Before I Begin
As I explained in the first part of this article
series, my goal is to create a troubleshooting guide that anyone with
basic skills can follow. That being the case, I am starting with basic
troubleshooting techniques, and as the series progresses, I will
gradually move into more advanced techniques.
Confirming Connectivity
In the previous article, I showed you the basics of
using the PING command to test network connectivity. However, if you
are having trouble communicating with other hosts on the network, or
hosts on remote networks, then there are a few more PING tests that you
can perform in order to get a better idea of what’s going on.
Before I show you those techniques though, it is
important to understand how the host that is having communications
problems is configured. The procedure for doing so varies from one
version of Windows to the next, so I will show you how to check the
network configuration on a machine that’s running Windows Server 2003
The first thing that you must do is to determine
whether the machine in question is running a static or a dynamic IP
address configuration. To do so, open the Control Panel, and choose the
Network Connections option. Now, right click on the connection that you
are trying to diagnose, and choose the Properties command from the
resulting shortcut menu. Upon doing so, you will see the connection’s
properties sheet, as shown in Figure A.
Figure A: This is the network connection’s properties sheet
Now, scroll through the list of items that the
connection uses until you locate the TCP/IP protocol (selected in Figure
A). Select this protocol, and click the Properties button to reveal the
Internet Protocol (TCP/IP) Properties sheet, shown in Figure B.
Figure B: The Internet Protocol (TCP/IP) Properties sheet is used to configure the TCP{/IP protocol
Once you arrive at this screen, it is important to
make note of the machine’s IP configuration. Specifically, you will want
to make note of the following items:
- Is the machine using a static or a dynamic configuration?
- If a static configuration is being used, what is the IP address, subnet mask, and default gateway?
- Is the DNS server address being obtained automatically?
- If the DNS server address is being manually specified, what address is being used?
Before I move on, I also want to mention that if a
computer has multiple network adapters installed, then there will be
multiple connections that are listed in the Control Panel. It is very
important that you know which connection corresponds to which network
adapter, or else the techniques that I am about to show you will not
work.
If you have any doubt as to which connection
corresponds to which network adapter, then check the adapter type. If
you look at Figure A, you will notice that the adapter type is listed at
the top of the screen. If need be, you can open the case to see which
network adapter the network cable is connected to, so that you can be
absolutely sure that you are looking at the correct network connection.
Now that you know how TCP/IP is configured for the
network adapter in question, we must determine whether or not Windows
acknowledges the configuration. To do so, open a Command Prompt window,
and enter the following command:
IPCONFIG /ALL
It might seem strange to have to make sure that
Windows acknowledges your configuration, but IPCONFIG can really tell
you a lot about what’s going on. For example, take a look at the screen
that’s shown in Figure C. When you enter the IPCONFIG /ALL command, the
first thing that you must do is to locate the correct network adapter.
In this case, locating the correct adapter is easy, because only one
adapter is listed. Notice though that IPCONFIG provides you with the
connection number (in this case it’s Ethernet adapter Local Area
Connection 2). If you look back at Figure A, you will notice that the
title of the properties sheet shown in the figure bears the same name.
That along with the description of the physical network adapter tells
you exactly which network connection you are looking at.
Figure C: The IPCONFIG /ALL command shows you the machine’s IP configuration as Windows sees it
Of course the first thing that you will probably
notice about Figure C is that it lists many different IP addresses for
the connection. The reason for this is that I created the screenshot on a
Web server. The Web server hosts multiple Web sites, each with its own
IP address. I wanted to use this server to illustrate the point that the
IP address configuration that you see when you glance at the TCP/IP
properties sheet isn’t always what Windows is using. In this case, the
IP configuration information shown in Figure B is still valid. It serves
as the machine’s primary IP address. However, there are many other IP
addresses that are also in use.
The next step in the troubleshooting process varies
depending on whether the machine is using a static or a dynamic IP
address configuration. If the machine is using a static configuration,
then for right now, just check to make sure that the IP address, subnet
mask, default gateway, and DNS server address that is listed matches
those entered on the TCP/IP properties sheet.
If the machine is using a dynamic IP address, then
you will want to look at the address and see if it falls within the
expected address range. If you are troubleshooting a problem on an
unfamiliar network, then you may not know what the address range should
be. If that’s the case, there are a few values that you can look for
that have special meanings.
The most obvious clue that something has gone wrong
is an IP address of 0.0.0.0. This presence of this address usually
indicates one of three things:
The network adapter is not connected to the network (possibly because of a cable problem or a bad switch port)
The IP address was released
An IP address conflict has occurred.
If you receive this address, then try entering the following three commands:
IPCONFIG /RELEASEIPCONFIG /RENEWIPCONFIG /ALL
These commands will essentially tell the computer
to give up its current address, try to obtain a new address, and then
show you the new configuration information. Sometimes this process will
fix the problem, and sometimes it won’t. Often though, it will yield
clues as to the cause of the problem.
Another tell tale clue that something has gone
wrong is that the IP address falls into the 169.254.x.x range with a
subnet mask of 255.255.0.0. Some versions of Windows will automatically
use this address if an IP address cannot be acquired from a DHCP server.
Conclusion
In this article, I began showing you how to examine
a machine’s IP address configuration for possible clues to the cause of
the problem. In the next article in the series, I will show you how to
use the configuration information that you’ve found to test for network
connectivity.
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