[ovs-discuss] [OVN] running bfd on ecmp routes?

Han Zhou zhouhan at gmail.com
Tue Jun 16 17:45:08 UTC 2020


On Mon, Jun 15, 2020 at 7:22 AM Tim Rozet <trozet at redhat.com> wrote:

> Hi All,
> While looking into using ecmp routes for an OVN router I noticed there is
> no support for BFD on these routes. Would it be possible to add this
> capability? I would like the next hop to be removed from the openflow group
> if BFD detection for that next hop goes down. My routes in this case would
> be on a GR for N/S external next hop and not going across a tunnel as it
> egresses.
>
> Thanks,
>
> Tim Rozet
> Red Hat CTO Networking Team
>
> Hi Tim,

Thanks for bringing this up. Yes, it is desirable to have BFD support for
OVN routers. Here are my thoughts.

In general, OVN routers are distributed. It is not easy to tell which node
should be responsible for the BFD session, especially, to handle the
response packets. Even if we managed to implement this, the node detects
the failure needs to populate the information to central SB DB, so that the
information is distributed to all nodes, to make the distributed route
updated.

In your particular case, it may be easier, since the gateway router is
physically located on a single node. ovn-controller on the GR node can
maintain BFD session with the nexthops. If a session is down,
ovn-controller may take action locally to enforce the change locally.

For both cases, more details may need to be sorted out.

Alternatively, it shouldn't be hard to have an external monitoring
service/agent that talks BFD with the nexthops, and react on the session
status changes by updating ECMP routes in OVN NB.

Thanks,
Han
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