August 2002 by RFC 3363.

Notation for IPv6 addresses

IPv6 addresses are 128 bits long but are normally written as eight groups of 4 hexadecimal digits each. For example, 2001:0db8:85a3:08d3:1319:8a2e:0370:7344 is a valid IPv6 address.

If a 4 digit group is 0000, it may be omitted. For example, 2001:0db8:85a3:0000:1319:8a2e:0370:7344 is the same IPv6 address as 2001:0db8:85a3::1319:8a2e:0370:7344

Following this rule, if more than two consecutive colons result from this omission, they may be reduced to two colons, as long as there is only one group of two or more consecutive colons. Thus

2001:0DB8:0000:0000:0000:0000:1428:57ab
2001:0DB8:0000:0000:0000::1428:57ab
2001:0DB8:0:0:0:0:1428:57ab
2001:0DB8:0::0:1428:57ab
2001:0DB8::1428:57ab

are valid and mean the same thing, but 2001::25de::cade is invalid. (As it is ambiguous how many 0000 groups should be on each side.)

Also leading zeros in all groups can be omitted, thus 2001:0DB8:02de::0e13 is the same thing as 2001:DB8:2de::e13

If the address is an IPv4 address in disguise, the last 32 bits may be written in decimal; thus ::ffff:192.168.89.9 is the same as ::ffff:c0a8:5909, but not the same as ::192.168.89.9 or ::c0a8:5909. The ::ffff:1.2.3.4 format is called an IPv4-mapped address. The ::1.2.3.4 format is an IPv4-compatible address.

IPv4 addresses are easily convertible to IPv6 format. For instance, if the decimal IPv4 address was 135.75.43.52 (in hexadecimal, 0x874B2B34), it could be converted to 0000:0000:0000:0000:0000:0000:874B:2B34 or ::874B:2B34. Then again, one could use the hybrid notation (IPv4-compatible address), in which case the address would be ::135.75.43.52.

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