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

By ServerWatch Staff (Send Email)
Posted Aug 5, 2002


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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