Wireshark-dev: Re: [Wireshark-dev] Promiscouos mode and pseudo-device
From: Satish Chandra <[email protected]>
Date: Mon, 17 Aug 2009 20:39:04 +0530
Hi Mark,

The option of "any" enables us to monitor multiple interfaces on the machine at the same time.

One example, where I use "any" is, when I attach more than one applications to different virtual IP address on the same machine and I wish to track the message exchanges between these applications.

Thanks Regards,
Satish

On Mon, Aug 17, 2009 at 5:42 PM, Mark Ryden <[email protected]> wrote:
Guy,
Thanks a lot for your answer !

This cause me to ask myself: why, in fact, do we need  the "any" pseudo-device
when sniffing in Linux ? Is there any information that we can get with
the "any" pseudo-device when sniffing, that we can't get without it?

Regards,
Mark


On Thu, Aug 13, 2009 at 3:35 PM, Guy Harris<[email protected]> wrote:
>
> On Aug 13, 2009, at 2:44 AM, Mark Ryden wrote:
>
>>  I had noticed that when running tshark in Pseudo-device mode (tshark
>> -i any), the
>> machine does not enter promiscuos mode, whereas in the usual case,
>> such as
>> thsark -i eth0 (or without "-i" option at all), it does enter
>> promiscuos mode.
>> (I tested it on Linux).
>
> There is no notion at the hardware level of a machine being in
> promiscuous mode; there is only a notion, for devices on "broadcast"
> networks such as Ethernet, of a network adapter being in promiscuous
> mode.  Neither Linux nor any other OS I know of have any notion of a
> machine being in promiscuous mode, either, just of a device being in
> that mode.
>
>> I would appreciate if somebody can explain in few sentences why is
>> it so.
>
> It's because libpcap implements the "any" pseudo-device on Linux by
> creating a PF_PACKET socket but not binding it to a particular
> device.  (On other platforms, it's not implemented at all.)  The Linux
> socket calls to turn promiscuous mode on don't work on sockets such as
> that - the kernel rejects them rather than setting promiscuous mode on
> all devices in the system.
>
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--
Satish Chandra