Learn Windows XP Professional in 15 Minutes a Week: TCP/IP Addressing in Windows XP Professional

Monday Aug 5th 2002 by ServerWatch Staff
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Jason Zandri's latest article in the Learning Windows XP Professional in 15 Minutes a Week series covers the TCP/IP Protocol with a specific focus on administration and management of the network protocol under Windows XP Professional.

by Jason Zandri
www.2000trainers.com

Welcome to this week's installment of Learn Windows XP Professional in 15 minutes a week, the 13th in this series. This article will continue covering the TCP/IP Protocol within Windows XP Professional with a specific focus on administration and management of the network protocol under Windows XP Professional.


Internet Protocol Addressing Overview

The Transmission Control Protocol/Internet Protocol is a network communication protocol. It can be used as a communications protocol on private networks and is the default protocol in use on the internet. When you set up any system to have direct access to the Internet, whether it is via dial-up or one of the high speed technologies in use today, your system will need to utilize the TCP/IP protocol (whether it is a Windows-based system or not).

Also, if the given system needs to communicate with other TCP/IP systems on the local LAN or WAN, it will need to utilize the TCP/IP protocol as well.

[NOTES FROM THE FIELD] - This is just a basic overview of TCP/IP, and I didn't want to get too involved with it within this article. There is bountiful information on TCP/IP all over the internet and before pouring through the RFCs I would first suggest you try these two resources -- TCP/IP Frequently Asked Questions or TCP/IP Protocol Suite - Questions & Answers.

I have gone into a more detailed overview of the TCP/IP Protocol in last week's article, which covered the four-layer conceptual model of TCP/IP and how the model stacks up against the seven layer Open System Interconnection (OSI) protocol model.


TCP/IP version 4 (IPv4) addresses are made of up four 8-bit fields (octets) and are 32-bits in size total. Microsoft TCP/IP version 4 supports the standard classes of address, which defines which bits are used for the network ID and which bits are used for the host ID. There are five TCP/IP version 4 (IPv4) addresses, although for the most part, only the A, B, and C classes are used. The system of IP address classes described here form the basis for IP address assignment. Classless Inter-Domain Routing (CIDR) addressing is now being used more often, and I will cover that later in the article. Classless Inter-Domain Routing is making the IP address classes in their current form "less defined", for lack of a better term. Still, the classes form the base of any addressing scheme.

TCP/IP version 4 addresses are made of both a network ID and a host ID. The network ID address identifies the physical network where the hosts exist. The host ID address identifies the individual TCP/IP host on a network. The host ID must be unique on the internal network; that is, no two nodes on a given network can have the same network ID AND host ID.

[NOTES FROM THE FIELD] - You can have two hosts with the IP host name of 112.12.44 if one is on network 10 and another is on network 11. (The full IP addresses of these hosts would be 10.112.12.44& and 11.112.12.44. The subnet mask would be 255.0.0.0.) You cannot assign both of these nodes the host address of 112.12.44 if they are both on network 10 or both on network 11.

The "division" point between the network ID and the host ID is called the subnet mask. The subnet mask is used to determine where the network number in an IP address ends and the node number in an IP address begins.

The bits in a subnet mask are set consecutively from left to right and there can be no "skips" in the setting structure. The subnet mask of 255.255.128.0 is valid because all eight bits are set in the first two octets and the first bit of the next octet is also set. (11111111.11111111.10000000.00000000). The subnet mask of 255.255.64.0 is not valid because there is a "missing" bit that is not allowed. (11111111.11111111.01000000.00000000).

[NOTES FROM THE FIELD] - The left most bit in a TCP/IP version 4 address is called the Most Significant Bit (MSB) and has the highest value. The right most bit in a TCP/IP version 4 address is called the Least Significant Bit (LSB) and has the lowest value.

I have detailed subnet masks in a little more detail in the following section.

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.

Subnet Masks - Implementing subnewtorks (commonly referred to as subnets in the field) helps to control network traffic. Every node on the same physical Ethernet network sees all the packets of data sent out on the network. This commonly has the result of multiple collisions causing network performance to be slow. Routers or gateways are used to separate networks into subnets. Subnet masks on each of the nodes allow the nodes on the same subnetwork to continue to communicate with one another and with the routers or gateways they use to send their messages.

Subnet masks allow you to identify the network ID and the host (node) ID of an IP address.

Given the following example of a default B Class subnet mask:

10011110.00010101.00111001.01101111 158.21.57.111
11111111.11111111.00000000.00000000 255.255.000.000
--------------------------------------------------------
10010110.11010111.00000000.00000000 158.21.000.000

we can determine that the network ID is 158.21 and the host ID is 57.111

Network Address : 158.21.0.0

Subnet Address : 158.21.0.0
Subnet Mask : 255.255.0.0
Subnet bit mask : nnnnnnnn.nnnnnnnn.hhhhhhhh.hhhhhhhh
Subnet Bits : 16
Host Bits : 16
Possible Number of Subnets : 1
Hosts per Subnet : 65534


Additional bits can be added to the subnet mask for a given class of addresses to subnet networks further.

Given the following example of a B Class address using an additional bit subnet mask:

10011110.00010101.00111001.01101111 158.21.57.111
11111111.11111111.11110000.00000000 255.255.240.000 Subnet Mask
--------------------------------------------------------
10010110.11010111.00010000.00000000 150.215.016.000 Network address

Subnet Mask : 255.255.240.0
Subnet bit mask : nnnnnnnn.nnnnnnnn.nnnnhhhh.hhhhhhhh
Subnet Bits : 20
Host Bits : 12
Possible Number of Subnets : 16
Hosts per Subnet : 4094

we can see that rather than having the single subnet and 65534 Hosts per Subnet allowed under the default subnet mask, we are able to have up to 16 subnets with up to 4094 Hosts per Subnet by using a Subnet Mask of 255.255.240.000.

Selected Subnet : 158.21.0.0/255.255.240.0
Usable Addresses : 4094
Host range : 158.21.0.1 to 158.21.15.254
Broadcast : 158.21.15.255

Subnet Mask Subnet  Host Range Broadcast
158.21.0.0 255.255.240.0 4094 158.21.0.1  to  158.21.15.254 158.21.15.255
158.21.16.0 255.255.240.0 4094 158.21.16.1  to  158.21.31.254 158.21.31.255
158.21.32.0 255.255.240.0 4094 158.21.32.1  to  158.21.47.254 158.21.47.255
158.21.48.0 255.255.240.0 4094 158.21.48.1  to  158.21.63.254 158.21.63.255
158.21.64.0 255.255.240.0 4094 158.21.64.1  to  158.21.79.254 158.21.79.255
158.21.80.0 255.255.240.0 4094 158.21.80.1  to  158.21.95.254 158.21.95.255
158.21.96.0 255.255.240.0 4094 158.21.96.1  to  158.21.111.254 158.21.111.255
158.21.112.0 255.255.240.0 4094 158.21.112.1  to  158.21.127.254 158.21.127.255
158.21.128.0 255.255.240.0 4094 158.21.128.1  to  158.21.143.254 158.21.143.255
158.21.144.0 255.255.240.0 4094 158.21.144.1  to  158.21.159.254 158.21.159.255
158.21.160.0 255.255.240.0 4094 158.21.160.1  to  158.21.175.254 158.21.175.255
158.21.176.0 255.255.240.0 4094 158.21.176.1  to  158.21.191.254 158.21.191.255
158.21.192.0 255.255.240.0 4094 158.21.192.1  to  158.21.207.254 158.21.207.255
158.21.208.0 255.255.240.0 4094 158.21.208.1  to  158.21.223.254 158.21.223.255
158.21.224.0 255.255.240.0 4094 158.21.224.1  to  158.21.239.254 158.21.239.255
158.21.240.0 255.255.240.0 4094 158.21.240.1  to  158.21.255.254 158.21.255.255

[NOTES FROM THE FIELD] - A subnet address cannot be all 0's or all 1's.

TCP/IP Class A Address Overview

The "A" class addressing scheme has an official start address of 0.0.0.0 and an official last address of 127.255.255.255. Not all of these address can be used, and you will OFTEN see conflicting information on this.

1.0.0.1 to 126.255.255.254 is the range of IP addresses that are included in the "A" class addressing scheme that are the useable range for node assignment

126.255.255.255 is a broadcast address and in most cases cannot be assigned. (There are exceptions to the rule.)

The local host will use 0.0.0.0 when it cannot reach a DHCP server when it is set to use one and cannot assign itself an address using APIPA.

1.0.0.1 to 126.255.255.254 is the useable range. There are 126 Class A networks total, each allowed to have up to 16,777,214 hosts. The 127.x.x.x range is used for internal host loopback.

There are three IP network addresses reserved for private networks:  10.0.0.0 - 10.255.255.255 with the subnet mask 255.0.0.0 is the range for Class A IP addresses.

They can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a NAT or proxy server or a router. It is always safe to use these because routers on the Internet will never forward packets coming from these addresses.

These addresses are defined in RFC 1918.

While 10.0.0.0 - 10.255.255.255 addresses with the subnet mask 255.0.0.0 are available only to internal IP networks, they are still considered part of the Class "A" range.


TCP/IP Class B Address Overview

The "B" class addressing scheme has an official start address of 128.0.0.0 and an official last address of 191.255.255.255. Not all of these address can be used, and you will OFTEN see conflicting information on this.

128.0.0.1 to 191.255.255.254 is the range of IP addresses that are included in the "B" class addressing scheme that are the useable range for node assignment.

The local host will use 0.0.0.0 when it cannot reach a DHCP server when it is set to use one and cannot assign itself an address using APIPA.

There are three IP network addresses reserved for private networks:  172.16.0.0 - 172.31.255.255 with the subnet mask 255.240.0.0 is the range for Class B IP addresses.

They can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a NAT or proxy server or a router. It is always safe to use these because routers on the Internet will never forward packets coming from these addresses.

These addresses are defined in RFC 1918.

While 172.16.0.0 - 172.31.255.255 addresses with the subnet mask 255.240.0.0 are available only to internal IP networks, they are still considered part of the Class "B" range.


TCP/IP Class C Address Overview

The "C" class addressing scheme has an official start address of 192.0.0.0 and an official last address of 223.255.255.255.

Not all of these address can be used and you will OFTEN see conflicting information on this.

192.0.0.1 to 223.255.255.254 is the range of IP addresses that are included in the "C" class addressing scheme that are the useable range for node assignment.

The local host will use 0.0.0.0 when it cannot reach a DHCP server when it is set to use one and cannot assign itself an address using APIPA.

There are three IP network addresses reserved for private networks:  192.168.0.0 - 192.168.255.255 with the subnet mask 255.255.0.0 is the range for Class C IP addresses.

They can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a NAT or proxy server or a router. It is always safe to use these because routers on the Internet will never forward packets coming from these addresses.

These addresses are defined in RFC 1918.

While 192.168.0.0 - 192.168.255.255 addresses with the subnet mask 255.255.0.0 are available only to internal IP networks, they are still considered part of the Class "C" range.

TCP/IP Class D Address Overview

The IP version 4 addresses of 224.0.0.0 through 239.255.255.255 are set aside through IANA (Internet Assigned Numbers Authority) as a special class of addresses for Multicast uses.

At the present, ISPs are unable to allocate Class D address space to their customers. These addresses must be allocated through IANA.

Class D addresses are only required if you wish to be a multicast source. You can still receive multicast data without the need for a separate Class D address.


TCP/IP Class E Address Overview

The IP version 4 addresses of 240.0.0.0 to 254.255.255.255 are set aside by IANA (Internet Assigned Numbers Authority) as a special class of addresses for experimental and future use.

The IP address of 255.255.255.255 broadcasts to all hosts on the local network and therefore is not to be considered as part of the E class of IP addresses.


That's a wrap for this week. Be sure to check back in next week for the next article in this series.

In the meantime, best of luck in your studies and please feel free to contact me with any questions on my column and remember,


"The fact that the grass is greener on the other side of the fence is directly proportional to how much manure is being used on the property."


Jason Zandri
Jason@Zandri.net

www.2000trainers.com


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