Re: [Lsr] Prefix Unreachable Announcement Use Cases

Tony Przygienda <> Fri, 20 November 2020 21:02 UTC

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From: Tony Przygienda <>
Date: Fri, 20 Nov 2020 13:02:08 -0800
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To: Robert Raszuk <>
Cc: Aijun Wang <>, lsr <>, Jeff Tantsura <>, "Acee Lindem (acee)" <>
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Subject: Re: [Lsr] Prefix Unreachable Announcement Use Cases
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Yeah, so to give e'one his due, negative disaggregation is Pascal's
brilliant brain-child, I bow to this. And I bow to his patience grinding me
down to convince me the complexity of it is by far outweighted by elegance
it brings to ugly failure repair. Then it took a lot of brow-beating until
e'one on RIFT understood that no, we will not get negative entry silicon
and hence need to remap negative to proper resolution as positive. Not the
simplest things but once you implemented it it turns out simpler than it
looks @ first

my 2c, I'll be watching here from a distance probably until it gelled a bit

-- tony

On Fri, Nov 20, 2020 at 12:45 PM Robert Raszuk <> wrote:

> Hey Tony,
> >  people somehow implying a map of RIFT negative disaggregation in
> relation to this work
> I think those people just made a subtle point that considering IGP alone
> if you want to influence your data plane forwarding by advertising PUA in
> today's hardware you really need to install more specific blocks of the
> summary routes which PUA punched the hole in as sent by say one of the
> ABR's. Analogy made to RIFT was just limited to this data plane fragment
> only.
> And that comment was not to compare PUA to RIFT negative routing in any
> way. It was just to a) realize what could be required if such a use case
> continues and more importantly b) highlight that if we just use PUA in the
> control plane to for example invalidate BGP next hops or other overlay
> service routes the disaggregation piece does not apply.
> Cheers,
> R.
> On Fri, Nov 20, 2020 at 9:09 PM Tony Przygienda <>
> wrote:
>> On Fri, Nov 20, 2020 at 6:27 AM Aijun Wang <>
>> wrote:
>>> Hi, Tony:
>>> Aijun Wang
>>> China Telecom
>>> On Nov 20, 2020, at 17:45, Tony Przygienda <> wrote:
>>> Yes, acknowledging the idea of negative disaggregation is inspired by
>>> RIFT work is fine (and normally, when inspired by an idea at least in
>>> research cycles it is considered basic courtesy to refer to the according
>>> source, something has been lost more and more in IETF over time I dare to
>>> observe which in itself reflects on the community IMO) but please do not
>>> try to compare the two beyond that.
>>> [WAJ] PUA has no relation with RIFT. I have not yet study what’s problem
>>> it encountered, but welcome the experts have such design experience to
>>> point out the pitfall that PUA can bypass.
>> aha, ok, I just chimed in because I saw people somehow implying a map of
>> RIFT negative disaggregation in relation to this work but if this is a
>> completely different mechanism than I just watch from the sidelines
>> thanks
>> -- tony