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