Hi Les, > If we can agree that an IGP solution is useful, then we can use this thread to > set a direction for the IGP solution
I think this thread aimed to answer both of those questions hence some comments. But even if we assume that Event Flooding via IGP have a valid use case (regardless if PE down is a right one) I am a bit concerned with adding this new such functionality to existing IGPs. Event flooding with IGPs (the way I see similar opaque information and how they got into other protocols) may quickly become a huge burden to them. Yes I see you are already proposing separation of LSDBs via FSP Scope Specific LSDB - but is this enough ? How about redistribution between IGP instances across domains ? So assuming we want to do that new event transport how about running new instance of link state dedicated for event flooding ? It seems (no matter how we look at it) that there are many differences in operational models for state advertisement vs events in an IGP. Moreover such new instance could only be spanning PEs and if we do it right it can be based on a pub/sub model. Thx, R. On Wed, Oct 13, 2021 at 8:44 PM Les Ginsberg (ginsberg) <ginsberg= [email protected]> wrote: > This thread is becoming "diverse". > We are trying to talk about many different solutions (IGP, BGP, BFD) - all > of which may be useful and certainly are not mutually exclusive. > > If we can agree that an IGP solution is useful, then we can use this > thread to set a direction for the IGP solution - which seems to me to be > something we should do independent of whether the other solutions are also > pursued. > > With that in mind, here is my input on the IGP solutions: > > PUA > ------- > > For me, the solution has two major drawbacks: > > 1)It tries to repurpose an existing (and fundamental) Reachability > Advertisement into an UnReachability advertisement under certain conditions > > The interoperability risks associated with this make me very reluctant to > go down this path. > And the use of the same advertisement to indicate Reachability and > Unreachability is IMO highly undesirable. > > 2)The withdrawal of the "Unreachability Advertisement" after some delay > (which is necessary) remains problematic despite the authors attempts to > address thus > > Event Notification > ------------------------ > > This avoids the drawbacks of PUA and is flexible enough to handle future > and unforeseen types of notifications. > > I would like to extend the offer already made by Peter to the authors of > PUA to join us and work on the Event Notification draft. > The authors of PUA certainly deserve credit for raising awareness of the > problem space and it would be good to have them working with us on a single > IGP solution. > > But PUA is not an alternative that I can support. > > Les > > > -----Original Message----- > > From: Lsr <[email protected]> On Behalf Of Acee Lindem (acee) > > Sent: Wednesday, October 13, 2021 9:49 AM > > To: Peter Psenak <[email protected]>; [email protected] > > Subject: Re: [Lsr] "Prefix Unreachable Announcement" and "IS-IS and OSPF > > Extension for Event Notification" > > > > Hi Peter, > > > > See inline. > > > > On 10/13/21, 4:42 AM, "Peter Psenak" > > <[email protected]> wrote: > > > > Hi Acee, > > > > On 12/10/2021 21:05, Acee Lindem (acee) wrote: > > > Speaking as WG Chairs: > > > > > > The authors of “Prefix Unreachable Announcement” have requested an > > > adoption. The crux of the draft is to signal unreachability of a > prefix > > > across OSPF or IS-IS areas when area summarization is employed and > > > prefix is summarised. We also have “IS-IS and OSPF Extension for > Event > > > Notification” which can be used to address the same use case. The > drafts > > > take radically different approaches to the problem and the authors > of > > > both drafts do not wish to converge on the other draft’s method so > it is > > > understandable that merging the drafts really isn’t an option. > > > > just for the record, I offered authors of "Prefix Unreachable > > Announcement" co-authorship on "Event notification" draft, arguing > the > > the event base solution addresses their use case in a more elegant > and > > scalable way. They decided to push their idea regardless. > > > > One solution to this problem would have definitely been better. > > > > > Before an adoption call for either draft, I’d like to ask the WG: > > > > > > 1. Is this a problem that needs to be solved in the IGPs? The use > case > > > offered in both drafts is signaling unreachability of a BGP > peer. > > > Could this better solved with a different mechanism (e.g., > BFD) > > > rather than flooding this negative reachability information > across > > > the entire IGP domain? > > > > we have looked at the various options. None of the existing ones > would > > fit the large scale deployment with summarization in place. Using BFD > > end to end to track reachability between PEs simply does not scale. > > > > It seems to me that scaling of BFD should be "roughly" proportional to > BGP > > session scaling but I seem to be in the minority. My opinion is based on > > SDWAN tunnel scaling, where BFD is used implicitly in our solution. How > > many other PEs does a BGP edge PE maximally peer with? > > Thanks, > > Acee > > > > > > Some people believe this should be solved by BGP, but it is > important to > > realize that while the problem statement at the moment is primarily > > targeted for egress PE reachability loss detection for BGP, the > > mechanism proposed is generic enough and can be used to track the > peer > > reachablity loss for other cases (e.g GRE endpoint, etc) that do not > > involve BGP. > > > > We went even further and explored the option to use completely out of > > band mechanism that do not involve any existing protocols. > > > > Simply, the advantage of using IGP is that it follows the existing > MPLS > > model, where the endpoint reachability is provided by IGPs. Operators > > are familiar with IGPs and know how to operate them. > > > > On top of the above, IGP event notification can find other use cases > in > > the future, the mechanism defined in draft is generic enough. > > > > > > > 2. Assuming we do want to take on negative advertisement in the > IGP, > > > what are the technical merits and/or detriments of the two > > approaches? > > > > we have listed some requirements at: > > > > https://datatracker.ietf.org/doc/html/draft-ppsenak-lsr-igp-event- > > notification-00#section-3 > > > > From my perspective the solution should be optimal in terms of > amount > > of data and state that needs to be maintained, ideally separated from > > the traditional LS data. I also believe that having a generic > mechanism > > to distribute events has it own merits. > > > > thanks, > > Peter > > > > > > > > We’ll reserve any further discussion to “WG member” comments on the > > two > > > approaches. > > > > > > Thanks, > > > Acee and Chris > > > > > > > > > _______________________________________________ > > Lsr mailing list > > [email protected] > > https://www.ietf.org/mailman/listinfo/lsr > _______________________________________________ > Lsr mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/lsr >
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