Identifying and Troubleshooting Network Problems

     

Network problems can fall under a number of different categories. Problems can be related to malfunctioning hardware, cabling issues, incorrect protocol configurations, or a network device. The following sections look at some of the network problems you may encounter as well as ways to diagnose and resolve them.

Troubleshooting Hardware Problems

If users report that they are unable to communicate on the network, one of the first things you should do is verify that a network connection is present. For example, if users report they cannot connect to the Internet when using hyperlinks in a Word document, you should begin troubleshooting by identifying whether the problem is hardware related.

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Microsoft publishes a Hardware Compatibility List (HCL) for its operating systems. Hardware devices on the HCL are guaranteed to work with the given operating system. When troubleshooting hardware problems, you should verify that the device appears on this list. Microsoft guarantees only that devices appearing on the list will function correctly under the operating system.


Network Interface Cards

When you are troubleshooting, start with the most obvious to eliminate it as the source of the problem. To verify the network connection, begin by checking the physical network connection. Are the link lights flashing on the network adapter card? Is the network cable securely attached? Is the correct network protocol being used?

Although this check may seem trivial, one of the first things you should do when troubleshooting network problems is to check the physical connections. Make sure the network interface card is properly seated and the cables are securely fastened. The network cable should be inspected for any damage. Trying a different cable may also be worthwhile to eliminate it as the source of the problem.

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Keep in mind the hardware problem may be with another network device such as a hub or router.


If users are unable to establish a network connection using a network adapter, consider the following points when troubleshooting the problem:

  • The network adapter may be conflicting with another hardware device. You can use Device Manager to determine whether this is the case. Device Manager can also provide you with the device's status information (functioning or not functioning).

  • Make sure the network cable is properly connected and the network card is not loose.

  • Try using a different network cable to ensure the existing one is not faulty, thereby causing the loss of network connection.

  • Verify that the correct device driver is installed.

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A lack of network connection can affect applications in a number of ways, such as a user not being able to send or receive email, access shared documents on the network, or use hyperlinks in a Word document.


Modems

Because network access may be made through a modem (for example, a cable modem, ISDN, or ADSL), you need to look for some common issues when troubleshooting network connectivity. One of your first tasks should be verifying that the modem has power, it is properly connected to the computer, and any cables are securely in place.

Because the problem may also be with the cabling, you should also inspect it for any damage. (Again, you should try a different cable to eliminate this as being the problem.) Cycling the power may also be worthwhile, either by using an external modem or by restarting the local computer if the modem is internal.

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If you suspect a problem with the hardware on the local computer, you can use Device Manager to determine whether the device is functioning correctly.


If you suspect a problem with an internal modem, you can use the modem diagnostics to test the hardware. To access this feature, open the Phone and Modem Options applet within the Control Panel. On the Modems tab, select the modem you want to test, click Properties, and click Diagnostics. Click the Query Modem button shown in Figure 7.1.

Figure 7.1. Using the Phone and Modems Options applet to test a modem.

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If the modem appears to be working, but you still cannot establish a connection, check the modem's configuration. For example, if a user is trying to establish a connection with an ISP, she should consult the documentation or consult the ISP for the correct modem settings.

One common message that users may encounter when trying to establish a connection is that the port is in use by another application. In this case, you can try a number of different approaches to resolve the problem, such as rebooting the computer, verifying that a connection is not already established, or using a different port.

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To assist in troubleshooting modem problems, you can enable logging of modem commands through the Phone and Modem Options applet. The default location for the log file is %systemroot%\system 32\ModemLog_ model.txt .


Troubleshooting LAN Problems

Troubleshooting a LAN problem can be difficult because several different components can be the source of the problem. For example, the problem can be with a specific computer, another hardware device, the configuration, or even authentication.

If users are experiencing network connectivity problems on a local area network, one of the more common causes is a misconfiguration of network protocols. The default protocol installed with Windows XP is TCP/IP (the most common protocol used). It is also the protocol that requires the most configuration and can therefore be difficult to troubleshoot. So after you've eliminated any problems with the hardware, you should ensure TCP/IP is not the source of the problem.

Troubleshooting TCP/IP

TCP/IP requires considerable configuration either on individual clients or centrally on a server. Many issues can appear ”for example, incorrect Internet Protocol (IP) parameters on a client or a nonresponsive DHCP server. To successfully implement TCP/IP and DHCP on a network, you must have a general understanding of some of the common issues that can arise as well as ways to troubleshoot them. The following sections describe some of the more common problems that you may encounter on a TCP/IP network.

Diagnosing and Resolving Issues Related to Automatic Private IP Addressing

Automatic Private IP Addressing (APIPA) was introduced in Windows 98, second edition. It is enabled by default and supported by the following clients:

  • Windows 98, second edition

  • Windows ME

  • Windows 2000 (all platforms)

  • Windows XP

  • Windows Server 2003

Clients that support this feature are able to self-assign an IP address in the following situations:

  • A DHCP client is unable to contact a DHCP server, or no DHCP server is available on the network.

  • A DHCP client's attempt to renew its IP address leased from a DHCP server fails.

In both cases, the client assigns itself an IP address in the range of 169.254.0.1 “169.254.255.254 (see Figure 7.2). You can use the ipconfig command-line utility to verify that APIPA is enabled and that an IP address within the specific range has been assigned. Remember that APIPA is enabled by default. However, this feature can be disabled through the registry or with the use of Group Policy Objects (GPOs).

Figure 7.2. Automatic Private IP Addressing.

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If your network consists of multiple subnets, clients using APIPA can communicate only with hosts on their local subnet. APIPA does not include optional parameters. Clients assign themselves only an IP address and a subnet mask. Without the IP address of the default gateway and Domain Name System (DNS) server, communication outside the local subnet will fail.

Diagnosing and Resolving Issues Related to Incorrect TCP/IP Configuration

You can use several command-line utilities to test and diagnose incorrect TCP/IP configurations. To do so, open the Command Prompt window and type ipconfig . Using the /all parameter brings up more detailed configuration information, as shown in Figure 7.3. Table 7.1 outlines some of the common parameters you can use with the ipconfig command.

Figure 7.3. Verifying TCP/IP configuration using the ipconfig /all command.
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Table 7.1. Parameters for Use with the ipconfig Command

Parameter

Description

/all

Displays detailed IP configuration information

/release

Releases the IP address for the specified adapter

/renew

Renews the IP address for the specified adapter

/flushDNS

Purges the entries in the DNS cache

/registerDNS

Refreshes all leased IP addresses and reregisters DNS names

/displayDNS

Displays the contents of the DNS cache


Troubleshooting with the ping Command

If the communications themselves are at fault, you should look at your software, the path between your system and the remote host, and the remote host itself. Start with the remote host and work back to your local system. The best practice in general is to first ping the remote system to see whether it is online. Test other systems located in the same general area as well (somewhere else on the Internet). As long as you use a handful of hosts, you should be able to determine the source of the problem.

If you are unable to ping only a single host, you can deduce that the host is offline, it does not respond to pings , or the path to the host is interrupted . If multiple hosts ”but not all ”fail to ping, a router is at fault somewhere in the chain, or a serious network overload is occurring. If all hosts fail to ping, your Internet connection may be at fault.

If you've determined that a network connection is present, the problem may be with a another device on the network such as a router. You can use the ping command to ensure that the network connection is not being interrupted.

The ping command-line utility is useful in verifying connectivity with another TCP/IP host. Connectivity on the network is verified by sending Internet Control Message Protocol (ICMP) echo requests and replies. When the ping command is issued, the source computer sends echo request messages to another TCP/IP host. The remote host, if reachable , then responds with four echo replies. The ping command is also issued at the command prompt, along with the TCP/IP address or domain name of the other TCP/IP host, as follows :

 

 C:> ping 124.120.105.110 C:> ping www.contoso.com 

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To determine whether TCP/IP is initialized on the local computer, issue the ping command and specify the loopback address 127.0.0.1. The loopback address is the address used to route outgoing packets back to the local computer. It is used for testing purposes.


The general steps for troubleshooting TCP/IP using the ping command are as follows:

  1. Ping the loopback address 127.0.0.1 to ensure TCP/IP is initialized on the local computer. This step does not test any connectivity with other hosts.

  2. If successful, ping the IP address assigned to the local computer. This step determines whether the IP address of the computer was successfully added to the network.

  3. Ping the IP address of the default gateway. If this step fails, verify that the IP address of the default gateway is correct and the gateway is operational.

  4. Ping the IP address of a host on a remote network. If this step is unsuccessful , verify that the remote host is operational, verify the IP address of the remote host, and verify that all routers and gateways between the local computer and remote computer are operational.

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A quick way of verifying TCP/IP connectivity is to complete step 4 of the preceding routine. If you can successfully ping the IP address of a remote host, steps 1 through 3 will be successful.


Two other utilities that you can use for TCP/IP troubleshooting are tracert and pathping . The tracert command determines the route taken to a specific destination. You may want to use the tracert command if you cannot successfully ping the IP address of a remote host. The results of the tracert command indicate whether a problem exists with a router or gateway between the local computer and the remote destination.

The pathping command is basically a combination of the ping and tracert commands. When the command is issued, packets are sent to each router between the local computer and a remote computer. The results determine which routers and gateways may be causing problems on the network.

If the problem is indeed related to the network connection, the actions outlined in this section should help you locate the cause of the problem.

Troubleshooting Routing and Remote Access Configuration Problems

Troubleshooting is a major part of an administrator's job. Issues can arise related to connection problems or the ability to access resources beyond the remote access server. If the remote access server is configured as a router, you may encounter problems related to demand dialing. The following section outlines some of the more common problems you may encounter with a remote access server.

Diagnosing and Resolving Issues Related to Establishing a Remote Access Connection

One of the most common problems you may find yourself troubleshooting is related to establishing a remote access connection with a server. It may be a remote access server on your private network or with an ISP. In the event such connection problems occur, use the following tips to start troubleshooting:

  • Verify that the modem installed is working and correctly configured (refer to the section "Troubleshooting Hardware Problems" earlier in the chapter).

  • Verify the number the user is dialing. Also consider that the problem may exist with the phone line.

  • Verify the credentials the user is providing.

  • If the user is dialing into a remote access server on your network, check that the remote access service is enabled and started on the server.

  • On the server side, verify the availability of ports. If necessary, disconnect any idle sessions or increase the number of available ports.

  • If you are using remote access policies to control remote access connections, verify that the remote access policy is not prohibiting the connection.

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If a user receives an access denied message when attempting to establish a remote access connection, check the credentials the user is providing and verify that the user has indeed been granted remote access permissions.




MCDST 70-272 Exam Cram 2. Supporting Users & Troubleshooting Desktop Applications on a Windows XP Operating System (Exam Cram 2)
MCSA/MCSE 70-291 Exam Cram: Implementing, Managing, and Maintaining a Microsoft Windows Server 2003 Network Infrastructure (2nd Edition)
ISBN: 0789736187
EAN: 2147483647
Year: 2003
Pages: 119
Authors: Diana Huggins

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