Subject: [bess] My fumbled answer :-)

From: "Adrian Farrel" <[email-masked]>
Date: Thu, 20 Jul 2017 15:29:32 +0100

Hi Wim,

That wasn't my most glorious moment :-)

I don't think that draft-drake-bess-datacenter-gateway and
draft-ietf-idr-segment-routing-te-policy are anything other than complementary.
Nor, apparently does Eric as he is a co-author of both documents :-)

I think high-level document names can sometimes lead to some confusion, but the
combination of "BGP", "SR", and "TE" in the same overviews only goes to show
that they are in the same general space, not that they overlap.

If you take a look at draft-farrel-spring-sr-domain-interconnect-00 you'll see
it references [I-D.previdi-idr-segment-routing-te-policy] (now adopted by the
IDR working group) as the assumed mechanism for advertising intra-AS links that
are SR TE policies. We also note that
[I-D.previdi-idr-segment-routing-te-policy] offers a method for label stack
compression.

I think the two mechanisms provide different functions, but functions that could
(or even should) be integrated into a deployable solution.

Thanks (and sorry again),

Adrian

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From: "Henderickx, Wim (Nokia - BE/Antwerp)" <[email-masked]>
Date: Thu, 20 Jul 2017 15:02:22 +0000

Adrian, the question is mainly what we are trying to achieve here with the draft.
If the goal is providing E2E SR-TE and utilizing all paths between the different DC(s) e.g. SR-TE policy does this as well.

You advertise a BGP SR-TE-policy with the different paths and you bind the prefix to them using the BGP-NH/colour. You can define a colour and weights and preferences to determine if you want to use ECMP, different weights or active standby, etc. A similar use case is described here: https://tools.ietf.org/html/draft-filsfils-spring-segment-routing-policy-01

I am mainly arguing the way we convey the different SR-TE path information. With SR-TE policy you get a level of indirection which means every time the path changes you don’t need to re-advertise the prefix, but just update the SR-TE policy update.

What is not part of SR-TE policy is GW discovery and you would need a controller to achieve the same thing. 

Hope this clarifies

On 20/07/2017, 16:29, "Adrian Farrel" <[email-masked]> wrote:

    Hi Wim,

    

    
    
    Adrian