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 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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://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 June 10, 2014. Xu, et al. Expires June 10, 2014 [Page 1] Internet-Draft Performance-based BGP Routing Mechanism December 2013 Copyright Notice Copyright (c) 2013 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must 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. 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 Xu, et al. Expires June 10, 2014 [Page 2] Internet-Draft Performance-based BGP Routing Mechanism December 2013 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 Xu, et al. Expires June 10, 2014 [Page 3] Internet-Draft Performance-based BGP Routing Mechanism December 2013 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). Xu, et al. Expires June 10, 2014 [Page 4] Internet-Draft Performance-based BGP Routing Mechanism December 2013 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 Xu, et al. Expires June 10, 2014 [Page 5] Internet-Draft Performance-based BGP Routing Mechanism December 2013 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. Xu, et al. Expires June 10, 2014 [Page 6] Internet-Draft Performance-based BGP Routing Mechanism December 2013 [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 Xu, et al. Expires June 10, 2014 [Page 7] Internet-Draft Performance-based BGP Routing Mechanism December 2013 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