Ipv6 Address Notation; Ipv6 Address Prefix Notation - Alcatel-Lucent OmniSwitch 6850-48 Network Configuration Manual

Configuring IPv6

IPv6 Address Notation

IPv4 addresses are expressed using dotted decimal notation and consist of four eight-bit octets. If this
same method was used for IPv6 addresses, the address would contain 16 such octets, thus making it diffi-
cult to manage. IPv6 addresses are expressed using colon hexadecimal notation and consist of eight 16-bit
words, as shown in the following example:
1234:000F:531F:4567:0000:0000:BCD2:F34A
Note that any field may contain all zeros or all ones. In addition, it is possible to shorten IPv6 addresses by
suppressing leading zeros. For example:
1234:F:531F:4567:0:0:BCD2:F34A
Another method for shortening IPv6 addresses is known as zero compression. When an address contains
contiguous words that consist of all zeros, a double colon (::) is used to identify these words. For exam-
ple, using zero compression the address 0:0:0:0:1234:531F:BCD2:F34A is expressed as follows:
::1234:531F:BCD2:F34A
Because the last four words of the above address are uncompressed values, the double colon indicates that
the first four words of the address all contain zeros. Note that using the double colon is only allowed once
within a single address. So if the address was1234:531F:0:0:BCD2:F34A:0:0, a double colon could not
replace both sets of zeros. For example, the first two versions of this address shown below are valid, but
the last version is not valid:
1
1234:531F::BCD2:F34A:0:0
2
1234:531F:0:0:BCD2:F34A::
3
1234:531F::BCD2:F34A:: (not valid)
With IPv6 addresses that have long strings of zeros, the benefit of zero compression is more dramatic. For
example, address FF00:0:0:0:0:0:4501:32 becomes FF00::4501:32.
Note that hexadecimal notation used for IPv6 addresses resembles the notation which is used for MAC
addresses. However, it is important to remember that IPv6 addresses still identify a device at the Layer 3
level and MAC addresses identify a device at the Layer 2 level.
Another supported IPv6 address notation includes embedding an IPv4 address as the four lower-order bits
of the IPv6 address. This is especially useful when dealing with a mixed IPv4/IPv6 network. For example:
0:0:0:0:0:0:212.100.13.6

IPv6 Address Prefix Notation

The Classless Inter-Domain Routing (CIDR) notation is used to express IPv6 address prefixes. This nota-
tion consists of the 128-bit IPv6 address followed by a slash (/) and a number representing the prefix
length (IPv6-address/prefix-length). For example, the following IPv6 address has a prefix length of 64
bits:
FE80::2D0:95FF:FE12:FAB2/64
OmniSwitch AOS Release 6 Network Configuration Guide September 2009
IPv6 Overview
page 26-7