On Thu, 3 Aug 2006, Jeff Dike wrote: > On Thu, Aug 03, 2006 at 01:08:51PM -0700, Stephens, Allan wrote: >> Where I think my confusion is arising is in the details of how the >> filtering >> controlled by the promiscuous setting is actually done. If a packet >> with >> the "wrong" destination address arrives at an interface, who checks to >> see >> whether the interface has been configured as promiscuous and >> passes/discards it >> accordingly? I have naively assumed that this was handled in hardware >> on the >> NIC card in a real system, but is it really done by software? > > Ah, a light goes on. I believe that it is done on the card. > >> What I seem to >> be >> observing in my UML testing is that *nobody* is doing this filtering, >> resulting in >> unwanted packets being handed to my protocol (which sits directly on top >> of the >> Ethernet driver). > > And since UML doesn't have "cards", it may be that the driver should do the > filtering at the bottom layer and it isn't.
IIRC, most but not all cards will do the filtering in hardware unless they're in promiscuous mode. However if the card is in promiscuous mode or doesn't support filtering, the next step is when eth_type_trans sets the pkt_type of the skb to PACKET_OTHERHOST. I remember there being something odd about the handling of ethernet headers a good while ago. In any event, doing the filtering in the device would help, but won't work when it's promisc (for example if tcpdump is running). G'day, sjames > > Jeff > ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ User-mode-linux-user mailing list User-mode-linux-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-user
