Hi Albert, Thank you for confirming that BFD needs to be kept simple and there is already reluctance to add to it. So Les's suggestion to put additional logic into BFD is likely not a realistic one.
Your note also confirms my points that there is likely to be different holdtime timer requirements depending on the link type and peer type. With that please notice what Les said: *And once OSPF strict-mode support becomes widely deployed there won’t be a need for such a timer for OSPF either.* That to me clearly means that he is going to retire the current timer once we get that RFC out of the door. That is why I proposed to add it to the document. But of course authors will decide. Dear WG, After thinking about this draft I would suggest that what we really need is not a point solution, but a general mechanism which will allow us to bring the protocol full up after some time from the moment the test suite is up. BFD is only one way to detect if the path to a peer is up or down. There are shipping alternatives to this today which could be used instead of BFD (for example any form of object tracking). As the current version of the draft says there is need to not only detect if the path is up or down but also if it meets quality expectations. New wave of INT tools is becoming available to allow us to measure those characteristics today. So while the draft could still bring BFD as one example of such a tool - in my opinion it deserves to be generalized a bit to allow other ways to determine if the link over which we are to establish IGP adj. meets the requirements. Kind regards, Robert On Sun, Jan 30, 2022 at 3:28 PM Albert Fu (BLOOMBERG/ 120 PARK) < af...@bloomberg.net> wrote: > I feel it is better to keep the standard simple and not add timer delay as > part of BFD strict draft, as different customers may have different > requirements, and there may also be vendor/platform dependency. > > For example, in the core where there are a lot of link > redundancy/diversity, we could afford to have longer time delay since we > can tolerate multiple link failures. For majority of the edge connectivity, > there are typically only 2 links - in this situation, we would want a lower > time delay. > > I found the current BFD Strict holddown/dampening mechanism as implemented > by the two vendors sufficient for our need. If there is an issue causing > BFD to fail during this time, OSPF will take longer time to come up. And > the delay only needs to be configured on one side. > > So, in current implementation, there's some sanity "check" that BFD is > stable for a period of time before OSPF can come up. > > In discussion with the BFD working group on my other MTU draft, there's a > keen interest among the WG to keep the BFD simple. > > > > > From: rob...@raszuk.net At: 01/29/22 15:20:06 UTC-5:00 > To: ginsb...@cisco.com > Cc: Albert Fu (BLOOMBERG/ 120 PARK ) <af...@bloomberg.net>, a...@cisco.com, > ketant.i...@gmail.com, draft-ietf-lsr-ospf-bfd-strict-m...@ietf.org, > lsr@ietf.org > Subject: Re: [Lsr] Working Group Last Call for "OSPF Strict-Mode for BFD" > - draft-ietf-lsr-ospf-bfd-strict-mode-04 > > Hi Les, > > > Discussion of how to make BFD failure detection more robust belongs in > the BFD WG > > If you do not want the BFD session to come back up too quickly after a > failure > > Nothing I suggested is related to any of the above. > > Let me perhaps provide a very simple example. > > BFD being used is *AS*IS*. > > All the operator wants is to run it for say X sec without ever going > down before bringing OSPF adj up. > > That timer and its consistency on both ends clearly belongs to OSPF not to > BFD. > > Now what happens within those 30 sec, what BFD packets are formed and how > they are exchanged is all BFD business - but I am not suggesting to include > any of those in this draft. > > Do we have a common understanding so far ? > > Hint: Albert already stated that he needs that timer and that both vendors > provided it via cfg. All that confirms is that timer is needed. All I am > suggesting (even before being aware of the manual cfg for it) was to > synchronize the value or pick lower configured between two peers. > > Kind regards, > R. > > > > > > > > > > > > > > > > > On Sat, Jan 29, 2022 at 9:08 PM Les Ginsberg (ginsberg) < > ginsb...@cisco.com> wrote: > >> Robert – >> >> >> >> It is good that you take an active interest in this technology – but I >> think the suggestions you are making should not be targeted at IGP use of >> BFD. >> >> >> >> Discussion of how to make BFD failure detection more robust belongs in >> the BFD WG – and – as you know – that WG has taken an interest in such >> problems e.g., MTU. >> >> >> >> In regards to “dampening” = which I think is the relevant term for the >> timer related suggestions you are making - this also does not belong in the >> IGP. If you do not want the BFD session to come back up too quickly after a >> failure, the proper place to put timers is either at the interface layer or >> in the BFD implementation. >> >> I am familiar with implementations which apply this timer at the protocol >> level (AKA BFD client in this context) and this is done precisely because >> the protocol does NOT have the functionality being defined in this draft. >> Once you have implemented “wait-for-BFD” logic as defined in this draft you >> do not need additional delay timers in the protocol. >> >> >> >> I don’t think the suggestions you are making belong in this document. >> >> >> >> Les >> >> >> >> >> >> *From:* Lsr <lsr-boun...@ietf.org> *On Behalf Of * Robert Raszuk >> *Sent:* Saturday, January 29, 2022 11:25 AM >> *To:* Acee Lindem (acee) <a...@cisco.com> >> *Cc:* Ketan Talaulikar <ketant.i...@gmail.com>; >> draft-ietf-lsr-ospf-bfd-strict-m...@ietf.org; Albert Fu < >> af...@bloomberg.net>; lsr <lsr@ietf.org> >> *Subject:* Re: [Lsr] Working Group Last Call for "OSPF Strict-Mode for >> BFD" - draft-ietf-lsr-ospf-bfd-strict-mode-04 >> >> >> >> Hi Acee, >> >> >> >> Can you suggest text which with you’d be happy? I’m sure the authors >> would add you to the acknowledgements. >> >> >> >> Actually instead of suggesting any new text I would suggest to delete the >> two below sentences and it will be fine: >> >> >> >> *"In certain other scenarios, a degraded or poor quality link will allow >> OSPF adjacency formation to succeed* >> >> *but the BFD session establishment will fail or the BFD session >> will flap. In this case, traffic that gets * >> >> *forwarded over such a link may experience packet drops while the failure >> of the BFD session establishment * >> >> *would not enable fast routing convergence if the link were to go down or >> flap."* >> >> >> >> This could be described but I don’t think it should be normative. This >> begs the question as to why a hold down timer is not a part of the BFD >> protocol itself. >> >> >> >> There is one - BFD calls it multiplier. >> >> >> >> But the timer I am suggesting is not related to BFD operation, but to >> OSPF (and/or ISIS). It is not about BFD sessions being UP or DOWN. It is >> about allowing BFD for more testing (with various parameters (for example >> increasing test packet size in some discrete steps) before OSPF is happy to >> bring the adj. up. >> >> >> >> Thx, >> >> R. >> > >
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