[one-users] Gratuitous ARP replies: VM live-migration without loss of IP connectivity

[Javier Fontan]

Thanks Stefan!

Do you think it could be do this in the network scripts? Those script
are executed in the node to prepare the node for a new machine or a
migrated one. Does it make sense for newly created VMs? They take more
to get the IP but it may also be good to tell the switch beforehand.

Even if this does not make sense it is a nice candidate for an addon.

Cheers

On Wed, May 28, 2014 at 6:50 PM, Stefan Kooman <stefan at bit.nl> wrote:
> Hi List,
>
> In some larger cloud / network environments IPv4 connectivity issues may
> arise when VM's get (live-)migrated from one HOST to the other. The MAC
> address(es) of the Virtual Machine (VM) might still be mapped to the
> wrong port on switches/routers upstream from the switch the HOST is
> patched on. This might lead to IPv4 connectivity issues for the VM being
> migrated. This issue becomes escpecially noticable when the VM doesn't
> generate a lot of network traffic and/or the MAC address table timeout on the
> switch(es) is large. To overcome this issue I made a "VM_HOOK" and script(s) that run
> on the HOST when the hook is triggered [1]. It will execute a script that
> sends Gratuitous ARP replies (unsollicited ARP reply) on the virtual
> network interface(s) on behalf of the VM. These VM_HOOK and script(s)
> will work on a KVM/QEMU environment with OpenvSwitch. It should be
> fairly easy to adjust the scripts to support other enviroments (i.e. Xen
> with "legacy" bridging). Environments based on VMware with VM's that
> have "vmware-tools" installed are covered by VMware ESX. VMware will
> have the VM send gratuitous ARP replies as soon as the live-migration
> finishes. It does _not_ work for VM's without vmware-tools installed
> though. I hope "one-grarp" will be useful for some of you out there
> suffering from this issue.
>
> Gr. Stefan
>
> [1]: https://github.com/hydro-b/one-grarp
>
> P.s. In so called "switched fabric" networks the issue above might not
> occur because the "fabric" operates as one (logical) switch (like
> Brocade's Ethernet Fabric).
>
>
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-- 
Javier Fontán Muiños
Developer
OpenNebula - Flexible Enterprise Cloud Made Simple
www.OpenNebula.org | @OpenNebula | github.com/jfontan