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

Peter Psenak <ppsenak@cisco.com> Wed, 10 March 2021 10:40 UTC

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To: Robert Raszuk <robert@raszuk.net>
Cc: Gyan Mishra <hayabusagsm@gmail.com>, Aijun Wang <wangaijun@tsinghua.org.cn>, Aijun Wang <wangaj3@chinatelecom.cn>, Tony Li <tony.li@tony.li>, lsr <lsr@ietf.org>, "Acee Lindem (acee)" <acee@cisco.com>, draft-wang-lsr-prefix-unreachable-annoucement <draft-wang-lsr-prefix-unreachable-annoucement@ietf.org>
References: <22FDE3EA-B5D1-4E4D-B698-1D79173E8637@tony.li> <6E0281D2-7755-499A-B084-CA8472949683@chinatelecom.cn> <D6B0D95F-68AD-4A18-B98C-69835E8B149B@tony.li> <018801d71499$9890feb0$c9b2fc10$@tsinghua.org.cn> <CABNhwV2SpcDcm-s-WkWPpnVLpYB2nZGz2Yv0SfZah+-k=bGx4A@mail.gmail.com> <BFB3CE24-446A-4ADA-96ED-9CF876EA6A00@tony.li> <CAOj+MMGeR4bodbgpPqDCtLZD6XmX6fkjyxLWZAKa4LC2R1tBzg@mail.gmail.com> <ecf2e8b4-fdae-def6-1a29-ec1ae37f5811@cisco.com> <CAOj+MMFSEqVkM62TDAc6yn19Hup+v-9w=kiq_q6dVn39LcOkqQ@mail.gmail.com> <fdf0e62a-21fa-67e9-811d-5aa8749bb077@cisco.com> <CAOj+MMGqab_MSeZuwu0jLpCiDoZrcjnjebScscULsvnJt4_Sgw@mail.gmail.com> <2b2e9a39-ee2d-ab1c-2d59-ff5847c943e8@cisco.com> <CAOj+MMETEOgA_QO0V_k052cu10a2ZVkf8at-1+kut7OQwf=Kug@mail.gmail.com> <14e8038e-338f-599e-3c40-fdaac247fc10@cisco.com> <CAOj+MMF4xdh2TsMWVEmw_qUxxTS-zFbtE4xK8-cL-cw3xmcrgg@mail.gmail.com>
From: Peter Psenak <ppsenak@cisco.com>
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Date: Wed, 10 Mar 2021 11:40:01 +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 10/03/2021 11:29, Robert Raszuk wrote:
> Peter,
> 
>  > But suddenly the DOWN event distribution is considered
>  > problematic. Not sure I follow.
> 
> In routing and IP reachability we use p2mp distribution and flooding as 
> it is required to provide any to any connectivity.
> 
> Such spray model no longer fits services where not every endpoint 
> participates in all services.
> 
> So my point is that just because you have transport ready we should not 
> continue to announce neither good nor bad news in spray fashion for 
> services.
> 
> Sure it works, but it is hardly a good design and sound architecture.
> 
> It happened to BGP as the convenience of already having TCP sessions 
> between nodes was so great that we loaded loads of stuff to go along 
> basic routing reachability.
> 
> And now it seems time came to do the same with IGPs :).
> 
> I think unless we stop and define a real pub-sub messaging protocol 
> (like FB does with open-R)  we will continue this.

you are of course free to do that. Here we are at the LSR WG.

thanks,
Peter



> 
> And to me it is like building a tower from the cards ... the higher you 
> go the more likely your entire tower is to collapse.
> 
> Cheers,
> R.
> 
> PS.
> 
>  > with MPLS loopback address of all PEs is advertised everywhere.
> 
> Is this a feature or a day one design bug later fixed by RFC5283 ?
> 
> 
> 
> 
> On Wed, Mar 10, 2021 at 9:10 AM Peter Psenak <ppsenak@cisco.com 
> <mailto:ppsenak@cisco.com>> wrote:
> 
>     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
>      >
>