Exploring Network Fundamentals

A network consists of two or more computer systems set up to communicate with each other. To some extent, the media you use doesn t matter. You can set up a network using parallel cables, telephone modems, Ethernet cards, wireless adapters, or any other media that allow your computers to exchange information. If you can connect these computers directly or through a hub, you can set up a local area network (LAN). Each LAN typically has a special IP address known as a network address .

A LAN connects computers that are close to each other, such as within an office or a building. An internet consists of two or more connected LANs. Some internets are wide area networks (WAN). A WAN consists of two or more geographically separate networks. The biggest WAN is the Internet.

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Any network or group of networks that are managed by the same group is often known as a domain. For example, you could configure two separate networks, linux.sybex.com and windows .sybex.com; both would be part of the sybex.com domain.

LANs and WANs

Linux LANs are usually configured to a standard known as IEEE 802.3, more popularly known as Ethernet. This type of network is much faster than a telephone modem. While standard Ethernet networks allow computers to communicate at speeds of 10 or 100Mbps (Ethernet and Fast Ethernet), Gigabit Ethernet (1000Mbps) is currently coming on line in many locations, and even faster networks (10Gbps Ethernet) are currently under development.

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Ethernet is actually a trade name. The proper name for this network is taken from the standard implemented by the Institute of Electrical and Electronics Engineers, IEEE 802.3. Fast Ethernet and Gigabit Ethernet are known by similar names , IEEE 802.3u and IEEE 802.3ae.

But the distance between computers on an Ethernet is limited to a few hundred meters , depending on the type of connection. In essence, while the amount of area that a LAN can cover is limited, LANs are fast. In contrast, connections between LANs in a WAN can cover thousands of miles, but the speed of the connection is typically limited. Even high-speed WAN connections are typically limited to 1.4Mbps or less.

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This speed limit on WANs is based on cost. Internet WAN backbones can carry tens of gigabits of data and are expensive to build; consequently, the associated bandwidth is shared among the customers of this WAN.

The Internet

Even if you ve never set up a network, chances are good that you already know something about networking from your experience with the Internet. When connecting to the Internet, most users and many Linux administrators work through an Internet Service Provider (ISP). If you re responsible for a larger network, you may have your own direct connection to the Internet and thus act as your own ISP.

You connect to the Internet through your ISP s gateway, which is a computer that connects that ISP to the rest of the Internet. When you search for a domain name, such as www.mommabears.com , your computer has to find the appropriate computer address. On the Internet, this is known as an IP address, which is usually stored on a Domain Name Service (DNS) server.

Domains

When you installed Red Hat Linux, you may have entered a hostname, such as computer1, or a fully qualified domain name (FQDN), such as linux1.mommabears.com . Unless your computer serves information or otherwise directly connects to the Internet, the name you use does not matter. If you use a FQDN, make sure to use the same domain name when you install Linux on each of the computers on your network.

Alternatively, some ISPs may assign you a specific FQDN for your connection to the Internet. This is a common practice with higher speed connections such as cable modems or DSL (Digital Subscriber Line) adapters.

You can divide a domain into a number of subdomains. Each subdomain can represent a different LAN. For example, linux.mommabears.com , windows.mommabears.com , and other.mommabears.com can represent three different LANs.

Hostname

The alternative to an FQDN on a network is a hostname such as computer1. The FQDN of a computer includes the hostname and domain name, assembled together. For example, if your computer has a hostname of berkeley and your domain name is california.now , your fully qualified domain name is berkeley.california.now . Every hostname or FQDN is associated with a numeric address such as an IP address.

Hardware Address

Computers contact each other through the hardware address on their network cards. A hardware address might look like 00-60-08-8D-41-93. These are hexadecimal numbers , also known as base 16. Every network card built today is configured with a unique hexadecimal hardware address. When you configure a TCP/IP network, you associate an IP address with a hardware address.

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In hexadecimal notation, there are 16 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, and f.