Re: [Lsr] Flooding across a network

Robert Raszuk <> Thu, 07 May 2020 09:20 UTC

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From: Robert Raszuk <>
Date: Thu, 7 May 2020 11:20:31 +0200
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To: Jeff Tantsura <>
Cc: "Les Ginsberg (ginsberg)" <>, "" <>, "" <>
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Subject: Re: [Lsr] Flooding across a network
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Hey Jeff,

What if in your analysis A-D link metric is 1500 ? Still A will send to B !

See in all of this discussion from my pov it is not really about danger of
making LSDB inconsistent for much longer.

It is however about operator upgrading to new release a router, maybe even
reading release notes stating that flooding speed optimizations defined in
RFC ZZZ are implemented and final effect he sees are microloops lasting 10s
of seconds for his traffic.

Yes some vendors have good tools to protect from microloops, but those must
be enabled. Moreover those still require manual timer configuration how
long to keep loop free protection in place. And I am not aware any vendor
has a cli command showing how long it took in all routers in my area/level
to install in FIB result of various levels/cases of topology changes.

So I am not saying faster is not good. I am saying if you make car faster
do not forget to equip it with seat belts and make enough of warnings that
driver will actually fasten them.


On Thu, May 7, 2020 at 6:41 AM Jeff Tantsura <>

> Robert,
> Assuming C and E provide access to the same set of destinations, that are
> closer of further away from C and E.
> B (which is fast), after it notifies A that it can’t reach C directly will
> cause A to send traffic to D. D - dependent on total cost would start
> happily sending some traffic towards destinations behind C to B so LFA on B
> wouldn’t really help.
> Cheers,
> Jeff