--- 1/draft-ietf-idr-bgp-optimal-route-reflection-26.txt 2021-06-17 08:13:12.764675133 -0700 +++ 2/draft-ietf-idr-bgp-optimal-route-reflection-27.txt 2021-06-17 08:13:12.792675837 -0700 @@ -1,39 +1,39 @@ IDR Working Group R. Raszuk, Ed. Internet-Draft NTT Network Innovations Updates: 4456 (if approved) B. Decraene, Ed. Intended status: Standards Track Orange -Expires: December 18, 2021 C. Cassar +Expires: December 19, 2021 C. Cassar E. Aman K. Wang Juniper Networks - June 16, 2021 + June 17, 2021 BGP Optimal Route Reflection (BGP ORR) - draft-ietf-idr-bgp-optimal-route-reflection-26 + draft-ietf-idr-bgp-optimal-route-reflection-27 Abstract This document defines an extension to BGP route reflectors. On route reflectors, BGP route selection is modified in order to choose the best route from the standpoint of their clients, rather than from the standpoint of the route reflectors. Depending on the scaling and precision requirements, route selection can be specific for one client, common for a set of clients or common for all clients of a route reflector. This solution is particularly applicable in deployments using centralized route reflectors, where choosing the - best route based on the route reflector's Interior Gateway Protocol - (IGP) location is suboptimal. This facilitates, for example, best - exit point policy (hot potato routing). + best route based on the route reflector's IGP location is suboptimal. + This facilitates, for example, best exit point policy (hot potato + routing). The solution relies upon all route reflectors learning all paths which are eligible for consideration. BGP Route Selection is performed in the route reflectors based on the IGP cost from configured locations in the link state IGP. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. @@ -41,21 +41,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on December 18, 2021. + This Internet-Draft will expire on December 19, 2021. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -78,26 +78,26 @@ 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction - There are three types of BGP (Border Gateway Protocol) deployments - within Autonomous Systems today: full mesh, confederations and route - reflection. BGP route reflection [RFC4456] is the most popular way - to distribute BGP routes between BGP speakers belonging to the same - Autonomous System. However, in some situations, this method suffers - from non-optimal path selection. + There are three types of BGP deployments within Autonomous Systems + today: full mesh, confederations and route reflection. BGP route + reflection [RFC4456] is the most popular way to distribute BGP routes + between BGP speakers belonging to the same Autonomous System. + However, in some situations, this method suffers from non-optimal + path selection. [RFC4456] asserts that, because the IGP cost to a given point in the network will vary across routers, "the route reflection approach may not yield the same route selection result as that of the full Internal BGP (IBGP) mesh approach." One practical implication of this fact is that the deployment of route reflection may thwart the ability to achieve hot potato routing. Hot potato routing attempts to direct traffic to the closest Autonomous System (AS) exit point in cases where no higher priority policy dictates otherwise. As a consequence of the route reflection method, the choice of exit point @@ -224,21 +224,21 @@ interior cost. The interior cost of a route is determined by calculating the metric from the selected IGP location to the NEXT_HOP for the route using the shortest IGP path tree rooted at the selected IGP location. In order to be able to compute the shortest path tree rooted at the selected IGP locations, knowledge of the IGP topology for the area/ level that includes each of those locations is needed. This knowledge can be gained with the use of the link state IGP such as IS-IS [ISO10589] or OSPF [RFC2328] [RFC5340] or via BGP-LS [RFC7752]. - When specifing logical location of a route reflector for a group of + When specifying logical location of a route reflector for a group of clients one or more backup IGP locations SHOULD be allowed to be specified for redundancy. Further deployment considerations are discussed in Section 4. 3.1.1. Restriction when BGP next hop is a BGP prefix In situations where the BGP next hop is a BGP route itself, the IGP metric of a route used for its resolution SHOULD be the final IGP cost to reach such next hop. Implementations which cannot inform BGP of the final IGP metric to a recursive next hop MUST treat such paths @@ -284,26 +284,25 @@ into account either the IGP cost between the client and the NEXT_HOP (rather than the IGP cost from the route reflector to the NEXT_HOP) or other user configured policies. The achievement of optimal routing between clients of different clusters relies upon all route reflectors learning all paths that are eligible for consideration. In order to satisfy this requirement, BGP add-path [RFC7911] needs to be deployed between route reflectors. This solution can be deployed in traditional hop-by-hop forwarding - networks as well as in end-to-end tunneled environments. In networks - where there are multiple route reflectors and hop-by-hop forwarding - without encapsulation, such optimizations MUST be consistently - enabled on all route reflectors. Otherwise, clients may receive an - inconsistent view of the network, in turn leading to intra-domain - forwarding loops. + networks as well as in end-to-end tunneled environments. To avoid + routing loops in networks with multiple route reflectors and hop-by- + hop forwarding without encapsulation, it is essential that the + network topology be carefully considered in designing a route + reflection topology (see also Section 11 of [RFC4456]). As discussed in section 11 of [RFC4456], the IGP locations of BGP route reflectors is important and has routing implications. This equally applies to the choice of the IGP locations configured on optimal route reflectors. If a backup location is provided, it is used when the primary IGP location disappears from the IGP (i.e. fails). Just like the failure of a RR [RFC4456], it may result in changing the paths selected and advertised to the clients and in general the post-failure paths are expected to be less optimal. This is dependent on the IGP topologies and the IGP distance between the @@ -367,22 +366,23 @@ 6. IANA Considerations This document does not request any IANA allocations. 7. Acknowledgments Authors would like to thank Keyur Patel, Eric Rosen, Clarence Filsfils, Uli Bornhauser, Russ White, Jakob Heitz, Mike Shand, Jon Mitchell, John Scudder, Jeff Haas, Martin Djernaes, Daniele Ceccarelli, Kieran Milne, Job Snijders, Randy Bush, Alvaro Retana, - Francesca Palombini, Benjamin Kaduk, Zaheduzzaman Sarker and Lars - Eggert for their valuable input. + Francesca Palombini, Benjamin Kaduk, Zaheduzzaman Sarker, Lars + Eggert, Murray Kucherawy, Tom Petch and Nick Hilliard for their + valuable input. 8. Contributors Following persons substantially contributed to the current format of the document: Stephane Litkowski Cisco System slitkows.ietf@gmail.com