Tcpdump showing ghost traffic

[Ian Smith]

On Fri, 22 Oct 2010, Thomas Sevestre wrote:
 > 							Le 21 oct. 10 à
 > 19:04, Julian Elischer a écrit :
 > 
 > > On 10/21/10 8:26 AM, Thomas Sevestre wrote:
 > > > Hi all,
 > > > 
 > > > I'm using freebsd 8 as a router. Say I have a sis0 interface. The
 > > > interface is up and negociated, Ethernet LEDs are fine.
 > > > Sometimes tcpdump shows traffic on the interface (tcpdump -lni sis0) but
 > > > traffic LEDs doesn't blink and there is nothing going out of the router.
 > > > 
 > > > Do you have any idea of what the problem could be?
 > > > May be a link-layer driver bug?
 > > 
 > > who is the traffic for and from?
 > 
 > For instance, the router is pinging some address on his LAN. In this case I
 > had a machine wired directly to the router.
 > By the way, it is not a firewall issue, packets wasn't blocked.

tcpdump is in promiscuous mode, also seeing any traffic visible on the 
wire for other than your MAC address.  Is there any of that?  Would the 
LEDs flash when receiving that?  Is the LAN off a switch, or a hub?

Details like ifconfig and tcpdump output might help, obscured as needed.

cheers, Ian