IPv6 Address Representation CCNA Coaching Institute in New delhi

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RFC 2373 specifies the IPv6 addressing architecture. IPv6 addresses are 128 bits in length. For display, the IPv6 addresses have eight 16-bit groups. The hexadecimal value is x:x:x:x:x:x:x:x, where each x represents four hexadecimal digits (16 bits).

An example of a full IPv6 address is 1111111000011010 0100001010111001 0000000000011011 0000000000000000 0000000000000000 0001001011010000 0000000001011011 0000011010110000.

The hexadecimal representation of the preceding IPv6 binary number is

FE1A:42B9:001B:0000:0000:12D0:005B:06B0

Groups with a value of 0 can be represented with a single 0. For example, you can also represent the preceding number as

FE1A:42B9:001B:0:0:12D0:005B:06B0

You can represent multiple groups of 16-bit 0s with ::, which might appear only once in the number. Also, you do not need to represent leading 0s in a 16-bit piece. The preceding IPv6 address can be further shortened to

FE1A:42B9:1B::12D0:5B:6B0

Tip

Remember that the fully expanded address has eight blocks and that the double colon represents only 0s. You can use the double colon only once.

You expand a compressed address following the same rules used earlier. For example, the IPv6 address 2001:4C::50:0:0:741 expands as follows:

2001:004C::0050:0000:0000:0741

Because there should be eight blocks of addresses and you have six, you can expand the double colon to two blocks as follows:

2001:004C:0000:0000:0050:0000:0000:0741

IPv4-Compatible IPv6 Addresses

In a mixed IPv6/IPv4 environment, the IPv4 portion of the address requires the last two 16-bit blocks, or 32 bits of the address, which is represented in IPv4 dotted-decimal notation. The remaining portion of the IPv6 address is all 0s. Six hexadecimal 16-bit blocks are concatenated with the dotted-decimal format. The first 96 bits are 0, and the last 32 bits are used for the IPv4 address. This form is x:x:x:x:x:x:d.d.d.d, where each x represents the hexadecimal digits and d.d.d.d is the dotted-decimal representation.

An example of a mixed full address is 0000:0000:0000:0000:0000:0000:100.1.1.1; this example can be shortened to 0:0:0:0:0:0:100.1.1.1 or ::100.1.1.1.

IPv6 Prefix Representation

IPv6 prefixes are represented similar to IPv4, with the following format:

IPv6-address/prefix

The IPv6-address portion is a valid IPv6 address. The prefix portion is the number of contiguous bits that represent the prefix. You use the double colon only once in the representation. An example of an IPv6 prefix is 200C:001b:1100:0:0:0:0:0/40 or 200C:1b:1100::/40.

For another example, look at the representations of the 60-bit prefix 2001000000000ab0:

2001:0000:0000:0ab0:0000:0000:0000:0000/60
2001:0000:0000:0ab0:0:0:0:0/60
2001:0000:0000:ab0::/60
2001:0:0:ab0::/60

The rules for address representation are still valid when using a prefix. The following is not a valid representation of the preceding prefix:

2001:0:0:ab0/60

The preceding representation is missing the trailing double colon:

2001::ab0/60

The preceding representation expands to 2001:0:0:0:0:0:0:0ab0, which is not the prefix 2001:0000:0000:0ab0::/60.

When representing an IPv6 host address with its subnet prefix, you combine the two. For example, the IPv6 address 2001:0000:0000:0ab0:001c:1bc0:08ba:1c9a in subnet prefix 2001:0000:0000:0ab0::/60 is represented as the following:

2001:0000:0000:0ab0:001c:1bc0:08ba:1c9a/60