Robert,
On 30/11/2021 10:29, Robert Raszuk wrote:
Les,
*/I was just trying to illustrate that prefixes covered by the
summary could be advertised using existing IGP advertisements even
when the summary is being advertised. /**/It is still reachability.
The determination of when to advertise the prefix and when not to is
still based upon whether the ABR has a path to the prefix based on
latest SPF calculation./*
*/__ __/*
*/You choose to rename such an advertisement as “liveness” rather
than “reachability” for no reason that I can see. It then allows you
claim an “architectural violation” – but this to me is a meaningless
distraction. /**/I was hoping to get rid of this distraction – but
no such luck I see./*
You are correct that from ABR it may look like atomic reachability.
But if you look at the bigger picture what triggers this reachability is
liveness detection between P and PE routers.
And I guess what really matters is not how we call it - what matters is
what truly triggers our protocol actions.
*/[LES:] This wasn’t the point of the example. I wasn’t promoting
the example as desirable deployment choice. I was only illustrating
that it is the change in reachability(sic) that is the event. With
current IGP advertisements we would (of course) stop advertising
reachability when we do not have a path to a given prefix. The new
advertisements propose to advertise the loss of reachability to
destinations which are covered by a summary. That has advantages
over a withdrawal (the absence of an advertisement)./*
Perhaps. But it also has huge complexity on the clients (src PEs) which
now need to bend to use this info. Something which is not in RIB
disappears. I recall when you worked on RIB architecture one of the
basic primitives was to always communicate protocol to protocol via RIB.
Here we are talking about some not so elegant shortcuts. And not only in
respect to protocols. Also touching FIB.
we have done the prototype. The changes to consume the pulse and trigger
the BGP PIC were very small and simple.
It is perhaps the vendor's secret sauce how you use this new info. But
by all means this is not what is today well known operational monitoring
practice.
that does not make it wrong, does it?
thanks,
Peter
That is why the ephemeral nature of the proposed advertisements is IMO
its disadvantage.
Thank you,
R.
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