CTS2134 Introduction to Networking Module 10.1 10.3: Troubleshooting
Troubleshooting Methodology Facts 1. Identify the symptoms and potential causes. 2. Identify the affected area and determine how large the problem is. 3. Establish what has changed. 4. Review the list of potential causes (look for common errors) 5. Escalate the problem if it is beyond your ability to fix or your scope of management. 6. Create an action plan 7. When all concerns have been addressed, fix the problem. 8. After you think you have resolved the problem, test the result. 9. Identify the results and effects of the solution. 10. Document the solution
Troubleshooting Utility Facts Task View the ARP table View IP configuration View routing statistics View NetBIOS information Test host to host connectivity Identify the pathway between two hosts Test name resolution View and modify the routing table Tool arp (Windows) Ipconfig or ifconfig (Linux) Netstat (Windows) Nbtstat (Windows) ping Tracert (Windows) or Traceroute (Linux) nslookup route
Identifying Communication Problems Task Check physical connectivity Description NIC and Wall Jack Ping the Loopback address ping 127.0.0.1 Validate the TCP/IP settings ipconfig /all Ping your IP address ping 192.168.10.201 Ping other hosts on your network Ask a peer s IP address and ping ping 192.168.10.202 Ping your default gateway ping 192.168.10.1 Ping the interface on the router that connects to your ISP ping 192.168.1.1 Ping a host on a remote network ping 130.10.5.200 Ping another host on the same remote network ping 130.10.5.201
Fault Domain Troubleshooting Facts Topology Bus Star Ring Mesh Effect A break in the network bus means that the end of the bus is no longer terminated. Therefore no devices can communicate. Identifying the location of the break is difficult on a true bus network. A break in a cable means that the device connected to the central device (hub or switch) can no longer communicate on the network. All other hosts will be able to communicate with all other devices. A break in the ring means that messages can only travel in one direction (downstream) to the break. Computers can send messages downstream to other devices, but will not be able to receive any responses. A break in a single link in a mesh topology has no effect on communications. Data can be routed to the destination device by taking a different path through the mesh topology.
Link Status Troubleshooting Facts Light No lights lit Red/Amber light lit Solid Green Green flashing Green flashing and periodic orange Green flashing constantly and periodic orange Green constantly flashing and orange constantly flashing Meaning The network card does not have a connection to the network. The NIC has detected a signal that was not what was expected. A valid network connection Normal activity over a valid network connection Normal activity over a valid network connection. Some collisions are to be expected on an Ethernet network. An Activity light that is constantly flashing indicates constant traffic being sent or received on the link. Causes may be a very busy device or a jabbering NIC. If the collision light is constantly flashing, then there are too many collisions on the network. Causes may include too many devices on the segment, faulty cabling or cable runs that are too long or a jabbering NIC.
Wiring Troubleshooting Facts Issue Interference Crosstalk Attenuation Echo Shorts Open circuit Miswired Description Excessive EMI or RFI. Use fiber optic, shielded cables or conduits Interference that is caused by signals within the twisted pairs of wires. Use a higher category UTP cable or reinstall connectors. Loss of signal strength from one end of a cable to the other. Install a repeater or change cable configuration. Impedance mismatch. Choose cabling with the correct rating. Shorts are caused by worn wire jackets or crushed wires so that two wires touch. Replace the cable. A cut in the wire that prevents the original signal from reaching the end of the wire. Replace the cable. the individual wires are not in the correct positions within both connectors. Correctly reinstall the connectors.
Troubleshooting Tool Facts Tool/Method Loopback plug Smart jack Known good spares Cable tester Time Domain Reflector (TDR) Description Reflects a signal from the transmit port on a device to the receive port on the same device. Use the loopback plug to verify that a device can both send and receive signals. A special loopback plug installed at the demarcation point for a WAN service to test connectivity between the central office and the demarc. Keep a set of components that you know are in proper functioning order. If you suspect a problem in a component, swap it with the known good component. Checks for miswire conditions and can tell the difference between a crossover and a straight through cable. Measures impedance discontinuities (echo), cable length, identifies location of splices/connectors and short/open circuits.
Troubleshooting Tool Facts Tool/Method Certifier Toner probe Butt set Multimeter Voltage event recorder Temperature monitor Description Verifies/validates that a cable or an installation meets the requirements for a specific architecture implementation Two devices used together to trace the end of a wire from a known endpoint into the termination point. Used for testing analog telephone installations A device for testing AC and DC voltage, Current (amps), Resistance (ohms), ect. Keep track of the occurrence of under or over voltage conditions over time. Some UPS systems include a simple voltage event recorder. Records temperature over time. May be internal to a computer or keep track of temperatures in a server room. May include the ability to notify you when an excessive temperature threshold is reached.