Posts

Cellular Failover with an Android Phone and Raspberry Pi

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The great CenturyLink outage of late 2018 is under way. At the time of this writing, we're 16.5 hours in, and I'm tired of using my Android phone as a Wi-Fi hotspot. I want my network back up.

Fortunately, I have some tools to work with. I have a spare Android phone complete with an unlimited data plan (T-mobile ran a 3rd line for free promo a couple years ago) and a spare Raspberry Pi (seriously who doesn't have several of those kicking around). The idea here is that we can use the Raspberry Pi to turn that USB cell phone tether into ethernet, so our router can treat it basically like a modem.

Now in my setup, I have a "WAN2" port on my Ubiquiti UniFi Secure Gateway. If WAN1 goes down, the USG will automatically flop over to WAN2. You might have do to "manual failover" when your ISP goes down, but shoot, even my CenturyLink DSL modem has a configurable WAN2 port, so it all depends on your setup.

So let's get to work, and get some packets flowing on…

Aliasing MAC Addresses with Wireshark

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I love Wireshark, but one thing is for sure: tracking 802.11 conversations with my human brain is difficult. Coloring rules help, but I find it very difficult to remember which MAC address is which wireless station.

Fortunately, Wireshark has the ability to alias IP and MAC addresses! These are defined in the "ethers" file. You should be able to do nearly the same thing on Windows, but here's how to do it on macOS.


1. Open a terminal, and run:
nano ~/Users/your_username/.config/wireshark/ethers



2. Define the MAC address and the desired alias in the file. Separate the MAC and alias with any number of spaces. Aliases themselves can't contain spaces.

ab:cd:ef:12:34:56 (AP)Aruba205H
12:34:56:ab:cd:ef (Client)Nokia6.1
ab:12:ef:cd:34:56 (Client)MacBookPro



Tip: I like to lead with either (AP) or (Client) so I can immediately tell which side is talking.

3. Save the file by pressing Ctrl+X, then Y for yes, then Enter.
4. Restart Wireshark, and now friendly, readable aliases will…

Sounding Good on the Phone

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As a Sales Engineer and part-time Technical Trainer (which is what sales engineering basically is), I spend a LOT of time talking to customers on the phone. Usually, these conversations are recorded for reference, and they're typically done in conjunction with video or screen sharing.

Usually, calls are done with a computer-based conferencing tool like GoToMeeting, Zoom, Cisco WebEx, Microsoft Teams, or Google Hangouts. Long ago, I decided that if I was going to spend so much time on the phone, why not ensure that my audio was crystal clear? This would make everyone on the call more comfortable, it would make me easier to understand, and it would make me sound more professional.

Here's where my setup is today:

Yeti Blue MicThis mic is about $140 on Amazon, but you can find it on sale for as low as $80, which is what I paid for mine. It connects with MiniUSB, and functions as both a microphone and soundcard. It also has a 3.5mm headphone jack on the bottom, which gives both ins…

Reading Mileage from a 1997 Volvo 850R

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I'm a huge fan of Volvo 850's, but they aren't without a few flaws. One of them is the odometer: the mechanical odometer is driven by a small electric motor in the gauge cluster, and it has a tiny nylon gear that loses a tooth, causing it to stop counting miles.

Fixing it costs a couple of bucks, but it's a pain. The dash has to come out, which takes a couple of hours, and comes with the inherent risk of breaking things. As a result, there are many 850's on the road with inaccurate odometers.

Pre-OBDII Volvo 850's (1993-1995) provide the ability to plug in a fly wire under the hood, press a special button pattern, and then watch an LED blink back the mileage, which is stored digitally in the gauge cluster. Then, you can fix the odometer gear, and roll up the mileage to the correct number in the process.

Sadly, OBDII Volvo 850's (1996-1997) lack the fly wire, button, and LED. Fortunately, there's a way to read the mileage through the OBDII port with an E…

Octets, Bytes, and Nibbles in MAC Addresses

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It's helpful to use terms like octet and nibble to refer to positions in a MAC address or BSSID, but I can never remember which is which. This chart labels them so I can remember.

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.