Network Working Group                                              X. Xu
Internet-Draft                                              Alibaba, Inc
Intended status: Standards Track                                S. Hegde
Expires: June 24, 2021                                           Juniper
                                                           K. Talaulikar
                                                            M. Boucadair
                                                            C. Jacquenet
                                                          France Telecom
                                                       December 21, 2020

                Performance-based BGP Routing Mechanism


   The current BGP specification doesn't use network performance metrics
   (e.g., network latency) in the route selection decision process.
   This document describes a performance-based BGP routing mechanism in
   which network latency metric is taken as one of the route selection
   criteria.  This routing mechanism is useful for those server
   providers with global reach to deliver low-latency network
   connectivity services to their customers.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on June 24, 2021.

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Copyright Notice

   Copyright (c) 2020 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
   ( in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Performance Route Advertisement . . . . . . . . . . . . . . .   4
   4.  Capability Advertisement  . . . . . . . . . . . . . . . . . .   5
   5.  Performance Route Selection . . . . . . . . . . . . . . . . .   5
   6.  Deployment Considerations . . . . . . . . . . . . . . . . . .   6
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   8
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     11.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Network latency is widely recognized as one of major obstacles in
   migrating business applications to the cloud since cloud-based
   applications usually have very clearly defined and stringent network
   latency requirements.  Service providers with global reach aim at
   delivering low-latency network connectivity services to their cloud
   service customers as a competitive advantage.  Sometimes, the network
   connectivity may travel across more than one Autonomous System (AS)
   under their administration.  However, the BGP [RFC4271] which is used
   for path selection across ASes doesn't use network latency in the
   route selection process.  As such, the best route selected based upon
   the existing BGP route selection criteria may not be the best from
   the customer experience perspective.

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   This document describes a performance-based BGP routing paradigm in
   which network latency metric is disseminated via a new TLV of the
   AIGP attribute [RFC7311] and that metric is used as an input to the
   route selection process.  This mechanism is useful for those server
   providers with global reach, which usually own more than one AS, to
   deliver low-latency network connectivity services to their customers.

   Furthermore, in order to be backward compatible with existing BGP
   implementations and have no impact on the stability of the overall
   routing system, it's expected that the performance routing paradigm
   could coexist with the vanilla routing paradigm.  As such, service
   providers could thus provide low-latency routing services while still
   offering the vanilla routing services depending on customers'

   For the sake of simplicity, this document considers only one network
   performance metric that's the network latency metric.  The support of
   multiple network performance metrics is out of scope of this
   document.  In addition, this document focuses exclusively on BGP
   matters and therefore all those BGP-irrelevant matters such as the
   mechanisms for measuring network latency are outside the scope of
   this document.

   A variant of this performance-based BGP routing is implemented (see

2.  Terminology

   This memo makes use of the terms defined in [RFC4271].

   Network latency indicates the amount of time it takes for a packet to
   traverse a given network path [RFC2679].  Provided a packet was
   forwarded along a path which contains multiple links and routers, the
   network latency would be the sum of the transmission latency of each
   link (i.e., link latency), plus the sum of the internal delay
   occurred within each router (i.e., router latency) which includes
   queuing latency and processing latency.  The sum of the link latency
   is also known as the cumulative link latency.  In today's service
   provider networks which usually span across a wide geographical area,
   the cumulative link latency becomes the major part of the network
   latency since the total of the internal latency happened within each
   high-capacity router seems trivial compared to the cumulative link
   latency.  In other words, the cumulative link latency could
   approximately represent the network latency in the above networks.

   Furthermore, since the link latency is more stable than the router
   latency, such approximate network latency represented by the
   cumulative link latency is more stable.  Therefore, if there was a

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   way to calculate the cumulative link latency of a given network path,
   it is strongly recommended to use such cumulative link latency to
   approximately represent the network latency.  Otherwise, the network
   latency would have to be measured frequently by some means (e.g.,
   PING or other measurement tools).

3.  Performance Route Advertisement

   Performance (i.e., low latency) routes SHOULD be exchanged between
   BGP peers by means of a specific Subsequent Address Family Identifier
   (SAFI) of TBD (see IANA Section) and also be carried as labeled
   routes as per [RFC3107].  In other word, performance routes can then
   be looked as specific labeled routes which are associated with
   network latency metric.

   A BGP speaker SHOULD NOT advertise performance routes to a particular
   BGP peer unless that peer indicates, through BGP capability
   advertisement (see Section 4), that it can process update messages
   with that specific SAFI field.

   Network latency metric is attached to the performance routes via a
   new TLV of the AIGP attribute, referred to as NETWORK_LATENCY TLV.
   The value of this TLV indicates the network latency in microseconds
   from the BGP speaker depicted by the NEXT_HOP path attribute to the
   address depicted by the NLRI prefix.  The type code of this TLV is
   TBD (see IANA Section), and the value field is 4 octets in length.
   In some abnormal cases, if the cumulative link latency exceeds the
   maximum value of 0xFFFFFFFF, the value field SHOULD be set to
   0xFFFFFFFF.  Note that the NETWORK_LATENCY TLV MUST NOT co-exisit
   with the AIGP TLV within the same AIGP attribute.

   A BGP speaker SHOULD be configurable to enable or disable the
   origination of performance routes.  If enabled, a local latency value
   for a given to-be-originated performance route MUST be configured to
   the BGP speaker so that it can be filled to the NETWORK_LATENCY TLV
   of that performance route.

   A BGP speaker that is enabled to process NETWORK_LATENCY, but it was
   not provisioned with the local latency value SHOULD remove the
   NETWORK_LATENCY attribute when it advertises the corresponding route

   When distributing a performance route learnt from a BGP peer, if this
   BGP speaker has set itself as the NEXT_HOP of such route, the value
   of the NETWORK_LATENCY TLV SHOULD be increased by adding the network
   latency from itself to the previous NEXT_HOP of such route.
   Otherwise, the NETWORK_LATENCY TLV of such route MUST NOT be

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   As for how to obtain the network latency to a given BGP NEXT_HOP is
   outside the scope of this document.  However, note that the path
   latency to the NEXT HOP SHOULD approximately represent the network
   latency of the exact forwarding path towards the NEXT_HOP.  For
   example, if a BGP speaker uses a Traffic Engineering (TE) Label
   Switching Path (LSP) from itself to the NEXT_HOP, rather than the
   shortest path calculated by Interior Gateway Protocol (IGP), the
   latency to the NEXT HOP SHOULD reflect the network latency of that TE
   LSP path, rather than the IGP shortest path.  In the case where the
   latency to the NEXT HOP could not be obtained due to some reason(s),
   that latency SHOULD be set to 0xFFFFFFFF by default.

   To keep performance routes stable enough, a BGP speaker SHOULD use a
   configurable threshold for network latency fluctuation to avoid
   sending any update which would otherwise be triggered by a minor
   network latency fluctuation below that threshold.

4.  Capability Advertisement

   A BGP speaker that uses multiprotocol extensions to advertise
   performance routes SHOULD use the Capabilities Optional Parameter, as
   defined in [RFC5492], to inform its peers about this capability.

   The MP_EXT Capability Code, as defined in [RFC4760], is used to
   advertise the (AFI, SAFI) pairs available on a particular connection.

   A BGP speaker that implements the Performance Routing Capability MUST
   support the BGP Labeled Route Capability, as defined in [RFC3107].  A
   BGP speaker that advertises the Performance Routing Capability to a
   peer using BGP Capabilities advertisement [RFC5492] does not have to
   advertise the BGP Labeled Route Capability to that peer.

5.  Performance Route Selection

   Performance route selection only requires the following modification
   to the tie-breaking procedures of the BGP route selection decision
   (phase 2) described in [RFC4271]: network latency metric comparison
   SHOULD be executed just ahead of the AS-Path Length comparison step.
   Prior to executing the network latency metric comparison, the value
   of the NETWORK_LATENCY TLV SHOULD be increased by adding the network
   latency from the BGP speaker to the NEXT_HOP of that route.

   The Loc-RIB of the performance routing paradigm is independent from
   that of the vanilla routing paradigm.  Accordingly, the routing table
   of the performance routing paradigm is independent from that of the
   vanilla routing paradigm.  Whether the performance routing paradigm
   or the vanilla routing paradigm would be applied to a given packet is
   a local policy issue which is outside the scope of this document.

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   For example, by leveraging the Cos-Based Forwarding (CBF) capability
   which allows routers to have distinct routing and forwarding tables
   for each type of traffic, the selected performance routes could be
   installed in the routing and forwarding tables corresponding to high-
   priority traffic.

6.  Deployment Considerations

   This section is not normative.

   Enabling the performance-based BGP routing at large (i.e., among
   domains that do not belong to the same administrative entity) may be
   conditioned by other administrative settlement considerations that
   are out of scope of this document.  Nevertheless, this document does
   not require nor exclude activating the proposed route selection
   scheme between domains that are managed by distinct administrative

   The main deployment case targeted by this specification is where
   involved domains are managed by the same administrative entity.
   Concretely, this performance-based BGP routing mechanism can
   advantageously be enabled in a multi-domain environment, where all
   the involved domains are operated by the same administrative entity
   so that the processing of the low latency routes can be consistent
   throughout the domains.  Besides security considerations that may
   arise (and which are further discussed in Section 9), there is indeed
   a need to consistently enforce a low-latency-based BGP routing policy
   within a set of domains that belong to the same administrative
   entity.  This is motivated by the processing of traffic which is of
   very different nature and which may have different QoS requirements.
   Moreover, the combined use of BGP-inferred low latency information
   with traffic engineering tools that would lead to the computation and
   the establishment of traffic-engineered LSP paths between "low
   latency"-enabled BGP peers based upon the manipulation of the
   Unidirectional Link delay sub-TLV [RFC7810] [RFC7471] would
   contribute to guarantee the overall consistency of the low latency
   information within each domain.  Furthmore, a BGP color extended
   community could be attached to the performance routes so as to
   associates a low-latency Segment Routing (SR) LSP towards the BGP
   NEXT_HOP with these low-latency BGP routes, in this way, those
   traffic matching the low-latency BGP routes would be forwarded to the
   BGP NEXT_HOP via the low-latency SR LSP towards that BGP NEXT_HOP.

   In network environments where router reflectors are deployed but
   next-hop-self is disabled on them, route reflectors usually reflect
   those received routes which are optimal (i.e., lowest latency) from
   their perspectives but may not be optimal from the receivers'
   perspectives.  Some existing solutions as described in [RFC7911], [I-

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   D.ietf-idr-bgp-optimal-route-reflection] and [RFC6774] can be used to
   address this issue.

   From a network provider perspective, the ability to manipulate low
   latency routes may lead to different, presumably service-specific
   designs.  In particular, there is a need to assess the impact of
   using such capability on the overall performance of the BGP peers
   from a route computation and selection procedure as a function of the
   tie-breaking operation.  A typical use case would consist in
   selecting low latency routes for traffic that for example pertains to
   the VoIP, or whose nature demands the selection of the lowest latency
   route in the Adj-RIB-Out database of the corresponding BGP peers.
   Typically, live broadcasting services or some e-health services could
   certainly take advantage of such capability.  It is out of scope of
   this document to exhaustively elaborate on such service-specific
   designs that are obviously deployment-specific.

7.  Contributors

      Ning So

      Yimin Shen

      Uma Chunduri

      Hui Ni

      Yongbing Fan
      China Telecom

      Luis M. Contreras
      Telefonica I+D

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8.  Acknowledgements

   Thanks to Joel Halpern, Alvaro Retana, Jim Uttaro, Robert Raszuk,
   Eric Rosen, Bruno Decraene, Qing Zeng, Jie Dong, Mach Chen, Saikat
   Ray, Wes George, Jeff Haas, John Scudder, Stephane Litkowski and
   Sriganesh Kini for their valuable comments on this document.  Special
   thanks should be given to Jim Uttaro and Eric Rosen for their
   proposal of using a new TLV of the AIGP attribute to convey the
   network latency metric.

9.  IANA Considerations

   A new BGP Capability Code for the Performance Routing Capability, a
   new SAFI specific for performance routing and a new type code for
   NETWORK_LATENCY TLV of the AIGP attribute are required to be
   allocated by IANA.

10.  Security Considerations

   In addition to the considerations discussed in [RFC4271], the
   following items should be considered as well:

   a.  Tweaking the value of the NETWORK_LATENCY by an illegitimate
       party may influence the route selection results.  Therefore, the
       Performance Routing Capability negotiation between BGP peers
       which belong to different administration domains MUST be disabled
       by default.  Furthermore, a BGP speaker MUST discard all
       performance routes received from the BGP peer for which the
       Performance Routing Capability negotiation has been disabled.

   b.  Frequent updates of the NETWORK_LATENCY TLV may have a severe
       impact on the stability of the routing system.  Such practice
       SHOULD be avoided by setting a reasonable threshold for network
       latency fluctuation.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3107]  Rekhter, Y. and E. Rosen, "Carrying Label Information in
              BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001,

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   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <>.

11.2.  Informative References

              Raszuk, R., Cassar, C., Aman, E., Decraene, B., and K.
              Wang, "BGP Optimal Route Reflection (BGP-ORR)", draft-
              ietf-idr-bgp-optimal-route-reflection-21 (work in
              progress), June 2020.

              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-09 (work in progress),
              November 2020.

   [RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Delay Metric for IPPM", RFC 2679, DOI 10.17487/RFC2679,
              September 1999, <>.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <>.

   [RFC6774]  Raszuk, R., Ed., Fernando, R., Patel, K., McPherson, D.,
              and K. Kumaki, "Distribution of Diverse BGP Paths",
              RFC 6774, DOI 10.17487/RFC6774, November 2012,

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   [RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,

   [RFC7810]  Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and
              Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions",
              RFC 7810, DOI 10.17487/RFC7810, May 2016,

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,

Authors' Addresses

   Xiaohu Xu
   Alibaba, Inc


   Shraddha Hegde


   Ketan Talaulikar


   Mohamed Boucadair
   France Telecom


   Christian Jacquenet
   France Telecom


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