Re: [Lsr] https://tools.ietf.org/html/draft-wang-lsr-prefix-unreachable-annoucement-05

Peter Psenak <ppsenak@cisco.com> Wed, 10 March 2021 08:10 UTC

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To: Robert Raszuk <robert@raszuk.net>
Cc: Tony Li <tony.li@tony.li>, Gyan Mishra <hayabusagsm@gmail.com>, Aijun Wang <wangaijun@tsinghua.org.cn>, Aijun Wang <wangaj3@chinatelecom.cn>, lsr <lsr@ietf.org>, "Acee Lindem (acee)" <acee@cisco.com>, draft-wang-lsr-prefix-unreachable-annoucement <draft-wang-lsr-prefix-unreachable-annoucement@ietf.org>
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From: Peter Psenak <ppsenak@cisco.com>
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Date: Wed, 10 Mar 2021 09:10:47 +0100
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Subject: Re: [Lsr] https://tools.ietf.org/html/draft-wang-lsr-prefix-unreachable-annoucement-05
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Robert,


On 09/03/2021 19:30, Robert Raszuk wrote:
> Hi Peter,
> 
>      > Example 1:
>      >
>      > If session to PE1 goes down, withdraw all RDs received from such PE.
> 
>     still dependent on RDs and BGP specific. 
> 
> 
> To me this does sound like a feature ... to you I think it was rather 
> pejorative.

not sure I understand your point with "pejorative"...

There are other ways to provide services outside of BGP - think GRE, 
IPsec, etc. The solution should cover them all.

> 
>     We want app independent way of
>     signaling the reachability loss. At the end that's what IGPs do without
>     a presence of summarization.
> 
> 
> Here you go. I suppose you just drafted the first use case for OSPF 
> Transport Instance.

you said it, not me.


> 
> I suppose you just run new ISIS or OSPF Instance and flood info about PE 
> down events to all other instance nodes (hopefully just PEs and no Ps as 
> such plane would be OTT one).  Still you will be flooding this to 100s 
> of PEs which may never need this information at all which I think is the 
> main issue here. Such bad news IMHO should be distributed on a pub/sub 
> basis only. First you subscribe then you get updates ... not get 
> everything then keep junk till it get's removed or expires.

with MPLS loopback address of all PEs is advertised everywhere. So you 
keep the state when the remote PE loopback is up and you get a state 
withdrawal when the remote PE loopback goes down.

In Srv6, with summarization we can reduced the amount of UP state to 
minimum. But suddenly the DOWN event distribution is considered 
problematic. Not sure I follow.

thanks,
Peter

> 
> Many thx,
> Robert
>