Background:
Networking is the art of connecting two or more computers together to share information. If you are new to the Internet, I recommend you read this page first. A network in your home or workplace is called a Local Area Network (LAN). A global network such as the Internet is called a Wide Area Network (WAN). The distinction between WAN and LAN is growing smaller due to the Internet. Both LAN and WAN networking is defined in terms of physical interfaces, protocols, and software. On this page we will discuss networking in general terms, for a specific example see the BUILD YOUR OWN NETWORK page.
Physical Interfaces:
Types of physical interfaces include Ethernet, T-spans, Fiber Optic, analog, DSL, Cable and ISDN modems. The most common devices used on the Internet are computers and routers. Computers are connected by modems and Ethernet Network Interface Cards (NICs) to Internet segments. To connect multiple computers to the Internet through one modem, a combination Hub and Router is used. All of the computers are connected to the Hub. Then the Hub is connected to an analog, DSL, or Cable modem. Routers are also used to connect the Internet segments together. Routers Bridge differing physical interfaces and route packets of information to the correct destination based on the protocol used. A typical Router found at your local Internet Service Provider (ISP) bridges Ethernet to T-Span, two physically different interfaces. There are other form of bridges, such as a "LAN Modem. A LAN Modem bridges Ethernet to analog modem.
Ethernet cabling is called 10/100 BASE-T and is based on twisted pair 8 conductor wire with RJ-45 connectors on either end. The 10 means 10 Mega bits per second and the 100 means 100 Mega bits per second. The 10 or 100 is determined by the capabilities of the equipment you have. There are two types of Ethernet cables, straight and crossover. Straight Ethernet cables are for connecting computers to Hubs. Crossover cables are for connecting Hubs and Routers, although must Hubs and Routers today have a switch to convert one of it's ports to an uplink port thereby eliminating the need for a special crossover cable as straight cables are the most prevalent. Here is an example of a typical Home or Small Office LAN / Intranet to WAN / Internet configuration based on Ethernet:
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TO THE INTERNET VIA TELEPHONY |
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HOME NETWORK EXAMPLE
The modem connects the Ethernet LAN to the Internet. The router serves as the Gateway to the Internet for the PCs.
Protocols:
Due to the Internet, the most prevalent protocol used on LANs and WANs today is the Transmission Control Protocol / Internet Protocol (TCP/IP). Other protocols such as NETBEUI and IPX are not commonly used and are not routable on the Internet. TCP/IP works by an addressing scheme. There are two addressing schemes for TCP/IP, one is known as V4 and the other as V6. TCP/IP V6 is a future addressing scheme now in testing. TCP/IP V6 is needed because as the internet grows, the number of TCP/IP V4 addresses become limited. For now however, the Internet uses TCP/IP V4.
A TCP/IP V4 address is 4 sets of binary octets . A binary octet is 8 bits, where each bit can be a one or a zero. Since binary is difficult to use, a TCP/IP address is written in decimal form. For example:
255.255.255.254 (decimal notation) == 11111111.11111111.11111111.11111110 (binary notation)
Every computer on the Internet must have a unique routable IP address (commonly referred to as just IP). By unique we mean that no two computers may have the same IP. A routable IP is determined by the configuration settings on the computers and routers connected to the Internet. Allowable configurations are controlled by registration with www.arin.net so that no two computers can get the same IP address. This control is accomplished through the registration of subnets and the configuring of the physical equipment (computers and routers) on the Internet.
There are three classes of TCP/IP subnets Known as class A, B, and C. Subnetting is accomplished through masking (a.k.a. subnet mask). A class A subnet is represented by the subnet mask of 255.0.0.0. A class B subnet is represented by the subnet mask of 255.255.0.0. A class C subnet is represented by the subnet mask of 255.255.255.0. Therefore an IP address is completely specified by it's IP and subnet. For Example:
255.255.255.254, 255.255.255.0
This means 255.255.255.254 is an IP with a subnet of 255.255.255.0. It is important to know both the IP and subnet mask because this is the information that is used to configure all of the computers and routers on the Inetnet.
In a class C subnet there would be 255 IPs. In a class B subnet there would be 255 X 255 = 65,025 IPs. In a class C subnet there would be 255 X 255 X 255 = 16,581,375 Ips. For the Entire TCP/IP V4 there would be 255 X 255 X 255 X 255 = 4,228,250,625 IPs. However, the TCP/IP V4 specification includes IPs for subnet ID and broadcast.
Subnet ID and broadcast is conducted on the first and last IP of any subnet. Therefore 255.255.255.0 and 255.255.255.255 are not assignable IPs in the 255.255.255.0 class C subnet.
There are also subnets dedicated for intranets. These Intranets are networks that are not directly routable on the Internet. A device known as a Network Address Translater (NAT) is required to connect an Intranet to the Internet. A NAT is a type of Router. IP subnets for intranets are:
10.0.0.0, 255.0.0.0
192.168.0.0, 255.255.0.0
It is possible to further subnet class A, B, and C subnets. For example:
65.168.104.65, 255.255.255.248
This provides a subnet with 6 routable IP's with 65.168.104.64 and 65.168.104.71 used for Subnet ID and broadcast. This type of a subnet is simply termed a subnet and does not have a class identifier. Subnets can also be written in slash notation. For example:
65.168.104.65/29 == 65.168.104.65, 255.255.255.248
The 29 indicates the number of net mask bits : 11111111.11111111.11111111.11111000 (29 "1's")
Possible subnet masks are: /9 through /30
In the HOME NETWORK EXAMPLE pictured above, the modem and/or Router (depends on exact hardware) would have a single routable Internet address while the computers would have Intranet addresses. The Router would translate the Intranet addresses to the Internet address via NAT. For example the router would have an address of 65.162.104.68, 255.255.255.0 and the Computers on the Intranet would have the address of 10.0.0.1-4, 255.255.255.0. The subnet masks on either side of the router do not have to match. In this example, all four computers share one Internet connection and one Internet IP.
The capabilities of NATs and Routers are dependent upon the manufacturer/device. Each IP transmits data through ports. Every IP has 65,535 logical ports. Using different ports is why you can browse the web and receive your email at the same time, each application uses the same IP but different ports. Some NAT's and Routers block or filter certain ports. The blocking/filtering of ports is not a true Firewall, but can be useful. Therefore some NATs may prevent the use of unwanted programs and wanted programs such as ICQ, Netmeeting, multiplayer games, etc because all of these programs use different ports.
Software:
TCP/IP networking software is an integral part of the Windows operating system. Networking components are installed through the Network Properties icon in Control Panel.
Use this Icon to access Windows Networking. |
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Client for Microsoft Networks is not necessary for typical users of the TCP/IP protocol and networking adapters. However, if you choose to use additional services such as File and Printer sharing, the Client for Microsoft Networks is necessary. Note: Enabling File and Printer sharing opens up your computer on the world wide web for access. I strongly recommended that you do not enable File and Printer sharing.
It is important to visit the windowsupdate.microsoft.com web site often to maintain the latest your TCP/IP software. As security vulnerabilities and functionality bugs are discovered and fixed, this site will have the latest patches.
If you are looking for information on how to setup TCP/IP properties on your computer, see this page to setup TCP/IP properties for your NIC.
ICS, Proxy Server, Software Router/Bridge, & NAT:
There are several shareware and commercial programs available that allow you to share your internet connection with other computers on a local network or intranet. In fact, Windows 98 Second Edition comes with a service called Internet Connection Sharing (ICS) that you can install. There are also shareware and commercial Proxy servers. All of these programs serve to bridge one interface to another and route packets from one TCP/IP interface to another. These programs also perform rudimentary forms of NAT or Proxy. Proxy servers perform essentially the same function as a NAT. Proxy servers proxy out intranet IPs and bridge two Ethernet interfaces. What sets ICS apart from Proxy servers and NATs is that it bridges modem connections to Ethernet adapters allowing you to share a single modem dial-up Internet account with other computers on an Ethernet LAN.
However, there are inexpensive hardware routers that perform these functions without loading your computer down with these programs.
