SemFio Networks - SemFio

The 802.11ax Trigger Frame

12/9/2019

802.11ax - The Trigger Frame - SemFio Networks

In 802.11ax communications, the trigger frame is used for multiple purposes. One of them is to allocate ressources for a specific multi-user OFDMA transmission.

In this article, we are going to take a deeper look at some of the interesting fields we will find in this trigger frame. For more details, you can look at section "9.3.1.22 Trigger frame format" of the 802.11ax-D4 IEEE draft.

The Frame Format

Here is the format of the frame:

The trigger frame is a broadcast frame and you can use this filter to fidn it in Wireshark: wlan.fc == 0x2400.

It has the following characteristics:

Type: Control (wlan.fc.type == 1)
Sub-Type: 2 (wlan.fc.subtype == 2)

Here is what you see in the packet capture:

Two information fields are very interesting:

The Common Info
The User Info

Let's take a deeper look at what they contain.

The Common Info Field

Here is the structure of the common info field:

Here are some of the interesting sub-fields:

UL Length: it indicates the length of the expected response frame (filter = wlan.trigger.he.ul_length)
UL BW (Up Link Bandwidth): it indicates the bandwidth of the transmission (filter = wlan.trigger.he.ul_bw)
- 0 means 20MHz
- 1 means 40MHz
- 2 means 80MHz
- 3 means 80+80MHz or 160MHz
GI and LTF Type: it indicates which guard interval and long training field will be used for the transmission (filter = wlan.trigger.he.gi_and_ltf_type)
- 0 means 1x HE-LFT + 1.6us GI will be used
- 1 means 2x HE-LFT + 1.6us GI will be used
- 3 means 4x HE-LFT + 3.2us GI will be used
AP TX Power: when the AP sends the trigger frame, it will provide the Tx Power used to transmit the frame (filter = wlan.trigger.he.ap_tx_power)

Here is an example of a common field:

In this example we can see that we will be using a 20MHz wide channel, 2x LFT + 1.6us GI for the multi-user communication. The AP used a combined transmit power of 21dBm to send the trigger frame.

The User Info Field

The User Info field provides details on each client devices participating in the same upcoming OFDMA transmission.

Here are some of the interesting sub-fields:

Association ID: indicates the association ID of the addressed STA (filter =

wlan.trigger.he.user_info.aid12)

RU Allocation: indicates the size and location of the ressource unit allocated for the addressed STA (filter = wlan.trigger.he.ru_allocation)
UL MCS: indicates which MCS is expected the STA to use (filter = wlan.trigger.he.mcs)
SS Allocation: indicates the number of spatial streams to be used by the addressed STA. You will have to minus 1 to the number. (filter = wlan.trigger.he.ru_number_of_spatial_stream)
Target RSSI: indicates the the expected RSSI of the PPDU to be sent on the RU (filter = wlan.trigger.he.target_rssi)

Here is an example of a common field:

In this example, we can see that 2x STA will be sharing the 20MHz channel in 2x 106-tones Ressource Units.
Both client devices are expected to be using MCS 11, 1 spatial streams. And their PPDUs is expected to be received with a RSSI of -30dBm.

Some Additional Resources

Here are a couple of interesting articles you can read to learn more about it:

UL OFDMA Basic Trigger Frame and Multi-STA-BlockACK From Gjermund Raeen: https://gjermundraaen.com/2019/08/26/ul-ofdma-basic-trigger-frame-and-multi-sta-blockack/
LENGTH - The Underestimated Parameter in 802.11 by Gjermund Raeen: https://gjermundraaen.com/2019/11/19/length-the-underestimated-parameter-in-802-11/
802.11ax remote packet captures: https://www.semfionetworks.com/blog/80211ax-remote-packet-captures-using-the-jetson-nano
Clear To Send Podcast Series on 802.11ax: http://cleartosend.net/ax
Identifying 802.11ax support using Wireshark by Rowell Dionicio: https://rowelldionicio.com/identifying-802-11ax-support-wireshark/

Thank you for reading!

written by François Vergès

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Wireshark - Find out the data rate of an 802.11ax Data Frame

12/7/2019

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As you know, all data rates are changing with 802.11ax, Hence, the new MCS table you can find here: https://www.semfionetworks.com/blog/mcs-table-updated-with-80211ax-data-rates

In this article, we will see how we can figure out the data rate of a specific 802.11ax data frame.

If you want to know how to capture 802.11ax data frames, refer to this article first: https://www.semfionetworks.com/blog/80211ax-remote-packet-captures-using-the-jetson-nano

The HE RadioTap header provided by the Intel AX card installed on Ubuntu is great and provides a lot of valuable information that we will use to figure out the data rate.

Step 1 - Filter to find the 802.11ax Data Frames

First, once you have your 802.11ax packet capture in Wireshark, you can filter 802.11ax Data Frames by using the following filter: wlan.fc.type == 2 && (radiotap.he.data_1.ppdu_format == 0x0 || radiotap.he.data_1.ppdu_format == 0x2)

wlan.fc.type == 2 means that we are filtering for 802.11 Data Frames
radiotap.he.data_1.ppdu_format == 0x0 means that we are filtering for HE Single User PPDUs.
radiotap.he.data_1.ppdu_format == 0x2 means that we are filtering for HE Multi User PPDUs.

Step 2 - Select the frame you want to analyse

We simply need to choose the frame we want to analyse. Once you have selected the frame, look for the RadioTap Header in the bottom panel in Wireshark:

Step 3 - Find the transmission details in the RadioTap header

In order to be able to find the exact Data Rate used, we need these pieces of information:

MCS Index
Guard Interval
Channel Width or Ressource Unit size
Number of Spatial Streams

We can find these information in the RadioTap Header.

The MCS Index is located in the "HE Information/HE Data 3" section. In this example, we have a MCS Index of 9:

The Guard Interval and the Channel Width/Ressource Unit size are located in the "HE Information/HE Data 5" section. In this example, we have a GI of 1.6us and a channel width of 20MHZ:

The number of spatial streams information is located in the "HE Information/HE Data 6" section. In this example, we are using 1 spatial stream:

Step 4 - Reference the MCS Table to find the exact Data Rate

Once you have all of the transmission details, you can reference the 802.11ax MCS Table and find out exactly which data rate is used for the communication.

To summarize, here are transmission details what we have for our example:

PHY: 802.11ax
MCS Index: 9
Guard Interval: 1.6us
Channel Width: 20MHz (OFDMA)
Number of Spatial Streams: 1

If we reference the MCS Table with this information, we see that the data rate is 108.3Mbps:

Bonus - Configure your Wireshark column to display these transmission details

As a bonus, you can add the following columns to your Wireshark to display the transmission details we have talked about here:

radiotap.he.data_3.data_mcs: For the MCS Index
radiotap.he.data_5.gi: For the Guard Interval
radiotap.he.data_5.data_bw_ru_allocation: For the Channel Width or RU Allocation
radiotap.he.data_6.nsts : For the number of Spatial Streams

Here is what it will look like:

Thank you!

François Vergès

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Wi-Fi Design Day - Sydney

12/6/2019

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I was invited to attend and present at the Wi-Fi Design Day in Sydney organized by Ekahau and Dicker Data. I would like to thank Grant, Antony, Darko and the rest of Ekahau's team for organizing such a nice event. We presented at the Opera House, which is such an iconic venue in Sydney!

Stephen Cooper and I talked about Wi-Fi 6 and did a demo showcasing OFDMA spectrum activity and packets.

You can find a copy of my presentation slide deck here:

Here is a copy of Stephen's presentation. He talked about Wi-Fi 6 Key Features:

Once I have a little more time, I will analyze the packet capture we did during the presentation and present my findings here.

In the meantime, here are a few pictures from the event:

At the end of the presentation, we asked attendees owning a Wi-Fi 6 device to connect to our Wi-Fi 6 network and generate some traffic (speedtest). We looked at the activity on the spectrum analyzer. We also took a packet capture to show them a couple of interesting HE packets.

On my way home, I took some time analyze and get some statistics out of these packets. Here are the results:

Note: No Multi-User data frames were captured

See you next time Australia!

Cheers!

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WLAN Pi - Bridge Wi-Fi Hotspot to Ethernet Interface

10/11/2019

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In my previous article, I was explaining how you could configure the WLAN Pi to be used in a hotspot mode. Following the article, the configurations have been added to the new WLAN Pi image (starting at 1.7) and it is now part of the default WLAN Pi image (Thanks to Nigel Bowden and Jerry Olla).

One of the feedback I got is that the Wi-Fi interface is not bridged to the ethernet interface. So, if you are connected to the Wi-Fi network, you will not be able to communicate back to the wired network.

So, in this article, I explain how you can configure the WLAN Pi to allow the Wi-Fi interface to be bridged to the ethernet interface. To make it work, I received huge help from Florent Lassia.

The first thing to do is to enable ip forwarding. To do so, open the /etc/sysctl.conf file and uncomment the following line:

This will enable traffic forwarding between the wlan0 and eth0 interfaces.

Then, we need to modify the DHCP server configurations in order to add the default gateway and DNS server information. To do so, open the /etc/wlanpihotspot/dhcp/dhcpd.conf file and add the following lines:

Once this is done, you will have to reload the DHCP service on the WLAN pi using the following command:

Here is the output you should see from running this restart test:

Then, we need to configure the firewall to allow communications between the two interfaces. In order to do so, you need to modify a line in the /etc/default/ufw file. You will need to set the default forward policy to ACCEPT. It is set to DENY by default.

Finally, we need to configure a NAT so that all the traffic coming from the Wi-Fi hotspot is natted behind the eth0 IP address. In order to do so, we need to modify the /etc/ufw/before.rules file. At the bottom of the file, after COMMIT, add the following lines:

Once this is done, you can test your configurations by disabling and re-enabling the firewall. In order to do so, use the following command:

Here is the output you should get:

Note: the configuration of both the /etc/default/ufw and /etc/ufw/before.rules will not revert back to the default if you go back to the normal mode of the WLAN Pi. You will have to manually re-configure them if you don't want to allow them in the normal mode.

You can now reboot the WLAN Pi into the hotspot mode using the buttons and it should reboot in the Hotspot mode supporting these bridging configurations. You should be able to connect a client device to the Wi-Fi network and get network connectivity to the LAN if the WLAN Pi is connected to your LAN.

The plan now is to integrate this into the next version of the WLAN Pi image so it could be enabled by default in the Hotspot mode. To be continued…

written by François Vergès

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802.11ax Remote Packet Captures using the Jetson Nano

10/9/2019

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This solution will allow you to perform remote 802.11ax packet capture from your own laptop using the Jetson Nano.
The benefit of using the Jetson Nano (and the Intel AX200 Wi-Fi card) to perform 802.11ax packet capture is that you get a lot more information in the RadioTap Header you get.
The benefit of doing it remotely is that you never need to directly interact with the Jetson Nano OS (no need for keyboards, screens nor mouses)

To make it work, I received help from a couple of talented guys:

They pretty much found the solutions, I was just the one implementing it ;)

Hardware Requirements

Here is the equipment you need to make it work:

A Nvidia Jetson Nano
An Intel AX200 802.11ax Wi-Fi card
Dual band antennas (Here is the one I use)
OPTIONAL: A case for the Jetson Nano (Here is the one I use)

Initial Setup of the Jetson Nano

Here is what you need to do on the Jetson Nano right after you have loaded the image on the SD card and created your username name:

Initial Wireshark Configurations (On your laptop)

Then you need to configure Wireshark to do the following:

Establish a SSH connection between your laptop and the Jetson Nano
Run a tcpdump remotely on the Jetson Nano
Stream the packets back to your laptop

Thankfully for us, Wireshark has a plugin you can install to make it work. It is called SSHdump. You need to make sure that it is checked when you install Wireshark (Under the "Tool" section) (especially when you install Wireshark on Windows).

Capture Time!

When you are ready to perform the packet capture, first you need to SSH into your Jetson Nano and set the Wi-Fi card into monitor mode on the proper channel using the proper channel width:

Then you can open Wireshark. In the interface list, look for "SSH remote capture: sshdump" and click on the setting gear to modify its settings:

Under the server tab, enter the IP address of the Jetson Nano and enter "22" as the port used (since we are using SSH default port here):

Under the Authentication tab, enter the username and password to connect to your Jetson Nano.
Note: You will have to re-enter your password every time you want to do a packet capture.

Under the "Capture" tab, you need to enter the following command in the "Remote capture command" field: /usr/sbin/tcpdump -i wlan0mon -U -w -. Make sure that you also check the "Use sudo on the remote machine" check box:

Then you can click on "Start" and it will start capturing packets and streaming them back to your Wireshark session.

Additional Resources

Here are additional resources you can visit to get more details:

Remote Wireless Capturing with a Jetson Nano from Gjermund Raaen: https://gjermundraaen.com/2019/10/01/remote-wireless-capturing-with-a-jetson-nano/
Capturing 802.11ax with jetson nano from Gjermund Raaen: https://gjermundraaen.com/2019/09/25/capturing-802-11ax-with-jetson-nano/
Using the WLAN Pi to scan for networks in WiFi Explorer Pro from Adrian Granados: https://www.adriangranados.com/blog/wlanpi-as-a-sensor
You too can have a sub-$200 802.11ax client from John Kilpatrick: http://wifi.hypergeek.net/you-too-can-have-a-sub-200-11ax-client/
How to setup Wi-Fi 6 sniffer Wireshark in Ubuntu from Tiger Lee: https://wifilogic.wordpress.com/2019/09/21/how-to-setup-wifi6-sniffer-in-ubuntu/
The State of Wi-Fi 6 in Practise (WLPC EU Presentation): https://www.cleartosend.net/wp-content/uploads/2019/10/Wi-Fi6_in_the_real_world_wlpc_prague_2019.pdf

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Customize your WLAN Pi

8/3/2019

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In this article, I will show you how you can customize your WLAN Pi and make it your own! Feel free to comment and tell me how you guys customize yours.

Here is the video tutorial that explains these customizations.

Create Your Own User

Creating your own user allows you to have your own password and your own home directory. It is more secure and you are free to modify your profile as much as you want.
Note: I would also recommend you to change the default password for the wlanpi account.

In order to create a new user, you need to ssh into the WLAN. By default, if you connect the WLAN Pi to your laptop via the USB connection, this should establish an Ethernet over USB connection and your laptop should receive an IP address in the 192.168.42.0/24 IP address subnet.

You can now ssh into the WLAN Pi from your laptop using the default username and password:

Username: wlanpi
Password: wlanpi

Once connected, we will create a new user and give this new user some privileges.

Use the following command to create a new user: sudo adduser username
In the following prompts, specify which password you want to use for this user
Use the following command to give this user sudo privileges: sudo usermod -aG sudo username
Finally, try to connect using this new username and password: su - username

Finally, we will modify the user PATH so we can get access to some basic commands such as ifconfig, iwconfig or iw.

In the home directory of the user, open the .profile file using the following command: sudo nano .profile
Modify this file by adding the following line at the end of the .profile file: PATH=$PATH:/sbin:/usr/sbin
Save and close the .profile file
Once back in the shell, reload the profile using this command: source .profile
You should now be able to use the ifconfig command

Change the Hostname of the WLAN Pi

The name of the WLAN Pi is configured under the /etc/hostname file. In order to change the hostname permanently, you will have to modify this file:

Open the file using the following command: sudo nano /etc/hostname
Modify the hostname to your liking
Save and close the /etc/hostname file
Reboot the WLAN Pi

When the WLAN Pi comes back online, you should be able to ssh into it and see the new hostname. The new hostname will also appear on the home screen:

One more thing you need to do here. You need to change the hostname used for dns resolutions. If you don't, you will realize that it takes longer for sudo commands to execute. To do so, open the /etc/hosts file and replace "wlanpi" by your new name:

Create Your Aliases

On linux, an alias allows you to create your own command shortcut. For example, instead of typing ls --color=auto, you could create the following alias : alias ls='ls --color=auto'. Then when you type ls, it will execute the full command line.

Everyone has their own set of aliases they like to use. Here I will just share the ones I use. Feel free to use them as well and feel free to create your own.

In order to create your aliases, you need to do the following:

ssh back to the WLAN Pi using your new user: ssh francois@192.168.42.1
Once connected to the WLAN Pi, modify the .bashrc file using the following command: nano .bashrc
Add your aliases at the end of this .bashrc file
Save and close the .bashrc file
Reload your bash profile using the following command: source .bashrc
Validate that your aliases have been applied using the alias command.

Here is the list of my aliases:

Customize Your Prompt

You can also customize your prompt to your liking. You can go wild here. I actually like it simple. I like the default prompt. I just changed the colors for fun!

In order to change the look of your prompt, you can do the following:

From the WLAN Pi and from your user home directory, open the .bashrc file using the following command: nano .bashrc
Inside the .bashrc file, scroll down until you find the PS1 variable. Then replace the value of that PS1 variable with whatever you would want to use.
Save and close the .bashrc file
Reload your bash profile using the following command: source .bashrc

Here is the PS1 value that I used for mine:

You can use the following website to customize your prompt to your liking: https://www.howtogeek.com/307701/how-to-customize-and-colorize-your-bash-prompt/

Change the Picture Displayed when Booting

When the WLAN Pi, you can see an image appearing on the screen. By default, it is the logo of the Wireless LAN Professionals company.

However you could change it to something else if you want to.

First, you need to retrieve the original image used. It is located on the WLAN Pi at the following location: /home/wlanpi/NanoHatOLED/BakeBit/Software/Python/wlanprologo.png

In order to retrieve this image, I used the scp command from my laptop. This command allows you to copy files from the WLAN Pi to your laptop over an SSH connection. Here is the command I used:

This will copy the image on your laptop. Then I studied the picture and retrieve the resolution of it: 128 x 64.

Once I knew the resolution, I created my own image using Illustrator. I actually created the two following ones:

Then you need to replace the image that's currently on the WLAN Pi with your new image, freshly created. You won't be able to do it in one shot because you don't have the permission to do so over scp.

So first, you need to transfert the new image back to the WLAN Pi. I transfered mine back to my home directory using the following command:

Second, you need to ssh back into the WLAN Pi.

And finally, you need to replace the old image with the new one. I used the following command to do so: sudo cp WLANPi-SemFio-StartUp.png /home/wlanpi/NanoHatOLED/BakeBit/Software/Python/wlanprologo.png

Note: It is very important here that you use the same destination name. The picture name will still be the same as before (wlanprologo.png) but its content will be different. I tried to do it a different way by changing the configuration files of the NanoLED program, but it didn't work properly.

Then, you can reboot your WLAN Pi, you should see the new picture when the WLAN Pi boots.

Ideas

In order to improve this customization, I would like to create a Python script that automates all of these tasks. I will then be able to run the script every time I update my WLAN Pi to a newer image and I will be able to retrieve my customizations.

If you manage multiple WLAN Pi, you could also create a Python script that you could run on multiple WLAN Pi to speed up their configurations and customizations.

Please share how you like to customize yours!

Thank you for reading!

Written by François Vergès

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Python - How to Connect to a Cisco WLC (Aireos)

7/25/2019

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This is a very simple article just explaining how you can connect to a Cisco WLC (aireos) using a python script.

You could use this as a first step in developing more advanced Python scripts to monitor or configure your Cisco Wireless Lan Controllers.

I am still learning Python so this might not be the only and easiest way to do it!

Note: starting with version 8.8, you could interact with your Cisco WLC in a easier way using YANG models. See this presentation from Cisco Live: https://www.ciscolive.com/c/dam/r/ciscolive/us/docs/2018/pdf/BRKEWN-2050.pdf

Prerequisites

We will assume that you have already Python installed on your computer. I would also advise you to use virtual environment when developing Python scripts on your computer.

Here is the tutorial I have followed in order to setup my laptop (macOS) for Python programming: https://developer.cisco.com/learning/lab/dev-mac/step/1

Here are the program and libraries we will be using here:

Python 3.7
netmiko

Here is how I setup a virtual environment for Python 3.7 on my laptop:

Here is how I installed the netmiko library within this new virtual environment:

Code - How To

Here is the Python code you will need to in order to connect via SSH to a Cisco WLC. Obviously you need to gather this information first:

IP address of the WLC
Username allowed to SSH into the WLC
Password associated with that user

In this example, we are using the object called ConnectHandler from the netmiko library to establish an SSH connection to the WLC (192.168.20.2).

Once connected, we are sending the command "show ap summary" and we are displaying the output of this command.

Go a Step Further

Connecting to the Cisco WLC could be the first step in a more complex script. Therefore, I have done the following in order to ease the process:

Created a configuration file where I keep my WLC details (IP address, username and passwords)
Created a script that I called ssh_wlc.py that defines function that will establish the connection based on the WLC configuration file

I then re-use my script as a "library" whenever I work on a script and I need to connect to a Cisco WLC.

Note: Python 3.5+ is required here since we are using PEP 484 type hints.

Here is what my configuration file looks like (I used xml so it is easier to parse):

Here is what my ssh_wlc.py script looks like:

As I continue to learn more about Python, I will continue to share it with you guys on the blog.

If you know other alternatives to do the same thing, please feel free to add a comment.

Thank you!

written by François Vergès

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WLAN Pi - Setup a Wi-Fi Hotspot

7/22/2019

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Update (October 2019)

Thanks to Florent Lassia, we were able to configure the Wi-Fi NIC to bride to the Ethernet NIC. In the Hotspot mode, you can now have your Wi-Fi hotspot running, connect a client device to that Wi-Fi network and receive network connectivity to the LAN if your WLAN Pi is connected to the LAN via its Ethernet interface. We have detailed how to do it on this blog post: https://www.semfionetworks.com/blog/wlan-pi-bridge-wi-fi-hotspot-to-ethernet-interface

Udpate (August 2019)

Thanks to Nigel Bowden and Jerry Olla. This feature has been incorporated into the image of the WLAN Pi OS starting with version v1.7. Visit this link to see how it has been implemented: https://github.com/WLAN-Pi/wlanpi-hotspot

It has also been implemented as a new "Action" mode in the new NanoLED menu: https://github.com/WLAN-Pi/wlanpi-nanohat-oled

I love the fact that the WLAN Pi is very small and compact. It is very easy to have it always available with me in my backpack. So I like to use it as a Wi-Fi source when I measure wall attenuation. In order to do so, you need to setup a Wi-Fi hotspot so that the WLAN Pi can broadcast a Wi-Fi signal when you connect a Wi-Fi NIC.

In this article, I will explain how to configure the WLAN Pi so you can use it as a Wi-Fi hotspot. You could then use your WLAN Pi to perform the following:

Use it as a source to measure wall attenuation (see this article by Nigel Bowden for more details on how to do these measurements: https://www.ekahau.com/blog/2015/09/07/wi-fi-planning-walls-and-dbs-measuring-obstruction-losses-for-wlan-predictive-modelling/)
Use it to perform Wi-Fi speedtests (I personally use this to show the students what a typical OFDM signal looks like on the spectrum)

Here is the video tutorial that explains the whole setup. You can also find the same steps detailed in this article.

Initial Steps

I started this configuration from scratch so you can (hopefully) replicate it on your end. I started from the newest wlanpi image available on github. Follow these steps to start the process:

Download the latest version of the wlanpi image on this website: https://github.com/WLAN-Pi/wlanpi/releases
Load it unto the microSD card that you will use for your wlanpi (I use the program called etcher on macOS)
Insert the microSD card into the wlanpi
Connect the wlanpi to your network (via the ethernet interface)
Connect the Wi-Fi NIC to the wlanpi (via the USB port)
Power the wlanpi ON

Here is a picture of my setup (I connected the wlanpi directly to my laptop):

Once the wlanpi is UP and RUNNING, you should be able to see the IP address that the wlanpi received on its Ethernet adapter. Use this IP address to establish an SSH connection between your computer and the wlanpi. By default, the following credentials are used to connect to the wlan:

Username: wlanpi
Password: wlanpi

Once connected, we will create a new user and give this new user some privileges.

Use the following command to create a new user: sudo adduser username
In the following prompts, specify which password you want to use for this user
Use the following command to give this user sudo privileges: sudo usermod -aG sudo username
Finally, try to connect using this new username and password: su - username

Finally, we will modify the user PATH so we can get access to some basic commands such as ifconfig, iwconfig or iw.

In the home directory of the user, open the .profile file using the following command: sudo nano .profile
Modify this file by adding the following line at the end of the .profile file: PATH=$PATH:/sbin:/usr/sbin
Save and close the .profile file
Once back in the shell, reload the profile using this command: source .profile
You should now be able to use the ifconfig command

Configure Hostapd

In order to configure the Hotspot, we are going to use a linux program called hostapd. This program should already be installed on the wlanpi based image.

1 - Verify that the hostapd is installed by using the following command: dpkg --list | grep hostapd

If hostapd is not installed, you can install it using the following command: sudo apt-get install hostapd

2 - Then, we need to configure hostapd so it create a Wi-Fi network. In my case I create a network on channel 36 called "Allez Les Bleus". I defined it on 5GHz as I would use the tool to perform my wall measurements attenuations. In order to modify the configurations, you need to modify the file called /etc/hostapd.conf. You can open it with nano to modify it: sudo nano /etc/hostapd.conf

If you want to modify other settings, feel free to take a look at the hostapd documentations: https://w1.fi/cgit/hostap/plain/hostapd/hostapd.conf

Configure the Network Interfaces

Now we need to modify the way the W-Fi NIC interface (wlan0) is configured. By default, it will be configured to be used in monitor mode in order to perform Wi-Fi analysis. In order to use it to start up a hotspot, we need to change its configuration and give it an IP address.

1 - Validate that the wlan0 interface is UP (it should be up if you connected the NIC) using the following command: ifconfig.

2 - The network interfaces configurations are located in the following file: /etc/network/interfaces. Update the wlan0 configurations as follow by opening the file with nano: sudo nano /etc/network/interfaces

Feel free to choose whichever IP network you want to use.

Note: some Engineers had to add the following line in the /etc/network/interface file in order to make it work: hostapd /etc/hostapd.conf. You could try it out if this is not working out for you after the first try.

Configure the DHCP Server

This task gave me a little bit more work. I originally tried to make it work with dnsmasq but failed. I couldn't make it work. So I started to look at alternatives and came across a program called isc-dhcp-server. It also turns out that the package is already installed on the wlanpi base image. In this section, we will explain how to configure the isc-dhcp-server to provide IP address to our hotspot Wi-Fi network.

1 - Verify that the isc-dhcp-server is installed by using the following command: dpkg --list | grep isc-dhcp-server

2 - We need to tell the isc-dhcp-server that we will be expecting to receive DHCP requests on the wlan0 interface. To do so, modify the /etc/default/isc-dhcp-server file as follow: sudo nano /etc/default/isc-dhcp-server

2 - Then, we need to configure the new DHCP pool that we will be using for our Wi-Fi Hotspot network. To do so, we need to update the following configuration file: sudo nano /etc/dhcp/dhcpd.conf

Make sure that the pool is within the subnet you are using for the wlan0 interface.

Test & Validate

All we have to do now is test and validate that everything is working well.

1 - Start the hostapd application using the following command: sudo hostapd -d /etc/hostapd.conf

2 - Validate that the SSID is broadcasting. In my case, I used my iPad to validate that the "Allez Les Bleus" SSID was broadcasting. You can also use a Wi-Fi scanner to validate that it is broadcasting on the configured channel.

3 - Try to connect to this SSID and see if you receive an IP address within the pool configured. In my case, I used my iPad to connect and I received the following IP address: 192.168.88.100.

4 - Navigate the http://192.168.88.1 to validate that you can reach the HTML5 speedtest installed on the wlanpi. From there, you can start a speedtest and validate that everything works fine.

5 - (optional) Open up a spectrum analyzer and look at the activity on the channel while performing the speedtest. This can help you to understand what a Wi-Fi signal (OFDM) looks like on the spectrum.

Run it at Startup

We will use the crontab program to tell the OS to start hostapd when the WLAN Pi boots up.

1 - Enter the following command to configure the crontab configuration file: sudo crontab -e
2 - In the configuration file, add the following line: @reboot sudo hostapd -d /etc/hostapd.conf

3 - Save and close the file
4 - Reboot and see if it works!

Ideas

Working on this a couple of other ideas came to mind on how we could improve this:
1 - Work on a script that would active the hotspot automatically when the Wi-Fi NIC is connected
2 - OR EVEN BETTER, reprogram one of the button to start the hotspot when pressed and disable it when pressed again. UPDATE: this is now part of the standard WLAN Pi image starting at v1.7. See https://github.com/WLAN-Pi/wlanpi/releases.
3 - Complete the configuration to bridge the Wi-Fi Hotspot to the Ethernet interface so we can pass traffic through. You could then use it to setup your own local connection when the Hotel Wi-Fi is bad ;). UPDATE: we made it work, check out this blog post: https://www.semfionetworks.com/blog/wlan-pi-bridge-wi-fi-hotspot-to-ethernet-interface.

Please let me know if you have more ideas and please let me know if you have the skills to make the three listed above happen!

I hope this can be useful for some.

Thank you!

written by François Vergès

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Setup Cisco Catalyst 9800 Controller On Your Laptop

6/19/2019

3 Comments

In this article, we will explain how to install the new Cisco Catalyst 9800-CL controller on a VM (under VMFusion) on macOS.

The goal here is to have a lab controller that you can bring with you wherever you go and can be booted anytime and intended to be used for testing purposes.

This is the first article of a series of Cisco Catalyst 9800-CL article.

Note: If you want to know how to set it up on a VMware ESXI platform, please check out Rowell Dionicio's article: https://rowelldionicio.com/deploying-cisco-catalyst-9800-controller-on-vmware-esxi/

Step 1: Download the Controller Image

The first step is to download the new Cisco Catalyst 9800-CL Wireless Controller for Cloud. The latest version available to me was called Gibraltar-16.11.1b. It might be different for you if you are downloading it at a later date.

Here is the link (you will have to log in using your Cisco credentials): https://software.cisco.com/download/home/286322605/type/282046477/release/Gibraltar-16.11.1b

For this setup, we will download the .iso file. Note that you can now download the controller code for free. The licences are not tied to the AP.

Step 2: Create a New VM in VMWare Fusion VM

Note: In this article, we will present how to create a VM to support the new Wireless controller using VMWare Fusion on MacOS.

Open VMWare Fusion, and select the menu “File / New…” to create the new VM. In the new window opening, select the “Create a custom virtual machine” as shown below:

The operating system to select is “Linux / Other Linux 4.x or later kernel 64-bit” as shown below:

Select “Legacy BIOS” as the boot firmware as shown below:

Select Create a new virtual disk as shown below:

Validate that all the settings are good and click on Finish. VMware will ask you to save your vm and to choose a name. Note: I have chosen “C9800-Lab” for my VM name.

Step 3: Change the VM Settings using the GUI

We are now going to use the GUI to adjust the RAM allocated to the VM and load the iso file. We need to change the default settings to allocate at least 4Gig of RAM. In order to do so, click on the settings icon located on the top-righthand corner of the Virtual Machine Library window:

Click on the “Processors & Memory” icon to change the RAM settings:

Adjust the Memory to 4096MB (Note: this is aimed to be used in a lab environment, please refer to Cisco deployment guides in order size the VM properly):

Click on “Show All” to go back to apply the new settings.

Then click on “CD/DVD (IDE)” in order to load the iso file previously downloaded on Cisco website:

In the drop down menu, click on “Choose a disc or disc image…” and select the .iso file download before (the name should look like this: C9800-CL-universalk9.16.11.01b.iso).

Click on “Show All” to go back to apply the new settings.

Step 4: Change the VM Settings Using the Configuration File (.vmx)

Before we start the VM, we need to adjust the network settings. In my case, the network settings were greyed out in the VM settings. So I couldn’t modify them using the GUI. I had to modify the configuration file of the VM in order to adjust the network settings.

On macOS, the VM configuration file was located at the following location (/replace "C9800-Lab" by the name your chose for your VM and "francoisverges" by your macos username/):

Here is what we need to do:

Network Adapter 1: Configure the first network interface as a “custom” interface on a local network. This will be used as the management interface of the controller.
Network Adapter 2: Configure the second network interface behind the Wi-Fi card. This will be used to connect the Wi-Fi clients to the internet.

In order to configure your VM network interfaces, you will have to know the name of the interfaces used on your Mac. Open your favourite terminal application and use the `ifconfig` command in order to find it out. In my case, en0 is the name of the Wi-Fi interface and en7 is the name of my ethernet interface:

In your terminal application, open the VM configuration file in order to change its configuration:

Here is how to configure the first network adapter in the configuration file, change your configuration file accordingly:

Here is how to configure the second network adapter in the configuration file, change your configuration file accordingly:

Here is how the network interfaces were configure on my macbook:

Step 5: Start the VM for the First Time

In order to start the VM for the first time, go back to the settings icon located on the top-righthand corner of the Virtual Machine Library window:

Select the “Startup Disk” menu:

Select the “CD/DVD" option and click on “Restart” to start the VM for the first time as shown below:

The controller will boot. The first time, VMWare Fusion might ask you to enter your MacOS password a couple of time. Once the bootup process will be done, you will be ready to perform the initial configurations.

Step 6: Catalyst 9800 Initial Setup via CLI

I usually like to perform the inital setup via CLI. The new Catalyst 9800 allows you to do it. But first, you need to decline the autoinstall.
When asked to start the initial configuration dialog, write "no". Then press RETURN when asked to terminate the autoinstall. Press RETURN one more time and you should then see the WLC prompt:

Then you will need to configure the following:

Configure the enable password
Create an admin account
Configure the network interface G1
Configure a default route
Configure the country code
Configure which interface will be used for management purposes (G1 in our case)
Generate the certificate that will be used to establish DTLS connections with the APs

Use the following commands in order to configure all these items:

Notes:

The IP address used here is specific to my setup. Please use one relevant to your network topology.
The passwords have not been disclosed here, please replace "secret_password" and "user_password" by the passwords you want to use
Configure these items in the proper order if you want to avoid issues
The last command doesn't configure anything, it is just used to validate that the trustpoint has been generated properly
Since we are disabling the 802.11a and 802.11b radios to configure the country code, you will have to renable them later if you want your APs to be operational

Once these configurations are done on the Catalyst 9800 controller, you should be able to ping it from your laptop:

If this works well, you should now be able to open a browser, and navigate to https://10.0.0.10 to connect to the controller GUI. Use the admin username defined earlier to login and gain access to the GUI:

Mission accomplished! You should now have the controller up and running. The next step would be to add an AP and configure an SSID.

To be continued...

Resources

Cisco Catalyst C9800-CL Wireless Controller Virtual Deployment Guide: www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-8/b_c9800_wireless_controller_virtual_dg.html
Catalyst 9800 CL Install Guide: www.cisco.com/c/en/us/td/docs/wireless/controller/9800/9800-cloud/installation/b-c9800-cl-install-guide.pdf
Release Notes for Cisco Catalyst 9800 Series Wireless Controller, Cisco IOS XE Gibraltar 16.11.x: www.cisco.com/c/en/us/td/docs/wireless/controller/9800/16-11/release-notes/rn-16-11-9800.html
C9800-CL for my Homelab by Tim Saas: http://wifi-blog.com/2019/01/31/c9800-cl-for-my-homlab/

written by François Vergès

3 Comments

MCS Table (Updated with 802.11ax Data Rates)

4/11/2019

13 Comments

I recently purchased a Wi-Fi 6 device (Samsung Galaxy S10), and when I checked which date rate it was using over the Wi-Fi, this is what I got:

I wanted to find out which MCS index and which modulation was used but after doing some research online, I couldn't find any easy resources that could give me the new data rates available with 802.11ax (Wi-Fi 6). So I decided to create that resource myself.

This blog presents the results of the new MCS table updated to include all the new 802.11ax data rates. It also presents how these data rates are calculated.

Complete MCS Table

The following table includes all the MCSs data rates defined by the 802.11n (HT), 802.11ac (VHT) and 802.11ax (HE) amendments:

Here is a link to the full MCS Table: http://bit.ly/2G0DIcD

As you can see, the table is getting very big. In fact, 802.11ax is introducing 2880 new data rates. However, not all data rates will be used in the real world. In order to focus on what will be most useful to Wi-Fi Engineers, I have created some smaller tables which only focuses on sections of the complete table.

MCS Table up to 3 Spatial Streams

This table presents 802.11n (HT), 802.11ac (VHT) and 802.11ax (HE) data rates for up to 3 spatial streams:

Here is a link to the spreadsheet: http://bit.ly/2KksViN

802.11ax MCS Table

This table only presents the data rates for 802.11ax communications up to 3 spatial streams:

Here is a link to the spreadsheet: bit.ly/2Ia1Pc2

802.11ax MCS Table (OFDM)

This table only presents the data rates for 802.11ax communications when OFDM is used:

Here is a link to the spreadsheet: http://bit.ly/2VwYNSk

802.11ax MCS Table (OFDMA)

This table only presents the data rates for 802.11ax communications when OFDMA is used:

Here is a link to the spreadsheet: http://bit.ly/2VztdmU

The Math Behind It

First we need to understand how the MCS data rates are calculated prior 802.11ax. I am only going to focus on 802.11n (HT) and 802.11ac (VHT) here.

Here is the formula we can use to calculate which data rate is used for both 802.11n and 802.11ac:

Let's detail each of these variables and which value they can have for both 802.11n and 802.11ac:

HT and VHT OFDM Parameters

Now, the formula doesn't change much with 802.11ax. However, some new features will impact the way we calculate data rate for 802.11ax:

A new symbol duration is used: 12.8µs
Different Guard Intervals are used: 0.8µs, 1.6µs and 3.2µs
The size and number of data subcarriers is not the same (especially with the different RU sizes introduced by OFDMA.

Even though the formula doesn't change much, the IEEE does define 2 different formulas depending on if OFDMA is used or not. When OFDMA is not used, we can used the formula previously presented above.

Here is the formula we can used when OFDMA is used (it is pretty much the same except that we define the number of data subcarriers per RU and not per channel):

Let's now details each of these variables and which values they can have when HE (802.11ax) is used. The first table details the parameters used when OFDMA is not used. The second table details the parameters when OFDMA and resource units are used.

HE OFDM Parameters

HE OFDMA Parameters

Due to the addition of a new modulation technique (QAM-1024), 2 new MCS indexes are now available with 802.11ax:

Index 10: when the 1024-QAM modulation is used with a coding of 3/4
Index 11: when the 1024-QAM modulation is used with a coding of 5/6

Example

So now that we have this information, let's try to understand the data rate that my phone was using.
The phone is a Samsung GS10 which supports 802.11ax and up to 2 spatial streams. The AP used is an Aerohive AP630. I have configured it with an 80MHz wide channel. OFDMA is not used here because ODFMA was not activated at the time of this capture.

So based on this information, we can determine some of the variables required to calculate the data rate and narrow down the data rates that will be used by this device:

Number of Data Subcarriers for an 80MHz wide channel: 980
Number of Coded bit per subcarrier (Modulation): we don't know yet
Coding: we don't know yet
Number of Spatial Streams: 2
OFDM Symbol Duration: 12.8µs
Guard Interval: we don't know yet

So here is the list of possible data rates used by this device when connecting to this AP:

Because we know that the data rate used was 1200.95 Mbps (as indicated on the picture above), we can now determine that:

MCS 11 was used
1024QAM with a coding of 5/6 was being used
A guard interval of 0.8µs was used

Resources

Here are some resources that I have used or that can be interesting if you want to learn more about:

IEEE 802.11ax Draft D4.0 ($400): https://www.techstreet.com/ieee/standards/ieee-p802-11ax?gateway_code=ieee&vendor_id=7180&product_id=2019792
"802.11 OFDM Data Rates – The Math Behind The Numbers" great article from Renzo Notter: http://dot11.exposed/2018/11/29/802-11-ofdm-data-rates-the-math-behind-the-numbers/
MCS Table by Keith Parsons at WirelessLAN Proffesionals: https://d2cpnw0u24fjm4.cloudfront.net/wp-content/uploads/802.11ac-VHT-MCS-SNR-and-RSSI.pdf
Clear To Send Podcast - 802.11ax OFDMA Subcarriers: https://www.cleartosend.net/802-11ax-ofdma-subcarriers/
Clear To Send Podcast - 802.11ax OFDMA Resource Units: https://www.cleartosend.net/802-11ax-ofdma-resource-units/
802.11ac Missing MCSs by Jérôme Henry: https://www.youtube.com/watch?v=vTIy-rjopY8

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<<Previous

The Frame Format

The Common Info Field

The User Info Field

Some Additional Resources

Step 1 - Filter to find the 802.11ax Data Frames

Step 2 - Select the frame you want to analyse

Step 3 - Find the transmission details in the RadioTap header

Step 4 - Reference the MCS Table to find the exact Data Rate

Bonus - Configure your Wireshark column to display these transmission details

Hardware Requirements

Initial Setup of the Jetson Nano

Initial Wireshark Configurations (On your laptop)

Capture Time!

Additional Resources

Create Your Own User

Change the Hostname of the WLAN Pi

Create Your Aliases

Customize Your Prompt

Change the Picture Displayed when Booting

Ideas

Prerequisites

Code - How To

Go a Step Further

Update (October 2019)

Udpate (August 2019)

Initial Steps

Configure Hostapd

Configure the Network Interfaces

Configure the DHCP Server

Test & Validate

Run it at Startup

Ideas

Step 1: Download the Controller Image

Step 2: Create a New VM in VMWare Fusion VM

Step 3: Change the VM Settings using the GUI

Step 4: Change the VM Settings Using the Configuration File (.vmx)

Step 5: Start the VM for the First Time

Step 6: Catalyst 9800 Initial Setup via CLI

Resources

Complete MCS Table

MCS Table up to 3 Spatial Streams

802.11ax MCS Table

802.11ax MCS Table (OFDM)

802.11ax MCS Table (OFDMA)

The Math Behind It

Example

Resources

François Vergès

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