Re: [Xen-devel] [PATCH v3] xen-netfront: delay gARP until backend switches to Connected

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Laszlo Ersek <lersek@xxxxxxxxxx> 07/13/11 6:11 PM >>>
>After a guest is live migrated, the xen-netfront driver emits a gratuitous ARP
>message, so that networking hardware on the target host's subnet can take
>notice, and public routing to the guest is re-established. However, if the
>packet appears on the backend interface before the backend is added to the
>target host's bridge, the packet is lost, and the migrated guest's peers become
>unable to talk to the guest.
>
>A sufficient two-parts condition to prevent the above is:
>
>(1) ensure that the backend only moves to Connected xenbus state after its
>hotplug scripts completed, ie. the netback interface got added to the bridge;
>and
>
>(2) ensure the frontend only queues the gARP when it sees the backend move to
>Connected.
>
>These two together provide complete ordering. Sub-condition (1) is satisfied
>by pvops commit 43223efd9bfd.

Is it guaranteed that either side not having the respective change will
still work correctly with the other side having its part of the change?

Jan

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