Re: [GROW] I-D Action:draft-ietf-grow-diverse-bgp-path-dist-01.txt

[Robert Raszuk <[e-mail]>]

Hi Richard,

> Certainly RR works with clusters, but this is not something essential to my
> concern.
>
> In order to make it work, all planes MUST have a consistent/same view about
> whether a path P1 is better than another path P2 for any two paths P1 and P2
> associated to the same route so that they will have the same ordering in
> terms of "n-best/better" path.

I think RR clusters are essential to your concern as the entire point is 
that the above consistency you are referring to has to be accomplished 
per RR cluster and not per full network to achieve diverse-path 
functional correctness.

> Let's go back to your remarks. You have assumed three conditions:
> (1) RRs have equal IGP point of the network
> (2) IGP metric consideration is disabled for best path calculation
> (3) RRs have a way to learn what the best path of other plane is.
>
> Well, if the IGP metric is taken out of consideration, it will work (but IGP
> metric is already built into many production codes for best path selection).

AFAIK many shipping implementations have ways already to not consider 
IGP metric to next hops or will have it shortly :).

> But I am not convinced with the other two conditions. For the first
> condition, it may be too much for an operator to have to deploy RRs with the
> same IGP metric.

It is relative to the design, but if you considering control plane RRs 
same IGP metric is reality in most cases. They are usually "on the 
stick" connected to some common switch/router.

> For the third condition, there hasn't been
> such a spec about how to learn what the best path of another plane is.

It is pretty straightforward, does not require any changes to BGP 
protocol on the wire, but stay tuned. I will encourage

> Anyhow, I would appreciate it if you spell it out in length about path
> consistency in your next draft.

Ok I will make it more clear.

Thx,
R.