ALTO L. M. Contreras Internet-Draft Telefonica Intended status: Informational 9 July 2023 Expires: 10 January 2024 Extending ALTO by using BGP Communities draft-contreras-alto-bgp-communities-01 Abstract This memo introduces a proposal to extend ALTO by using BGP Communities as PIDs. This proposal is meant to ease the integration of ALTO in operational networks by leveraging existing resource identifiers. 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 https://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 10 January 2024. Copyright Notice Copyright (c) 2023 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 (https://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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Contreras Expires 10 January 2024 [Page 1] Internet-Draft Extending ALTO by using BGP Communities July 2023 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. BGP Communities Overview . . . . . . . . . . . . . . . . . . 2 3. Extending ALTO with BGP communities . . . . . . . . . . . . . 3 3.1. Usage of BGP Communities in ALTO . . . . . . . . . . . . 3 3.2. BGP Community representation in ALTO . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 7. Informative References . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction The Provider-defined Identifiers (PIDs) in the ALTO Protocol [RFC7285] provide an indirect and network-agnostic way to aggregate a set of network endpoints, that grouped together creates a network map. Network endpoints that share a common PID are expected to receive similar treatment on the decisions assisted by ALTO. With the same goal of grouping destinations, BGP Communities [RFC1997] were introduced in the past to tag a grouping of destinations so that the routing decision can also be based on the identity of a group. As per [RFC1997], a community is a group of destinations which share some common properties. Given that BGP communities are widely used in operational networks, and for the sake of simplifying the integration of ALTO into these networks, this document specifies an extension to [RFC7285] by defining a new PID type based on the BGP community concept. 2. BGP Communities Overview A BGP Community, as per [RFC1997], is a BGP attribute that is used to group destinations. It is represented as a 32-bit integer number, typically written as the combination of two 16-bit integer numbers separated by a colon. The first number is usually the Autonomous System (AS) number, while the second one is determined by the service provider according to some internal logic. In order to support 4-octet ASNs, [RFC8092] specifies a BGP Large Communities attribute. Another form of BGP communities is defined in the BGP Extended Communities Attribute [RFC4360]. IP prefixes can be part of distinct BGP Communities, with different purposes, typically to influence the traffic reaching the particular prefixes of a community. Contreras Expires 10 January 2024 [Page 2] Internet-Draft Extending ALTO by using BGP Communities July 2023 The BGP Communities attribute is useful for applying policies of applicability to a certain set of prefixes, grouped as a community at the criteria of the service provider. For instance, BGP Communities can be useful for indicating local preferences for a route to the receive to a set of IP prefixes in a peering scenario. The initial approach in the usage of BGP Communities in ALTO that we follow in this document is to consider [RFC1997] and [RFC8092] as the means to identify groupings of IP prefixes in networks with either 2-octet or 4-octet ASNs. 3. Extending ALTO with BGP communities Network operators use BGP Communities extensively as a mechanism to group some destinations (i.e., IP prefixes) for different purposes. Typically, they are used by administratively-defined filters for applying policies, thus influencing the behavior of the traffic towards the associated destinations. On the other hand, the ALTO Protocol is based on IP prefixes. When considering queries to IP prefixes, it could be the case that those queries apply to IP addresses associated to the same topological element. This is for instance the case of aggregation nodes in the network (such as BNG or PGW), which have associated a number of IP prefixes (that can evolve along the time). The same response will be obtained from an ALTO server for all the prefixes associated with such a node, since the topological information is essentially the same. For assisting an efficient usage of ALTO resources in this kind of situations, the usage of BGP Communities simplifies the process by reducing the number of queries to the ALTO server, but also by smoothly absorbing the modification of prefixes for a given aggregation node. 3.1. Usage of BGP Communities in ALTO Some potential use cases of BGP Communities in ALTO are envisaged: * In situations where a BGP Community and an ALTO PID scope the same grouping of prefixes, leveraging BGP Communities simplifies network operations by using an existing identifier for the purpose of retrieving ALTO information. * In situations where the purpose is to retrieve ALTO information applicable to a superset of PIDs, a BGP Community can be defined in order to group the prefixes of all those PIDs. Contreras Expires 10 January 2024 [Page 3] Internet-Draft Extending ALTO by using BGP Communities July 2023 * In situations where the purpose is to retrieve ALTO information applicable to a subset of prefixes across multiple PIDs, a BGP Community can be defined in order to group the subset of prefixes of all the PIDs. Furthermore, it is needed to define how BGP Communities become populated to the ALTO server. One means of doing that could be the augmentation of [I-D.ietf-alto-oam-yang] with the purpose of configuring the same communities, or to retieve such information from a BGP session with route reflectos in the network. 3.2. BGP Community representation in ALTO BGP Communities are defined at BGP level, by associating IP prefixes to a given BGP Community identifier. The same BGP Community can be applied to prefixes representing reachable sub-networks (i.e., a set of network endpoints) attached to different nodes. Thus, in that cases, the network and cost map generated by ALTO can present topological situations of one-to-many or many-to-many nodes. As said, a BGP Community is a representation of a number of IP prefixes. Thus, conceptually, it can be defined in the same manner the PIDs are currently defined. Then, the representation of a BGP Community in ALTO maps could follow the same way in which PIDs are represented. In any case, more discussion is needed in the WG to agree on the way of representing BGP Communities. Finally, it is also interesting to note that because a BGP Community can span more than one network node with different topological cost metrics from a single origin endpoint, it seems necessary to define the cost value to be applied for handling BGP Communities. That cost value could be the average cost value per node, the weighted average cost value based on the number of prefixes for a given BGP Community per node, etc. Again, more dicussion is expected in ALTO WG for these definitions. 4. Security Considerations BGP Communities are extensively used by network operators, usually not bein disclosed to external parties. Thus privacy could be a key aspect to address when using BGP Communities in ALTO. Moreover, since BGP Communities are used in many cases to apply policies to the corresponding IP prefixes, the exposure of information related to BGP Communities could imply a risk in the sense of revealing behaviors, scope or magnitude of the endpoints associated to that Communities. Contreras Expires 10 January 2024 [Page 4] Internet-Draft Extending ALTO by using BGP Communities July 2023 Specific security measures need to be detailed, and this will be done in future verisons of the document. 5. IANA Considerations To be provided. 6. Acknowledgements The author thanks Med Boucadair and Jordi Ros-Giralt for their review, comments and suggestions to make this document and solution more complete. 7. Informative References [I-D.ietf-alto-oam-yang] Zhang, J., Dhody, D., Gao, K., Schott, R., and Q. Ma, "YANG Data Models for the Application-Layer Traffic Optimization (ALTO) Protocol", Work in Progress, Internet- Draft, draft-ietf-alto-oam-yang-10, 15 June 2023, . [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996, . [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, DOI 10.17487/RFC4360, February 2006, . [RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S., Previdi, S., Roome, W., Shalunov, S., and R. Woundy, "Application-Layer Traffic Optimization (ALTO) Protocol", RFC 7285, DOI 10.17487/RFC7285, September 2014, . [RFC8092] Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas, I., and N. Hilliard, "BGP Large Communities Attribute", RFC 8092, DOI 10.17487/RFC8092, February 2017, . Author's Address Contreras Expires 10 January 2024 [Page 5] Internet-Draft Extending ALTO by using BGP Communities July 2023 Luis M. Contreras Telefonica Ronda de la Comunicacion, s/n 28050 Madrid Spain Email: luismiguel.contrerasmurillo@telefonica.com URI: http://lmcontreras.com Contreras Expires 10 January 2024 [Page 6]