That's true. I am pointing out that this in some networks may be much slower then invalidating the next hops from BGP route reflectors by running *local* multihop BFD sessions to subject PEs (all within an area).
So I have a question ... Let's forget about BGP and RRs and just stay focused on IGP: Would it be feasible to trigger UPA on ABRs by running multihop BFD sessions between ABRs and local area PEs and not wait for PE-P detection of link down as well as flooding to carry the information to ABRs ? Thx, R. On Thu, Jul 7, 2022 at 12:18 PM Peter Psenak <ppse...@cisco.com> wrote: > Robert, > > BGP PIC depends on the IGP convergence. We are not changing any of that > by UPA. > > thanks, > Peter > > > On 07/07/2022 12:02, Robert Raszuk wrote: > > Peter, > > > > All I am saying is that this may be pretty slow if even directly > > attached P routers must way say 6 seconds (3 x 2 sec BFD) to declare > > peer down. > > > > And that is in contrast to running BFD from say BGP RR to all PEs in an > > area. > > > > The fundamental point is that in the case of PUA you MUST wait for all P > > routers to tell you that PE in fact went down. While in case of > > invalidating service routes the first trigger is good enough. > > > > To me this is significant architectural difference. > > > > Many thx, > > R. > > > > > > On Thu, Jul 7, 2022 at 11:54 AM Peter Psenak <ppse...@cisco.com > > <mailto:ppse...@cisco.com>> wrote: > > > > On 07/07/2022 11:38, Robert Raszuk wrote: > > > > > > > there is no such thing. > > > > > > By far away ABR I mean ABR far away from failing PE connecting > local > > > are to the area 0. There can be number of P routers in between. > > > > ABR has the full visibility of the local area and knows when any > > node or > > prefix becomes unreachable. It is determined by the SPF computation > and > > prefix processing that is triggered as a result of the change in the > > local area. > > > > thanks, > > Peter > > > > > > > > Let me provide you with an illustration: > > > > > > PE can be in Honolulu. ABR in Huston. All in one area. For me > > this ABR > > > is far away from PE. > > > > > > On Thu, Jul 7, 2022 at 11:35 AM Peter Psenak <ppse...@cisco.com > > <mailto:ppse...@cisco.com> > > > <mailto:ppse...@cisco.com <mailto:ppse...@cisco.com>>> wrote: > > > > > > Robert, > > > > > > On 07/07/2022 11:25, Robert Raszuk wrote: > > > > Hi Peter, > > > > > > > > > Section 4: > > > > > > > > > > "The intent of UPA is to provide an event driven signal > > of the > > > > > transition of a destination from reachable to > > unreachable." > > > > > > > > That is too vague. > > > > > > it's all that is needed. > > > > > > > > > > > I am asking how you detect that transition on a far away > ABR. > > > > > > there is no such thing. The detection is done based on the > prefix > > > transition from reachable to unreachabile in a local area by > > local > > > ABRs. > > > Remote ABRs just propagate the UPA. > > > > > > thanks, > > > Peter > > > > > > > > > > > For example, are you tracking flooding on all links to > > subject PE > > > from > > > > all its neighbours and only when all of them remove that > > link from > > > > topology you signal PUA ? > > > > > > > > If so practically such trigger may be pretty slow and > > > inconsistent as in > > > > real networks as links over which PEs are connected are > > often of a > > > > very different quality, coming from different carriers and > may > > > have for > > > > stability varying BFD timers. So here you would have to > > wait for the > > > > slowest link to be detected on the neighbouring P router > > as down. > > > > > > > > Thx, > > > > R. > > > > > > > > On Thu, Jul 7, 2022 at 10:16 AM Peter Psenak > > <ppse...@cisco.com <mailto:ppse...@cisco.com> > > > <mailto:ppse...@cisco.com <mailto:ppse...@cisco.com>> > > > > <mailto:ppse...@cisco.com <mailto:ppse...@cisco.com> > > <mailto:ppse...@cisco.com <mailto:ppse...@cisco.com>>>> wrote: > > > > > > > > Robert, > > > > > > > > On 06/07/2022 15:07, Robert Raszuk wrote: > > > > > Hi Peter, > > > > > > > > > > Can you please point me in the draft > > > > > > > > > > > > > > > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > > > > > > > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > >> > > > > > > > > > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt> > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > >>> > > > > > > > > > > > > > > > > > > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt> > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > >> > > > > > > > > > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt> > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > < > https://www.ietf.org/id/draft-ppsenak-lsr-igp-ureach-prefix-announce-00.txt > >>>> > > > > > > > > > to some section which specifies based on exactly > > what network > > > > flooding > > > > > changes UPA will be generated by ABRs ? > > > > > > > > Section 4: > > > > > > > > "The intent of UPA is to provide an event driven > > signal of the > > > > transition of a destination from reachable to > > unreachable." > > > > > > > > > > I think such text is not an implementation detail, > > but it is > > > > critical > > > > > for mix vendor interoperability. > > > > > > > > > > Can UPA also be generated by P node(s) ? > > > > > > > > only if they are ABRs or ASBRs. > > > > > > > > > > > > > > > > > > Specifically I was looking to find some information > on > > > how do you > > > > > achieve assurance that UPA really needs to be > generated > > > when using > > > > > various vendor's nodes with very different flooding > > behaviours > > > > and when > > > > > subjects PEs may have a number of different links > > each with > > > > different > > > > > node/link down detection timer ? > > > > > > > > sorry, I don't understand the above. > > > > > > > > thanks, > > > > Peter > > > > > > > > > > > > > > Many thx, > > > > > R. > > > > > > > > > > > > > > > >
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