[CentOS] how to find out promiscuous mode

Markus Falb markus.falb at fasel.at
Sun Feb 7 03:15:10 UTC 2010


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On 03/02/2010 23:28, Bill Campbell wrote:
> On Wed, Feb 03, 2010, Vadkan Jozsef wrote:
>> How can I find out that someone is using it's network card in
>> promiscuous mode in a subnet?
> 
> We use the swatch log watcher, to detect lines like this in
> /var/log/messages (this is from a system running VMware virtual
> machines in bridging mode so this is normal):

i believe the interface flags are defined in the kernel sources in
include/linux/if.h
#define IFF_PROMISC     0x100      /* receive all packets  */

You can read the flags from /sys

Promiscous mode off:
#$ cat /sys/class/net/eth0/flags
0x1003

Promiscous mode on:
#$ cat /sys/class/net/eth0/flags
0x1103

Anyway, both grepping the logs or looking at /sys requires local access.

- -- 
best regards,
markus
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