*> [WAJ] No. Link or Node Failures are not detected via BFD within one IGP domain.*
What makes you say so ? Thx, R. On Wed, Oct 13, 2021 at 3:27 AM Aijun Wang <[email protected]> wrote: > Hi, Robert: > > > > Answers to your comments are inline below. > > > > > > Best Regards > > > > Aijun Wang > > China Telecom > > > > *From:* [email protected] <[email protected]> *On Behalf Of *Robert > Raszuk > *Sent:* Wednesday, October 13, 2021 3:52 AM > *To:* Acee Lindem (acee) <[email protected]> > *Cc:* [email protected] > *Subject:* Re: [Lsr] "Prefix Unreachable Announcement" and "IS-IS and > OSPF Extension for Event Notification" > > > > Hi Acee, > > > > I would like to make a comment on your point #1. > > > > You said: > > > > "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)..." > > > > That is not a very precise statement - simply due to the fact that to > signal anything in any solution requires a peer to detect giben network > event. > > > > In both cases such an event will likely be detected using BFD (if we are > talking about unreachability of a BGP or IGP peer). > > *[WAJ] No. Link or Node Failures are not detected via BFD within one IGP > domain. It just rely on the normal IGP flooding procedures. Once the ABRs > receive the updated LSA, they will make the calculation and find the > missing prefixes.* > > > > Neither of the drafts mentioned here replaces local BFD detection. > > *[WAJ] Deploy such mechanisms can replace the BFD for BGP configuration > between PEs that located in different IGP domains.* > > > > I do infer from your message that what was meant to be said was an > alternative to support BFD sessions across areas/levels for example between > PEs. Clearly that would get very ugly very quickly. > > > > However IMO the natural signalling in this case would be to use BGP > itself. Here are the few reasons: > > *[WAJ] How the BGP peer be detected that the peer has been unreachable? > Via BFD for BGP?* > > > > * detection time will be the same for IGP or BGP > > *[WAJ] It is the ABR’s summarization action hides the unreachable > prefixes, then BGP peers located in different IGP domains can’t know the > failure as quickly as IGP within the same domain.* > > > > * only those network elements which keep "interesting" state will be > notified > > *[WAJ] To be more accurate, your above statement should be **【* only > those network elements which keep "interesting" state will act upon the PUA > messages.】* > > > > * speed of withdraw can be argued to be as fast as IGP flooding especially > considering hierarchical IGP design > > *[WAJ] When we let ABR send the PUA messages, not hide them, the speed of > withdraw can certainly be accelerated.* > > > > * withdraws can be easily aggregated (when we loose PE single prefix can > be used to remove all paths advertised by given PE) > > *[WAJ] This is the effects PUA mechanism. when the BGP peer receives the > PUA message that includes the PE itself, all the path advertised by the > given PE can certainly be removed.* > > * withdraws can be injected as the next hop /32 or /128 prefixes and > remote next hop validation can be set not to consider less specific routes > to resolve next hops (in any case due to MPLS data plane host routes are > used in many networks today to resolve BGP service routes to LSPs in spite > of efforts to make this more scalable). > > *[WAJ]This the effect of PUA mechanism.* > > > > Only when we prove that BGP based solutions are not sufficient we > could/should explore moving such signalling to IGPs. > > *[WAJ] Do the above responses prove the BGP based solution are not > sufficient?* > > > > Kind regards, > > R. > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Tue, Oct 12, 2021 at 9:06 PM Acee Lindem (acee) <acee= > [email protected]> 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. > > > > 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? > > 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’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 > >
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