Ethernet

The Mike Meyers CompTIA Network+ All-in-One Exam Guide Fourth Edition is an excellent guide book you can use to study for the Network+ certification.  Click on the Amazon adjacent Amazon link for  a detailed synopsis of the book and an easy way to purchase it.

Below, are a few notes I have taken during my course of study at New Horizons for the Network+ certification that you might find useful.



The Ethernet standard dominates networking technology today and has been around since Xerox developed it in 1973.  The Ethernet is standardized as 802.3 and is based on the bus topology using twisted pair wiring.

Every version of Ethernet uses either unshielded twisted pair (UTP) or fiber.  Every version of Ethernet uses a hub or a switch, hubs being very rare today.
Only 10 megabit and 100 megabit Ethernet use a hub.
1 gigabit and 10 gigabit Ethernet networks must use a switch.
Every version of Ethernet has a limit of 1024 nodes.
The maximum distance from the switch or hub to the node for UTP Ethernet is 100 meters.

Since 1990, Ethernet uses a hybrid star-bus topology and the hub acts like nothing more than a repeater. These ethernet hub networks use half-duplex and CSMA/CD for transmitting data. Every network breaks up data into pieces, called frames.  This prevents a computer from hogging the shared cable.  The data frames contain MAC addresses to identify the sending and receiving computer.  CSMA/CD stands for carrier sense, multiple access/collision detection and determines which computer can access the wire and when.  CSMA/CD is an 802.3 IEEE standard.

A basic Ethernet frame contains the following:  the preamble, the MAC address of the receiving computer, the MAC address of the sending computer, the data length, the data itself, a pad, and a CRC (cyclic redundancy check, i.e., a frame check sequence).

Preamble: 64-bit series of alternating ones and zeros that end with 11.  The preamble lets the receiving computer know a data frame is imminent.

MAC address:  Every NIC has a unique MAC address.  The hub sends out a copy of the frame to each computer on the wire.  The computer with the matching MAC address recognizes the frame, while the other computers ignore it.

Length:  A frame can carry 1500 bytes of data in a frame and the length field tells the receiving computer how many bytes of data are coming.

Data:  The data part of the frame actually contains the data and also the IP address.

Pad:  A pad is added to the frame if the data is less than 64 bytes.

CRC:  The frame check sequence is like a check sum that enables the system to verify if all of the data was received.  The sending computer computes the CRC by using a special mathematical formula and attaches the result to the frame.  The receiving computer does the same thing, and if the CRC does not match, the receiving machine lets the sending machine know so that the data can be retransmitted.

The earliest version of Ethernet was 10Base5 and 10Base2, now obsolete.
10BaseT was created in 1990 and became the most popular networking standard in the world.
The number 10 refers to 10 Mbps and the word Base refers to baseband.  The letter T refers to UTP cabling.  10BaseT requires the use of CAT3 or higher.  CAT3 is a two pair wire, UTP (unshielded twisted pair) cable.  One pair of wire sends data and one pair receives data.  10BaseT only requires two pair of wires, however, most people uss the four-pair wire to ensure against future technological advancements.  The RJ-45 was also introduced at this time for 10BaseT.  Each wire in the cable attaches to a pin in the RJ-45 connector.  The real name for an RJ-45 is 8P8C, however, everyone calls it the RJ-45 connector.  The TIA/EIA (Telecommunications Industry Association/Electronics Industries Alliance) defined the standard used called the TIA/EIA 568A and 568B.

10BaseT has a distance limitation of 100 meters.  A 10BaseT hub can connect no more than 1024 computers.

10BaseFL was introduced a few years after 10BaseT.  10BaseFL is the fiber-optic version and transmits data using pulses of light.  10BaseFL signals can travel much further than 10BaseT electrical signals.  The maximum length is up to two kilometers, and is immune to electrical interference (EMI).  10BaseFL uses multi-mode fiber-optic and uses either an SC or ST connector.

Media converters can be used to connect different kinds of cable, such as 10BaseT and 10BaseFL.  Once the network expands in size, you need a way to connect efficiently.  A bridge can be used to connect hubs or an uplink port or crossover cable.

With an uplink port, two hubs can be connected using a straight-thru cable.  In order to connect two hubs, insert one end of the cable into the uplink port and the other end into the other regular port.  You must daisy chain the ports, to connect multiple hubs.

Hubs can also connect using crossover cables.  A crossover cable reverses the sending and receiving pairs on one end of the cable.  This allows the two hubs to hear each other.

A bridge can be used to connect two Ethernet segments.  The bridge acts like a repeater, but also monitors network traffic.  Bridges are mainly used in wireless networks.  Switches are mainly used in wired networks to connect segments.

An Ethernet switch looks like a hub but is intelligent.  The switch uses the MAC addresses, creating point to point connections.  Point-to-point is when two nodes have a dedicated connection.  The switch creates an electronic table of the MAC addresses and acts like a telephone operator.  Speed is enhanced and there is no longer a need for CSMA/CD.  All devices connected to the switch will hear a broadcast sent from any one system, essentially a broadcast domain.

Spanning Tree Protocol was something that added a bit more intelligence to the switches to take care of the problem called bridge loop.  The loop happened when there were too many switches which caused an endless bridge loop.

By the late 1990s, 100BaseTX became the most popular 100 megabit Ethernet standard.  100BaseTX is referred to as 100BaseT and uses CAT 5 cables. 100BaseT has a speed of 100 Mbps, a signal type of Baseband, 100 meters distance between the hub and node, CAT 5e or better UTP cables with RJ-45 connectors, and is a star-bus topology.

In a 100BaseT network, you must have a CAT 5 cable or better.  Most network cables today are at least CAT 5, so this probably isn't an issue.  You must have 100BaseT NICs and a 100BaseT hub or switch.  100BaseT NICs are called 10/100 NICs, and when the NIC first connects with the network it automatically determines the hub or switch speed.  If the hub or switch only does 10BaseT, then the NIC does 10BaseT.  If the hub or switch does 100BaseT, then the NIC does 100BaseT.  100BaseT NICs have totally replaced 10BaseT NICs.

Most Ethernet networks use UTP cabling, but there are many that are fiber-based because UTP cabling doesn't meet the needs of the network requirements.  If the property is large, the 100 meter distance limitation doesn't work.  UTPs unshielded twisted pair cabling containing a lack of electrical shielding does not work if there is a lot of electrical interference.  Not to mention, it is easy to tap, and if you need a secure environment, 100BaseFX fiber-optic cable is better.  10BaseFX looks just like 10BaseFL, and has a maximum cable length of 2 kilometers, and is 100 Mbps.  100BaseFX uses ST or SC connectors.

By the end of the 1990s, the IEEE approved the 1000BaseT and the 1000BaseX standards.  1000BaseX is divided into other standards such as 1000BaseCX, 1000BaseSX, and 1000BaseLX.  1000BaseT uses four-pair UTP cabling and like 10BaseT and 100BaseT, has 100 meters maximum cable length.  1000BaseT is now the dominant Gigabit Ethernet standard.

1000BaseCX uses twinaxial cable with a length limit of only 25 meters.  1000BaseSX uses multimode fiber-optic cabling, and has a maximum cable length of 220-500 meters and rely on the SC type of connector.  1000BaseLX use single-mode laser cables up to 5 kilometers, and with a repeater, the distance can be increased up to 70 kilometers.  1000BaseLX connectors look like 1000BaseSX SC connectors.

10 Gigabit and 100 Gigabit Ethernet was soon developed and standardized by the IEEE members, to satisfy the increased desire for more bandwidth.  In 2006, IEEE came up with a standard for 10 Gigabit Ethernet running UTP, 10GBaseT.  Unfortunately, 10GBaseT, running on CAT6 cable has a maximum cable length of only 55 meters.  CAT 6a cabling enables 10GBaseT to run at a distance of 100 meters.



Questions

1.  Ethernet hubs take an incoming packet and repeat it out to the connected ports.

2.  What begins an Ethernet frame?  preamble

3.  What type of bus does 10BaseT use?  Star bus

4.  What is the maximum distance for an ethernet segment?  100 meters

5.  When used for Ethernet, unshielded twisted pair uses what type of connector?  RJ-45

6.  What is the maximum number of connected segments for 100BaseT?  1024

7.  Which connectors are used by 10BaseFL cable?  SC and ST

8.  Which network devices can use the Spanning Tree Protocol (STP)?  Switches

9.  What device filters and forwards traffic based on MAC addresses?   Bridge


10.  What is the maximum distance between the hub/switch and node for 100BaseT Ethernet?  100 meters


11. What is the type of cable and connector that 100BaseFX uses?  Multimode fiber with ST or SC connectors

12.  How many pairs of wires do 10BaseT and 100BaseT user? 10BaseT and 100BaseT use two wire pairs

13.  What is the standard IEEE 802.3ab?  IEEE 802.3ab describes 1000BaseT which is known as Gigabit Ethernet and uses four pair UTP cabling to achieve gigabit performance.  

14.  What is the max distance for 1000Base LX with out repeaters?  5000 meters/5 kilometers.  Some manufacturers increase the distance up to 70 kilometers with special repeaters.


15.  What is the big advantage of using fiber-optic cabling?  Fiber is not affected by electrical magnetic (EM) interference.

16.  What is the standard connector for the 10-GbE fiber standard?  There is no standard.  It is left up to the manufacturers.

17.  How many wire pairs does 1000 BaseT use?  1000BaseT uses four pairs of wires


18.  What is the maximum cable length of 10GBaseT on CAT 6?  10GBaseT on CAT 6 cables are limited to 55 meters.

Related articles by Zemanta

• Bel's New RJ45 SFP Transceiver Module Delivers Gigabit Ethernet Speeds over Category 5/5e UTP Cables (eon.businesswire.com)
• How to Build Solid, Reliable Networks (pcworld.com)

The OSI Model

Image via Wikipedia

Open Systems Interconnection (OSI) seven-layer model

The seven layers are:

• Layer 7   Application
• Layer 6   Presentation
• Layer 5   Session
• Layer 4   Transport
• Layer 3   Network
• Layer 2   Data Link
• Layer 1   Physical

The Seven Layers of the OSI Model




Questions 


1.  Where does a hub send the data?  Data comes into a hub through one wire and the data is sent out to all other connected wires to the other systems.

2.  What uniquely defines every NIC?  A NIC is a network interface card and what identifies the NIC is the MAC address, the media access control address.

3.  What Windows utility is used to determine the MAC address?  IPCONFIG /ALL from the command line.

4.  A MAC address is known as what type of address?  The physical address, a 48-bit value.  It is a unique address assigned to each NIC.  An example of a MAC address is 00-50-57-A4-05-0D.

5.  A NIC sends data in chunks called what?  Frames.  Networks use frames to prevent one NIC from hogging the wire.

6.  Which MAC address begins a frame?  The MAC address of the receiving NIC begins a frame, followed by the sending NIC MAC address, and then followed by the data and CRC.

7.  What does the CRC do?  CRC stands for cyclic-redundancy check, a special bit of checking information that the receiving NIC uses to verify the data arrived correctly.

8.  What layer of the OSI model controls the assembly and disassembly of data?  The Transport Layer, the breaking up of data into chunks that are sent across a network and reassembled on the receiving end.  Refer to the link above for a detailed explanation of the Transport layer.

9.  What layer of the OSI model keeps track of a system's connections in order to send the right response to the right computer?  The Session layer keeps track of a system's connections so that the right response will be sent to the right computer.

Image via Wikipedia

Related articles by Zemanta

• The Web Is Finally Evolving To A More Semantic Future (regulargeek.com)
• IP Transmission Technologies Hourglass of TCP/IP Protocols (slideshare.net)

Cabling

There are three different types of cables used in networking:

1. Coaxial (coax)
2. Twisted Pair
3. Fiber Optic

Coaxial Cable

Coaxial cable has an inner copper core surrounded by insulating material, and the insulating material is surrounded by a braided wire, that has an outside rubber insulating layer.  The center wire and the braided metal shield share a common axis or centerline.

Coaxial Cables shield data transmissions from electro-magnetic interference (EMI).  Lights, cable televisions, cordless telephones, microwave ovens, refrigerators, anything where the electrical current is being turned on or off, can generate magnetic fields that cause electrical current along the wire.  This type of interference can disrupt transmissions on a network.

The most popular connectors for coaxial cables used to be BNC connectors.

BNC Connector

Vampire connections, sometimes called vampire taps, that pierced the cable, were also popular in early bus topology networks.

Coaxial cable used today is mostly used for connecting to an Internet Service Provider (ISP) via cable modem.  The same type of cable is used to connect televisions to cable boxes and satellite receivers.  An F-type connector that screws on is used to connect the cable.

F-type Connector

Cable modems connect using RG-6 type cables, predominately used in cable television.  Coax cables have an RG rating.  The U.S. military developed the ratings during WWII to provide a quick reference for the different types.  The most important measure of coax cabling is its Ohm rating.  The Ohm rating is the characteristic impedance or electrical resistance of the cable.

If you have a situation where you need to split a single coaxial cable, coaxial splitters can be used to connect two cables together using a barrel connector.  This allows you to add some distance to a connection.

Coaxial Splitter

Barrel Connector

Twisted Pair

The most common type of cabling used in networks is twisted pair, twisted pairs of cables, bundled together.  Networks use two types of twisted pair cabling, shielded twisted pair and unshielded twisted pair.  The twists reduce interference, which is called crosstalk.  The more twists, the better. 

Shielded Twisted Pair

Shielded twisted pair, STP, consists of twisted pairs of wires surrounded by shielding.  This protects the wires from EMI.  Shielded twisted pair is used in areas of excessive electronic noise.  The most common type is the IBM Type 1 cable used in Token Ring network topology.

Unshielded Twisted Pair

Unshielded twisted pair, UTP, is the most common type of network cabling used today.  UTP consists of twisted pairs of wires surrounded by a plastic jacket.  This type of jacket does not provide protection against EMI, so you must be careful when installing to avoid interference.

Telephone systems use STP, so they sometimes present a problem when installing alongside cable.  However, there are installation standards to help those who work with UTP.  Telephones use RJ-11 connectors with two pairs of wires.  Networks use RJ-45 connectors with four-pairs of wires.

UTP cabling has something called category, CAT, ratings to help network installers get the right cable for the right network technology.  CAT ratings are officially rated in megahertz (MHz), indicating the highest frequency the cable can handle.  The maximum amount of data that goes through cable per second is called bandwidth.  CAT 5e cable can handle a throughput of up to 1000 Mbps, even though it is rated to handle a bandwidth of only up to 100 MHz.  Most new cabling installations use CAT 5e, even though a number are using the new CAT 6.  CAT 6a is the latest update, doubling the bandwidth of CAT 6 to 550 MHz to accomodate 10-Gbps speeds up to 100 meters.



Fiber-Optic

Fiber-optic cable transmits light rather than electricity.  Fiber-optic cabling will operate for long distances.  Fiber-optic cabling has many different diameters of core and cladding.  The core is the glass fiber itself.  The cladding is the part that makes the light reflect down the fiber.  Fiber-optic cables require pairs of cables, and are usually clumped together like a lamp cord.  There are single-mode and multimode fiber-optic cables.  Light can be sent down as regular light or as laser light.  Using laser light and single-mode fiber-optic enables a network to achieve very high transfer rates over long distances.

Fiber-optic cables have over one hundred different connector types.  The most common are ST, SC, and LC.  LC is unique in that it is a duplex connector and will accept two fiber cables.

Other Cables Types

Serial cabling, RS-232, is the recommended standard that all serial cabling is based on.  The most common is the 9-pin, male D-subminiature connector.  Serial ports have very slow data rates...about 56,000 bps.

9-pin d-subminiature connector

25-pin female DB type connector front and rear side

Parallel connections use a 25-pin female DB type connector and run to around 2 Mbps.  The IEEE 1284 committee sets the standards for parallel communications.  Parallel is also limited to point-to-point communications.

FireWire is based on the IEEE 1394 standard and is the next best thing to fiber-optic or UTP.  FireWire is fast and runs up to 800 mbps.  FireWire is point-to-point and has a connector like the one pictured below. Microsoft has removed the ability to network via FireWire in Windows Vista.

Questions 
1.  Which topology requires termination?  Bus topology.
2.  Star-bus is an example of what type of topology? Star-bus in an example of a Hybrid topology.
3.  What topology is the most fault tolerant?  Star topology.
4.  What is a topology?  The interconnectivity of network components.

5.  Coaxial cablesOhm rating, a relative measure of the resistance on the cable.
6. Which type of network topology is mostly seen in wireless networks?   Mesh topology.
7.  What is the most common type of UTP used in new cable installations?  CAT 5e, though CAT 6 is becoming more popular.

Can't get on the Internet?

Image via Wikipedia

Having problems getting on the internet?  Use whatever tool your operating system provides to check your IP address.

Is it an APIPA address?  If the address begins with 169.254, then it is an APIPA address.  This indicates you have a DHCP problem.  DHCP stands for Dynamic Host Configuration Protocol. DHCP automatically assigns an IP address when a computer connects to the network.

An older and less popular protocol is called the Bootstrap Protocol.  BOOTP is common on UNIX/Linux and Macintosh OS X systems.  BOOTP is like DHCP.

A computer configured to use DHCP is called a DHCP client.  When a computer boots up, it automatically sends out a DHCP discovery packet using the broadcast address.  Normally, your ISP sets up your router to act as a DHCP server.  The server responds to DHCP discovery requests with a DHCP offer.  The DHCP server passes out IP addresses from a range, called a DHCP scope, a subnet mask, and a default gateway.

The DHCP client (your computer) sends out a DHCP request (the name is misleading because actually it is accepting the offer).  The DHCP server (your router) then sends a DHCP acknowledgement and lists the MAC address and the IP information.  The DHCP client accepts the DHCP server's data with a lease for a fixed amount of time, determined by the DHCP setup configuration.  At about halfway through the lease time, the DHCP client makes another DHCP discovery message.  The DHCP server looks at the MAC address and will always give the same IP address and IP information unless another computer has taken the lease.

When a DHCP client (your computer) tries to get an IP address from the DHCP server and fails, your computer's operating system generates an error message and the IP address generated begins with 169.254.  This unusual address is APIPA, generated by Automatic Private IP Addressing.   The last two octets of the IP address are generated by the client (your computer).  This allows all of the clients on the network to communicate because they are on the same network ID.  However, you can't get on the internet, because APIPA cannot generate a default gateway, which is required to get on the Internet.

If you can't get on the Internet, and you know you have a DHCP problem because you have a 169.254 address, try to reestablish the lease manually.   In Windows, type the following into the command line interface:

ipconfig /renew

On a Macintosh, go to System Preferences and the Network utility.

Sometimes you still can't get an IP address for whatever reason.  Try to force the computer to release the lease.  In Windows, type

ipconfig /release
(hit enter)
ipconfig /renew
(hit enter)

In UNIX/Linux and Macintosh, use the IFCONFIG command to release.

sudo ifconfig eth0 down

To renew:

sudo ifconfig eth0 up

How DHCP Technology Works:

The TCP/IP Guide

Remote Assistance Instructions

Remote Assistance allows a person that is experiencing computer problems, a novice, to invite a trusted person, an expert, to remotely and interactively assist that person with a problem. Both computers must have Windows XP and be connected to the Internet.  Both the novice and the expert must be sitting at their computers.  Establishing a Remote Assistance Invitation behind a firewall might require you to make a network configuration change to open TCP Port 3389.

To send a Remote Assistance Invitation

To send out a request for help/support, to send an Invitation for Remote Assistance, select from the Windows Start menu, Programs/Remote Assistance.  This starts up the Windows XP Help and Support Center/Remote Assistance page.

There are three methods to sending an invitation.  You can send an invitation via Microsoft Windows Messenger, via email using Microsoft Outlook Express, or via saving an invitation as a file on a shared folder on the network, thus allowing you to use other email programs.  Select the method you want to use.

Enter your name and define how long the invitation stays open, then click Continue.

For security, it is highly recommended for you to define a password, which must be used by the expert recipient to connect to your novice system.

It is your job to advise the expert of the password, either by email or phone.

When selecting 'Save Invitation', you will be asked to define the location to save the file.  (For example, to My Documents).

Remote Assistance gives you a few last instructions.  The instructions notify the novice the Invitation has been saved successfully and where it has been saved.  It tells the novice to send the Invitation to the assistant by email or place it in a shared folder.  It also instructs the novice to tell the assistant to open the Invitation in order to start the Remote Assistance session.  It further instructs the novice, that if the Invitation is accepted, the novice will be notified that the recipient is ready to connect to their computer.

Click Send Invitation.

If you have a problem sending the Invitation

Verify that Remote Assistance is enabled.  In Control Panel, select the System icon or right click My Computer and select Properties.

Select the Remote Tab.

By default, Remote Assistance is activated.  Check the Advanced settings.  (Note:  the other option on this tab, Remote Desktop, is NOT available for Windows XP Home Edition.)

Define whether you allow the expert only to view your activities or whether the expert can also take control, i.e., use his mouse and keyboard to operate the system.

Define the maximum amount of time the Invitation can remain open.

Important note:  While waiting for the expert to connect, make sure your TCP/IP address does NOT change!  Do NOT terminate your connection, or when you reconnect you might get another IP address and your invitation is invalid. 

To respond to a Remote Assistance Invitation sent from a novice

Once the expert has received the Invitation on the remote Windows XP system, double-click on the Invitation file, which opens the Remote Assistance window.  If a password was defined, enter it now.  Continue with YES.  

Your system is then connecting to the novice system.  Once an expert connects to a novice system, a confirmation message is displayed.  The novice must click on YES to allow the expert to continue and to view the novice system. The expert will then see the novice windows of Remote Assistance.

After the Remote Assistance connection is established, the novice will see a User Console and the expert will see a Helper Console.

The User Console allows you to chat via keyboard... type under 'Message Entry' or via 'Start Talking', if both the novice and the expert are equipped with a sound-card with speakers and a microphone. 

If allowed in the settings of the invitation, the expert can take control of the system of the novice by selecting the Toolbar 'Take Control' on the Helper Console.  

When the expert clicks 'Take Control', a message will pop-up on the screen of the novice informing about the request. 

If you agree to this request, accept it by clicking 'Yes'. 

Once the 'novice' accepts the request, a message will pop-up on the 'expert' system to advise about having control and to press Esc or any key sequence or combination including the Esc-key to return control to the 'novice'.

The section 'Chat History' of the User Console will show that control has been taken by the 'expert'.
The 'expert' now uses the mouse and/or keyboard of the expert system to operate the novice system to identify the problem, checking for example, the Control Panel, Device Manager, Event Log.

To terminate a 'Remote Assistance' connection, both the expert and the novice can select in their Console section to 'Disconnect'.
The expert will be informed about the disconnection from the system of the novice.

File Recovery

Free software for file recovery can be found here:  Pandora Recovery - Free software

CNET also has a free app called Tech Tracker that will tell you when the software is out of date and lets you download an update.  You can also choose to be emailed when there is an update to Pandora Recovery.  What's better than that!

Related articles by Zemanta

• Top Five Tools for Corrupted Hard Drive Recovery (brighthub.com)

Rollback a device driver

You have downloaded and installed the latest version of a video card driver for your computer.
Afterwards, you find your Windows XP Professional operating system seems unstable. You need to restore the original version of the device driver.

Open the System applet in Control Panel, and roll back the device driver.  
Device drive rollback allows you to restore a previous version of an updated device driver. Driver rollback affects only the changed hardware device. No other hardware or software on the computer is affected.


Navigate to the Hardware tab, and click Device Manager.  
From Device Manager, select the affected hardware device and click Properties.  
From the Properties dialog box, navigate to the Driver tab and click Roll Back Driver.

You can also open the System Restore utility, and load a restore point from a date before you installed the defective device driver.  System restore points are stored in the C:\Windows\system32\restore directory. 
To access System Restore, click Programs/Accessories/System Tools/System Restore


Using Windows XP, How to Roll Back a Device Driver

Steps to take to Increase Windows XP Performance

Image by KushalHada via Flickr

You are running several applications at once in Windows XP, and performance starts to slow down.  What can you do to improve the response time without turning off the computer?

Answer:  Increase the size of the PAGEFILE.SYS.

The virtual memory page file is PAGEFILE.SYS, in Windows XP.  PAGEFILE.SYS is used as a temporary storage area for data when main memory capacity is exceeded.

Increasing the size of this file increases the available storage area and improves system performance.  To change the size of PAGEFILE.SYS, go to the START button.  Click on SETTINGS, CONTROL PANEL, SYSTEM, ADVANCED, PERFORMANCE, OPTIONS, CHANGE. Select the Drive list, and click the drive that contains the paging file you want to change.  Under Paging file size for the selected drive, type a new paging file size in megabytes in the Initial size (MB) or Maximum size (MB) box, then click Set.  The optimal paging file settings allow Windows to manage the paging file size.

Steps To Take to Increase Windows XP Performance

Related articles by Zemanta

• Windows Hangs during Shutdown? (helpdeskgeek.com)

SCSI Termination

You have both internal and external devices on a SCSI chain.  All devices are Fast SCSI-2 devices.  How should you place terminators for the SCSI bus?

Answer:  Place an active terminator on both end devices on the chain.  Active terminators are required for Fast or Wide SCSI, according to SCSI-2 specification.  Each end of the SCSI bus must be terminated.

SCSI Termination Tutorial

Network Troubleshooting

Image via Wikipedia

A user is unable to connect to a file server on your 10BaseT network (twisted pair Ethernet), although he is able to connect to folders on other computers.  A single hub exists on the network.  10BaseT Twisted Pair Ethernet  What hardware problems should you investigate?

Answer:  Either a defective network interface card (NIC) on the file server or a defective hub port connected to the file server would prevent users from connecting to the file server.  A defective cable between the file server and the hub would prevent communications between users and the server.  Client/server communication problems can also be related to software issues.  The user may not have permission to access the file server, or the user may not have the correct name or address of the file server.  If the network has multiple subnets, problems could occur because of incorrect subnet mask settings or incorrect gateway address. 
Advanced Network Adapter troubleshooting for Windows workstations

Computer Post Beep Codes and What They Mean

Computer Post / Beep codes

Startup Phases for X86 Windows Systems

Troubleshooting Startup

Startup Phases for x86-based Systems


The Windows XP Professional startup process closely resembles that of Microsoft® Windows NT® version 4.0 and Microsoft® Windows® 2000, but significantly differs from Microsoft® MSDOS®, Microsoft® Windows® 95, Microsoft® Windows® 98, and Microsoft® Windows® Millennium Edition (Windows Me).

All computers running Windows XP Professional share the same startup sequence:



Power-on self test (POST) phase



Initial startup phase



Boot loader phase



Detect and configure hardware phase



Kernel loading phase



Logon phase



The preceding startup sequence applies to systems started or restarted after a normal shutdown, and does not apply when you bring your computer out of hibernation or standby.

Cabling

Image via Wikipedia

Network Cable Types

Related articles

• Universal Network Cable (thinkgeek.com)
• An Error Message Appears when I diagnose my networking controller saying a cable is not plugged in.? (grand-alliance.com)
• LAN cable tester (electronics-lab.com)

Installing a Second IDE Hard Drive

Motherboard Form Factors and Components

Motherboard Components