Bài giảng Network Certification Microsoft Press - Chapter 17

1Chapter Overview  Identifying Network Components  Troubleshooting a Network 2Locating Ports  The ports on a typical computer are located either on the motherboard or on expansion cards that plug into the system bus.  If the same type of port can have more than one function, you can sometimes tell what a port does by where it is located.  The locations of the motherboard ports vary, depending on the design of the computer. 3The Back Panel of an Older Computer 4The Back Panel of a Newer Computer 5DB-9 Serial Ports 6DB-9 and DB-25 Serial Ports on an Older Computer 7The Female DB-25 Connector Used by a Parallel Port 8A 15-Pin VGA Connector 9Six-Pin Mini-DIN Connectors 10 A Five-Pin DIN Connector 11 Universal Serial Bus (USB) Ports  The USB is a relatively recent innovation that is replacing many of the ports on computers, such as the serial, parallel, keyboard, and mouse ports.  The USB is a multipurpose bus that  Runs at up to 12 megabits per second (Mbps)  Supports a wide range of devices through the same interface  Computers today typically have two USB ports, which use rectangular, female, four-conductor connectors. 12 USB A-Connectors 13 SCSI Ports  The Small Computer System Interface (SCSI) is a mass storage interface that supports many different internal and external devices at speeds up to 160 Mbps.  SCSI implementations typically involve a host adapter card that plugs into the computer's expansion bus.  A few computers have a SCSI adapter integrated into the motherboard.  A SCSI host adapter usually has both internal and external connectors.  Internally, SCSI uses ribbon connectors that attach to hard drives and other devices.  External SCSI cables are thick and relatively inflexible because of their heavy shielding and the tight bundling of wires contained inside. 14 SCSI Connectors 15 A Combination Ethernet NIC 16 A BNC Connector with a T Attached 17 An Ethernet NIC with an RJ-45 Jack 18 A Token Ring Media Filter 19 The Back of a 10Base-T/100Base-TX Ethernet Hub 20 Hubs  A hub can be either a stand-alone box or a unit that mounts into a standard 19-inch-wide rack used for large network installations.  Hubs can support any one of several data-link layer protocols, including Ethernet, Fiber Distributed Data Interface (FDDI), and Token Ring.  A hub can have as few as 4 ports or as many as 24.  The basic identifying feature of a hub is one or more rows of female connectors.  In most cases, a hub has rows of light-emitting diode (LED) lamps that correspond to the network cable ports. 21 The LED Display on a 10Base-T/100Base-TX Ethernet Hub 22 Switches  Switches look like hubs.  The difference between a hub and a switch is in the internal manipulation of incoming data.  Switches are available in most of the same configurations as hubs, ranging from small units intended for home or small business networks to large rack-mounted devices.  Some switches include an additional nine-pin serial port that connects the device to a computer with a null modem cable. 23 A Patch Panel 24 A Typical Stand-Alone Router 25 A Router Frame with Modules Installed 26 Internal and External Print Servers 27 Uninterruptible Power Supplies (UPSs) 28 The Back Panel of a UPS 29 Network Troubleshooting Procedure 1.Establish the symptoms. 2. Identify the affected area. 3.Establish what has changed. 4.Select the most probable cause. 5. Implement a solution. 6.Test the result. 7.Recognize the potential effects of the solution. 8.Document the solution. 30 Establish the Symptoms  Determine exactly what is going wrong, and note the effect of the problem on the network.  Assign a priority to the problem.  In a large network environment, it is essential to establish a system of priorities that dictate which calls get addressed first.  Most often, the severity of the problem determines who gets attention first. 31 Rules for Establishing Priorities  Shared resources take precedence over individual resources.  Network-wide problems take precedence over workgroup or departmental problems.  Departmental issues should be rated according to the function of the department.  System-wide problems take precedence over application problems. 32 Identify the Affected Area  See if the problem can be duplicated.  Network problems that you can easily duplicate are far easier to fix, primarily because you can easily test to see if your solution was successful.  Having the user reproduce the problem can sometimes lead to the solution.  If the problem can be duplicated, you can start determining the actual source of the problem.  Eliminate the elements that are not the cause, in a logical and methodical manner. 33 Establish What Has Changed  When a computer or other network component that used to work properly now does not work, some change has probably occurred.  Major changes, such as the installation of new hardware or software, are obvious possible causes of the problem.  Tracking down the source of a networking problem can often be a form of detective work, and learning to "interrogate" your "suspects" properly can be an important part of the troubleshooting process. 34 Select the Most Probable Cause  Follow this axiom: when you hear hoofbeats, think horses, not zebras.  When you look for possible causes of a problem, start with the obvious first.  Work methodically and document everything you check so that you do not duplicate your efforts. 35 Implement a Solution  After you have isolated the problem, determine if it is caused by hardware or software.  If it is a hardware problem, you might replace the faulty unit or use an alternate.  Example: for a communication problem, you might replace network cables until you find one that is faulty.  Example: if the problem is in a server, you can replace components until you find the culprit.  If it is a software problem, you might  Use a different computer to run the application or store the data  Reinstall the software on the offending system 36 Test the Results  After you resolve the problem, you should return to the beginning of the process and repeat the task that originally caused the problem.  If the problem no longer occurs, you should test the other functions related to the changes you made to ensure that fixing one problem has not created another.  Repeat the procedures you used to duplicate the problem exactly, to ensure that the problem the user originally experienced has been completely eliminated and is not just temporarily masked.  If the problem was intermittent, it might take some time to ascertain if your solution worked.  Check with the user several times to make sure that the problem is not recurring. 37 Document the Solution  Begin documenting your actions as soon as the user calls for help.  A well-organized support organization uses a system to register each problem call as a trouble ticket that eventually contains  A complete record of the problem  The steps taken to isolate and resolve the problem  A support organization often operates by using tiers.  Calls come in to the first tier.  If the problem is complex or the first-tier technician cannot resolve it, the call is escalated to the second tier, which is composed of senior technicians.  If all technicians document their activities, there should be no problem when one technician hands off the trouble ticket to another.  Keeping careful notes prevents duplication of effort. 38 Chapter Summary  Identifying network components  Computers have a variety of ports, some of which are implemented by the motherboard and others by expansion cards.  Computers use many different types of connectors fortheir various interfaces, and in some cases the same connector type can provide different functions.  SCSI host adapters can use any one of several types of connectors, which are not interchangeable.  Troubleshooting a network  The network troubleshooting procedure involves several steps, including identifying, duplicating, isolating, resolving, and documenting the problem.  Isolating a network problem is a matter of eliminating hardware and software components as possible causes.  Maintaining documentation and following a methodical troubleshooting procedure are essential parts of maintaining a network.