Windows

# Windows Server 2012 : IPv6 Introduction (part 2) - IPv6 Addressing

3/15/2015 5:28:14 AM

Okay folks, get out your scientific calculators. It is time to do some binary, decimal, and hexadecimal conversions. Fun! With the expanded address space associated with IPv6, the developers of IPv6 decided to leverage the hexadecimal numbering system to simplify and reduce the number of characters to identify the IPv6 address. IPv6 addresses are 128 bits in length and much longer than the 32-bit IPv4 address. But before we can dive deeper, the bit count is actually derived from the binary numbering system, which uses only 0s and 1s to represent any number. Binary numbering is also called base-2, because it uses only two numeric values, 0 and 1. Decimal uses base-10 numbering that ranges from 0 to 9, and hexadecimal uses base-16 numbering that ranges from 0 to f, as shown in Table 1.

Table 1. Number Conversions

From our well-known decimal system to convert to and from binary and hexadecimal, you need to learn how to add in each of the three systems. Figure 1 shows the representation of 165 in all three systems and may help explain how addition works in each system.

Figure 1. Counting in binary, decimal and hexadecimal.

By now, you are probably building a base of information about hexadecimal numbering, and so we will continue with an actual example of an IPv6 IP address.

Network addressing for IPv4 is broken down into four 8-bit groups, totaling 32 bits and divided by periods. Each group can range from 0 to 255 and is represented in three decimal digits, such as the IP address 192.168.101.101. It is common with IPv4 addresses to drop leading 0s. For example, the IP address 192.168.100.010 is normally written as 192.168.100.10. IPv6 addresses, being 128 bits in length, are broken down into eight 16-bit boundaries or groups and are separated by colons. With IPv6 addresses, it is also common to drop leading 0s, but because the addresses are so long, other actions are often taken to shorten the address. The following IPv6 address is written using different forms of character reduction to simplify the notation of the full address, which is listed first:

• 2001:0dba:1234:aaaa:0000:0000:3a5f:0456

• 2001:dba:1234:aaaa:0000:0000:3a5f:456 (leading 0 dropped from last two groups)

• 2001:dba:1234:aaaa:0:0:3a5f:456 (0 groups compressed)

• 2001:dba:1234:aaaa::3a5f:456 (consecutive 0 groups replaced with ::)

Reducing the address as much as possible is highly preferred and now considered the correct way to notate an IPv6 address. You can find more information about notation standards for IPv6 in RFCs 4291, 5952, and 6052. One important point with character reduction, particularly with 0 groups, is that there can only be one set of double colons; if there happens to be more than one consecutive set of 0 groups, the double colon should be used to compress the larger of the two groups to make the biggest character reduction as possible.

Note

The IPv6 network prefix of 2001:db8 has been designated as the range to use for IPv6 documentation examples only as detailed in RFC 3849. Do not use this address range on any production IPv6 deployments.

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