because older legacy rates, particularly
802.11b, are sometimes blocked from operation at the access point to preserve
precious airtime. A device that only supports these older data rates will be unable to connect to the network.
Another problem is older devices that
don’t support the 5.0-GHz band. Many
corporate networks have been migrated
to support the 5.0-GHz band only, because there are more channels available and less interference. So in cases
like this, legacy 802.11 devices will not
be able to connect to the corporate
WiFi network anymore. Not only that,
some older client devices may support
the 5.0-GHz band, but not all the channels on that band. For example, many
older devices don’t support the Dynamic
Frequency Selection (DFS) channels, and
because of that won’t be able to connect
to the network.
Regarding how to easily identify
these limitations, the easiest way is to
use a tool that can identify the capabilities of a client device. Following is some
of the information you want the tool to
provide on client devices.
• SSID (Service set identifier)—Allows
you to verify which network the client device is connected to. Only
available when the device is connected to a network, and used to verify that the client device is connected
to the right network.
• Access point name—Allows the user
to verify what access point the client
device is connected to. It’s very useful
when you want to make sure client
devices are connecting to the closest
• Connection rate—Provides the con-
nection data rate being used by the
client device. Helps you verify the
maximum data rates supported by
the client device, and thus determine
if the device has any rate limitations
that could prevent it from connecting
to the WiFi network.
· Security—Provides information
on the type of security being used
by the client device, which allows
you to verify the client device security configuration.
• 802.11 type—Provides information on
the types of 802.11 technologies supported by the client device. This helps
you verify if the client device can support the latest 802.11 technologies
and the higher data rates.
• Band—Provides information on the
band being used by the client device,
allowing you to verify if the client device can support both the 2.4- and
• Channel—Provides information on
the channel being used by the client
device. Some older client devices may
not be able to support all the 5.0-
The only solutions to this type of
channel problem is to have the user
upgrade their device to one that supports the latest 802.11 technology, or to
change the configuration on your access
point so they will support older technologies. Notice though, that upgrading
the client device would be the preferred
option. Adding support for older 802.11
technologies could affect the performance of newer client devices.
Security is a good thing, but managing security on access points and clients
isn’t easy. Any passphrase mismatch,
certificate missing, or mistake can leave
client devices unable to connect.
Besides that, some networks are secured by allowing only certain MAC addresses to connect and authenticate. If
a device’s MAC address isn’t on the authorized list, the client device won’t successfully connect.
Both the access points and the cli-
ent devices must have the proper
security credentials to successfully form
a connection. Errors in the configura-
tion of these credentials on either end
can prevent authorized users from be-
As for identifying connection problems caused by security configuration
problems, here are a few tips.
1) If you are using WPA-P or WPA2-P
on your network, the first thing to
verify is that the correct passphrase
is being used.
2) If you are using WPA-E or WPA2-E
on your network, you should start by
verifying that the correct credentials are
being used and that the client device has
the required certificates installed.
3) If you are restricting access to the
network to authorized devices only, using their MAC address, then you also
should verify that the MAC address for
the client device is on the approved list.
4) If you are using WPA-E or WPA2-E
and more than one device is having
the same issue, you may want to make
sure that the authentication server is
After identifying the security configuration problem, you just need to fix the
configuration on the client device, wireless network, or authentication server to
resolve the issue.
In conclusion, WiFi connectivity
problems don’t have to be difficult to
troubleshoot or resolve. With the right
tools and a little knowledge, you should
be able to resolve WiFi connectivity
problems quickly and easily. u
Julio Petrovitch is principal wireless technical
marketing engineer with NetScout ( www.net-
scout.com). More-detailed information on WiFi
troubleshooting is available via white papers and
other content on the NetScout website. Also on
its website, NetScout offers an interactive, infor-mation-based library of troubleshooting information arranged in a “
choose-your-own-adven-ture” style. That page is found at netsout.com/