Re: [Discuss-gnuradio] find_usrps only succeed when an sniffer is ON

[Marcus D. Leech]

On 09/07/2010 04:43 AM, Jorge Miguel wrote:
> I installed GNU Radio on a ThinkPad Lenovo T4410 under Ubuntu 10.04.
> After connecting the USRP2 with the original Ettus code on the SD card
> D and F LEDs are ok and when executed:
>
> ~$ sudo find_usrps
> No USRP2 found.
>
> I run wireshark or tcpdump to see what happens in my network and I got:
>
> ~$ sudo find_usrps
> 00:50:c2:85:35:a2 hw_rev = 0x0400
>
> If I stop the sniffer, I get again:
>
> ~$ sudo find_usrps
> No USRP2 found.
>
> My problem is that 'find_usrps' only works when a sniffer is running.
> How can it be explained?
>
> Jorge,
>   
When a sniffer is running, the ethernet interface is placed into
"promiscuous" mode in which all ethernet frames are processed and passed
  up to higher layers in the networking stack.  In  non-promiscuous
mode, only frames that are addressed to the particular hosts ethernet
  address, and the broadcast address, are forwarded up the stack.

My understanding is that find_usrps sends out a broadcast packet, and
the responding USRP2 replies using a broadcast packet, but even
  in non-promiscuous mode, the hosts interface should pass the broadcast
traffic "upwards".  I wonder if there's some interaction with
  firewall rules at play here as well?


-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org