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Troubleshooting TCP/IP


TCP/IP Commands

  • Ping: Tests connections

    Options:

    • -t (Continuous ping)
    • -a (resolve the tcp/ip address to the hostname)
    • -n count (set the number of echo requests to send)
    • -l size (Send the buffer size)

    Comment: There are more options you can use with the ping command. However, the only two I use are -t and -a. I don't know that I've ever used any of the others.


  • ARP: Displays locally resolved IP addresses as physical addresses
  • Ipconfig: Displays the current TCP/IP configuration
  • Nbtstat: Displays statistics and connections using NetBIOS over TCP/IP
  • Netstat: Displays TCP/IP protocol statistics and connections
  • Route: Displays or modifies local routing table
  • Hostname: Returns the local computer's host name
  • Tracert: Checks the route to a remote system

    All of the above utilities are executed from a command prompt. For more information on any of these commands, except Hostname and Tracert, go to a command prompt and type the command followed by /? then press Enter. For example Ping /? then press Enter.

Testing the TCP/IP Configuration

Use ipconfig and ping command-prompt utilities to test configuration and connections to other TCP/IP hosts and networks.

  • Using Ipconfig - Use the ipconfig utility to verify the TCP/IP configuration on a host. This helps determine whether the configuration is initialized, or whether a duplicate IP address exists. Use ipconfig with the /all switch.

    Type ipconfig /all | more to prevent scolling off of the screen.

    The following is the result of the ipconfig /all command.

  • If a configuration has initialized, the ipconfig utility displays the IP address and subnet mask, and, if it is assigned, the default gateway.
  • If a duplicate IP address exists, the subnet mask is 0.0.0.0

Finding Computer Names

If you know the IP address of a workstation but don't know the computer name, you can find out the computer name two ways. The first is to run tracert. From a DOS prompt, type tracert (space) and then the ip address. Hit enter and it should resolve the computer name for you.

The other way is to ping it with the "-a" flag. In other words, ping (space) -a (space) ip address. This should also resolve the computer name for you.

Finding the MAC Address

The MAC address is a unique number assigned to every Network Interface Card (NIC). The address is created and assigned when the card is manufactured. The number is in hexadecimal form. It will look something like this: 00-10-D0-B9-AA-A4 Sometimes when you see this address, the numbers are separated by colons rather than dashes; as in 00:10:D0:B9:AA:A4

To find the MAC address of a workstation using Windows NT, Windows 2000 Professional or Windows XP, click on the "Start Button", click on "Programs", click on "Accessories", click on "Command Prompt". Type "ipconfig /all" (minus the quotation marks) at a DOS prompt. Or you can click on "Start", click on "Run", type "cmd" in the box, and click on "OK". Then type "ipconfig /all" at the DOS prompt. The MAC address is listed as "physical" address.

If you are using Windows 95, Windows 98, or Windows ME, clcik on "Start", click on "Run", type "winipcfg" in the box click on "OK". The number next to "Adapter Address" is what you are looking for.


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