Friday, July 15, 2011

Comprehending IPv6 Addressing

Comprehending IPv6 addressing can become a steep uphill challenge, as well as hard on the fingers due to all the typing. The addresses are so long that abbreviation mechanisms and conventions are used to ease the burden. However, this makes learning the addressing that much more difficult. Here are a few rules and tips to assist with the future IPv6 change, as well as some conventions that reduce the typing needed to enter the addresses:

» IPv6 DNS records show as AAAA records (or quad A).

» With IPv6 prefixes, a / slash in IPv6 defines the network with addresses (for example, fc00:db8:1234::/48 is fc00:1234:5678:0000:0000:0000:0000:0000 through FC00:0db8:1234:FFFF: FFFF: FFFF: FFFF: FFFF). Thus, FC00:db8:1234::/48 implies that the first 48 bits are assigned to the network portion of the address—4 bits for each hexadecimal digit, visible or not, totaling 16 bits for each segment and 48 bits for three segments. This leaves 80 bits remaining out of a total of 128 bits in the address. 80 bits translates into five groups of four hexadecimal digits. Because each hexadecimal digit represents 4 bits, four multiplied by four, and then by five (for the five groupings), makes 80. After you get the hang of it, it is similar to dealing with “/24” being three groups of eight represented as in IPv4.

» With IPv6 zero compression, consecutive groups of zeros can be subbed with a double “:” (colon). This means that FC00:db8:bc92:0000:0000:1293:91c2:0012 would be the same as FC00:db8:fb92::1293:91c2:0012.

» RFC 2732 dictates that IPv6 address can be used in a URL syntax. As an example, FBAC:FA9A:B6A54:3910:A81C:C1A8:B6A4:A2BB can be literally used in a URL as long as it is enclosed in brackets [ and ], as seen in this example: http://[FBAC:FA9A:B6A54:3910:A81C:C1A8:B6A4:A2BB].

» Loopback for IPv6 is ::1. This might be the only case where an IPv6 address is shorter than the equivalent IPv4 address.

These conventions make it much easier to enter the addresses, if not quite as easy as
IPv4 addresses.

The caveat is that there can be only one double colon used in an IPv6 address to compress consecutive groups of zeros. Otherwise, it would not be possible to determine how many zeros were compressed.

The fc00::/7 prefix is the private reserved IPv6 address range. The private ranges in IPv6 are called the unique local addresses (ULA) and are not globally routable. This is equivalent to the 10.x.x.x, 172.16-31.x.x, and 192.168.x.x IPv4 private addresses. The unique local address range (fc00::/7) is further divided into 2 /8 address ranges. The first is the fc00::/8 range, which is available for private use. The second is the fd00::/8 range, which is to include a random 40-bit string. The local link address is assigned the fe80::/10 range, which is from the second range.

Source of Information : Sams - Windows Server 2008 R2 Unleashed (2010)

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