Network Working Group                                              X. Xu
Internet-Draft                                                    Huawei
Intended status: Standards Track                            M. Boucadair
Expires: July 11, 2015                                      C. Jacquenet
                                                          France Telecom
                                                                   N. So
                                                           Vinci Systems
                                                                 Y. Shen
                                                             U. Chunduri
                                                                   H. Ni
                                                                  Y. Fan
                                                           China Telecom
                                                         January 7, 2015

                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.

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
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   This Internet-Draft will expire on July 11, 2015.

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Copyright Notice

   Copyright (c) 2015 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
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   ( in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Performance Route Advertisement . . . . . . . . . . . . . . .   4
   4.  Capability Advertisement  . . . . . . . . . . . . . . . . . .   5
   5.  Performance Route Selection . . . . . . . . . . . . . . . . .   5
   6.  Deployment Considerations . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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

1.1.  Requirements Language

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

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

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   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
   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.

   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.

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   Otherwise, the NETWORK_LATENCY TLV of such route MUST NOT be

   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.  In the
   case where a router reflector is deployed without next-hop-self
   enabled when reflecting received routes from one IBGP peer to other
   IBGP peer, it is RECOMMENDED to enable such route reflector to

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   reflect all received performance routes by using some mechanisms such
   as [I-D.ietf-idr-add-paths], rather than reflecting only the
   performance route which is the best from its own perspective.
   Otherwise, it may result in a non-optimal choice by its clients and/
   or its IBGP peers.

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

6.  Deployment Considerations

   It is strongly RECOMMENDED to deploy this performance-based BGP
   routing mechanism across multiple ASes which belong to a single
   administrative domain.  Within each AS, it is RECOMMENDED to deliver
   a packet from a BGP speaker to the BGP NEXT_HOP via tunnels,
   typically TE LSP tunnels.  Furthermore, if a TE LSP is used between
   iBGP peers, it is RECOMMENDED to use the latency metric carried in
   Unidirectional Link Delay Sub-TLV
   [I-D.ietf-ospf-te-metric-extensions] if possible, rather than the TE
   metric [RFC3630][RFC5305] to calculate the cumulative link latency
   associated with the TE LSP and use that cumulative link latency to
   approximately represent the network latency.  Thus, there is no need
   for frequent measurement of network latency between IBGP peers.

7.  Acknowledgements

   Thanks to Joel Halpern, Alvaro Retana, Jim Uttaro, Robert Raszuk,
   Eric Rosen, Qing Zeng, Jie Dong, Mach Chen, Saikat Ray, Wes George,
   Jeff Haas, John Scudder, Stephane Litkowski and Sriganesh Kini for
   their valuable comments on the initial idea of 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.

8.  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.

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9.  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.

10.  References

10.1.  Normative References

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

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

   [RFC7311]  Mohapatra, P., Fernando, R., Rosen, E., and J. Uttaro,
              "The Accumulated IGP Metric Attribute for BGP", RFC 7311,
              August 2014.

10.2.  Informative References

              Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", draft-ietf-idr-
              add-paths-10 (work in progress), October 2014.

              Previdi, S., Giacalone, S., Ward, D., Drake, J., Atlas,
              A., Filsfils, C., and W. Wu, "IS-IS Traffic Engineering
              (TE) Metric Extensions", draft-ietf-isis-te-metric-
              extensions-04 (work in progress), October 2014.

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              Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", draft-ietf-ospf-te-metric-extensions-10 (work
              in progress), January 2015.

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

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

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

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

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

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

Authors' Addresses

   Xiaohu Xu


   Mohamed Boucadair
   France Telecom


   Christian Jacquenet
   France Telecom


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   Ning So
   Vinci Systems


   Yimin Shen


   Uma Chunduri


   Hui Ni


   Yongbing Fan
   China Telecom


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