GuidesLearn Windows XP Professional: TCP/IP Addressing in Windows XP Professional (Page 2)...

Learn Windows XP Professional: TCP/IP Addressing in Windows XP Professional (Page 2) Page 2




The value
of the bits, in order from the Most Significant Bit (MSB) to
the Least Significant Bit (LSB) are 128, 64, 32, 16, 8, 4,
2, 1. These numerical designations are what make up the
TCP/IP version 4 address. Each set bit (noted by a “1”) is
added to the others to give you the address. The TCP/IP version 4
address of 171.144.62.12 converts to a binary number of
10101011.10010000.00111110.00001100 and a hexadecimal number
of AB.90.3E.0C


[NOTES FROM THE FIELD] –
While it’s important to know that the TCP/IP version 4
address converts to a binary number or a hexadecimal number,
it is not often used in day to day operations of the
MCSA/MCSE. It is more so for the Network Administrator. For
the 70-270 exam, concentrate on the different classes of
addresses, how subnet masks work, Classless Inter-Domain
Routing (CIDR) addressing and a basic understanding of the
binary conversion of a TCP/IP version 4 address. Basically,
know the Most Significant Bit (MSB) and the Least
Significant Bit (LSB) and the order of numbers.

The way
I remember it was to remember that the


Least Significant Bit (LSB) of each octet was “1” and
each place to the left of it doubled in value up to the end
of the octet on the far left. After the DOT I would start
back at “1”

TCP/IP
version 6 (IPv6)
addresses are a set of specifications from
the Internet Engineering Task Force (IETF) and have been
designed to overcome the current shortage of addresses under
TCP/IP version 4. TCP/IP version 6 also has some other built-in
improvements that go beyond the scope of the discussion
here. The single most important thing you will need to know
for the 70-270 exam (although a little more depth may be needed for
the upcoming Exam 70-275: Installing, Configuring and
Administering Microsoft .NET Server and Exam 70-276:
Implementing and Administering a Microsoft .NET Server
Network Infrastructure) is that IPv6 addresses are 128 bits
in length as opposed to 32 bits under IPv4.


Classless Inter-Domain Routing
(CIDR) is a newer way to
allocate IP addresses that is more flexible than with the
original Class addressing scheme used in the past. This
makes it so that the utilization of the number of remaining
available Internet addresses has been increased. CIDR is now
the routing system used by virtually all gateway hosts on
the Internet’s backbone network.

The original Internet Protocol defines IP addresses in five
classes, Classes A through E. Each of these classes allowed
the use of one portion of the 32-bit Internet address scheme
to the network address and the remaining portion to the
nodes on the network. One of the main reasons for the IP
address shortage was the situation where many companies
needed more than the 254 host machines that were allowed under
the Class A scheme but far fewer than the 65,533 host
addresses allowed under the Class B scheme. They would request a unique
B Class address but often ended up not using many of the
addresses within their allotted block. This meant that many
addresses within their pool went unutilized. This is one of
the main reasons the IP address pool was drying up, and for
this reason, the big push was on for TCP/IP version 6 (IPv6)
and its 128-bit address. Because many of the Internet
authorities realized that it would be some time before IPv6
was in widespread use, Classless Inter-Domain Routing was
born.

Using Classless Inter-Domain Routing, each IP address has a
network prefix that identifies either a collection of
network gateways or an individual gateway. The length of the
network prefix is also specified as part of the IP address
and varies depending on the number of bits that are needed
(rather than any arbitrary class assignment structure). A
destination IP address or route that describes many possible
destinations has a shorter prefix and is said to be less
specific. A longer prefix describes a destination gateway
more specifically. Routers are required to use the most
specific or longest network prefix in the routing table when
forwarding packets.

A Classless Inter-Domain Routing network address looks like
this: 201.44.112.00/18

201.44.112.00 is the address of the network and the “18”
says that the first 18 bits are the network part of the
address, leaving the last 14 bits for the address of the
node. (Effectively, the 18 is the subnet mask from the “old”
style of address classes.) Classless Inter-Domain Routing
lets one routing table entry represent a collection of
networks that exist in the forward path that don’t need to
be specified on that particular gateway. This collecting of
networks in a single address is sometimes referred to as a
supernet as by their definition they mean the same thing.

Classless Inter-Domain Routing is supported by The Border
Gateway Protocol, the prevailing exterior (interdomain)
gateway protocol. (The older exterior or interdomain gateway
protocols, Exterior Gateway Protocol and Routing Information
Protocol, do not support Classless Inter-Domain Routing.)
Classless Inter-Domain Routing is also supported by the OSPF
interior or intradomain gateway protocol.

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