[ovs-discuss] Open vSwitch balance-slb bond mode with two upstream switches

Dan Sneddon dsneddon at redhat.com
Fri Jul 19 21:22:18 UTC 2019

On Fri, Jul 19, 2019 at 7:46 AM Grzegorz <juszczak.grzegorz at gmail.com>

> Hi Jason
> I have the same doubts - I would like to connect balance-slb in OpenStack
> Rocky to two separate switches.
> I see you wrote this post a few years ago.
> Have you figured it out finally?
> Thank you in advance for your reply
> BR
> Grzegorz Juszczak

This only works if the two switches are clustered, i.e. two or more chassis
running as a single logical switch.

The issue is that balance-slb will only use one link for a MAC+VLAN, but
when rebalancing happens the traffic may start using the other port. If the
switch attached to the original port doesn't know that the traffic is now
using the other port/different switch, then traffic to the OVS bond may be

You can use active-backup with OVS bonds and two switches, or attach a
bond/team using a different bonding technique (Linux kernel bonds, teamd
adapter teams, etc.) that supports disparate switches and then attach that
bond to OVS. There aren't many good options for attaching to multiple
switches, so I try to use switches that can be clustered when I'm not using
a chassis switch.

Look into teamd, it has more options for controlling how your traffic is
load balanced, and you can choose your own hash combinations. I've
configured OpenStack deployments with teams attached to OVS bridges for
Neutron. The best documentation I've found so far is here, but you may need
to adjust depending on Linux distribution:


Dan Sneddon
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