Re: [Lsr] Prefix Unreachable Announcement Use Cases

[Gyan Mishra <[e-mail]>]

Agreed.

Robert

Can you explain the BGP scenario you had in mind that you have mentioned a
number of times that you think this PUA feature would pertain?

I will respond to your other email separately.  I was trying to guess  as
to the BGP next hop use case you were referring to but apparently was way
off.

Thank you

Gyan

On Tue, Nov 17, 2020 at 9:43 AM Acee Lindem (acee) <[e-mail]> 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 <[e-mail]> on behalf of Gyan Mishra <
> [e-mail]>
> *Date: *Tuesday, November 17, 2020 at 4:02 AM
> *To: *Robert Raszuk <[e-mail]>
> *Cc: *lsr <[e-mail]>, Jeff Tantsura <[e-mail]>, Aijun
> Wang <[e-mail]>, "Acee Lindem (acee)" <acee=
> [e-mail]>
> *Subject: *Re: [Lsr] Prefix Unreachable Announcement Use Cases
>
>
>
>
>
>
>
> On Tue, Nov 17, 2020 at 3:36 AM Robert Raszuk <[e-mail]> wrote:
>
>
>
>
>
>    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.
>
>
>
> Please present us a picture indicating before and after ABRs behaviour.
>
>
>
>      Gyan> will do
>
>
>
>    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.
>
>
>
>
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> 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.
>
>
>
> Thx,
> R.
>
>
>
>
>
> --
>
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>
> *Gyan Mishra*
>
> *Network Solutions Architect *
>
>
>
> *M 301 502-1347 13101 Columbia Pike
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>
>
-- 

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*Gyan Mishra*

*Network Solutions A**rchitect *



*M 301 502-134713101 Columbia Pike *Silver Spring, MD