WLAN Scanner


The WLAN Scanner is probably the most well recognized wireless tool for any product. Almost all wireless products have a tool which is similar, although the implementation in RouterOS is a little more advanced than what most products offer. In addition to reporting the SSID (Service Set Identifier) and RSSI (Received Signal Strength Indicator), RouterOS will also report channel information, noise floor, SNR (Signal to Noise Ratio), the radio name, RouterOS version, and other information. 

How to use this tool

All of the wireless tools can be found in the Wireless Tables on the Interfaces tab along the top or by doubling clicking on the WLAN interface and selecting them from the right side. Using the tool is pretty simple and straight forward. First, you select which interface you want to use for the scanner from the drop down menu. Then click Start. Any time you use one of the wireless tools, that radio is no longer maintaining a wireless link, with one exception which is the Background Scan. More on that latter. The wireless scan tool can only see access points which are in a compatible mode with the wireless card. For example, if the WLAN interface is set to 10MHz channels, we won’t see normal 802.11 networks. Double clicking on an entry will open another window, however, there is no additional information in the new window; see below. By highlighting an entry and then clicking on the Connect button, the corresponding WLAN interface will prefill its own SSID field to match.

Scanner4

 

Scanner3

Scanner

Scanner2

Lets look at each of the fields:

Flags – The first block provides information such as what modes the AP may be using. Hovering your mouse over the flags will produce a tool tip that explains their meaning. Here is a list of the common flags:

  • A = Active – which means the wireless interface is currently able to see that access point. 
  • P = Privacy – which means some form encryption is being advertised by the AP.
  • R = RouterOS Network – Sometime, this will be reported in error. Its not uncommon for Ubiquiti APs to trigger this flag.
  • B = Bridge – This means the AP is in a bridge mode and expecting a client that is in a bridged mode.
  • N = Nstreme – The AP is running Nstreme
  • T = TDMA (Time-division Multiple Access) – The AP is running NV2
  • W = WDS (Wireless Distribution System) – The AP is in WDS mode

Address – The MAC address which the AP is presenting

SSID – Service Set Identifer – The network name

Channel – In addition to the frequency, the channel width, and associated modes (802.11 a/b/g/n/ac) are displayed.

Signal Strength – RSSI (Received Signal Strength Indicator) which is a relative signal strength from the perspective of this radio.

Noise Floor – The noise floor is measure of what threshold a discrete signal must be above in order for the radio to detect it as a discrete signal. This value is constantly changing due the background radiation levels changing. 

Signal to Noise – This is the diference in dBs between the Noise Floor and the Signal Strength (RSSI). For a link to work properly, there must be a minimum of 22dB of seperation. Its is possible to have a link with a received signal that is -65 on both sides that still does not work because the noise floor is too close to the RSSI value. This is especially common with omni style antennas. Also, keep in mind, that we are only looking at one 20MHz channel by default. We may have the needed SNR values on one 20MHz channel, but be experiencing link failures due to noise on adjacent channels when using larger bandwidths. 

Radio Name – This is actually a field in the wireless frame and many products allow you to change the radio name. In RouterOS this field is found on the wireless tab of the WLAN interface while in “Advanced Mode.”

RouterOS Version – The ROS version of the AP.

Hope you enjoyed this tutorial! If you have any questions or insights, please add a comment below.

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