Few doubts about ad-hoc devices

Raghavendra s.raghu at samsung.com
Thu Aug 21 23:39:50 EDT 2008

----- Original Message ----- 
From: "Dan Williams" <dcbw at redhat.com>
To: "Raghavendra" <s.raghu at samsung.com>
Cc: <hostap at lists.shmoo.com>
Sent: Thursday, August 21, 2008 7:36 PM
Subject: Re: Few doubts about ad-hoc devices

> On Thu, 2008-08-21 at 16:16 +0530, Raghavendra wrote:
>> Hi All,
>>   I have two doubts.
>>       *  Assume I have one wlan device enabled with ad-hoc mode and
>>         with no-security. I am using wpa_supplicant for this purpose.
>>         Since this is a first device to create a ad-hoc network, with
>>         no security. It is always possible that other devices can
>>         connect to my device easily in ad-hoc mode.  Is there a way to
>>         know other devices connecting to this device in ad-hoc mode?
>>         some indications/events using wpa_supplicant or some ioctls?
> In ad-hoc mode, every STA just sets a BSSID, SSID, and a channel, and
> ignores traffic on that channel that's not addressed to the SSID + BSSID
> that the STA is using.  Ad-Hoc means there's no central authority
> handing out association IDs and controlling who connects and who
> doesn't.
> It's like this: there's a really big open square in a city.  A crowd of
> people stand in the square.  Some speak English, others speak Chinese,
> others speak Spanish.  Anyone can walk into the square and start talking
> in a language they can speak.  Each language is like the SSID+BSSID
> +channel tuple, and each person is like an ad-hoc wifi node.
> To join an adhoc network, the STA just starts listening and transmitting
> because there's nothing to gate its entry into the network.  That's the
> definition of Ad-Hoc.  If you want security, either set an encryption
> key or use infrastructure mode.
> The only indications you have that something else is trying to talk to
> your STA is incoming traffic with the same SSID, BSSID, and channel as
> your device is on.
>>       * Is it possible to hide device ssid in ad-hoc mode? so that
>>         even if some body scans my ad-hoc device ssid should not get
>>         displayed in scan result.
> Ad-Hoc BSSIDs are auto-generated, thus to actually join an Ad-Hoc
> network you need to know what BSSID to connect to.  So you can hide the
> SSID all you want by not transmitting it in the Ad-Hoc beacon (which
> might violate standards, not sure) but then nothing else would be able
> to join the adhoc network because there would be no way to match the
> known SSID up with a given random adhoc BSSID.  And BSSID coalescing
> couldn't occur because you have no idea what SSID all the other BSSIDs
> are using, and thus you can't eventually converge on one BSSID.
> In short, no, unencrypted Ad-Hoc networks just can't do what you are
> asking here.  At least that's my understanding of it.

 My scenario is as below:

 Assume two or more persons are near to each other in some place. They are 
using wifi device in ad-hoc mode with no-security. In this case some unknown 
person can easily join this network if he scans and finds that there is some 
ad-hoc device with no-security.

In order to avoid this situation, if ssid broadcast is disabled on ad-hoc 
wifi device. Only known persons can scan for a particular ssid and join the 
ad-hoc network. Is this feature avaible?

> Dan

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