Live Migration (L2 network)

Live Migration (L2 network)

[William Lima Reiznautt]

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Hi folks,

I hope everything is well.

Sorry about that doubt in this channel.

I have a doubt about live migration interacting with layer 2 network, when
the live migration is running. How does the qemu signal the switch network
that the qemu instance changes port ? Because when the qemu migration to
another port switch, the switch has a time to understand that flow is
changed.

I saw the dump traffic in live migration and I noticed that one packet
(RARP). "This packet is created by qemu."

Does anyone know if there is documentation on this?

Thanks

- - -
William Lima Reiznautt
willreli@gmail.com
www.ic.unicamp.br/~william

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Re: Live Migration (L2 network)

[Dr. David Alan Gilbert]

* William Lima Reiznautt (willreli@gmail.com) wrote:
> Hi folks,
> 
> I hope everything is well.

Hi,

> Sorry about that doubt in this channel.

No, it's the right place to ask!

> I have a doubt about live migration interacting with layer 2 network, when
> the live migration is running. How does the qemu signal the switch network
> that the qemu instance changes port ? Because when the qemu migration to
> another port switch, the switch has a time to understand that flow is
> changed.
> 
> I saw the dump traffic in live migration and I noticed that one packet
> (RARP). "This packet is created by qemu."
> 
> Does anyone know if there is documentation on this?

I'm not sure we have documentation, but the code is in net/announce.c in
recent qemu.
When the migration has finished we send an ARP and then, when it starts
running, we tell the guest to send a RARP;  we send those a few times
to make sure we don't miss it.
Those are normally enough for the switch to realise that the VM
has moved port;  some very complex switch setups are less forgiving - in
recent qemu's you can send the announce again later and/or change the
timing of it.

Dave

> Thanks
> 
> - - -
> William Lima Reiznautt
> willreli@gmail.com
> www.ic.unicamp.br/~william
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK