link monitoring and BFD in SDN networks

Nitin Sharma nitinics at
Wed Jan 21 23:14:33 UTC 2015

On Wed, Jan 21, 2015 at 12:22 PM, Ronald van der Pol <
Ronald.vanderPol at> wrote:

> On Mon, Jan 19, 2015 at 22:55:04 +0000, Dave Bell wrote:
> > ""
> The 802.1ag code used is open source and available on:
> > Of course if you want fast failover, you need to send packets very
> > rapidly. Every 250ms is not unreasonable. This is going to cause the
> > control plane to get very chatty. Typically on high end routers,
> > processes such as BFD are actually ran on line cards as opposed to on
> > the routing engine. When a failure is detected this reports up into
> > the control plane to trigger a reconvergence event. I see no reason
> > why this couldn't occur using SDN.
> Exactly. This is something you want to do in hardware, especially
> if you want to do fast reroute with the OpenFlow group table.
> Problem is that many 1U OpenFlow switches do not support 802.1ag.
> We made the propotype mentioned above to show and investigate the
> benefits of OAM. The closed "open" networking foundation is supposed
> to be working on this, but I don't know the status because their
> mailing lists are closed.
> In SDN/OpenFlow I think a couple of things are needed:
> - configure 802.1ag on the interfaces (via ofconfig?)
> - configure OpenFlow paths (e.g. primary and backup) and also create
>   forwarding entries for 802.1ag datagrams along those paths
> - configure fast reroute with the group table (ofconfig?)

Fast reroute (in the form of fast failover) is supported in the OF spec
(1.3+), using Group Tables.

> By doing this detection and failover are handled in hardware.
>         rvdp

Data plane reachability could be performed in SDN/OpenFlow networks using
BFD/ Ethernet CFM (802.1ag), Y.1731, preferably on silicon if there is
support (which i believe every silicon vendor should work on). It would not
be ideal if these OAM frames are forwarded to a central controller. Today -
I think it is done on some form of software layer (ovs, sdks) that reside
on these OF switches.

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