IDR Z. Li Internet-Draft China Mobile Updates: 4271, 4360, 7153 (if approved) J. Dong Intended status: Experimental Huawei Technologies Expires: January 1, 2018 June 30, 2017 Carry congestion status in BGP extended community draft-li-idr-congestion-status-extended-community-05 Abstract A new extended community, called congestion status extended community, is introduced in this document to carry the link congestion status, especially for the exit link of one AS. Congestion status extended community can be used by the BGP speakers to steer the AS-outgoing traffic among the exit links. Requirements Language 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 [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 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 January 1, 2018. Copyright Notice Copyright (c) 2017 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 Li & Dong Expires January 1, 2018 [Page 1] Internet-Draft congestion status extended community June 2017 (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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Congestion Status Extended Community . . . . . . . . . . . . 4 3. Application Considerations . . . . . . . . . . . . . . . . . 5 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction Knowing the congestion status of the AS exit links is useful for traffic steering, especially for steering the AS outgoing traffic among the exit links. AS A, as shown in the following figure, has multiple exit links connected to AS B. Both AS A and B has exit link to AS C, and AS B provides transit service for AS A. Due to cost or some other reasons, AS A prefers using AS B to transmit its' traffic to AS C, not the directly connected link between AS A and C. If the exit routers, Router 7 and 8, in AS A tell their iBGP peers the congestion status of the exit links, the peers in turn can steer some outgoing traffic toward the less loaded exit link. If AS A knows the link between AS B and AS C is congested, it can steer some traffic towards AS C from AS B to the directly connected link by applying some route policies. Li & Dong Expires January 1, 2018 [Page 2] Internet-Draft congestion status extended community June 2017 +-------------------------------------------+ | AS C | | +----------+ +----------+ | +--| Router 1 |---------------| Router 2 |--+ +----------+ +----------+ | | | | | +----------+ | +--------| Router 3 |----------+ | | +----------+ | | | AS B | | | +----------+ +----------+ | | +-| Router 4 |----| Router 5 |-+ | +----------+ +----------+ | | | | | | +----------+ +----------+ +----------+ +--| Router 6 |--------| Router 7 |----| Router 8 |-+ | +----------+ +----------+ +----------+ | | AS A | +---------------------------------------------------+ In [constrained-multiple-path], authors from France Telecom also specified the requirement to know the congestion status of a link. This document introduces a new extended community [RFC4360] to deliver the congestion status of the exit link to other BGP speakers. The BGP receiver can then use this extended community to deploy route policy, thus steer AS outgoing traffic according to the congestion status of the exit links. This mechanisum can be used by both iBGP and eBGP. In a network deployed SDN (Software Defined Network) controller, congestion status extended community can be used by the controller to steer the AS outgoing traffic among all the exit links from the perspective of the whole network. For the network with Route Reflectors (RRs) [RFC4456], RRs by default only advertise the best route for a specific prefix to their clients. Thus RR clients has no opportunity to compare the congestion status among all the exit links. In this situation, to allow RR clients learning all the routes for a specific prefix from all the exit links, RRs are RECOMMENDED to enable add-path functionality [RFC7911]. Li & Dong Expires January 1, 2018 [Page 3] Internet-Draft congestion status extended community June 2017 2. Congestion Status Extended Community As described in [RFC4360], the extended community attribute is an 8-octet value with the first one or two octets to indicate the type of this attribute. Since congestion status extended community needs to be delivered from on AS to other ASes, and used by the BGP speakers both in other ASes and within the same AS as the sender, it MUST be a transitive extended community, i.e. the T bit in the first octet MUST be zero. We only define the congestion status extended community for four- octet AS number [RFC6793], since all the BGP speakers can handle four-octet AS number now and the two-octet AS numbers can be mapped to four-octet AS numbers by setting the two high-order octets of the four-octet field to zero, as per [RFC6793]. Congestion status extended community is a sub-type allocated from Transitive Four-Octet AS-Specific Extended Community Sub-Types defined in section 5.2.4 of [RFC7153]. Its format is as Figure 1. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type =0x02 | Sub-Type | Sender AS Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender AS Number (cont.) | Bandwidth | Utilization | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Congestion status extended community The "Type" field MUST be 0x02, which indicate this is a Transitive Four-Octet AS-Specific Extended Community. The "Sub-Type" field is used to indicate this is a Congestion Status Extended Community. Its value is to be assigned by IANA. The "Sender AS Number" field is 4 octets. Its value is the AS number of the BGP speaker who generates this congestion status extended community. If the generator has 2-octct AS number, it MUST encode its AS number in the last (low order) two bytes and set the first (high order) two bytes to zero, as per [RFC6793]. The "Bandwidth" field is 1 octet. Its value is the bandwidth of the exit link in unit of 10 gbps (gigabits per second). The link with bandwidth less than 10 gbps is not suitable to use this feature. Li & Dong Expires January 1, 2018 [Page 4] Internet-Draft congestion status extended community June 2017 The "Utilization" field is 1 octet. Its value is the utilization of the exit link in unit of percent. We can use the "Utilization" field together with the "Bandwidth" field to calculate the traffic load that we can further steer to this exit link. 3. Application Considerations To avoid route oscillation, the exit router SHOULD set a threshold. When the utilization change reaches the threshold, the exit router SHOULD generate a BGP update message with congestion status extended community. Implementations SHOULD further reduce the BGP update messages trigered by link utilization change using the method similar to BGP Route Flap Damping [RFC2439]. When link utilization change by small amounts that fall under thresholds that would cause the announcement of BGP update message, implementations SHOULD suppress the announcement and set the penalty value accordingly. To avoid traffic oscillation, i.e. more traffic than expected is attracted to the low utilized link, and some traffic has to be steered back to other links, route policy can be set at the exit router. Congestion status extended community is only conveyed for some specific routes or only for some specific BGP peers. Congestion status extended community can also be used in a SDN network. The SDN controller uses the exit link utilization information to steer the Internet access traffic among all the exit links from the perspective of the whole network. 4. Security Considerations This document only defines a new extended communities to carry the congestion status of the exit link. This new extended community does not directly introduce any new security issues. The same security considerations as for the BGP extended community [RFC4360] applies. 5. IANA Considerations One sub-type is solicited to be assigned from Transitive Four-Octet AS-Specific Extended Community Sub-Types registry to indicate the Congestion Status Extended Community defined in this document. 6. Acknowledgments Many thanks to Rudiger Volk, Susan Hares, John Scudder, Randy Bush for their review and comments to improve this document. Li & Dong Expires January 1, 2018 [Page 5] Internet-Draft congestion status extended community June 2017 7. References 7.1. 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, . [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, . [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, DOI 10.17487/RFC4360, February 2006, . [RFC7153] Rosen, E. and Y. Rekhter, "IANA Registries for BGP Extended Communities", RFC 7153, DOI 10.17487/RFC7153, March 2014, . 7.2. Informative References [constrained-multiple-path] Boucadair, M. and C. Jacquenet, "Constrained Multiple BGP Paths", October 2010. [RFC2439] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route Flap Damping", RFC 2439, DOI 10.17487/RFC2439, November 1998, . [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006, . [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet Autonomous System (AS) Number Space", RFC 6793, DOI 10.17487/RFC6793, December 2012, . [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, "Advertisement of Multiple Paths in BGP", RFC 7911, DOI 10.17487/RFC7911, July 2016, . Li & Dong Expires January 1, 2018 [Page 6] Internet-Draft congestion status extended community June 2017 Authors' Addresses Zhenqiang Li China Mobile No.32 Xuanwumenxi Ave., Xicheng District Beijing 100032 P.R. China Email: li_zhenqiang@hotmail.com Jie Dong Huawei Technologies Huawei Campus, No.156 Beiqing Rd. Beijing 100095 P.R. China Email: jie.dong@huawei.com Li & Dong Expires January 1, 2018 [Page 7]