Re: [Idr] Rtgdir early review of draft-ietf-idr-bgp-optimal-route-reflection-21

bruno.decraene@orange.com Mon, 07 December 2020 16:30 UTC

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From: <bruno.decraene@orange.com>
To: Daniele Ceccarelli <daniele.ceccarelli@ericsson.com>
CC: "draft-ietf-idr-bgp-optimal-route-reflection.all@ietf.org" <draft-ietf-idr-bgp-optimal-route-reflection.all@ietf.org>, "idr@ietf.org" <idr@ietf.org>, "rtg-dir@ietf.org" <rtg-dir@ietf.org>
Thread-Topic: Rtgdir early review of draft-ietf-idr-bgp-optimal-route-reflection-21
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Date: Mon, 7 Dec 2020 16:30:22 +0000
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Subject: Re: [Idr] Rtgdir early review of draft-ietf-idr-bgp-optimal-route-reflection-21
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Hi Daniele,

Please see inline [Bruno2]

> -----Original Message-----
> From: Daniele Ceccarelli [mailto:daniele.ceccarelli@ericsson.com]
> Sent: Monday, December 7, 2020 1:51 PM
> To: DECRAENE Bruno TGI/OLN <bruno.decraene@orange.com>
> Cc: draft-ietf-idr-bgp-optimal-route-reflection.all@ietf.org; idr@ietf.org; rtg-
> dir@ietf.org
> Subject: RE: Rtgdir early review of draft-ietf-idr-bgp-optimal-route-
> reflection-21
> 
> Hi Bruno,
> 
> Please see in line.
> 
> BR
> Daniele
> 
> -----Original Message-----
> From: bruno.decraene@orange.com <bruno.decraene@orange.com>
> Sent: den 7 december 2020 13:22
> To: Daniele Ceccarelli <daniele.ceccarelli@ericsson.com>
> Cc: draft-ietf-idr-bgp-optimal-route-reflection.all@ietf.org; idr@ietf.org; rtg-
> dir@ietf.org
> Subject: RE: Rtgdir early review of draft-ietf-idr-bgp-optimal-route-
> reflection-21
> 
> Daniele,
> 
> Thanks for your review and comments.
> Please see inline [Bruno]
> 
> > From: Daniele Ceccarelli via Datatracker [mailto:noreply@ietf.org]
> > Sent: Monday, December 7, 2020 10:01 AM
> > To: rtg-dir@ietf.org
> > Cc: draft-ietf-idr-bgp-optimal-route-reflection.all@ietf.org;
> > idr@ietf.org
> > Subject: Rtgdir early review of
> > draft-ietf-idr-bgp-optimal-route-reflection-21
> >
> > Reviewer: Daniele Ceccarelli
> > Review result: Ready
> >
> > The draft has been significantly improved since my previous review (v11).
> > Since the draft progressed till v21 i assume the working group found
> > an agreement on the usefulness of the idea. Please see my previous
> comment:
> >
> > "My concern, which is something the working group probably already
> > discussed, is about the complexity and usefulness of the idea. The
> > goal of draft is: "The core of this solution is the ability for an
> > operator to specify on a per route reflector basis or per peer/update
> > group basis or per peer basis the virtual IGP location placement of
> > the route reflector. This enables having a given group of clients
> > receive routes with  optimal distance to the next hops from the
> > position of the configured virtual IGP location.  This also provides
> > for freedom of route reflector location and allows transient or
> > permanent migration of such network control plane function to optimal
> > location.”
> >
> > But I understand that there is a number of workarounds and that
> > different paths are already used for redundancy reasons, hence my
> > questions is: is it worth defining a new solution? Is the usage of the
> > actual  mechanisms so disoptimized to require these changes? How many
> > possible paths  are there between the client and the AS border node?"
> >
> [Bruno] I don't read that you are calling for specific changes in the
> draft/specification.
> [DC] no. I added that I'm fine with the text added in appendix A.
> 
> For what it worth, I can offer my personal feedback.
> In the networks, there are multiple paths to a given destination/NLRI. BGP
> Route Reflector are a widely deployed tool but they may introduce non
> optimal routing in some cases. The typical solution to mitigate is to carefully
> position those BGP Route Reflectors in the IGP topology. This brings
> operational costs and inflexibilities during maintenance operations,
> addition/removal of RR for scaling purpose, moving this control plane
> function out of data plane/chassis routers in particular when 'virtualizing'
> them on generic x86 servers which are better suited in term of
> CPU/memory/power/cooling capability. So yes, I believe that the extension
> provided in §3.1 [1] is very useful to decouple the physical location of the
> BGP RR from the logical selection of the so called best routes. I find this a
> useful flexibility and don't find the cost of this extension high with regards to
> the benefit.
> [1] https://tools.ietf.org/html/draft-ietf-idr-bgp-optimal-route-reflection-
> 21#section-3.1
> 
> I could say more, but given that this document will eventually reach the IESG
> 10 years after its initial version, and multiple implementations, I think that the
> train left the station a while ago.
> 
> > I see that appendix A has been added with alternative solutions, very good.
> >
> > I only found minor comment and nits.
> > - Astract: "to choose the best path for their clients standpoint" i
> > guess this should be "From their clients standpoint" - Abstract:
> > "multiple type - multiple types"
> 
> [Bruno] Corrected *2. Thanks.
> 
> >- Section 3: there are some issues with bullet items
> 
> [Bruno] Sorry, could you be more specific? (There are 2*2 bullet items and
> the issue is not apparent to me).
> 
> [DC] i was just suggesting to have something as a bullet, eg. a dash.

[Bruno2] ok. Thanks. Done.

> 
> > - Section 3: "The
> > first change is related to the IGP cost to the BGP Next Hop, which is
> > done in the step e) in the BGP decision process" where is step e)
> > defined? maybe a missing reference? ...further reading the document i
> > find a description of step
> > e) in section 3.1. Maybe just saying "as described in section 3.1 "
> > would be enugh. - Section 3.1.
> 
> [Bruno] As you found out, this is step 2) of the BGP decision process
> https://tools.ietf.org/html/rfc4271#section-9.1.2.2
> 
> Since the latest version of the draft has more text on this in section 3.1, I
> would propose:
> OLD:
>       The first change is related to the IGP cost to the BGP Next Hop,
>       which is done in the step e) in the BGP decision process.
> 
> NEW:
>       The first change, introduced in section 3.1, is related to the IGP cost to the
> BGP Next Hop,
>       in the BGP decision process.
> 
> 
> I've also added the reference of the second bullet.
> [DC] great. That works.
> 
> > Since step e) is modified probably the draft should update RFC 4271?
> 
> [Bruno] I don't believe so.
> - In the sense that people implementing 4271 but not implementing this
> document do not need to be aware of this document.
> - This document is primarily an extension of BGP Route Reflector [2].  Note
> that BGP Route Reflector also changed the decision process and did not
> update 4271.
> 
> That been said, I leave this to the AD/IESG.
> [DC] indeed. What about compatibility issues with implementations based on
> old step e)?

[Bruno2]
There is a text covering this in 3rd paragraph of https://tools.ietf.org/html/draft-ietf-idr-bgp-optimal-route-reflection-21#section-6
In general, I'd say that the main issue is coming from/since RR / RFC 4456. Cf last paragraph of https://tools.ietf.org/html/rfc4456#section-11  From a route selection standpoint, I don't see that it really matters whether the RR is physically located on Node 3 as per RFC 4456, or 'logically located' on Node 3 as per  draft-ietf-idr-bgp-optimal-route-reflection

Thanks,
--Bruno

> [2] https://tools.ietf.org/html/rfc4456
> 
> > Overall i like the way that the abstract and the introduction have
> > been updated, with the former introducing the solution and the latter
> > well explaining the problem to be solved.
> 
> [Bruno] Thanks. Improvements come from review from new eyes. So thank
> you again for your time, you review and comments.
> [DC] you're more than welcome.
> --Bruno
> 
> 
> 
> 
> 
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