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wireles network hacks mods - briere D.

briere D. wireles network hacks mods - Wiley publishing, 2005. - 387 p.
ISBN: 0-7645-9583-0
Download (direct link): wirelesnetworkhacks.pdf
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If you select the NDIS driver for your wireless network adapter, NetStumbler will receive RSSI data instead of signal and noise data (measured in dBm). In this case, the signal strength data in NetStumbler will be useful, but any noise or SNR data will not be.
Figure 6-5:
Choosing a driver in NetStumbler.
102 Part II: Boosting Performance on Your Wireless Network
After NetStumbler has begun monitoring the airwaves, you can find different ways to display (and therefore analyze) the data. In the left pane of the NetStumbler window (shown in Figure 6-6), you see several different display options, each with an expand/collapse plus/minus sign next to it (they’re all expanded in the figure). You can sort through your networks using these controls by
^ Channel: You can look at individual 802.11a/b/g channels to see which access points are on which channels. This can be handy when you’re trying to figure out to which channel to assign your APs (you can figure out what the neighbors are using). Click on the plus signs next to individual channels to expand the listing of devices on each channel (listed by MAC address).
^ SSID: You can also sort by SSID. This may seem unnecessary, but it actually can be a good tool to see if there are multiple APs using the same SSID. (Maybe your neighbors all bought identical routers during the last sale at Fry’s!)
^ Filters: NetStumbler also provides a range of filters that let you sort through available networks to find only those that meet certain criteria. A number of these filters are available, but some of the most interesting include
• Encryption On or Encryption Off: You can quickly find “open” networks (or ensure that your APs have encryption enabled) by using these filters. This can be a handy tool when you’re searching for that “free” AP at the hotel or cafe to check your e-mail.
• ESS (AP) or IBSS (Peer): Use these filters to sort through the available networks by their status as access points and as peer-to-peer client networks. (You probably won’t want to try to associate with peer-to-peer wireless networks unless you’re absolutely sure who you’re connecting to.)
• Short Slot Time (11g): This filter tells you which 802.11g networks (if any are available) are set up for “802.11g only” mode. If you’re looking for the fastest networks around, this is one way (along with signal strength) to find them.
When you sort NetStumbler using these navigation tools, you see a listing of each AP or network that fits into that particular category. From this view, you can read the text columns on the right side of the window (shown in Figure 6-7) to see important network data (like SNR) at a quick glance.
Chapter 6: Better Living Through Network Monitoring
Figure 6-6:
expanding or collapsing the
navigation tools on the left.
Figure 6-7:
Viewing NetStumbler data in column form.
104 Part II: Boosting Performance on Your Wireless Network
To get a graphical representation of any particular network, simply click on the MAC Address of the device within the channels and SSID views and the right pane shifts to the display shown in Figure 6-8. From this view, you can see a running, time-based graphical representation of either signal strength (for the NSID drivers) or signal strength and noise (for other drivers).
This display can be very handy when you’re changing your network in some way because you can watch the effects of changes unfold on your computer screen in real-time.
For example, if you’re trying to find out how well your AP covers your home, you could use a laptop running NetStumbler and slowly move around the house (like the Verizon “Can you hear me now?” guy), and watch the signal strength or SNR dip and peak as you move in and out of good coverage.
If you find a room with poor coverage, have a helper adjust your AP or antenna placement while you watch the SNR and use NetStumbler as a tool for optimizing placement. You can also turn on the MIDI audio output we mentioned at the beginning of this section to add an aural dimension to this process.
We talk in more detail about how to do this kind of network optimization in Chapter 7, but we mention it here so you get an idea about how tools like NetStumbler can be used.
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Figure 6-8:
Using NetStumbler to graph performance over time.
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Chapter 6: Better Living Through Network Monitoring
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