Hi Robert, The draft text refers to dampening and hold-down. The latter can be used also for the initial session bring-up. The descriptions of those BFD mechanisms are outside the scope of this document. If this needs to be standardized at the IETF, then (IMHO) it would be best taken up in the BFD WG so it can be leveraged for other protocols and use-cases as well.
We can update the text in Sec 5 to clarify this aspect as below. OLD In network deployments with noisy links or those with packet loss, BFD sessions may flap frequently. In such scenarios, OSPF strict- mode for BFD may be deployed in conjunction with a BFD dampening or hold-down mechanism to avoid frequent adjacency flaps that cause routing churn. NEW In network deployments with noisy links with packet loss, BFD sessions may flap frequently. In such scenarios, OSPF strict- mode for BFD may be deployed in conjunction with mechanisms such as hold-down (to delay initial adjacency bring up) and dampening (to avoid frequent adjacency flaps) in BFD to avoid frequent OSPF adjacency flaps that cause routing churn. The details of these BFD mechanisms are outside the scope of this document. Thanks, Ketan On Sun, Jan 30, 2022 at 11:35 PM Robert Raszuk <rob...@raszuk.net> wrote: > Hi Ketan, > > I would like to point out that the draft discusses the BFD "dampening" or >> "hold-down" mechanism in Sec 5. We are aware of BFD implementations that >> include such mechanisms in a protocol-agnostic manner. >> > > BFD dampening or hold-time are completely orthogonal to my point. Both > have nothing to do with it. > > Those timers only fire when BFD goes down. In my example BFD does not go > down. But we want to bring up the client adj. only after X ms/sec/min etc > ...of normal BFD operation if no failure is detected during that timer. > > This draft indicates that OSPF adjacency will "advance" in the neighbor >> FSM only after BFD reports UP. >> > > And that is exactly too soon. In fact if you do that today without waiting > some time (if you retire the current OSPF timer) you will not help at all > in the case you are trying to address. > > Reason being that perhaps 200 ms after BFD UP it will go down, but OSPF > adj. will get already established. It is really pretty simple. > > Thx, > Robert. > > PS. And yes I think ISIS should also get fixed in that respect. > >>
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