Diagnosing network problems:    IPCONFIG

First you have to determine whether your computer is connected to a network. Open a Command window*.

At the prompt, type ipconfig /all and press Enter. If everything is working correctly, you’ll see a list like this:

Windows IP Configuration

       Host Name . . . . . . . . . . . . : IPTest
       Primary Dns Suffix  . . . . . . . :
       Node Type . . . . . . . . . . . . : Hybrid
       IP Routing Enabled. . . . . . . . : No
       WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter Local Area Connection:

       Connection-specific DNS Suffix  . : earthlink.net
       Description . . . . . . . . . . . : Network Connection
       Physical Address. . . . . . . . . : 00-07-E9-6D-A8-33
       Dhcp Enabled. . . . . . . . . . . : Yes
       Autoconfiguration Enabled . . . . : Yes
       IP Address. . . . . . . . . . . . : 192.168.0.109
       Subnet Mask . . . . . . . . . . . : 255.255.255.0
       Default Gateway . . . . . . . . . : 192.168.0.1
       DHCP Server . . . . . . . . . . . : 192.168.0.1
       DNS Servers . . . . . . . . . . . : 207.69.188.185
                                           207.69.188.186
       Lease Obtained. . . . . . . . . . : Tuesday, February 08, 2005 2:04:55 PM
       Lease Expires . . . . . . . . . . : Tuesday, March 22, 2005 6:04:55 AM

Fig 1
Here’s a description of the relevant information:

Host Name:     The name of your computer
Connection-specific DNS Suffix:     The network you’re connected to. At home, this is usually your ISP; at work, your company. Sometimes it may be blank.
Dhcp / Autoconfiguration Enabled:     These are two methods that your computer gets an address.
Physical Address:     This is the “serial number” of your network card and will never change.
IP Address:     This is the address of your computer.
Default Gateway:     This is the address of your router.
DNS Servers:     These are the computers that interpret internet names into their correct numeric address (such as Yahoo.com=66.94.234.13). Their function is provided by your ISP or contained in your router.
Lease Obtained / Expires:    “Obtained” is when you last connected to your router. “Expires” is a period determined by your router settings and varies from an hour to weeks.
Ethernet adapter ...: If you have more than one network adapter such as a wireless card, you may see some or all of this information for each adapter. If it says “Media disconnected”, that means there’s no connection on the cable or no wireless network available.


Likely problems


If you see all zeros for the IP addresses (Fig 2), you don’t have a network connection. This is means there is a bad cable between your computer and the router. It could also mean the computer and router are still negotiating their communication. Check that your wires are connected and wait up to several minutes to try ipconfig again (hit F3 to repeat the same command).

If instead of IP Address, you see Autoconfiguration IP Address that would typically start 168.254; (Fig 3) you have an electrical connection with the router, but do not have access to the network. If it is not cleared up after a reboot, there may be a failure in the network. For some reason, your computer is not communicating with a DHCP server.
You may be connecting to a downstream switch that is not connected to the router. The router may have its DHCP server turned off or the network may be expecting DHCP services from another device such as another router or a server.
You also may not have permission to connect to that network This is very unlikely in a home wired network, but might happen if you don’t have the correct password for a wireless network. You could also see it if you are trying to connect to a corporate network.
If you have a simple network and know you don’t have any of these problems, the easiest solution is probably to do a hardware reset of the router. This usually involves inserting a straightened paper clip into a hole to press a recessed button. You may need to hold the button several seconds, or hold it while powering up. Then you will need to restore the router configurations or reconfigure it from scratch.

Ethernet adapter Local Area Connection:

    Connection-specific DNS Suffix  :
    Description . . . . . . . . . . : 3Com 3C920
    Physical Address. . . . . . . . : 00-06-5B-36-71-B5
    Dhcp Enabled. . . . . . . . . . : Yes
    Autoconfiguration Enabled . . . : Yes
    IP Address. . . . . . . . . . . : 0.0.0.0
    Subnet Mask . . . . . . . . . . : 0.0.0.0
    Default Gateway . . . . . . . . :
    DHCP Server . . . . . . . . . . : 192.168.0.1

Fig 2
Ethernet adapter Local Area Connection:

    Connection-specific DNS Suffix  :
    Description . . . . . . . . . . : 3Com 3C920
    Physical Address. . . . . . . . : 00-06-5B-36-71-B5
    Dhcp Enabled. . . . . . . . . . : Yes
    Autoconfiguration Enabled . . . : Yes
    Autoconfiguration IP Address. . : 169.254.39.17
    Subnet Mask . . . . . . . . . . : 255.255.0.0
    Default Gateway . . . . . . . . :

Fig 3



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Last updated 10/10/07