Diagnose DHCP problems with ipconfig

Friday Apr 28th 2000 by Brien M. Posey

The TCP/IP protocol may be complex, but it contains powerful troubleshooting tools.

When it comes to troubleshooting network problems, many people are intimidated by the complexity of TCP/IP. Although TCP/IP is much more complex than other protocols, it tends to be easier to troubleshoot because it contains several tools designed to help you locate and solve a wide variety of problems. (Many network administrators wish that protocols such as IPX/SPX and Net BEUI had TCP/IP's troubleshooting tools.) One such tool is the ipconfig program.

Using ipconfig

To use ipconfig, simply open a Command Prompt window and enter "ipconfig". When you do, Windows NT will display a summary of each network adapter installed in your system, along with its TCP/IP configuration.

The ipconfig command is especially useful for diagnosing DHCP problems. If you're using a DHCP server, you can use ipconfig to see the address that DHCP has assigned to the adapter. If you're using a DHCP server, but you see the IP address, your computer has either lost communication with the DHCP server or the DHCP server is malfunctioning.

If you're using static IP addresses, you can use ipconfig to see the TCP/IP configuration as the Windows server sees it. The information displayed isn't simply a regurgitation of what's inserted into the TCP/IP properties sheet--rather, it's a way to tell if Windows has accepted the address that you've used.

By default, ipconfig lists the IP address, subnet mask, and default gateway of each network adapter. If you require more detailed information, you can use the /all switch after the ipconfig command. Doing so will cause the ipconfig program to display more detailed information, such as the MAC address of each network card, and an indication of whether the address was provided by a DHCP server.

DHCP leases

"Although TCP/IP is much more complex than other protocols, it tends to be easier to troubleshoot because of the powerful troubleshooting tools it contains. "

Fibre Channel, an emerging technology, consists of a technology converted from SCSI to optical to a very specialized packet. Fibre Channel does two things: It runs the SCSI protocol at 100MB per port over optical cables, and it runs a unique storage protocol at 1.06Gbps in packets. (Fibre Channel does not currently run IP.) It's really SCSI using a different protocol. As a network topology, Fibre Channel uses a hub or a switch as a concentrator. The switch runs faster than the hub. Fibre Channel supports up to 500 meters, which is suitable for most applications. (You can spend more money and purchase special cables and drivers to go up to 10 kilometers.)

Current Fibre Channel Arbitrated Loop (FC-AL) has one downside: it runs Class 3 service. Three classes exist for quality of service of transmission, and Class 3 service doesn't guarantee or acknowledge transmission. If a fibre drops a packet and the software fails to catch it, the result is a hang up (or a time out), causing the system to momentarily freeze. The reinitialization loop process begins, resetting the entire bus.

Use winipcfg in Windows 98

Unfortunately, the ipconfig command only works in Windows NT. If you have computers on your network running Windows 98, you'll have to use a different command. To do so, enter "winipcfg" at the Run prompt. Doing so will display a dialog box that displays the computer's TCP/IP configuration, as seen by Windows. Click the More Info button to get additional information, such as the WINS and DNS configuration.

You can select the network adapter on which you're viewing information by choosing the adapter from a drop-down list. If you need to release or renew a lease, you can do so by selecting the adapter from the drop-down list and clicking the Release or Renew button. Likewise, you can release or renew the lease for all installed adapters by clicking Release All or Renew All. //

Brien M. Posey is an MCSE who works as a freelance writer and as the director of information systems for a national chain of health care facilities. His past experience includes working as a network engineer for the Department of Defense. Because of the extremely high volume of e-mail that Brien receives, it's impossible for him to respond to every message, although he does read them all.

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