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Linux Systems Administrator

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Class Notes:

“Basic Networking”Part I

Basic Network – Part I

Configuring Basic Networking

Most linux systems are connected to a network, either as clients or servers (often as both). (see pic)

Setting up Linux’s basic networking tools is necessary for fully configuring Linux

You must first understand the basics of modern networking, such as the nature of network addresses and the type of tools that are commonly used on networks. . .From there you can move on to Linux network configuration, including tasks such as setting a computer’s address, routing, and name resolution

Unfortunately, network configuration sometimes goes wrong; understanding the tools and techniques used to diagnose and fix network problems is a necessary part of network configuration

Understanding TCP/IP Networking:

Networking involves quite a few components that are built atop one another, like: Network hardware Data packets and Protocols for data exchange

o Together, these components make up a “network stack”o The most common “network stack” today is the

“Transmission Control Protocol/Internet Protocol(TCP/IP), but it’s not the only stack available

o Understanding the basics of TCP/IP theory will help you to configure and manage networks

Knowing the Basic Functions of Network Hardware Network hardware is designed to enable two or more computers

to communicate with one another Modern computers have network interfaces built into their

motherboards, but internal network cards and external network interfaces are also available

Many networks rely on wires or cables to transmit data between machines as electrical impulses, but network protocols that use radio waves or even light to do the job are growing rapidly in popularity

At its core, network hardware is hardware that facilitates the transfer of data between computers

Investigating Types of Network Hardware Linux supports several types of common network

hardware. .the most common is “Ethernet”, which comes in several varieties (see ex):

Other types of network hardware exist, but most are less common than Ethernet, such as: Token Ring LocalTalk Fiber Distributed Data Interface (FDDI) High-Performance Parallel Interface (HIPPI) Fibre Channel

Wireless networking (aka Wi-Fi_ is an exception to Ethernet’s dominance.

Common wireless protocols include: 802.11a 802.11b 802.11g 802.11n

o These protocols support maximum speeds of 11Mbps (for 802.11b), 54Mbps (for 802.11a and 802.11g), or 300Mbps (for 802.11n)

o With the exception of the rarely used 802.11a, Wi-Fi protocols are compatible with one another

o WARNING: If you use wireless protocol, your data are transmitted via radio waves, which are easily intercepted

Wireless protocols include optional encryption, but this feature is sometimes disabled by default and some varieties of wireless encryption are notoriously poor

If you use Wireless network products, be sure to enable Wi-Fi Protected Access(WPA) or better, WPA2 encryption. The weaker Wired Equivalent Privacy(WEP) encryption is easily broken.

For added protection, use a strong encryption protocol, such as the Secure Shell(SSH) login tool or Secure Sockets Layer(SSL) encryption, when transferring any data that’s even remotely sensitive

In addition to the network hardware in your computers, you need network hardware outside the computers

With the exception of wireless networks, you need some form of network cabling that’s unique to your hardware type

Many network types require the use of a central device known as a “hub” or a “switch” (INCLUDE IMAGE on PAGE 384..Fig 8.1) (see ex)

pic of switch:

You plug every computer on a local network into this central device. . .the hub or switch then passes data between the computers

Network that includes a Switch and hub:

As a general rule, switches are superior to hubs “Hubs” mirror all traffic to all computers “Switches” are smart enough to send packets only to the

intended destination… Switches also allow “full-duplex” transmission, in which both parties can send data at the same time. . .”Hubs” permit only half-duplex transmission, in which the two computers must take turn (like 2 people using walkie-talkies)

Picture of Full and Half duplex transmission:

Results: switches let two pairs of computers engage in full-speed data transfers with each other; with a hub, these two transfers would interfere with each other

Computers with Wi-Fi adapters can be configured to communicate directly with one another, but it’s more common to employ a wireless router, which links together both wireless and Ethernet devices. . .Such routers also provide connections to an outside network—typically the Internet, sometimes via a broadband connection

Understanding Network Packets: Modern networks operate on discrete chunks of data known as

“packets”. Suppose you want to send a 100KiB file from one computer

to another. Rather than send the file in one burst of data, your computer breaks it down into smaller chunks. . .The system might send 100 packets of 1KiB each…this way, if there’s an error sending one packet, the computer can resend just that one packet rather than the entire file

When the recipient system receives packets, it must hold on to them and reassemble them in the correct order to re-create the complete data stream.

Examples of Packet Transmission:

There are several types of packets, and they can be stored within each other. For instance, Ethernet includes its own packet type

(known as frame), and the packets generated by networking protocols that run atop Ethernet, are stored within Ethernet frames

A data transfer can involve several layers of wrapping and unwrapping data. .each layer, packets from the adjacent layer may be merged or split up

Understanding Network Protocol Stacks

It's possible to think of network data as various levels of abstractness.

at one level, a network carries data packets for a specific network type (such as Ethernet). .the data packets are addressed to specific computers on a local network

The addresses used at different levels also vary, that will be explained in the upcoming section "Using Network Addresses"

The protocol stack is a set of software that converts and encapsulates data between layers of abstraction. .For example, the stack can take the commands of email transfer protocols, and the email messages that are transferred, and package them into packets.

o Another layer of the stack can take these packets and repackage them into Ethernet frames

o There are several layers to any protocol stack, and they interact in highly specified ways.

o It's often possible to swap out one component for another at any given layer

For Example: at the top of each stack is aprogram that uses the stack, such as an email client. .You can switch from one email client to another without too much difficulty; both rest atop the same stack

Likewise, if you change a network card, you have to change the driver for that card, which constitutes a layer very low in the stack. .Applications above that drive can remain the same

o Each computer in a transaction requires a compatible protocol stack.

o When they communicate, the computers pass data down their respective stacks and then send data to the partner system, which passes the data up its stack

o Each layer on the receiving system sees the data as packaged by its counterpart on the sending computer

Picture of TCP/IP Protocol stack, that dominates the Internet today, is shown below:

As shown above, client programs at the application layer initiate data transfers. . .These requests pass through the transport, internet, and link layers on the client computer, whereupon they leave the client system and pass to the server system

On the server, the process reverses itself, with the server program running at the application layer replying to the client program. . .This reply reverses the journey, traveling down the server computer's stack, across the network, and up the stack on the client

A full-fledged network connection can involve many back-and-forth data transfers

Each component layer of the sending system is equivalent to a layer on the receiving system, but these layers need not be absolutely identical

o For example: you can have different models of network card at the link layer, or you can even use entirely different network hardware types, such as Ethernet and

Token Ring, if some intervening system translates between them.

It's important that the stacks operate in compatible ways Linux was designed with TCP/IP in mind, and the Internet is

built atop TCP/IP

Other protocols stacks are available and you may occasionally run into them, such as:

o NetBEUI (the original Microsoft and IBM protocol stack for Windows)

o AppleTalk (Apple's initial protocol stacko Internet Packet Exchange/Sequenced Packet Exchange

(IPX/SPX) (was Novell's favored protocol stack All 3 are now fading in importance

o Linux supports AppleTalk and IPX/SPX, but not NetBEUI