troubleshooting network

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TROUBLESHOOTING NETWORKS

Troubleshooting is the process of identifying, locating and correcting problems that occur. Experienced individuals often rely on instinct to troubleshoot.

Approach to Troubleshooting

There are several different structured troubleshooting techniques available, including:

Top-down:Top-down starts with the application layer and works down. It looks at the problem from the point of view of the user and the application.

Bottom-up:Bottom-up starts with the physical layer and works up. The physical layer is concerned with hardware and wire connections.

Divide-and-conquer:Divide-and-Conquer typically begins trouble shooting at one of the middle layers and works up or down from there. For example, the troubleshooter may begin at the network layer, by verifying IP configuration information.

Software utlilities for troubleshooting connectivity

A number of software utility programs are available that can help identify network problems.

  • ipconfig – Displays IP configuration information
  • ping – Tests connections to other IP hosts
  • tracert – Displays route taken to destination

Troubleshooting using

Ipconfig:Ipconfig is used to display the current IP configuration information for a host. Issuing this command from the command prompt will display the basic configuration infor mation including: IP address, subnet mask and default gateway.

Ping:If the IP configuration appears to be correctly configured on the local host, next, test network connectivity by using ping. Ping is used to test if a destination host is reachable. The ping commandcan be followed by either an IP address or the name of a destination host.

Tracert:The ping utility can verify end-to-end connectivity. However, if a problem exists and the device cannot ping the destination, the ping utility does not indicate where the connection was actually dropped. To accomplish this, another utility known as tracert must be used.

Nslookup:When accessing applications or services across the network, individuals usually rely on the DNS name instead of the IP address. When a request is sent to that name, the host must first contact the DNS server to resolve the name to the corresponding IP. The host then uses IP to package the information for delivery.

Connectivity issues

Connectivity problems occur on wireless networks, wired networks and networks that use both. When troubleshooting a network with both wired and wireless connections , it is often best to troubleshoot using a divide-and -conquer technique to isolate the problem to either the wired or wireless network. The easiest way to determine if the problem is with the wired or the wireless network is to:

1. Ping from a wireless client to the default gateway – this verifies if the wireless client is connecting as expected.

2. Ping from a wired client to the default gateway – this verifies if the wired client is connecting as expected.

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