Let's assume that three planes of RR are deployed: The first plane distributes the best path for each route as usual, the second plane for the second best, and the third plane for the third best. Using your example, we take the IGP distance as the equally-good path tie-breaker. With different IGP topology, one RR may view a path as the second best while another RR may view the same path as the third best. For example, let's consider a route R with paths P1, P2, P3, where P2 and P3 are equally good and thus need to be broken by a tie breaker. On the first plane RR, P1 is viewed as the best, and is thus distributed as we hoped. On the second plane RR, P2 is viewed as the second best and is thus distributed. On the third plane RR, however, P2 is viewed as the third best and the P3 is viewed as the second best, and thus P2 is distributed, but this is not something we hoped to see. In order to make it work, all RRs on all planes should put all the paths in the same ordering, otherwise it will not correctly distribute the nth best path. But can you do that under all circumstances? The above example shows you can't, unless I have missed something. Regards, Renwei -----Original Message----- From: grow-bounces@ietf.org [mailto:grow-bounces@ietf.org] On Behalf Of Internet-Drafts@ietf.org Sent: Wednesday, June 23, 2010 1:30 AM To: i-d-announce@ietf.org Cc: grow@ietf.org Subject: [GROW] I-D Action:draft-ietf-grow-diverse-bgp-path-dist-01.txt A New Internet-Draft is available from the on-line Internet-Drafts directories. This draft is a work item of the Global Routing Operations Working Group of the IETF. Title : Distribution of diverse BGP paths. Author(s) : R. Raszuk, et al. Filename : draft-ietf-grow-diverse-bgp-path-dist-01.txt Pages : 20 Date : 2010-06-23 The BGP4 protocol specifies the selection and propagation of a single best path for each prefix. As defined today BGP has no mechanisms to distribute paths other then best path between it's speakers. This behaviour results in number of disadvantages for new applications and services. This document presents an alternative mechanism for solving the problem based on the concept of parallel route reflector planes. It also compares existing solutions and proposed ideas that enable distribution of more paths than just the best path. This proposal does not specify any changes to the BGP protocol definition. It does not require upgrades to provider edge or core routers nor does it need network wide upgrades. The authors believe that the GROW WG would be the best place for this work. A URL for this Internet-Draft is: http://www.ietf.org/internet-drafts/draft-ietf-grow-diverse-bgp-path-dist-01 .txt Internet-Drafts are also available by anonymous FTP at: ftp://ftp.ietf.org/internet-drafts/ Below is the data which will enable a MIME compliant mail reader implementation to automatically retrieve the ASCII version of the Internet-Draft. _______________________________________________ I-D-Announce mailing list I-D-Announce@ietf.org https://www.ietf.org/mailman/listinfo/i-d-announce Internet-Draft directories: http://www.ietf.org/shadow.html or ftp://ftp.ietf.org/ietf/1shadow-sites.txt
