MAC crash during switch to master mode with null ESSID

Simon Barber simon at
Sat Mar 29 00:09:29 EST 2003

Empty SSID is not allowed in 802.11 - the minimum length allowed for
SSID is 1.


-----Original Message-----
From: Jouni Malinen [mailto:jkmaline at] 
Sent: Friday, March 28, 2003 8:02 PM
To: hostap at
Subject: Re: MAC crash during switch to master mode with null ESSID

On Tue, Mar 25, 2003 at 03:32:48PM -0800, Mark Glines wrote:

> I've noticed that when you switch the mode to managed, change the 
> essid to any and switch back to master mode before the MAC has 
> associated with anything, the MAC seems to subsequently crash.

Using empty SSID (i.e., broadcast SSID) in AP mode does not have
well-defined use in IEEE 802.11. I do not think it should be allowed at

> The MAC needs a hard reset afterwards to be of any use.  Is this a 
> known problem?  Is it fixed in later firmware?

This is a known problem, but not only in the firmware code. Of course it
could argued that the firmware should not crash with such
misconfiguration (and this is not fixed at least in 1.7.2), but I would
say it is mostly up to the driver to make sure such configuration is not
tried. I just modified Host AP driver to deny changing to Master mode if
the SSID is set to empty in another mode.

Jouni Malinen                                            PGP id EFC895FA
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