Hi Paolo: OK, let me take one more try at explaining what I've observed. (And my apologies for making this whole issue more confusing than necessary ... I'm pretty inexperienced when it comes to detailing with the details of network interface operation.)
When I used "ethX=daemon", each interface I configured on a UML guest forwarded only the traffic that was destined for it to my network protocol software -- indicating that the uml_switch application was getting UML to filter things correctly. When I used "ethX=mcast", each interface I configured on a UML guest forwarded all packets sent to the associated multicast group to my network protocol software, even though the interfaces were not configured as "promiscuous". The latter observation was the source of my original concern, causing me to ask "why doesn't UML mark the device as promiscuous if it is passing on all packets?". Your subsequent explanations now make me think that I should have asked "why isn't UML filtering out the unwanted packets since the device isn't configured as promiscuous?". I just repeated my "ethX=mcast" testing to make sure I hadn't done something stupid, like configure both interfaces with the same MAC address, but I still see the same result. This leads me to conclude that there is a real problem with the way UML is filtering packets on "ethX=mcast" interfaces. Admittedly, I can circumvent this problem being by manually configuring the interfaces as promiscuous, but it still looks like a bug. Does this (finally) make sense? Regards, Al > -----Original Message----- > From: Blaisorblade [mailto:[EMAIL PROTECTED] > Sent: Tuesday, August 01, 2006 2:37 PM > To: Stephens, Allan > Cc: user-mode-linux-user@lists.sourceforge.net > Subject: Re: [uml-user] Promiscuous mode interface bug? > > On Tuesday 01 August 2006 19:41, Stephens, Allan wrote: > > Hi Paolo: > > > > Apparently I was unclear in my last email. I was not > trying to claim > > that "uml_switch -hub" was delivering promiscuously when "ifconfig > > promisc" was not set, > > This makes sense... > > > but rather that it was (correctly) delivering non-promiscuously > > uml_switch is broadcasting, the uml driver is doing the > filtering (so the network stack doesn't see unwanted stuff). > > > > -- meaning I didn't have to trick my protocol software > > into filtering out the unwanted packets using the "ifconfig promisc" > > approach that was required with "ethX=mcast". > This part of your mail doesn't make sense _to me_, you're > either missing or > adding some negations. > > If things are correct eth0=anything gives the same result: > non-promiscous by > default and promiscous only if you ask (with "ifconfig > promisc" or by default > by packet sniffers); the only difference is that some trasports > are "broadcast" (like Ethernet with hubs) and others not > (like Ethernet with > switches, even if technically this is still referred to as a > broadcast LAN > since you can do broadcast). > > Sorry, didn't you complain that promiscous mode wasn't auto-enabled > by "eth0=mcast"? Ok, you expected that your software had to > cope with this > situation and not coping with it is better, but there's still > somebody not > playing within the rules. > > Maybe it's all ok, but could you rewrite the above paragraph > to make it > clearer for me? You've flipped some sentences... since "promiscuos" > means "the interface accepts every packet" and non-promiscous > means "the > driver or the hardware only accepts packet with the right > destination MAC". > > > In short, I think everything is now working as it should. > But if I see > > anything else that looks strange I'll be sure to mention it! > > > Regards, > > Al Stephens > > Wind River > > -- > 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
