why is an interfcae in monitor mode (mon.wlan0) needed

[Kevin Wilson]

Hello,
I am running hostapd under backfire.

I use b43 kernel module.

I have a very basic hostapd.conf file. (see at the end of this mail)

When I start it in background:
hostapd -B /etc/hostpad

I see by iw dev this:

iw dev
phy#0
	Interface mon.wlan0
		ifindex 11
		type monitor
	Interface wlan0
		ifindex 3
		type AP

My question is:
for what do we need an interface in monitor mode ?

AFAIK, monitor mode is for using by a sniffer, when we want to sniff
on this interface and get radiotap addition to the ieee80211 header.

rgs,
Kevin

this is the hostapd.conf I am using:
driver=nl80211
interface=wlan0
hw_mode=g
channel=1
ssid=z
debug=4