On Thu, Sep 22, 2016 at 04:34:03PM +0100, Steven Hartland wrote:
S> On 22/09/2016 16:09, Gleb Smirnoff wrote:
S> > On Thu, Sep 22, 2016 at 08:21:08AM +0100, Steven Hartland wrote:
S> > S> On 22/09/2016 03:58, Gleb Smirnoff wrote:
S> > S> > On Wed, Sep 21, 2016 at 09:12:11PM -0400, Ryan Stone wrote:
S> > S> > R> > IMHO, the original patch was absolutely evil hack touching 
S> > S> > R> > layers, for the sake of a very special problem.
S> > S> > R> >
S> > S> > R> > I think, that in order to kick forwarding table on switches, lagg
S> > S> > R> > should:
S> > S> > R> >
S> > S> > R> > - allocate an mbuf itself
S> > S> > R> > - set its source hardware address to its own
S> > S> > R> > - set destination hardware to broadcast
S> > S> > R> > - put some payload in there, to make packet of valid size. Why 
should it be
S> > S> > R> >   gratuitous ARP? A machine can be running IPv6 only, or may 
even use
S> > S> > R> > whatever
S> > S> > R> >   higher level protocol, e.g. PPPoE. We shouldn't involve IP 
into this
S> > S> > R> > Layer 2
S> > S> > R> >   problem at all.
S> > S> > R> > - Finally, send the prepared mbuf down the lagg member(s).
S> > S> > R> >
S> > S> > R> > And please don't hack half of the network stack to achieve that 
S> > S> > R>
S> > S> > R> The original report in this thread is about a system where it 
takes almost
S> > S> > R> 15 minutes for the network to start working again after a 
failover.  That
S> > S> > R> does not sound to me like a switch problem.  That sounds to me 
like the ARP
S> > S> > R> cache on the remote system.  To fix such a case we have to touch 
S> > S> >
S> > S> > Does lagg(4) hardware address change when it failovers?
S> > S> >
S> > S> It moves the address between interfaces which typically moves it between
S> > S> switches too.
S> >
S> > So, the address doesn't change, which means ARP cache doesn't need to
S> > change as well. If it moves between switches, all that needs to be done
S> > is to send whatever packet from proper hardware address to broadcast.
S> >
S> That would be nice but unfortunately in the wild that won't work as 
S> without GARP devices can and do ignore :(

You can create a fake gratious ARP packet, if you want. Switches must not
require IP addresses matching the reality in the packet.

P.S. I always read GARP as Generic Attribute Registration Protocol.

Totus tuus, Glebius.
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