OmniPeek Support

Question about Promiscuous Mode

alef
Posts: 3
Joined: Mon Mar 12, 2012 12:33 pm

Question about Promiscuous Mode

Postby alef » Mon Mar 12, 2012 12:44 pm

Hello,
I'm reading a "802.11 WLAN Packets and Protocols" from Network Glossary on this site. There is explanation about Promiscuous Mode:
"Device C acknowledges the receipt and processes the packet normally, passing it to the next layer of the protocol software. Device D also captures the transmission and passes the packet to OmniPeek. The machine on which OmniPeek is running will not send any acknowledgement, because Promiscuous Mode is strictly a listening mode. Radio transceivers cannot listen and send at the same time on the same frequencies because their own transmission would drown out any incoming traffic."

My question is - how come device C is able to send an acknowledgement if it also listens on the same frequency and acknowledgement transmission may drop incoming traffic in the same way?

DJWP
Posts: 682
Joined: Tue Oct 30, 2007 11:42 am

RE: Question about Promiscuous Mode

Postby DJWP » Mon Mar 12, 2012 12:51 pm

Because Device C is not in promiscuous mode, it can send and receive. Device D is the capture adapter.

alef
Posts: 3
Joined: Mon Mar 12, 2012 12:33 pm

Re: RE: Question about Promiscuous Mode

Postby alef » Mon Mar 12, 2012 1:24 pm

[quote="DJWP"]Because Device C is not in promiscuous mode, it can send and receive. Device D is the capture adapter.[/quote]

Ok, thanks for the answer but as for next sentence: " Radio transceivers cannot listen and send at the same time on the same frequencies because their own transmission would drown out any incoming traffic." is it correct? Does it mean that Device C (which is not in promiscuous mode) can send and receive on the same frequency? Or it uses different frequency to send acknowledgements?

DJWP
Posts: 682
Joined: Tue Oct 30, 2007 11:42 am

RE: Re: RE: Question about Promiscuous Mode

Postby DJWP » Mon Mar 12, 2012 2:43 pm

Any single 802.11 radio must transmit and receive on the same frequency.

alef
Posts: 3
Joined: Mon Mar 12, 2012 12:33 pm

RE: RE: Re: RE: Question about Promiscuous Mode

Postby alef » Mon Mar 12, 2012 5:02 pm

So device D does not send acknowledgments not because of "Radio transceivers cannot listen and send at the same time on the same frequencies because their own transmission would drown out any incoming traffic." but because it is in listening mode, which does not allow to send something. Right?

DJWP
Posts: 682
Joined: Tue Oct 30, 2007 11:42 am

RE: RE: RE: Re: RE: Question about Promiscuous Mode

Postby DJWP » Tue Mar 13, 2012 7:59 am

Yes. Device D is listening only, it is the capture adapter

zonker
Posts: 5
Joined: Thu Jan 13, 2011 7:08 pm

RE: RE: RE: RE: Re: RE: Question about Promiscuous Mode

Postby zonker » Tue Mar 27, 2012 2:24 pm

To answer the root question, the 802.11 radio conversation must be half-duplex. When the adapter wants to transmit, it cannot simultaneously receive. So, when it receives a packet, it will stop listgening, transmit the ACK, and go back to listening.

Best regards,

-Z-

DJWP
Posts: 682
Joined: Tue Oct 30, 2007 11:42 am

RE: RE: RE: RE: RE: Re: RE: Question about Promiscuous Mode

Postby DJWP » Wed Mar 28, 2012 8:03 am

This is not correct. When the adapter using the WildPackets driver is used for capture, it cannot be used for transmission at all. It is always in receive mode only.

When OmniPeek is not using the adapter for capture it goes back to normal send/receive operation.

zonker
Posts: 5
Joined: Thu Jan 13, 2011 7:08 pm

RE: RE: RE: RE: RE: RE: Re: RE: Question about Promiscuous M

Postby zonker » Wed Mar 28, 2012 10:07 am

To clarify; The node that you are sniffing is the radio that stops listening when it transmits... The radio in the sniffer is going to be listening all the time.

DJWP
Posts: 682
Joined: Tue Oct 30, 2007 11:42 am

RE: Question about Promiscuous M

Postby DJWP » Wed Mar 28, 2012 10:56 am

Thank you for the clarification-


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