Re: [Idr] Adoption of draft-varlashkin-bgp-nh-cost-02 as IDR WG document?

Do not support.

Jim Uttaro

Ilya,

	Apologies for not responding sooner.. I do have some questions in re the draft..

1. Motivation

"ADDPATH solves this problem by letting
   route-reflector to advertise multiple paths for given prefix.  If
   number of advertised paths sufficiently big, route-reflector clients
   can choose same route as they would in case of full-mesh.  This
   approach however places additional burden on the control plane."

First of I do not anticipate having to send more than two paths for almost all cases. Secondly this is applied on a per prefix basis so there is not a doubling of routing state.. So I do not think this concern is warranted.. There are tools and guidelines for setting the number of paths see http://tools.ietf.org/html/draft-ietf-idr-add-paths-guidelines-02 for a complete description which examines a number of use cases..

"For example, if next-hop information itself has been learned via BGP then
   simple SPF run on link-state database won't be sufficient to obtain
   cost information."

The AIGP metric is used to carry the "cost" to the NH of the path.. This draft was developed to address the exact issue of carrying NH info in bgp and losing the notion of an accumulated cost.. Why is that not sufficient? 

I also do not see how you del with this except for the creation of a table of NHs and associated costs.. But how is that created? Does the new AFI/SAFI accumulate costs across multiple IPG domains?

I would like to understand what scenarios require this solution above and beyond a correct addpaths setting and/or AIGP..

2. Next-Hop Information Base

"  NHIB can be populated from various sources both static and dynamic.
   This document focuses on populating NHIB using BGP.  However it is
   possible that protocols other than BGP could be also used to populate
   NHIB."

This is a bit vague.. if you are learning NHs in BGP without the accumulated cost then the only way to populate is to statically define costs to NHs.. this seems burdensome and is not easily change to reflect the dynamic of cost due to maintenance or failure.. putting aside the difficulty in creating and maintaining this NHIB it seems that it cannot respond to changes in the topology..

3. BGP BEST PATH SELECTION MODIFICATION

Lots of chatter about the sanctity of the BGP Best path selection.. Have you spoken to folks who seem to be vehemently opposed?

4.

A general note about introducing AFI/SAFIs.. This is always not trivial as it introduces scale, control plane complexity and vulnerability.. What happens if the AFI/SAFI becomes compromised? It would be good if you could describe that here.. My assumption would be that you would fall back to igp cost?

In summary, I do not understand how addpaths and AIGP do not solve this problem. 

-----Original Message-----
From: idr-bounces@ietf.org [mailto:idr-bounces@ietf.org] On Behalf Of Anton Elita
Sent: Wednesday, November 23, 2011 11:05 AM
To: idr@ietf.org List
Subject: Re: [Idr] Adoption of draft-varlashkin-bgp-nh-cost-02 as IDR WG document?

Support

-- 
 Anton Elita
 Tinet

On Wed, Nov 16, 2011 at 10:06 AM, John Scudder <jgs@juniper.net> wrote:
> Folks,
>
> We have received a request from the authors to adopt draft-varlashkin-bgp-nh-cost-02 as an IDR WG document.  Please send your comments to the list.  The deadline for comments is December 5, 2011 at noon EST.
>
> Thanks,
>
> --John
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