Introduction to Computer Networks Introduction to Computer Networks

Troubleshooting Tools Troubleshooting network problems is often accomplished with the help of hardware and software. To troubleshoot effectively, you need to know how these tools can be used to solve network problems.

Hardware Tools Digital Voltmeters: is the primary all-purpose electronic measuring tool.Digital Voltmeters: is the primary all-purpose electronic measuring tool. Voltmeters can determine if:Voltmeters can determine if: The cable is continuous (has no breaks).The cable is continuous (has no breaks). The cable can carry network traffic.The cable can carry network traffic. Two parts of the same cable are exposed and touching (thereby causing shorts).Two parts of the same cable are exposed and touching (thereby causing shorts). An exposed part of the cable is touching another conductor, such as a metal surface.An exposed part of the cable is touching another conductor, such as a metal surface.

Time-Domain Reflectometers (TDRs) TDRs send sonar-like pulses along cables to locate breaks, shorts, or imperfections.TDRs send sonar-like pulses along cables to locate breaks, shorts, or imperfections. A TDR can locate a break within a few feet of the actual separation in the cable.A TDR can locate a break within a few feet of the actual separation in the cable. Used heavily during the installation of a new network, TDRs are also invaluable in troubleshooting and maintaining existing networks.Used heavily during the installation of a new network, TDRs are also invaluable in troubleshooting and maintaining existing networks.

Advanced Cable Testers Advanced cable testers work beyond the physical layer of the OSI reference model, in the data-link layer, network layer, and even the transport layer.Advanced cable testers work beyond the physical layer of the OSI reference model, in the data-link layer, network layer, and even the transport layer. They can also display information about the condition of the physical cable. They can also display information about the condition of the physical cable.

Oscilloscopes Oscilloscopes are electronic instruments that measure the amount of signal voltage per unit of time and display the result on a monitor.Oscilloscopes are electronic instruments that measure the amount of signal voltage per unit of time and display the result on a monitor. When used with TDRs, an oscilloscope can display:When used with TDRs, an oscilloscope can display: Shorts. Sharp bends or crimps in the cable. Opens (breaks in the cable). Attenuation (loss of signal power).Shorts. Sharp bends or crimps in the cable. Opens (breaks in the cable). Attenuation (loss of signal power).

Other Hardware Tools Crossover Cables: are used to connect two computers directly with a single patch cable.Crossover Cables: are used to connect two computers directly with a single patch cable. Crossover cables are useful in troubleshooting network connection problems. Two computers can be directly connected, bypassing the network and making it possible to isolate and test the communication capabilities of one computer, rather than the whole network.Crossover cables are useful in troubleshooting network connection problems. Two computers can be directly connected, bypassing the network and making it possible to isolate and test the communication capabilities of one computer, rather than the whole network. Hardware Loopback: is a serial port connector that enables you to test the communication capabilities of a computer's serial port without having to connect to another computer or peripheral device.Hardware Loopback: is a serial port connector that enables you to test the communication capabilities of a computer's serial port without having to connect to another computer or peripheral device.

Tone Generator and Tone Locator Tone generators are standard tools for wiring technicians in all fields.Tone generators are standard tools for wiring technicians in all fields. A tone generator is used to apply an alternating or continuous tone signal to a cable or a conductor.A tone generator is used to apply an alternating or continuous tone signal to a cable or a conductor. The tone generator is attached to one end of the cable in question.The tone generator is attached to one end of the cable in question. A matching tone locator is used to detect the correct cable at the other end of the run.A matching tone locator is used to detect the correct cable at the other end of the run. These tools are also able to test for wiring continuity and line polarity.These tools are also able to test for wiring continuity and line polarity.

Software Tools Software tools are needed to monitor trends and identify network performance problems.Software tools are needed to monitor trends and identify network performance problems. Network MonitorsNetwork Monitors Network monitors are software tools that track all or a selected part of network traffic.Network monitors are software tools that track all or a selected part of network traffic. They examine data packets and gather information about packet types, errors, and packet traffic to and from each computer.They examine data packets and gather information about packet types, errors, and packet traffic to and from each computer. Network monitors are very useful for establishing part of the network baseline.Network monitors are very useful for establishing part of the network baseline.

Protocol Analyzers (1) also called "network analyzers," perform real-time network traffic analysis using packet capture, decoding, and transmission data.also called "network analyzers," perform real-time network traffic analysis using packet capture, decoding, and transmission data. Protocol analyzers look inside the packet to identify a problem.Protocol analyzers look inside the packet to identify a problem. They can also generate statistics based on network traffic to help create a picture of the network, including the:They can also generate statistics based on network traffic to help create a picture of the network, including the: Cabling. Software. File servers. Workstations. Network interface cards.Cabling. Software. File servers. Workstations. Network interface cards.

Protocol Analyzers (2) Protocol analyzers have built-in TDRsProtocol analyzers have built-in TDRs The protocol analyzer can provide insights and detect network problems including:The protocol analyzer can provide insights and detect network problems including: Faulty network components. Configuration or connection errors. LAN bottlenecks. Traffic fluctuations. Protocol problems. Applications that might conflict. Unusual server traffic.Faulty network components. Configuration or connection errors. LAN bottlenecks. Traffic fluctuations. Protocol problems. Applications that might conflict. Unusual server traffic.

Protocol Analyzers (3) Protocol analyzers can identify a wide range of network behavior. They can:Protocol analyzers can identify a wide range of network behavior. They can: Identify the most active computers.Identify the most active computers. Identify computers that are sending error-filled packets. If one computer's heavy traffic is slowing down the network, the computer should be moved to another network segment. If a computer is generating bad packets, it should be removed and repaired.Identify computers that are sending error-filled packets. If one computer's heavy traffic is slowing down the network, the computer should be moved to another network segment. If a computer is generating bad packets, it should be removed and repaired.

Protocol Analyzers (4) View and filter certain types of packets. This is helpful for routing traffic. Protocol analyzers can determine what type of traffic is passing across a given network segment.View and filter certain types of packets. This is helpful for routing traffic. Protocol analyzers can determine what type of traffic is passing across a given network segment. Track network performance to identify trends. Recognizing trends can help an administrator better plan and configure the network.Track network performance to identify trends. Recognizing trends can help an administrator better plan and configure the network. Check components, connections, and cabling by generating test packets and tracking the results.Check components, connections, and cabling by generating test packets and tracking the results. Identify problem conditions by setting parameters to generate alerts.Identify problem conditions by setting parameters to generate alerts.

Network General Sniffer Sniffer, which is part of a family of analyzers from Network General, can decode and interpret frames from 14 protocols.Sniffer, which is part of a family of analyzers from Network General, can decode and interpret frames from 14 protocols. Sniffer measures network traffic in kilobytes per second, frames per second, or as a percentage of available bandwidth.Sniffer measures network traffic in kilobytes per second, frames per second, or as a percentage of available bandwidth. It will gather LAN traffic statistics, detect faults such as beaconing, and present this information in a profile of the LAN.It will gather LAN traffic statistics, detect faults such as beaconing, and present this information in a profile of the LAN. Sniffer can also identify bottlenecks by capturing frames between computers and displaying the results.Sniffer can also identify bottlenecks by capturing frames between computers and displaying the results.

Monitoring and Troubleshooting Tools Performance Monitors:Performance Monitors: Most current network operating systems include a monitoring utility that will help a network administrator keep track of a network's server performance.Most current network operating systems include a monitoring utility that will help a network administrator keep track of a network's server performance. These monitors can view operations in both real time and recorded time for:These monitors can view operations in both real time and recorded time for: Processors. Hard disks. Memory. Network utilization. The network as a whole.Processors. Hard disks. Memory. Network utilization. The network as a whole.

Performance Monitors: These monitors can:These monitors can: Record the performance data.Record the performance data. Send an alert to the network manager.Send an alert to the network manager. Start another program that can adjust the system back into acceptable ranges.Start another program that can adjust the system back into acceptable ranges. When monitoring a network, it is important to establish a baseline,When monitoring a network, it is important to establish a baseline,

Network Monitors Some servers include network monitoring software.Some servers include network monitoring software. This tool gives the administrator the ability to capture and analyze network data streams to and from the server. This tool gives the administrator the ability to capture and analyze network data streams to and from the server. This data is used to troubleshoot potential network problems.This data is used to troubleshoot potential network problems. The packets of data in the data stream consist of the following information: (1)The source and destination address (2)Headers (3)dataThe packets of data in the data stream consist of the following information: (1)The source and destination address (2)Headers (3)data

Simple Network Management Protocol (SNMP) In an SNMP environment, programs called "agents" are loaded onto each managed device. The agents monitor network traffic in order to gather statistical data. This data is stored in a management information base (MIB). In an SNMP environment, programs called "agents" are loaded onto each managed device. The agents monitor network traffic in order to gather statistical data. This data is stored in a management information base (MIB). If any of the data falls above or below thresholds, the management program can notify the administrator If any of the data falls above or below thresholds, the management program can notify the administrator