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

Hi Bruno,

I agree that we should not put everything in one basket and that was what I
have tried to communicate in my msg.

In fact my message was general applicable not solely to your document but
also to tunnel safi.

As far as example with EL I am not clear.

EL is function of the forwarding and I can not see why for given next hop
some packets carrying EL will be correctly switched by such nhs router vs
other would not.

Cheers,
R.
On Sep 30, 2015 11:15 AM, <bruno.decraene@orange.com> wrote:

> Hi Robert,
>
>
>
> The goal is to advertise next-hop dependent capabilities, more than
> next-hop capabilities. I agree that this may not have been clear from
> reading the title/name, and hence I’m considering changing the name
> (suggestions welcomed. Current candidate is :s/Next-Hop/Next-Hop
> dependent ).
>
>
>
> What we want is an attribute which is removed when the BGP Next-Hop is
> changed. Using this, we can advertise capabilities which are next-hop
> dependent. But they may also depend on other things, e.g. be NLRI specific.
>
> The entropy label capability is an example, defined in the draft. (for 2
> NLRI having the same BGP Next-Hop, you may have one which supports Entropy
> Label (EL) and the other which does not support).
>
>
>
> Bottom line, advertising capability only on a Next-Hop basis (e.g. using
> ietf-idr-bgp-nh-cost) is not a feasible option for the EL use case.
>
>
>
> Cheers,
>
> Bruno
>
>
>
>
>
> *From**:* rraszuk@gmail.com [mailto:rraszuk@gmail.com] *On Behalf Of *Robert
> Raszuk
> *Sent:* Tuesday, September 29, 2015 11:07 PM
> *To:* Jeff Tantsura
> *Cc:* Jakob Heitz (jheitz); DECRAENE Bruno IMT/OLN; idr wg;
> ilya.varlashkin@easynet.com
> *Subject:* Re: [Idr] decraene-idr-next-hop-capability <->
> ietf-idr-bgp-nh-cost
>
>
>
> Jakob, Jeff,
>
>
>
>
>
> At surface the point mentioned by Jakob looks very attractive. However the
> topic needs to be sorted into and looked with sufficient depth:
>
>
>
> - distributing critical reachability information in band of given update
> msg
>
> - distributing optimizations
>
>
>
> For critical reachability I agree (but hardly there are really cases like
> this in BGP).
>
>
>
> For optimizations I do not agree - Explanation: BGP next hops should
> resolve in their native way. If there is no resolution for next hop via
> recursion or IGP or static path is invalid.
>
>
>
> Once there is resolution path becomes valid and eligible for best path.
>
>
>
> If I change my next hop forwarding rewrite to different tunnel, LSP,
> segment or native IP that should not trigger re advertisement of millions
> of BGP routes which otherwise will be necessary if you always insist in
> carrying all information in the same message.
>
>
>
> Cheers,
>
> R.
>
>
>
>
>
>
>
>
>
>
>
>
>
> On Tue, Sep 29, 2015 at 10:54 PM, Jeff Tantsura <
> jeff.tantsura@ericsson.com> wrote:
>
> Very much support Jakob¹s points, in a reasonable big deployment different
> updates will inevitably arrive in a different order.
>
> Cheers,
> Jeff
>
>
>
>
>
> -----Original Message-----
> From: "Jakob Heitz   (jheitz)" <jheitz@cisco.com>
> Date: Tuesday, September 29, 2015 at 1:25 PM
> To: "bruno.decraene@orange.com" <bruno.decraene@orange.com>, idr wg
> <idr@ietf.org>
> Cc: "ilya.varlashkin@easynet.com" <ilya.varlashkin@easynet.com>,
> "robert@raszuk.net" <robert@raszuk.net>
> Subject: Re: [Idr] decraene-idr-next-hop-capability <->
> ietf-idr-bgp-nh-cost
>
> >Another benefit of advertising the next-hop capability in the same
> >update as the prefixes it applies to is that the receiving router
> >then will know the capabilities at the time that it receives the
> >prefixes.
> >
> >If this information were to come in a different update message in
> >a different SAFI, it will not know how to treat the prefix until
> >the update containing the next-hop capability is received.
> >The next-hop SAFI update could come at any time before or after
> >the prefix update. BGP updates are not synchronized unless the
> >NLRI is the same, especially if route reflectors or confeds are used.
> >
> >If there are multiple paths to a prefix and a new path with
> >unknown nexthop capabilities becomes bestpath, traffic loss can
> >occur until the nexthop capabilities are learnt.
> >
> >Therefore, it is best to keep all information about how to treat
> >a prefix in the update message that advertises that prefix.
> >
> >--Jakob
> >
> >> -----Original Message-----
> >> From: Idr [mailto:idr-bounces@ietf.org] On Behalf Of
> >>bruno.decraene@orange.com
> >> Sent: Wednesday, March 25, 2015 12:57 PM
> >> To: David Lamparter <equinox@diac24.net>
> >> Cc: idr wg <idr@ietf.org>; ilya.varlashkin@easynet.com;
> >>robert@raszuk.net
> >> Subject: Re: [Idr] decraene-idr-next-hop-capability <->
> >>ietf-idr-bgp-nh-cost
> >>
> >> 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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