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Re: [Xen-users] Automatically broadcast arp during a live migration.

To: mike@xxxxxxxxxxxx
Subject: Re: [Xen-users] Automatically broadcast arp during a live migration.
From: Ralf Schenk <rs@xxxxxxxxxx>
Date: Sun, 28 Jan 2007 14:23:21 +0100
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Michael Marineau schrieb:
> I am using Xen 3.0.4 on Gentoo. During a vm migration there is not an
> automatic arp broadcast to notify the switch the vm has changed
> network ports. This is not an issue if the vm is sending traffic at
> the time or another system sends an arp broadcast requesting the
> address for the vm. Both of which will cause the switch to update
> which port the vm is on. However if neither of those things happen all
> traffic to the vm will stall.
> 
> An easy way to demonstrate this is to start arping (from somewhere
> other than the destination dom0) before the migration, ie:
> arping <vm ip address>
> As soon as the migration finishes pings will stop.
> 
> An easy workaround is to do the same thing, but broadcast all pings so
> the switches arp cache doesn't prevent the delivery of the ping.
> arping -b <vm ip address>
> 
> So my questions are:
> Is Xend supposed to handle this issue automatically but for some reason
> is not?
> And if it isn't supposed to is there a good place to hook this into
> Xend so it does handle it?

Hello !

I'm testing xen live migration, too. I use drbd 8.0
(http://www.drbd.org) in primary/primary mode with OCFS2 on top.

I want to confirm your observations. Did you get any hint what can be
done to make the switches learn the new situation faster ?

Of course it would be sufficinet to let a deamon ping an external (=not
in the cluster) host in fast intervals but I would also like XEND to
handle this as it knows about the mac adress and the right time to send
out the broadcast arp.


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