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Tools for Troubleshooting (part 9) - TCPView, Telnet Client

7/11/2012 4:13:02 PM

17. TCPView

TCPView, shown in Figure 5, monitors both incoming and outgoing connections, as well as listening applications, in real time. You can use TCPView to identify exactly which servers a client connects to, including the port numbers, or identify the clients connecting to a server.

Figure 5. TCPView allows you to monitor network connections in real time.

To download TCPView, visit http://technet.microsoft.com/en-us/sysinternals/bb897437.aspx. You do not need to install TCPView; simply copy the executable file to a folder that allows applications to be run (such as C:\Program Files\) and then double-click Tcpview.exe. TCPView also includes Tcpvcon.exe, a command-line tool that provides similar functionality.

18. Telnet Client

Although it is not primarily a troubleshooting tool, Telnet Client is extremely useful for determining whether TCP-based network services are reachable from a client. Most commonly used network services are TCP based, including Web services, mail services, and file transfer services. Telnet Client is not useful for troubleshooting UDP-based network services such as DNS and many streaming media communications.

Telnet Client is not installed by default in Windows 7. To install it, run the following command from a command prompt with administrative privileges.

start /w pkgmgr /iu:"TelnetClient"

Alternatively, you can install it by following these steps:

  1. Click Start and then click Control Panel.

  2. Click Programs.

  3. Click Turn Windows Features On Or Off.

  4. In the Windows Features dialog box, select the Telnet Client check box. Click OK.

Telnet Client is useful only for determining whether a service is reachable, and it will not provide information that you can use for troubleshooting name resolution, network performance, or network connectivity problems. Use Telnet Client only after you have used Ping to eliminate the possibility of name resolution problems.

19. Testing Service Connectivity

After you have identified the port number for the service, you can use Telnet Client to test connectivity to that service. To test connectivity to a service, open a command prompt and run the following command.

telnet destination portnumber

For example, to test HTTP connectivity to www.microsoft.com, type the following command at the command line.

telnet www.microsoft.com 80

The destination might be a host name, computer name, or IP address. The response you receive will indicate whether a connection was established. If you receive the message "Could not open connection to the host," the host did not respond to the request for a connection on the port number you specified, and the service you are testing is unreachable.

If you receive any other response, including all text disappearing from the command window, the connection was successfully established. This eliminates the possibility that the problem you are troubleshooting is caused by a connectivity issue between the client and the server. Depending on the service you are testing, Telnet Client can be automatically disconnected, or the session might remain open. Either circumstance indicates a successful connection. If the Telnet Client session remains open, you should disconnect Telnet Client to close the connection.

To disconnect Telnet Client, follow these steps:

  1. Press Ctrl+].

  2. When the Microsoft Telnet> prompt appears, type quit.

20. Test TCP

With Test TCP, you can both initiate TCP connections and listen for TCP connections. You can also use the Test TCP tool for UDP traffic. With Test TCP, you can configure a computer to listen on a specific TCP or UDP port without having to install the application or service on the computer. This allows you to test network connectivity for specific traffic before the services are in place.

Test TCP (Ttcp.exe) is a tool that you can use to listen for and send TCP segment data or UDP messages between two nodes. Ttcp.exe is provided with Windows Server 2003 in the Valueadd\Msft\Net\Tools folder of the Windows Server 2003 or Windows XP Service Pack 2 (SP2) product CD-ROM.

Test TCP differs from Port Query in the following ways:

  • With Test TCP, you can configure a computer to listen on a specific TCP or UDP port without having to install the application or service on the computer. This allows you to test network connectivity for specific traffic before the services are in place. For example, you could use Test TCP to test for domain replication traffic to a computer before you make the computer a domain controller.

  • Test TCP also supports IPv6 traffic.

When you are using a TCP port, the following code shows the basic syntax for Ttcp.exe on the listening node (the receiver):

ttcp -r -pPort

When using a UDP port, use the following syntax.

ttcp -r -pPort -u

After starting Test TCP in receive mode, the tool will wait indefinitely for a transmission before returning you to the command prompt. The first time you use Test TCP to listen from a computer running Windows 7, you might be prompted to create a Windows Firewall exception. You must create the exception for Test TCP to work. If you choose to unblock the application, Windows Firewall will allow all traffic for that computer on the specified port in the future. Therefore, you will not need to create a new exception for that network type, even if you listen on a different port. In Windows Firewall, the exception is named Protocol Independent Perf Test Command.

When you are using a TCP port, the following code shows the basic syntax for Ttcp.exe on the sending node (the transmitter):

ttcp -t -pPort hostname

When using a UDP port, use the following syntax.

ttcp -t -pPort -u hostname

If the two computers are able to communicate, the transmitting computer will display output such as the following.

ttcp-t: Win7 ->
ttcp-t: local -> remote
ttcp-t: buflen=8192, nbuf=2048, align=16384/+0, port=81  tcp  -> Win7
ttcp-t: done sending, nbuf = -1
ttcp-t: 16777216 bytes in 1423 real milliseconds = 11513 KB/sec
ttcp-t: 2048 I/O calls, msec/call = 0, calls/sec = 1439, bytes/call = 8192

Meanwhile, the receiving computer will display output similar to the following.

ttcp-r: local <- remote
ttcp-r: buflen=8192, nbuf=2048, align=16384/+0, port=81  tcp
ttcp-r: 16777216 bytes in 1416 real milliseconds = 11570 KB/sec
ttcp-r: 3492 I/O calls, msec/call = 0, calls/sec = 2466, bytes/call = 4804

You can use Test TCP to connect to any computer listening for incoming TCP connections, even if that computer is not running Test TCP. However, to accurately test UDP connectivity, Test TCP must be running on both the receiver and transmitter. For example, to attempt a connection to www.microsoft.com on TCP port 80, you would run the following command.

ttcp -t -p80 www.microsoft.com

ttcp-t: local -> remote
ttcp-t: buflen=8192, nbuf=2048, align=16384/+0, port=80  tcp  -> www.microsoft.com
send(to) failed: 10053
ttcp-t: done sending, nbuf = 2037
ttcp-t: 81920 bytes in 16488 real milliseconds = 4 KB/sec
ttcp-t: 11 I/O calls, msec/call = 1498, calls/sec = 0, bytes/call = 7447


In this example, the TCP connection was successful, even though the output includes the line "send(to) failed." If the connection was unsuccessful, the output would have included the phrase "connection refused." Alternatively, some servers will simply not respond to invalid communications, which will cause the Test TCP transmitter to pause indefinitely while it awaits a response from the server. To cancel Test TCP, press Ctrl+C.

Each instance of Test TCP can listen on or send to only a single port. However, you can run it in multiple command prompts to listen or send on multiple ports. For additional command-line options, type Ttcp at the command prompt.

21. Windows Network Diagnostics

Troubleshooting network problems is complicated, especially for users. Many users discover network problems when they attempt to visit a Web page with Internet Explorer. If the Web page is not available, Internet Explorer returns the message "Internet Explorer cannot display the webpage." The problem could be any one of the following, however:

  • The user mistyped the address of the Web page.

  • The Web server is not available.

  • The user's Internet connection is not available.

  • The user's LAN is not available.

  • The user's network adapter is misconfigured.

  • The user's network adapter has failed.

The cause of the problem is important for the user to understand. For example, if the Web server is not available, the user does not need to take any action—the user should simply wait for the Web server to become available. If the Internet connection has failed, the user might need to call her Internet service provider (ISP) to troubleshoot the problem. If the user's network adapter has failed, she should attempt to reset it and contact her computer manufacturer's technical support for additional assistance.

Windows Network Diagnostics and the underlying Windows Troubleshooting Platform assist users in diagnosing and, when possible, resolving network connectivity issues. When Windows 7 detects network problems, it will prompt the user to diagnose them. For example, Internet Explorer displays a link to start Windows Network Diagnostics if a Web server is unavailable, and the Network And Sharing Center will display a diagnostic link if a network is unavailable.

Applications might prompt users to open Windows Network Diagnostics in response to connectivity problems. To start Windows Network Diagnostics manually, open Network And Sharing Center, click Troubleshoot Problems, and follow the prompts that appear.

Other -----------------
- Tools for Troubleshooting (part 8) - Route & Task Manager
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- Tools for Troubleshooting (part 3) - Netstat & Network Monitor
- Tools for Troubleshooting (part 1) - Arp & IPConfig
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