IBM TS4500, Introduction And Planning Manual

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An IPv6 (Dual) address combines an IPv6 and an IPv4 address and has the
following format:
y : y : y : y : y : y : x . x . x . x
. The IPv6 portion of
the address (indicated with y's) is always at the beginning, followed by the IPv4
portion (indicated with x's).
v
In the IPv6 portion of the address, y is called a segment and can be any
hexadecimal value between 0 and FFFF. The segments are separated by colons -
not periods. The IPv6 portion of the address must have six segments but there is
a short form notation for segments that are zero.
v
In the IPv4 portion of the address x is called an octet and must be a decimal
value between 0 and 255. The octets are separated by periods. The IPv4 portion
of the address must contain three periods and four octets.
The following list shows examples of valid IPv6 (Dual) addresses:
v 2001 : db8: 3333 : 4444 : 5555 : 6666 : 1 . 2 . 3 . 4
v : : 11 . 22 . 33 . 44
(implies all six IPv6 segments are zero)
v 2001 : db8: : 123 . 123 . 123 . 123
(implies that the last four IPv6 segments
are zero)
v
: : 1234 : 5678 : 91 . 123 . 4 . 56
(implies that the first four IPv6 segments
are zero)
v : : 1234 : 5678 : 1 . 2 . 3 . 4
(implies that the first four IPv6 segments are
zero)
v
2001 : db8: : 1234 : 5678 : 5 . 6 . 7 . 8
(implies that the middle two IPv6
segments are zero)
Subnet masks (IPv4) and prefixes (IPv6)
Subnet masks (IPv4) and prefix lengths (IPv6) identify a range of IP addresses that
are on the same network.
IPv4 subnet masks
All IP addresses are divided into portions. One part identifies the network (the
network number) and the other part identifies the specific machine or host within
the network (the host number). Subnet masks (IPv4) and prefixes (IPv6) identify
the range of IP addresses that make up a subnet, or group of IP addresses on the
same network. For example, a subnet can be used to identify all the machines in a
building, department, geographic location, or on the same local area network
(LAN).
Dividing an organization's network into subnets allows it to be connected to the
Internet with a single shared network address. Subnet masks and prefixes are used
when a host is attempting to communicate with another system. If the system is on
the same network or subnet, it will attempt to find that address on the local link. If
the system is on a different network, the packet is sent to a gateway which will
then route the packet to the correct IP address. This is called Classless-InterDomain
Routing (CIDR).
In IPv4, the subnet mask
255.255.255.0
is 32 bits and consists of four 8-bit octets.
The address:
10.10.10.0
subnet mask
255.255.255.0
means that the subnet is a
range of IP addresses from
10.10.10.0 - 10.10.10.255.
The prefix-length in IPv6 is the equivalent of the subnet mask in IPv4. However,
rather than being expressed in 4 octets like it is in IPv4, it is expressed as an
integer between 1-128. For example:
2001:db8:abcd:0012::0/64
specifies a subnet
with a range of IP addresses from:
2001:db8:abcd:0012:0000:0000:0000:0000 -
Chapter 1. Overview
63