Internet DRAFT - draft-xu-idr-performce-routing
draft-xu-idr-performce-routing
Network Working Group X. Xu
Internet Draft H. Ni
Category: Standard Track Huawei
Y. Fan
China Telecom
Expires: June 2014 December 10, 2013
Performance-based BGP Routing Mechanism
draft-xu-idr-performce-routing-00
Abstract
Network performance, especially network latency is widely recognized
as one of major obstacles in adopting public cloud services (e.g.,
cloud desktop service), especially in the scenario where the network
paths between cloud end-users and cloud data centers traverse more
than one Autonomous System (AS). However, the current Border Gateway
Protocol (BGP) specification [RFC4271] doesn't use network
performance metrics (e.g., network latency) in the route selection
decisions. This document describes a performance-based BGP routing
mechanism in which network latency metric is taken as one of the
route selection criteria.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 10, 2014.
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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
Table of Contents
1. Introduction ................................................ 3
2. Terminology ................................................. 3
3. Performance Route Advertisement ............................. 4
4. Capability Advertisement .................................... 5
5. Performance Route Selection ................................. 5
6. Deployment Considerations ................................... 6
7. Security Considerations ..................................... 6
8. IANA Considerations ......................................... 6
9. Acknowledgements ............................................ 6
10. References ................................................. 6
10.1. Normative References .................................. 6
10.2. Informative References ................................ 7
Authors' Addresses ............................................. 7
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1. Introduction
Network performance, especially network latency is widely recognized
as one of major obstacles in adopting public cloud services (e.g.,
cloud desktop service), especially in the scenario where the network
paths between cloud users and cloud data centers traverse more than
one Autonomous System (AS). However, the current Border Gateway
Protocol (BGP) specification [RFC4271] doesn't use network
performance metrics (e.g., network latency) in the route selection
decisions. As such, the best route selected based upon the existing
BGP route selection criteria may not be the best from the user
experience perspective.
This document describes a performance-based BGP routing mechanism in
which network performance metrics are conveyed as additional path
attributes of the Network Layer Reachability Information (NLRI) and
used in the route selection decisions. So far it's only the network
latency metric that would be used in the performance-based route
selection decisions. Whether or not other network performance
metrics (e.g., latency variation metric) should be considered as
well would be discussed in a future version of this draft. To make
the performance routing paradigm and the vanilla routing paradigm
coexist, performance routes SHOULD be exchanged as labeled routes as
per [RFC3107] while using a specified Subsequent Address Family
Identifier (SAFI).
Service providers deploying such mechanism in their networks could
provide performance routing service as a value-added service to
those users who are sensitive to network latency, while continually
offering vanilla routing service to other users as before.
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. 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
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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
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).
3. Performance Route Advertisement
Performance routes SHOULD be exchanged between BGP peers by using a
specified Subsequent Address Family Identifier (SAFI) of TBD.
Meanwhile, these routes SHOULD be carried as labeled routes as per
[RFC3107]. A BGP speaker SHOULD NOT advertise performance routes to
a particular BGP peer unless that peer indicates, through BGP
capability advertisement, that it can process update messages with
the specified SAFI field.
Network latency metric is attached to the performance routes as one
additional path attribute, referred to as NETWORK_LATENCY path
attribute, which is a well-known mandatory attribute. This attribute
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 attribute is TBD, 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.
When distributing a selected performance route learnt from one BGP
peer to another, unless this BGP speaker has set itself as the
NEXT_HOP of such route, the NETWORK_LATENCY path attribute of such
route MUST NOT be modified. Otherwise when setting itself as the
NEXT_HOP of such route, this BGP speaker SHOULD increase the value
of the NETWORK_LATENCY path attribute by adding the network latency
value from itself to the previous NEXT_HOP of such route. It's
strongly RECOMMENDED to use the cumulative link latency from this
BGP speaker to the NEXT_HOP to represent the network latency between
them if possible. Otherwise, the measured network latency between
them can be used instead. It's strongly RECOMMENDED that the type of
network latency SHOULD be kept consistent across all these AS's
(i.e., either cumulative link latency or measured network latency,
choose one).
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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 approximately reflect the network
latency of that TE LSP path, rather than an IGP shortest path.
To keep performance routes stable enough, a BGP speaker SHOULD use a
configurable threshold of network latency fluctuation to suppress
any update which would otherwise be triggered just 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.
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 path attribute 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's strongly RECOMMENDED to enable such
route reflector to reflect all received performance routes by using
some mechanisms such as [ADD-PATH], 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
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routing paradigm would be used for a given packet is a local policy
issue which is outside the scope of this draft.
6. Deployment Considerations
It's RECOMMENDED to deploy this performance-based BGP routing
mechanism across multiple ASs which are within a single
administrative domain. Whether it is practical to deploy such
mechanism across AS's of different administrative domains as well is
a matter of trust and/or policy, which is outside of the scope of
this document.
Within each AS, it's RECOMMENTED to deliver a packet from a BGP
speaker to the BGP NEXT_HOP via tunnels, especially TE LSP tunnels.
Furthermore, it's strongly RECOMMENDED to use the latency metric
carried in Unidirectional Link Delay Sub-TLV [OSPF-TE-EXT] [ISIS-TE-
EXT] if possible, rather than the TE metric [RFC3630] [RFC5305] to
perform the C-SPF calculation, unless the TE metric has already been
set to the link latency metric. In this way, it could avoid the need
for timely measurement of network latency between IBGP peers.
7. Security Considerations
This extension to BGP does not change the underlying security issues
inherent in the existing BGP specification [RFC4271].
8. IANA Considerations
A new BGP Capability Code for the Performance Routing Capability, a
new SAFI specific for performance routing and a new path attribute
for NETWORK_LATENCY are required to be allocated by IANA.
9. Acknowledgements
Thanks to Joel Halpern, Alvaro Retana, Jim Uttaro, Robert Raszuk,
Eric Rosen, Qing Zeng, Jie Dong and Mach Chen for their valuable
comments on the initial idea of this document.
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.
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[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
10.2. Informative References
[RFC5492] Chandra, R. and J. Scudder, "Capabilities Advertisement
with BGP-4", RFC 5492, February 2009.
[RFC4760] Bates, T., Rekhter, Y, Chandra, R. and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 4760, January
2007.
[RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label
Information in BGP-4", RFC 3107, May 2001.
[OSPF-TE-EXT] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", draft-ietf-ospf-te-metric-extensions-02 (work
in progress), December 2012.
[ISIS-TE-EXT] Previdi, S., Giacalone, S., Ward, D., Drake, J., Atlas,
A., and C. Filsfils, "IS-IS Traffic Engineering (TE)
Metric Extensions", draft-previdi-isis-te-metric-
extensions-02 (work in progress), October 2012.
[RFC3630] Katz, D., Kompella, K., Yeung, D., "Traffic
Engineering (TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[ADD-PATH] D. Walton, A. Retana, E. Chen, J. Scudder, "Advertisement
of Multiple Paths in BGP", draft-ietf-idr-add-paths-09
(work in progress), October 2013.
Authors' Addresses
Xiaohu Xu
Huawei Technologies,
Beijing, China
Phone: +86-10-60610041
Email: xuxiaohu@huawei.com
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Hui Ni
Huawei Technologies,
Beijing, China
Phone: +86-10-606100212
Email: nihui@huawei.com
Yongbing Fan
China Telecom
Guangzhou, China.
Phone: +86 20 38639121
Email: fanyb@gsta.com
