Running tcpdump on Ubiquiti Airmax Equipment

Ubiquiti Airmax gear has tcpdump included. We can easily use it to capture packets to a file and then use SCP from the device to copy the file for analysis.

SSH to the device

ssh ubnt@
cd /tmp/

Start tcpdump with the following command. Change ath0 and file.cap to the appropriate interface and file name.

tcpdump -i ath0 -w file.cap

After we are done collecting, we can quit with ctrl + c

Now we can use scp or sftp to copy the files off. There is an issue using scp or sftp from a normal Linux machine to the radio, fails with a “sh: /usr/libexec/sftp-server: not found”. It works fine if you initiate scp from the radio.

scp /tmp/file.cap username@remoteip:~/

Change VLAN ID Ubiquiti Radio from SSH

First we’ll need to ssh into the device

ssh ubnt@

Next lets open up the config file

vi /tmp/system.cfg

Now search for vlan and replace the vlan id with the appropriate number

In VI you can search by hitting / and then type in vlan

After you have changed all the vlan ids, save the file with esc, wq, enter.

Now we can save the config with

cfgmtd -f /tmp/system.cfg -w && reboot

Disable Wireless Security (WPA2) Preshared Key on Ubiquiti AC

Update: Found this handy dandy FAQs link

Included in the FAQ is a section on “How to Disable Wireless Security on airMAX AC Devices?”

The default security configuration for AC devices since firmware version 8.5.11 was changed to WPA2 AES with a pre-shared key 0000:0000.

Ubiquiti Default AC device WPA2 Preshared key

On Ubiquiti AC radios, you can not disable WPA 2 security through the web interface. This is not necessarily bad, however, what happens if you have a client that is reset and will only connect to the default ubnt SSID?

Fortunately there is a way to disable the WPA2 Preshared key.

  1. Log into the device over ssh.
  2. Run the following command to disable WPA2 in the config
    sed -i s/aaa.1.wpa.mode=2/aaa.1.wpa.mode=0/g /tmp/system.cfg
  3. Save the config file with
    /usr/etc/rc.d/rc.softrestart save
  4. Login to the client device and configure the SSID.

After you are done, you can click the enable button to re-enable Wireless Security.

Screenshot from UI help page on Wireless Security on airMAX AC devices

Unable to Remove Authorized SSH Keys from AirOS

For some reason I ran into an issue where I can not remove authorized SSH Keys in AirOS version 6.3. It redirects to a 404 page and then to the main page.

Attempting to remove SSH keys in AirOS
404 Error while attempting to remove SSH keys

Thankfully, we can still remove the authorized keys from the command line. For more information on making changes over SSH, refer to the following post.

SSH into radio. Replace username and IP address with your radios user and IP.

ssh ubnt@

Open up config file

vi /tmp/system.cfg

Search for the lines that contain

the sshd.auth.key and remove them

Remove the sshd.auth.key lines

Save the file and write the configuration with

/usr/etc/rc.d/rc.softrestart save

Once the command completes, you should be good to go.