[ovs-dev] [PATCH] bond: Send gratuitous ARPs when load balancing.

Ben Pfaff blp at nicira.com
Fri Jul 1 21:08:31 UTC 2011


On Fri, Jul 01, 2011 at 02:04:38PM -0700, Jesse Gross wrote:
> On Fri, Jul 1, 2011 at 11:07 AM, Ethan Jackson <ethan at nicira.com> wrote:
> > I'm not particularly convinced that this is important, but Sanjay
> > thinks it is. ??It was easy enough to write up so I thought we could
> > discuss it on the dev list. ??I'm not married to the patch either way.
> > ??Though agree I don't really see the value in forcing traffic to
> > ingress the same link we send it on.
> 
> Well the value is load balancing of incoming traffic.  Convincing the
> remote switch to send traffic on the same link as is used for outgoing
> packets is the only way that we have to do load balancing for SLB.
> 
> This is really only beneficial for largely unidirectional streams
> where we're not outputting traffic that would cause the remote switch
> to figure out the correct link by itself.

The SLB rebalancing logic is based solely on outgoing traffic, and we
only move MACs that have a significant amount of outgoing traffic, so
sending a gratuitous ARP is normally redundant.  The switch will find
out that the MAC has moved on the next packet we send, which will
normally be quite soon (since the MAC that was moved has a significant
amount of outgoing traffic).



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