Re: [Idr] decraene-idr-next-hop-capability <-> ietf-idr-bgp-nh-cost

<bruno.decraene@orange.com> Tue, 31 March 2015 10:22 UTC

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From: <bruno.decraene@orange.com>
To: "Jerome Durand (jerduran)" <jerduran@cisco.com>
Thread-Topic: [Idr] decraene-idr-next-hop-capability <-> ietf-idr-bgp-nh-cost
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Date: Tue, 31 Mar 2015 10:22:17 +0000
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Subject: Re: [Idr] decraene-idr-next-hop-capability <-> ietf-idr-bgp-nh-cost
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Hi Jérome, all

> From: Jerome Durand (jerduran) [mailto:jerduran@cisco.com] > Sent: Wednesday, March 25, 2015 9:32 PM
> 
> Hi Bruno,
> 
> Interesting there are some similarities to what I proposed here:
> draft-jdurand-idr-next-hop-liveliness-00

You are right. 
I had read your document and had considered chatting this with you, but then understood that you were now favoring a different approach (namely draft-jdurand-auto-bfd).


> Where I tried to describe how we could carry next-hop capability to
> implement a host liveliness mechanism and solve the route-server black-
> holing stuff we have been talking about lately. Having a kind of general
> framework for any capability (ie. not just host liveliness) makes sense.

Thanks. I clearly agree with you.
 
> But your proposal relies on a non transitive attribute and couldn't pass the
> route-server so I cannot adjust my proposal to fit in yours.

ID. next-hop-capability _needs_ a non transitive attribute so this is not something that I can accommodate.
Can't the route-server be extended to support the capability? Looks like a relatively small change (and if the Route Server is known to never change the next-hop, a (horrible) hack would be just a matter of recognizing the attribute to pass it unchanged. But I will deny having said this ;-) )
 
> Anyway note that now I more or less stopped that work for the moment to
> focus on a more automated solution as there were some challenges with BGP
> (issues described in the draft). Also it seems that it was quite heavy from a
> processing/memory point of view to have new attributes per route. Note we
> had the idea to use some kind of "magic route" in order to have the attribute
> transported only once. Maybe to be investigated further. This is also
> described in the draft.

Thanks for the feedback. As of today, IMO carrying the attribute in each update is simpler and more flexible. Some NH capability may need this (and as a matter of fact, the entropy label capability needs this).

Thanks for the comments and feedback.
/Bruno

 
> Thanks!
> 
> Jerome
> 
> 
> 
> 
> 
> 
> Le 25 mars 2015 à 20:56, <bruno.decraene@orange.com>
> <bruno.decraene@orange.com> a écrit :
> 
> > Hi David,
> >
> > Thanks for your comments.
> > Please see inline.
> >
> >> From: David Lamparter [mailto:equinox@diac24.net] > Sent: Tuesday,
> >> March 24, 2015 4:30 PM
> >>
> >> Hi Bruno, Ilya, Robert,
> >> Hi idr list,
> >>
> >>
> >> the next-hop-capability draft currently seems to target using the new
> >> nexthop capability on a per-advertisement level.  Considering that
> >> draft-idr-bgp-nh- cost adds a new SAFI to convey information about
> >> nexthops, it seems natural to tranposrt the capability information in that
> place?
> >
> > That's a valid comment.
> >
> > 1)  cost/benefit
> > Avertising the next-hop-capability on a per update basis has indeed a cost
> but also a benefit.
> > In term of cost, the simplest next-hop-capability is 5 octets. Compared to an
> update in the range of 100-1000 octets, that's 5% to 0,5%.
> > In term of benefit, this allow customizing the capability on a per
> update/routes granularity if required, which may be a useful possibility for
> some capabilities.
> > Engineering is about trade-off. IMO, the benefit, especially long term, out
> weight the fixe cost, which is small and will become smaller, in relative term,
> in the future (thanks to Moore's law).
> >
> > 2) deployability
> > In addition, in term of deployability, a new attribute has no impact.  On the
> other hand draft-idr-bgp-nh-cost use a new AFI/SAIF which requires
> reconfiguration and reboot of all BGP sessions. This is a much higher cost for
> IBGP alone. For EBGP, this is simply not an option IMO.
> >
> >
> > So, I agree that this is a valid option to consider, however I don't think that
> it's a better one.
> >
> >> (That would also remove the question of what behaviour should be when
> >> you get different advertisements with the same nexthop, but with a
> >> different nexthop capability attribute.)
> >
> > For a given route/NLRI, you use the next-hop capability attached to this
> route.
> > To rephrase, you do not consider next-hop capability that may have been
> advertised in another update.
> > I agree that this may not be crystal clear in the text, I will clarify in the next
> revision.
> >
> > Thanks again for your comments,
> > Bruno
> >
> >>
> >>
> >> -David
> >
> >
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