Hi Paolo: I tried configuring the Ethernet interfaces as "promiscuous" and this did indeed provide a workaround for the issue I raised. The root cause of my problems seems to have been a lack of understanding on my part as to what I was really asking UML to do for me; your explanation has helped clear things up significantly. It appears that I was using interfaces of the form "ethX=mcast" expecting them to behave like ones of the form "ethX=daemon" used with "uml_switch -hub". I've now reconfigured things to use the latter type of interface, and things are working as I expected.
Thanks so much for your help! Regards, Al Stephens Wind River > -----Original Message----- > From: Blaisorblade [mailto:[EMAIL PROTECTED] > Sent: Saturday, July 29, 2006 4:20 AM > To: user-mode-linux-user@lists.sourceforge.net > Cc: Stephens, Allan > Subject: Re: [uml-user] Promiscuous mode interface bug? > > On Wednesday 26 July 2006 16:34, Stephens, Allan wrote: > > Hi there: > > > > I've been running UML using Linux 2.6.17 (guest) and 2.6.12 > (host) and > > configured a guest with a pair of Ethernet multicast interfaces as > > shown below. (Note that I didn't configure any IP > addresses, as I'm > > not trying to use them to carry IP traffic.) > > > > uml_mconsole <session> config eth1=mcast,00:00:00:00:01:01 > > uml_mconsole <session> config eth2=mcast,00:00:00:00:02:02 > > > > When a second guest transmitted traffic using a destination > address of > > 00:00:00:00:01:01, the message showed up on both interfaces (as > > expected). However, the kernel protocol handled incoming > messages did > > not recognize and discard the unwanted copy that showed up at "eth2" > > because the associated "struct net_device" object did not have the > > "promiscuity" field set to indicate that the interface > might receive > > traffic other than its own. > > That's a slightly wrong interpretation of the flag (it > actually means that the interface should accept others' > packets; whether it may receive them or not is indicated by > the BROADCAST/POINTTOPOINT flag in ifconfig output). > > It's also a slightly complex way to check it: > > ifconfig eth2 |grep PROMISC would be simpler. > and ifconfig eth2 promisc would enable it. > > > It seems to me that any UML interface configured to use multicast > > should cause the promiscuity field of the associated > net_device to be > > set -- but maybe I'm missing something here. Is the scenario I > > encountered really a bug? > > No, it's a feature; I understand your point of view and what > you say makes sense from that, but you're looking from an > unusual point of view (and you went very fast up the > knowledge hill so it's not a problem, you must be a smart guy). > > You're more or less claiming that if you have a hub-based > Ethernet LAN (multicast networking has the same properties, > it's a broadcast LAN implemented over multicast IP) all PCs > should auto-configure their interfaces to work in promiscuos mode. > > That's wrong, as promiscuos mode only makes sense in > hub-based networks and reduces overhead. > > You can still configure your interface to work in promiscuos > mode as said above. > > All this said, if when trying what I suggested you see > unexpected behaviour, it _may_ be a bug (especially in UML > network support and/or UML multicast transport). > -- > Inform me of my mistakes, so I can keep imitating Homer > Simpson's "Doh!". > Paolo Giarrusso, aka Blaisorblade > http://www.user-mode-linux.org/~blaisorblade > Chiacchiera con i tuoi amici in tempo reale! > http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com > > ------------------------------------------------------------------------- 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
