Troubleshooting Name Resolution and Addressing


When troubleshooting any connectivity issues, it is important to first ascertain whether the error condition was caused by a failure in host name resolution (for example, http://www.reskit.com/) or in NetBIOS name resolution (for example, \\computername). If name resolution does not appear to be the problem, use TCP/IP troubleshooting tools such as Ping and Tracert to verify that IP addressing has been correctly configured on the Windows XPProfessional based client. For more information about TCP/IP troubleshooting tools, see Configuring TCP/IP in this book.

The easiest way to distinguish host name resolution problems from NetBIOS name resolution problems is to find out whether the failing application uses NetBIOS or Windows Sockets. Most Internet or intranet-based applications (such as Internet Explorer and other Web browsers, ftp clients and telnet) use Windows Sockets. If the application uses Windows Sockets, the problem lies with host name resolution. If the application uses NetBIOS, the problem is with NetBIOS name resolution (broadcast, Lmhosts or WINS). You can troubleshoot NetBIOS name-resolution problems with the various net commands and with the Windows NT 4.0 administrator tools.

Checking NetBIOS Name Resolution

Several methods are available for detecting and resolving the most common types of NetBIOS name-resolution problems.

Resolving NetBios Error 53

The most common symptom of a problem in NetBIOS name resolution is that the Ping tool returns an Error 53 message. The Error 53 message is generally returned when name resolution for a particular computer name fails, but Error 53 can also occur when there is a problem establishing a NetBIOS session. You can use the net view command to distinguish between these two cases.

To determine the cause of an Error 53 message

  • At the command prompt, type:

    net view * \\hostname

    where hostname is a network resource that you know is active.

    If the hostname and a list of the host s shares appear on the screen, name resolution is probably not the source of the problem. It is possible, on occasion, for name resolution to be functioning properly and yet net use still returns Error 53 (for example, when a DNS or WINS server has a bad entry).

To confirm that name resolution is definitely not the source of your problem, try pinging the host name. If Ping also shows that name resolution fails (by returning the Unknown host message), check the status of your NetBIOS session.

To check the status of your NetBIOS session

  • At the command prompt, type:

    net view \\ip address

    where ip address is the same network resource that you used to determine the cause of the Error 53 message. If this also fails, the problem is in establishing a session.

If the computer is on the local subnet, confirm that the name is spelled correctly and that the target computer is running TCP/IP as well. If the computer is not on the local subnet, be sure that its name and IP address mapping are available in the DNS database, the Hosts or Lmhosts file, or the WINS database.

If all TCP/IP elements appear to be installed properly, Ping the remote computer to be sure that it has TCP/IP enabled.

Checking the Lmhosts File

The name resolution problem might be in your Lmhosts file, which looks for addresses sequentially from the top down. If more than one address is listed for the same host name, TCP/IP returns the first value it encounters, whether or not that value is accurate.

You can find the Lmhosts file in \systemroot\System32\Drivers\Etc. Note that this file does not exist by default; a sample file named Lmhosts.sam is supplied. This file must be renamed to Lmhosts before it can be used.

Note 

Although \systemroot\System32\Drivers\Etc is the default directory for the Lmhosts file, exactly which Lmhosts file is parsed depends on the value of the registry entry databasepath located in the subkey HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters.

The database path tells the local computer where to look for the Lmhosts file.

Checking the WINS Configuration

Check to see that the WINS configuration is correct. In particular, check the address for the WINS server.

To check your WINS configuration

  1. In Control Panel, select Network and Internet Connections.

  2. In the Network and Internet Connections sheet, select Network Connections.

  3. In Network Connections, right-click the local area connection that you want to change, and then click Properties.

  4. In the Local Area Connection Properties sheet, select Internet Protocol (TCP/IP), and then click Properties.

  5. In the Internet Protocol (TCP/IP) Properties sheet, click Advanced.

  6. In the Advanced TCP/IP Settings dialog box, click the WINS tab.

  7. In the WINS configuration dialog box, add the server s IP address (if none is listed).

  8. Check to see whether Lmhosts lookup is enabled.

  9. Check to see whether NetBIOS settings are taken from the DHCP server, or whether NetBIOS is enabled or disabled. If you are using DHCP for this host computer, select Use NetBIOS setting from the DHCP server. Otherwise, select enable NetBIOS over TCP/IP.

Checking Hosts Files and DNS Name Resolution

If your problem is with Windows Sockets, rather than with NetBIOS, you might have either a Hosts file error or a DNS configuration error. If you are using a Hosts file for host name resolution, you need to verify that the settings in the file are correct. If you are using DNS for host name resolution, verify that the DNS configuration is correct.

Checking the Hosts File

If you are having trouble connecting to a remote system using a host name, and you use a Hosts file for name resolution, the problem might be with the contents of that file. Make sure that the name of the remote computer is spelled correctly in the Hosts file and by the application using the file.

The Hosts file or a DNS server is used to resolve host names to IP addresses whenever you use TCP/IP tools such as Ping. You can find the Hosts file in \systemroot\System32\Drivers\Etc.

This file is not dynamic; all entries are made manually. The file format is the following:

172.16.48.10    testpc1.reskit.com

The IP address and the friendly host name are always separated by one or more space or tab characters.

The following Hosts file problems can cause networking errors:

Checking Your DNS Configuration

If you are using DNS, be sure that you have checked the DNS tab of the Advanced TCP/IP Settings dialog box to confirm that the IP addresses of the DNS servers are correct and in the proper order. Use Ping with the remote computer s host name, and then use its IP address to determine whether the host address is being resolved properly. If the host name ping fails and the IP address ping succeeds, the problem is with name resolution.

To check DNS configuration

  1. In Control Panel, select Network and Internet Connections.

  2. In the Network and Internet Connections sheet, select Network Connections.

  3. In Network Connections, right-click the local area connection that you want to change, and then click Properties.

  4. Click Internet Protocol (TCP/IP), and then click Properties.

  5. In the Microsoft TCP/IP Properties sheet, click the Advanced tab.

  6. Click the DNS tab.

  7. Confirm that DNS is configured properly. If you find that the IP address of a particular DNS server is missing, be sure to add it to the list of DNS server addresses.

    Note 

    This procedure does not apply to network connections configured by DHCP servers, as DHCP servers configure network connections with preferred and alternate DNS servers.

You can test whether the DNS servers are running by pinging their IP addresses or by opening a Telnet session to port 53 on the DNS server. If the connection is established successfully, the DNS service is working on the DNS server. After you have verified that the DNS service is running, you can perform Nslookup queries to the DNS server to further verify the status of the DNS records for which you are looking. For more information about Nslookup and other aspects of DNS configuration, see Windows 2000 DNS in the TCP/IP Core Networking Guide of the Microsoft Windows 2000 Server Resource Kit.

If both pinging by IP address and pinging by name fail, the problem is with the network connection, possibly physical connectivity or routing. For more information about troubleshooting network connectivity, see Configuring TCP/IP in this book.

For more information about how DNS resolves host names, see Configuring DNS to Resolve Host Names and Domain Names earlier in this chapter.

DNS Error Messages

Errors in name resolution can occur when the entries in a DNS server or client are not configured correctly, when the DNS server is not running, or when there is a problem with network connectivity. To determine the cause of any name resolution problem, you can use the nslookup command-line tool.

Failed queries return a variety of messages, depending on whether the name cannot be resolved, the server does not provide a response, or the request times out. These messages generally indicate one of the following:

Troubleshooting IP Addressing

If host name resolution is successful, the problem must be something else. The solution might simply be a matter of correcting the IP configuration.

TCP/IP troubleshooting generally follows a set pattern. First, verify that the TCP/IP configuration on the problem computer is correct. The ipconfig command can be used to get the host computer configuration information, including the IP address, subnet mask, and default gateway. For more information about ipconfig, see Configuring TCP/IP in this book.

Next, verify that a connection and a route exist between the computer and the destination host by using Ping and/or PathPing. Ping helps to verify IP-level connectivity; PathPing detects packet loss over multiple-hop trips. For more information about how these tools can be used to troubleshoot IP addressing problems, see Configuring TCP/IP in this book.

If you have successfully pinged both your own machine and the loopback address, clear out the Address Resolution Protocol (ARP) cache and restart your computer (for information about clearing out the ARP cache, see Configuring TCP/IP in this book). In addition, make certain that the default gateway is on the same network that your client is on, that it is a router, and that its name has been entered correctly. Then, try Pinging a remote host to ensure that network-to-network communications are operating as expected. Use Tracert to examine the path to the destination.

For more information about troubleshooting IP addressing, see Configuring TCP/IP in this book.




Microsoft Windows XP Professional Resource Kit 2003
Microsoft Windows XP Professional Resource Kit 2003
ISBN: N/A
EAN: N/A
Year: 2005
Pages: 338
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