Global Routing Operations J. Snijders Internet-Draft NTT Intended status: Informational M. Schmidt Expires: June 10, 2017 i3D.net December 7, 2016 Usage of Large BGP Communities draft-ietf-grow-large-communities-usage-01 Abstract Examples and inspiration for operators on how to use Large BGP Communities. 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 June 10, 2017. Copyright Notice Copyright (c) 2016 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 Snijders & Schmidt Expires June 10, 2017 [Page 1] Internet-Draft Usage of Large BGP Communities December 2016 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. The Generic Design Pattern . . . . . . . . . . . . . . . . . 3 2.1. Informational Communities . . . . . . . . . . . . . . . . 3 2.2. Action Communities . . . . . . . . . . . . . . . . . . . 4 3. Examples of Informational Communities . . . . . . . . . . . . 4 3.1. Location . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1.1. An ISO 3166-1 numeric function . . . . . . . . . . . 4 3.1.2. An UNSD region function . . . . . . . . . . . . . . . 5 3.2. Relation . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3. Combining Informational Communities . . . . . . . . . . . 6 4. Examples of Action Communities . . . . . . . . . . . . . . . 6 4.1. Selective NO_EXPORT . . . . . . . . . . . . . . . . . . . 6 4.1.1. Peer ASN Based Selective NO_EXPORT . . . . . . . . . 6 4.1.2. Location Based Selective NO_EXPORT . . . . . . . . . 7 4.2. Selective AS_PATH Prepending . . . . . . . . . . . . . . 7 4.2.1. Peer ASN Based Selective AS_PATH Prepending . . . . . 7 4.2.2. Location Based Selective AS_PATH Prepending . . . . . 8 4.3. Location based manipulation of LOCAL_PREF . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . 10 8.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction Large BGP Communities [I-D.ietf-idr-large-community] provide a mechanism to signal opaque information between Autonomous Systems. This document presents a set of examples on how Large BGP Communities could be implemented by an operator to achieve various goals. This document draws from experience in Operational Communities such as NANOG [1] and NLNOG [2]. The opaque nature of Large BGP Communities allows for rapid deployment of new features or changes to the product. Operators are encouraged to publicly publish an up to date version of their routing policy in which they document what each Large BGP Community means. Snijders & Schmidt Expires June 10, 2017 [Page 2] Internet-Draft Usage of Large BGP Communities December 2016 2. The Generic Design Pattern Large BGP Communities are composed of a 4-octet Global Administrator field followed by two 4-octet Local Data fields. The design pattern described in this document uses a "ASN:Function:Parameter"-approach to fill the three fields. In deployments of both BGP Communities [RFC1997] and Large BGP Communities, two categories of Communities are recognised: o Informational Communities o Action Communities For each context ideas are provided regarding the contents of each of the three fields in Large BGP Communities. Throughout the document a topology of four Autonomous Systems is used to illustrate the usage of Communities in the following configuration: AS 65551 | ^ | AS 64497 / \ ^ \ / ^ AS 64498 \ | | `<->- AS 64499 AS 64497 obtains transit services from AS 65551. AS 64497 provides transit services to both AS 64498 and AS 64499. AS 64498 and AS 64499 maintain a peering relation in which they only exchange their customer routes. 2.1. Informational Communities Informational Communites serve as markers regarding the origin of the route announcement, the relation with the EBGP neighbor or for instance the intended propagation audience. Informational Communities also assist in network operations such as debugging. The Global Administrator field is set to the ASN which is marking the routes with the Informational Communities. As an example: on a route which AS 64497 announces to AS 64498, AS 64497 might add the Large Snijders & Schmidt Expires June 10, 2017 [Page 3] Internet-Draft Usage of Large BGP Communities December 2016 BGP Community 64497:100:31 to signal to AS 64498 that the route was learned in the Netherlands. In general the intended audience of Informational Communities are downstream networks, but any adjacent Autonomous System could benefit from receiving these communities. 2.2. Action Communities Action Communities are attached to routes to request non-default behaviour in an adjacent Autonomous System. For instance, Action Communities are used to change the route's propagation characteristics, the route's LOCAL_PREF value or the amount of AS_PATH prepends that should be added when exporting or importing a route. The Global Administrator field is set to the ASN which is expected to perform a non-default action upon receiving the route. For instance, if AS 64499 would want to request AS 64497 to lower the LOCAL_PREFERENCE below the default, AS 64499 could tag the route with 64497:20:50. In general the intended audience of Action Communities is an upstream provider. 3. Examples of Informational Communities 3.1. Location AS 64497 can inform its downstream networks about the geographical entity where AS 64497 learned a route by marking the route with Large BGP Communities following one or a combination of the following schemes. 3.1.1. An ISO 3166-1 numeric function AS 64497 could assign a value of 1 to the first Local Data field to designate the function of the parameter in the second Local Data field as ISO-3166-1 numeric country identifiers. Snijders & Schmidt Expires June 10, 2017 [Page 4] Internet-Draft Usage of Large BGP Communities December 2016 +---------------------+-------------------------------------------+ | Large BGP Community | Meaning | +---------------------+-------------------------------------------+ | 64497:1:528 | Route learned in Netherlands | | 64497:1:392 | Route learned in Japan | | 64497:1:840 | Route learned in United States of America | +---------------------+-------------------------------------------+ Example documentation for AS 64497 using Informational Communties describing the origin of routes using ISO 3166-1 numeric identifiers. Table 1: Information: ISO 3166-1 3.1.2. An UNSD region function AS 64497 could assign a value of 2 to the first Local Data field to designate the function of the parameter in the second Local Data field as an identifier for the macro geographical (continental) regions, geographical sub-regions, or selected economic and other groupings following a set of published identifiers by the United Nations Statistics Division [3]. +---------------------+-------------------------------+ | Large BGP Community | Meaning | +---------------------+-------------------------------+ | 64497:2:2 | Route learned in Africa | | 64497:2:9 | Route learned in Oceania | | 64497:2:145 | Route learned in Western Asia | | 64497:2:150 | Route learned in Europe | +---------------------+-------------------------------+ Example documentation for AS 64497 using Informational Communties describing the origin of routes using numeric identifiers provided by the UN Statistics Division. Table 2: Information: Regions 3.2. Relation AS 64497 could assign a value of 3 to the first Local Data field to designate that the second Local Data field contains an identifier showing the relation with the EBGP neighbor from whom the route was received. Snijders & Schmidt Expires June 10, 2017 [Page 5] Internet-Draft Usage of Large BGP Communities December 2016 +---------------------+-----------------------------------------+ | Large BGP Community | Meaning | +---------------------+-----------------------------------------+ | 64497:3:1 | Route learned from a customer | | 64497:3:2 | Route learned from a peering partner | | 64497:3:3 | Route learned from an upstream provider | +---------------------+-----------------------------------------+ Example documentation for AS 64497 using Informational Communties describing the relation with the ASN from which the route was received. Table 3: Information: Relation 3.3. Combining Informational Communities Multiple Informational Communities can be tagged on a route, for example: a route learned in the Netherlands from a customer can contain both 64497:1:528 and 64497:2:150 and 64497:3:1. 4. Examples of Action Communities 4.1. Selective NO_EXPORT As part of the commercial agreement between AS 64497 and AS 64498, AS 64497 might offer AS 64498 certain BGP Traffic Engineering features such as selectively not export routes learned from 64498 to certain EBGP neighbors of AS 64497. 4.1.1. Peer ASN Based Selective NO_EXPORT AS 64497 might assign function identifier 4 to allow preventing propagation of routes to the ASN listed in the second Local Data field. +---------------------+---------------------------------+ | Large BGP Community | Meaning | +---------------------+---------------------------------+ | 64497:4:2914 | Do not export route to AS 2914 | | 64497:4:7018 | Do not export route to AS 7018 | | 64497:4:65551 | Do not export route to AS 65551 | +---------------------+---------------------------------+ Example documentation for AS 64497 offering Action Communties to limit propagation of routes based on the Peer ASN described in the third field. Table 4: Action: Peer ASN NO_EXPORT Snijders & Schmidt Expires June 10, 2017 [Page 6] Internet-Draft Usage of Large BGP Communities December 2016 4.1.2. Location Based Selective NO_EXPORT AS 64497 might assign function identifier 5 to allow its customers to request selectively not exporting routes on EBGP sessions within a certain geographical area. This example follows the ISO 3166-1 numeric encoding. +------------------+------------------------------------------------+ | Large BGP | Meaning | | Community | | +------------------+------------------------------------------------+ | 64497:5:528 | Do not export to EBGP neighbors in the | | | Netherlands | | 64497:5:392 | Do not export to EBGP neighbors in Japan | | 64497:5:840 | Do not export to EBGP neighbors in United | | | States of America | +------------------+------------------------------------------------+ Example documentation for AS 64497 offering Action Communties to trigger NO_EXPORT on routes only when propagating the route to a certain geographical region. Table 5: Action: NO_EXPORT in Region 4.2. Selective AS_PATH Prepending As part of the commercial agreement between AS 64497 and AS 64498, AS 64497 might offer AS 64498 certain BGP Traffic Engineering features such as selectively prepending the AS_PATH with 64497's ASN to certain EBGP neighbors of AS 64497. 4.2.1. Peer ASN Based Selective AS_PATH Prepending AS 64497 might assign function identifier 6 to allow prepending the AS_PATH on propagation of routes to the ASN listed in the second Local Data field. Snijders & Schmidt Expires June 10, 2017 [Page 7] Internet-Draft Usage of Large BGP Communities December 2016 +---------------------+------------------------------------------+ | Large BGP Community | Meaning | +---------------------+------------------------------------------+ | 64497:6:2914 | Prepend 64497 once on export to AS 2914 | | 64497:6:7018 | Prepend 64497 once on export to AS 7018 | | 64497:6:65551 | Prepend 64497 once on export to AS 65551 | +---------------------+------------------------------------------+ Example documentation for AS 64497 offering Action Communties to trigger prepending of the AS_PATH only when propagating the route to a certain Peer ASN. Table 6: Action: Prepend to Peer ASN 4.2.2. Location Based Selective AS_PATH Prepending AS 64497 might assign function identifier 7 to allow prepending of the AS_PATH on propagation of routes to on any EBGP neighbor's interconnection in the geographical entity listed in the second Local Data field. This example follows the ISO 3166-1 numeric regions codes in the Local Data 2 field. +------------------+------------------------------------------------+ | Large BGP | Meaning | | Community | | +------------------+------------------------------------------------+ | 64497:7:528 | Prepend once to EBGP neighbors in the | | | Netherlands | | 64497:7:392 | Prepend once to EBGP neighbors in Japan | | 64497:7:840 | Prepend once to EBGP neighbors in United | | | States of America | +------------------+------------------------------------------------+ Example documentation for AS 64497 offering Action Communties to trigger prepending of the AS_PATH only when propagating the route to a certain geographical region. Table 7: Action: Prepend in Region 4.3. Location based manipulation of LOCAL_PREF In some cases, it can be desirable for an autonomous system to allow adjacent Autonomous Systems to directly influence the degree of preference associated with a route, usually expressed within the LOCAL_PREF attribute. Furthermore, in the case of large networks spanning significant geography, it is often also useful to be able to extend this Snijders & Schmidt Expires June 10, 2017 [Page 8] Internet-Draft Usage of Large BGP Communities December 2016 capability and scope its effect to a geographic region. This is a more powerful mechanism than AS_PATH prepending, but since degree of preference determines BGP route selection and thus onward advertisement, it can also be self-limiting in its scope. Since the LOCAL_PREF attribute which influences degree of preference is locally significant within each autonomous system, it is not usually practical or useful to compare LOCAL_PREF attribute values between autonomous systems. Instead it can be useful to classify the major types of route likely to exist within an autonomous system's routing hierarchy and provide an ability to set one's route to that preference: o A qualified customer route. Usually the highest preference. o A peer, or network-share, route. A co-operating network provider engaged in a partnership for customer coverage ("peering"). o A last resort, or backup route. It is entirely possible that some providers may have more classes of route preference but it is possible to codify both the route preference class and the regional scope within the Local Data fields of the Large Community attribute. For example, AS64497 might establish the following function identifiers to set route preference class, which could allow pairing with a location or peer-based operand to determine scope. +----------+-----------------------------------------------+ | Function | Preference Class | +----------+-----------------------------------------------+ | 10 | Qualified customer route. Highest preference. | | 15 | Peering partner. Median preference. | | 19 | Route of last resort. Lowest preference. | +----------+-----------------------------------------------+ Table 8: Action: Preference Function Identifiers Once established, these route preference setting functions can be linked with a scoping operand such as per-peer or per-location based identifiers in order to provide AS64497's customers with a comprehensive and rich toolset to influence route preference. Snijders & Schmidt Expires June 10, 2017 [Page 9] Internet-Draft Usage of Large BGP Communities December 2016 +--------------------+----------------------------------------------+ | Large BGP | Meaning | | Community | | +--------------------+----------------------------------------------+ | 64497:15:528 | Set as peer route in Netherlands | | 64497:19:840 | Set as backup route in United States of | | | America | +--------------------+----------------------------------------------+ Table 9: Action: Regional Preference Communities Since the degree of preference influences BGP best path selection (which in turn influences onward route propagation) Operators should take special care with a traffic engineering tool such as location based local preference influence (BGP Wedgies [RFC4264]). 5. Security Considerations Network operators should note the recommendations in Section 11 of BGP Operations and Security [RFC7454]. 6. IANA Considerations None. 7. Acknowledgements The authors would like to gratefully acknowledge the insightful comments, contributions, critique and support from John Heasley, Adam Chappell and Jonathan Stewart. 8. References 8.1. Normative References [I-D.ietf-idr-large-community] Heitz, J., Snijders, J., Patel, K., Bagdonas, I., and N. Hilliard, "BGP Large Communities", draft-ietf-idr-large- community-11 (work in progress), December 2016. [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Snijders & Schmidt Expires June 10, 2017 [Page 10] Internet-Draft Usage of Large BGP Communities December 2016 [RFC4264] Griffin, T. and G. Huston, "BGP Wedgies", RFC 4264, DOI 10.17487/RFC4264, November 2005, . [RFC7454] Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454, February 2015, . 8.2. URIs [1] http://nanog.net [2] http://nlnog.net [3] http://unstats.un.org/unsd/methods/m49/m49regin.htm Authors' Addresses Job Snijders NTT Communications Theodorus Majofskistraat 100 Amsterdam 1065 SZ NL Email: job@ntt.net Martijn Schmidt i3D.net Rivium 1e Straat 1 Capelle aan den IJssel 2909 LE NL Email: martijnschmidt@i3d.net Snijders & Schmidt Expires June 10, 2017 [Page 11]