Posts

Questions About the Early Days of 802.11

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In the grand scheme of things, I'm pretty new to wireless networking. My journey in Wi-Fi began in high school (~2006), when I decided to wirelessly network our dial-up connection in my parent's house. I distinctly remember making the decision to invest in relatively new 802.11g gear, instead of buying budget 802.11b hardware. A few eBay auctions later, I had a respectable pile of WLAN gear on desk to play with. Despite the awesome 9 dBi omnidirectional antenna, the room directly below my router had terrible signal strength, and I couldn't figure out why.

In college (~2009), the school had Wi-Fi across a parking lot, very far away from the dorms. I taped a draft 802.11n adapter in the window, networked it to a couple of wireless routers in my dorm room, ultimately providing Wi-Fi for everyone in the dorms. It was very useful for rounds of Halo 3 and StarCraft. More antenna trouble: my experimentations with soup cantennas failed miserably.

A few years later (~2012), I was t…

CWSP Study Guide Exercise PCAP Files

I'm really, REALLY enjoying the CWSP Study Guide. One thing I noticed is that the provided link to exercise PCAP files in the book does not seem to work. I dug around and was able to find them on Sybex' website.

Here's a direct download link.

Replaying Beacons with the AirPcap Nx

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The company I work for makes a Wi-Fi scanner, and while I think that it does a really good job of interpreting 802.11 beacons and probe responses, every now and then a customer finds a little bug, or at least a weird beacon from an access point or SOHO wireless router.

For a long time, I wished that I had a way to replay those beacons to see how our Wi-Fi scanner would interpret them, firsthand. Today, I had an epiphany. I have an AirPcap Nx, which in addition to being a packet capture device is also a packet injection tool!

If you have a PCAP file containing beacons, you can easily replay them with the AirPcap Nx. Here's how to do it:

1. Open the PCAP file in Wireshark.

2. Select the beacon that you wish to replay by clicking on it.

3. Save the selected beacon off to a new file in File > Export Specified Packet with the Selected Packet option.



4. Open AirPcapReplay.

5. Set the Transmit Mode to User-defined Packet Period, check Respect Packet Channel, and check Respect Packet R…

SE-Connect Mode via the GUI

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There are plenty of guides out there that explain how to put a Cisco AP in SE-Connect mode via SSH, but what about the GUI?

Remember that if you want to do this, you'll need to have converted your AP to autonomous mode. To convert my AP, I used this excellent guide. The only thing I had to do differently with my Cisco 3600 was hold down the "mode" button until the LED turned amber, and then turned off (instead of just holding the button until the LED turned red like the guide describes).

Once your AP is running an autonomous image, you're ready to go!

1. Log into your Cisco AP. If you haven't changed the password (and you should), the username is cisco, and the password is Cisco.

2. On the Home page, click on the 2.4 GHz link next to Radio0-802.11N.



3. Click on the Settings tab.



4. At Enable Radio, select Enable. At Role in Radio Network, select Spectrum. Click Apply at the bottom.





6. Go back to the Home screen, and do the same process for the 5 GHz radio (enabli…

Wireless Packet Capture with macOS

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One of my favorite things about macOS (formerly OS X) is how easy it makes wireless packet captures, compared to Windows.

In older versions of OS X, the Wireless Diagnostics tool provided a fast and simple way to capture wireless frames on a specific channel. 
To use it, you had to open Wireless Diagnostics with Spotlight, type in your password, open the Sniffer window, and finally select a channel and start the capture. As soon as the capture is stopped, a ".wcap" file was placed on your desktop, ready to be opened up with your favorite packet analysis software.
macOS Sierra brings a change that I'm not a big fan of. Files are now placed in /var/tmp (instead of on the desktop), which is just annoying to get to, and doesn't automatically share with the desktop on my Windows 10 virtual machine. That's annoying!

The replacement for me is Airtool by Adrian Granados. It's a lightweight application that runs in the status bar, offers packet capture in 2 clicks, an…

Pebble Time Bezel Sanding and Brushing

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I absolutely love my Pebble Time. For quick glances at my next calendar item, quick replies to text messages, and believe it or not, as a watch, it's amazing.

There's just one major drawback to the Pebble time: the bezel. It's a piece of stainless steel metal with a PVD coating, and while it's sort of tough, it's far from invincible.

Since the PVD coating has a bit of texture to it, items tend to scratch off on to it. For example, if you brush up against a wall, some of the paint will come off of the wall, and onto the watch. You think you've scratched it... until you wash it.

Eventually though, you'll scuff your watch up against something harder than the PVD coating. Zippers, wedding rings, and even my wife's Pebble Time Round (I'm a leftie, so our watches like to kiss when we hold hands) are all capable of scratching the delicate PVD coating.



The solution, which I first saw in this YouTube video, and then later in this Imgur album, is to sand off …

Printrbot Control with OctoPrint and Pi Link

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I've been a big fan of Printrbot since the beginning. I've owned a Printrbot Original, Printrbot Simple, Printrbot Simple 1405, and currently a Printrbot Play. After becoming a fan, I even got to "moonlight" on their support team for a year.

As with just about any 3D printer, Printrbots connect to a computer with USB, and the commands for the print are fed to it serially throughout the duration of the print with a program like Pr0nterface, Repetier-Host, or Cura. Interrupt that stream of commands, and your print stops, which means you have to start over. The stream can be interrupted by letting your computer fall asleep, closing the print software, or even by plugging in another USB device (like an iPod).
The solution is a $35 Raspberry Pi and an open-source program for it called OctoPrint. The Raspberry Pi takes the place of your computer (being a tiny computer itself), and OctoPrint is accessed via a web browser over the network. Not only do you minimize the risk o…