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NETWORK+ STUDY GUIDE

This is intended as a study guide to help you prepare for CompTIA’s Network+ certification only.  It is not intended to replace studying and learning from textbooks, instructors or hands-on experience.

Network Topologies

• Bus - The bus topology is a single cable that connects all of the workstations on the LAN.  This is the most commonly used topology in office environments, however it is risky.  If one computer goes down, or if there is one break in the cable the entire network goes down.
• Token Ring - With a token ring network, an electronic token is passed around the network.  When a computer has the token it is allowed to transmit and receive information.  Early token rings networks ran at 4 Mbps, but more modern token ring networks can run at 16 Mbps.   With a token ring network, there is no contention for the network, because the devices have to wait for the token before transmitting.
• Star - The star network has a central point such as the hub, with the cables coming out from the center going to the workstations almost resembling a star.  If there is a break in a cable only the computer on that segment will be affected, and it you need to make changes on your network, you can do them from one location.  If there is a cable problem it will only affect one user, and a star network is easily upgradeable.
• Mesh - A mesh network has multiple paths to the same place much like a spiders web.   The Internet is an example of a mesh network. The mesh topology has multiple connections to multiple locations, and is used mainly in large networks.  If the connection goes down, the information can be routed through another connection.

BASIC NETWORKING

• Local Area Networks or LANS are networks within your office.
• Wide Area Networks or WANS are networks in geographically separate locations.

Here is a table of your Network Cables and their specifications:

MORE ON CABLING

• 10Base5 is also known as thicknet because of a copper core making it thicker than other cabling.  It uses vampire taps that pierce the cable.
• 10Base2 is also known as thinnet, and uses BNC connectors

I remember my cabling by the following means:

• 10BaseT- T for Telephone – means RJ45, 10 starts with T, so if T is equal to 10, then 10x10 = 100 meters.
• 10Base2 – something you do twice a week is referred to as bi-weekly, bi starts with B – means BNC.  I remember the 185 meters, because I remember that it doesn’t quite go to 200 meters.
• 10Base5 – Thicknet because it is a bigger or thicker number than 2.  500 meters, because it ends in 5.

Patch Cables

• Can connect computers to UTP faceplates
• Can connect a patch panel to a hub or switch
• Made from stranded copper
• Must be kept as short as possible
• Cable types should not be switched

Patch Panels

• Can be used for horizontal or vertical patching
• Two categories – cable patching, which is used in, structured cabling environments, and fiber patching which links by fiber patching cables.

Crossover Cables

• Connect two network devices together
• Same as a patch cable expect that you need to switch two pairs of wires before you crimp on the RJ45 connector.

Network Cards

• Also known as a NIC
• The only physical layer device actually found inside the computer
• They have different connectors for different medium types
• Come with a MAC address preinstalled by the manufacturer

Client/Server Networks

• Central server
• Usernames and passwords to log onto the network
• Advantages are ease of management and centralized control

Peer to Peer Networks

• Each computer on the network can be both a client and a server
• Low security
• Computers will receive a performance hit, when someone is accessing a file on them.

The Seven Layers Of the OSI Model

The seven layers of the OSI Model are easily remembered in one of two ways:

1. All People Seem To Need Data Processing
2. Please Do Not Throw Sausage Pizza Away

Here are some charts to help you focus on remembering this.  Just remember to read the charts in the direction of the corresponding arrows.

OSI LAYER	CORRESPONDING WORD
Application Layer	All
Presentation Layer	People
Session Layer	Seem
Transport Layer	To
Network Layer	Need
Data Link Layer	Data
Physical Layer	Processing

OSI LAYER	CORRESPONDING WORD
Application Layer	Away
Presentation Layer	Pizza
Session Layer	Sausage
Transport Layer	Throw
Network Layer	Not
Data Link Layer	Do
Physical Layer	Please

Layer 1 – The Physical Layer

• Translates data into bits, or bits into data
• Deals only with electrical and mechanical level of data communication, which builds the foundation to allow higher OSI layers to walk through it.
• Physical Layer devices are:
• NIC Cards
• Ethernet Hubs
• Repeaters
• Multistation Access Units (MAUs)
• Transceiver
• Media Filters

Layer 2 – The Data Link Layer

• Provides flow and error control and synchronization for the Physical Layer
• Is made up of the Logical Link control and MAC sublayers
• Data Link Layer Devices are:
• Bridges
• Switches
• Brouters

The Protocols that operate at the Data Link Layer are:

• Point-to-Point Protocol (PPP)
• Serial Line Internet Protocol (SLIP)
• High-Level Data Link Control (HDLC)
• Logical Link Control (LLC)
• Link Access Protocol (LAP)

Layer 3- The Network Layer

• Manages communications routing for packets that are destined for addresses that are not on the LAN
• Uses routable protocols to deliver packets across interconnected networks joined by routers.
• Device which operate at the Network Layer are:
• Routers
• Connectionless Oriented services

The two main protocols that operate at the Network Layer are:

• TCP/IP
• IPX/SPX

Layer 4 – The Transport Layer

• Manages the end-to-end control and error checking by providing an end-to-end connection between the source and the destination node to ensure reliable data delivery
• Also responsible for providing end-to-end recovery, flow control, and releasing the connection

Connectionless-Oriented Protocols that operate at this layer are:

• UDP

Connection-Oriented Protocols that operate at this layer are:

• TCP/IP
• SPX/IPX

Layer 5 – The Session Layer

• The session layer manages the establishment of a continuing series of requests and responses between the applications at each end.
• Mainframes used to use this layer – modern networking does not.

Layer 6 - The Presentation Layer

• Usually part of the Operating System
• It prepares incoming data for the Application layer and formats outgoing data that the Application layer sends and receives.
• Data compression and data encryption.

Layer 7 – The Application Layer

• The top layer of the OSI model
• Provides information services
• FTP and Telnet access the OSI model at this layer.

Fault Tolerance

TCP/IP

TCP/IP fundamentals are:

The TCP/IP Protocol Suite is made up of the following utilities:

Some common TCP and UDP Port Numbers Are:

IP addressing to the extent it will appear on this exam is as follows:

Class A networks:

Class B networks:

Class C networks: 

The TCP/IP Utilities are:

Backup Types

Normal or Full Backup

• Copies all selected files and marks each one as backed up.
• Will allow you to restore data quickly
• Can be time consuming and redundant

Copy Backup

• Copies all selected files but does not mark each one as backed up.
• Use this if you want to back up files between normal and incremental backups

Incremented Backup

• Copies only those files that have been created or changed since the last normal or incremental backup, and marks those files as backed up
• Can make files difficult to control because the can be on several tapes
• Least time consuming
• Requires the least amount of data storage space

Differential Backup

• Copies those files that have been created or changed since the last normal or incremental backup, but it does not mark the files as backed up

Daily Backup

• Copies only the selected files that have been modified on the day that you perform the daily backup, and does not mark the files as backed up.
• The fastest way to backup files that have changed during the day.

Encryption

Data Encryption Standard

• Also known as DES
• Divides message into blocks and processes the blocks into multiple iterations
• Both parties have to know the key that encrypted the message
• Has been compromised on the internet and is therefore not a good choice

Public-Key Encryption

• Uses two keys
• All users get a copy of the public key, but the private key is kept secret
• Guarantees that messages will not be tampered with

Viruses

Boot Sector Virus

• Attaches itself to the boot sector of a floppy disk or an executable file
• Copies all or part of itself onto the boot sector of your hard drive when you turn on your computer or try to run an executable file
• Can get one from an infected disk or the Internet

File-Infecting Virus

• Attach themselves to executable files associated with other programs
• Mostly attach to .EXE or .COM files but can infect .SYS, .DLL, and .BIN files
• When you open a program that contains a virus, the virus loads into your computer’s memory and then infects any other executed program.

Macro Virus

• Affect the Microsoft Word and Excel templates
• Once infected, every document or spreadsheet opened with the program becomes corrupted.
• Widespread

Polymorphic Virus

• Can infect the boot sector, files, or both
• Can modify their appearance and signature
• Use code alteration and encryption so that they can not be detected by anti-virus search screens

Stealth Viruses

• Infects a file by adding bytes to the infected file, and then subtracting the same number of bytes to from the directory entry of that file, so that it appears that nothing is different
• Stay in memory

Multipartite Virus

• Can infect the boot sector and executable files
• Combine characteristics of memory-resident and nonresident files, and boot sector viruses incorporating stealth and polymorphic characteristics.

• The first viruses known to infect data files and work on multiple platforms
• Normally carried in data files for Microsoft Word and AmiPro documents

Other Destructive Programs

Worms

• Often mistaken for a virus
• A single destructive program on a single system
• Often planted by someone with direct access to the system
• Do not replicate themselves

 Trojan Horses

• Appears to be a program
• Waits for an user to execute it
• Can infect other files on the system, or other computers on the network

Logic Bombs

• Similar to a Trojan Horse but it has a timing device that is keyed to go off on a certain day or time
• Can do damage anywhere from destroying data on the hard drive to releasing a virus

Network Troubleshooting

The following tools can be used for network troubleshooting:

By: Tracey J. Rosenblath

Copyright 2000 http://www.CERTguide.com/