How can someone get the BSSID of a router without connecting to it?

Question

1. How can someone get the BSSID of a router without connecting to it in order to differentiate between duplicate SSIDs?

2. Does a router broadcast the BSSID?

Answer 1

Applying the command

netsh wlan show all 

in windows would show details of all the routers including the BSSID in your wireless range, even though you might not have been connected to the router.

Answer 2

You can get all the BSSID you have around with this command:

netsh wlan show networks mode=bssid

Answer 3

For Mac OS and macOS that's

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I

for the currently connected wifi, which you can also get by alt+click on the wifi menu.

To get a list of all hotspots/network available use

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -s