On 11/23/2015 11:11 AM, Ben Pfaff wrote: > On Mon, Nov 23, 2015 at 10:56:34AM -0500, Russell Bryant wrote: >> On 11/23/2015 10:49 AM, Ben Pfaff wrote: >>> I think we'll need more rationale than that. BFD is expensive without a >>> good reason. >> >> It was on the ovn/TODO list, at least. :-) >> >>> * Use BFD as tunnel monitor. > > I think I wrote that. It came from an NVP mindset. In NVP, the > hypervisors use a set of "service nodes" to implement broadcast: a > hypervisor sends a broadcast packet to a service node, then the service > node replicates it and sends it to all of the destination hypervisors. > In that design, it's really important for the hypervisors to have BFD > set up between the hypervisors and the service nodes, because if one > service node goes down the hypervisors need to shift to using a > different service node to ensure availability. The same goes for the > "gateway nodes" that provide access to physical networks. > > For OVN, we're not using service nodes (which simplifies the system a > great deal; service nodes were never well-motivated), so we don't need > BFD for that reason. We'll need something for the OVN gateways when we > start supporting HA for gateways, and that something will probably > involve BFD. > > For hypervisor-to-hypervisor tunnels, it's much less important to have > tunnel monitoring (such as BFD), because when the tunnel goes down > there's no alternative to switch to. If there's someone working on some > kind of monitoring system for OVN, then it might make sense to turn on > BFD (probably at a slow rate) to allow monitoring of the physical > network. But absent that I don't think it's really worth the cost. > > Anyway, that's my story and I'm sticking to it ;-) >
Thanks for that explanation. It makes sense to me. I'll see if I can incorporate that into the TODO item. -- Russell Bryant _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
