Date: Wed, 23 Mar 2011 13:17:02 +0100 From: Viktor Petersson <petersson@gmail.com> To: Daniel Hartmeier <daniel@benzedrine.cx> Cc: freebsd-net@freebsd.org Subject: Re: Possible CARP bug? Message-ID: <F144C723-2653-429B-8B9F-B2FB9CD0AB47@gmail.com> In-Reply-To: <20110320185856.GA7703@insomnia.benzedrine.cx> References: <00612801-A0F4-4EDC-9BED-3364A86E4F9C@gmail.com> <20110320185856.GA7703@insomnia.benzedrine.cx>
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On Mar 20, 2011, at 7:58 PM, Daniel Hartmeier wrote: > On Fri, Mar 18, 2011 at 04:43:59PM +0100, Viktor Petersson wrote: >=20 >> Mar 7 14:42:57 nas0 kernel: carp0: MASTER -> BACKUP (more = frequent advertisement received) >=20 > This could mean that the master is receiving its own CARP = advertisements > back, and, thinking they come from another host, backs off. >=20 > CARP advertisements are sent through the physical interface to a > broadcast MAC address (01:00:5e:00:x:y) and the broadcast IP address > 224.0.0.18. >=20 > A real physical switch will forward that frame to all ports except the > one it was received on, i.e. the frame will not be sent back to the > sender. >=20 > You mention a virtual enviroment, so maybe the switch is virtual, too, > and behaves differently. You can check by tcpdump'ing on the physical > interface of the master. You should see each advertisement once (going > out, but tcpdump doesn't indicate the direction). Look at the IP IDs, = if > you see each ID twice, you're getting the broadcasts back. >=20 > I think newer versions of CARP (in OpenBSD) contain an explicit check = to > detect this case (it can be thought of as a form of replay attack), > which could be ported. >=20 > But there might also be a setting in Qemu's virtual switch, that deals > with such broadcasts. >=20 > HTH, > Daniel Thank you for the analysis Daniel. You're dead on. The node did indeed = receive its own broadcast package back.=20 Unfortunately that didn't really resolve the problem.=20 Matthew Grooms did however reach out to me with a patch that did resolve = the problem that he wrote for VMware ESX, which apparently is having the same issue.=20 The patch, along with instructions can be found here: http://www.mail-archive.com/freebsd-net@freebsd.org/msg30562.html It would be great if someone could merge that fix into the main branch.=20= Thanks for all the help guys!. Regards, Viktor=
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