We have been discussing for quite some time and in different wg's (there’s IX with RS use case) BFD verification based on next-hop extraction, Robert - you should know. (also built a well working prototype in previous life).
Very simple logic: Upon route import (BGP update received and imported), extract next-hop, walk BFD session table, if no match (no existing session) - establish (S)BFD session (Discriminators distribution is a solved problem) to the next-hop, associate fate of all routes received from it, keep timers reasonable to prevent false positives. State is limited to PE’s importing each others routes (sharing a service) only High degree of automation No IGP pollution Cheers, Jeff On Nov 17, 2020, 6:43 AM -0800, Acee Lindem (acee) <a...@cisco.com>, wrote: > Speaking as WG member: > > I think it would be good to hone in on the BGP PE failure convergence use > case as suggested by Robert. It seems there is some interest here although > I’m not convinced the IGP is the right place to solve this problem. > > Thanks, > Acee > > From: Lsr <lsr-boun...@ietf.org> on behalf of Gyan Mishra > <hayabusa...@gmail.com> > Date: Tuesday, November 17, 2020 at 4:02 AM > To: Robert Raszuk <rob...@raszuk.net> > Cc: lsr <lsr@ietf.org>, Jeff Tantsura <jefftant.i...@gmail.com>, Aijun Wang > <wangai...@tsinghua.org.cn>, "Acee Lindem (acee)" > <acee=40cisco....@dmarc.ietf.org> > Subject: Re: [Lsr] Prefix Unreachable Announcement Use Cases > > > > On Tue, Nov 17, 2020 at 3:36 AM Robert Raszuk <rob...@raszuk.net> wrote: > > quote_type > > > > > > > quote_type > > > Robert, I believe the original intention was related to having the > > > data plane converge quickly when summarization is used and flip so > > > traffic converges from the Active ABR to the Backup ABR. > > > > I do not buy this use case. Flooding within the area is fast such that both > > ABRs will get the same info. As mentioned before there is no practical use > > of PUA for making any routing or fwd decision on which ABR to use. If your > > ABRs are not connected with min redundancy this draft is a worst patch ever > > to work around such a design. > > Gyan> Agreed. The point of PUA in ABR use case is the ability to track > the component prefixes and in case where component is down and traffic is > still forwarded to the ABR and dropped. The other more important use case is > when links are down within the area and the area is partitioned and so one > ABR has all component prefixes however other ABR is missing half the > component prefixes. So since the ABR will by default advertise the summary > as long as their is one component UP the summary is still advertised. So > this use case is severely impacting as now you have an ECMP path to the other > area for the summary via the two ABRs and you drop half your traffic. So now > with PUA the problem is fixed and the PUA is sent and now traffic is only > sent to the ABR that has the component prefixes. > > quote_type > > > > Please present us a picture indicating before and after ABRs behaviour. > > Gyan> will do > > quote_type > > > > > quote_type > > > However PUA can be used in the absence of area segmentation within a > > > single area when a link or node fails to converge the data plane quickly > > > by sending PUA for the backup path so the active path. > > > > If there is no area segmentation then there is no summaries. So what are we > > missing in the first place ? > > Gyan> Sorry I am stating that PUA feature can also be used intra area > where if a link or node goes down to improve data plane convergence. > > quote_type > > > > > > > quote_type > > > With the IGP tuned with BFD fast detection on ISIS or OSPF links and LFA > > > & RLFA for MPLS or TI-LFA for SR local protection - with those tweaks the > > > convergence is well into sub second. So for Intra area convergence with > > > all the optimizations mentioned I am not sure how much faster the data > > > plane will converge with PUA. > > > > Even without any of the above listed chain of acronymous things will > > generally work well intra-area without PUAs. > > Gyan> Agreed which is why I mentioned the BGP next hop self use case if I > could figure out how PUA could help there that would be a major benefit of > PUA. > > quote_type > > > > Thx, > > R. > > > > > -- > <> > Gyan Mishra > Network Solutions Architect > M 301 502-1347 > 13101 Columbia Pike > Silver Spring, MD >
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