Date: Thu, 02 Jan 2003 08:56:42 -0500 From: "Bill Moran" <bill_moran2@hotmail.com> To: y.grossel@hexanet.fr, freebsd-questions@freebsd.org Subject: Re: promiscuous mode / strange ethernet packets duplication problem Message-ID: <F104YTxHwMQFLcVcvIh0001dacb@hotmail.com>
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>From: Yann GROSSEL <y.grossel@hexanet.fr> > >Hi, > >We have several FreeBSD 4.7 boxes that put automatically >all their interfaces into promiscuous mode during the >boot process. What should I do to prevent this from >happening ? > >Our boxes are connected on a D-Link switch. We have noticed >a very weird behaviour from a few of these machines, I'll >try yo explain it : > >Our switch has a standard MAC address aging value of 300 seconds. >When one MAC address expires on the switch, the next packet targeted >to this MAC address is broadcasted on all ports of the switch (because >the switch doesn't remember anymore on what port the target MAC address >is). That at least seems to be normal. > >But each time an ethernet packet broadcasted as descrbibed above arrives >on the interfaces of our machines, these machines resend the packet to >the network, decrementing the TTL value bye one. I mean, these machines >are resending packets that are NOT targeted to them - neither the >destination MAC address OR the destination IP address of the packet >match the interface of the machine. > >This happends only on machines with interfaces in promiscuous mode >AND with net.inet.ip.forwarding = 1. There's your answer. Any machine with forwarding turned on will resend a packet that isn't destin for it. That's by design. It doesn't make much sense to me that you'd have a lot of machines with forwarding turned on. Usually only gateways use this. Honestly, I can't thing of any reason to have forwarding on if your machine only has 1 IP address. >As several boxes have this problem, they resend packets to each others >very quickly, generating a flood on the network. This flood only stop >when all TTL of packets reach 0 or when the switch finally re-learn >on what port is located the interface with the target MAC address. > >Does anybody have any clue about what this kind of problem may be ? Turn forwarding of on all but your gateways. -Bill _________________________________________________________________ STOP MORE SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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