Network Working Group A. Azimov Internet-Draft E. Bogomazov Intended status: Standards Track Qrator Labs Expires: September 22, 2016 R. Bush Internet Initiative Japan March 21, 2016 Route Leak Detection and Filtering using Roles in Update and Open messages draft-ymbk-idr-bgp-open-policy-00 Abstract Route Leaks are propagation of BGP prefixes which violate assumptions of BGP topology relationships; e.g. passing a route learned from one peer to another peer or to a transit provider, passing a route learned from one transit provider to another transit provider or to a peer. Today, approaches to leak prevention rely on marking routes according to some configuration options without any check of the configuration corresponds to that of the BGP neighbor, or enforcement that the two BGP speakers agree on the relationship. This document enhances BGP Open to establish agreement of the (peer, customer, provider, internal) relationship of two BGP neighboring speakers to enforce appropriate configuration on both sides. Propagated routes are then marked with a flag according to agreed relationship allowing detection and mitigation of route leaks. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [RFC2119] only when they appear in all upper case. They may also appear in lower or mixed case as English words, without normative meaning. 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 Azimov, et al. Expires September 22, 2016 [Page 1] Internet-Draft Route Leak Detection and Filtering March 2016 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 September 22, 2016. 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 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. BGP Role . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Role capability . . . . . . . . . . . . . . . . . . . . . . . 4 4. Role correctness . . . . . . . . . . . . . . . . . . . . . . 4 4.1. Strict mode . . . . . . . . . . . . . . . . . . . . . . . 5 5. BGP Only To Customer attribute . . . . . . . . . . . . . . . 5 5.1. Attribute usage . . . . . . . . . . . . . . . . . . . . . 5 6. Additional Considerations . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction For the purposes of this document BGP route leaks are when a BGP route was learned from transit provider or peer and is announced to another provider or peer. See [I-D.ietf-grow-route-leak-problem-definition]. These are usually the result of misconfigured or absent BGP route filtering or lack of coordination between two BGP speakers. [I-D.ietf-idr-route-leak-detection-mitigation] describes a method of marking and detecting leaks which relies on operator maintained Azimov, et al. Expires September 22, 2016 [Page 2] Internet-Draft Route Leak Detection and Filtering March 2016 markings. Unfortunately, in most cases, a leaking router will likely also be misconfigured to mark incorrectly. The proposed mechanism provides an opportunity to detect route leaks made by third parties but provides no support to avoid route leak creation. The leak avoidance still relies on communities which are optional and often missed due to mistakes or misunderstanding of the BGP configuration process. It has been suggested to use white list filtering, relying on knowing the prefixes in the customer cone as import filtering, in order to detect route leaks. Unfortunately, a large number of incidents is created by leaking routes defined in customer cone; a lot of medium size transit operators use a single prefix list as only the ACL for export filtering, without community tagging and and paying attention to the source of a learned route. So, if they learn a customer's route from their provider or peer - they will announce it in all directions, including other providers or peers. This misconfiguration affects a limited number of prefixes; but such route leaks will obviously bypass customer cone import filtering made by upper level upstream providers. Also, route tagging which relies on operator maintained policy configuration is too easily and too often misconfigured. This document specifies a new BGP Capability Code, [RFC5492] Sec 4, which two BGP speakers MAY use to ensure that they MUST agree on their relationship; i.e. customer and provider or peers. Either or both may optionally be configured to require that this option be exchanged for the BGP Open to succeed. Also this document specifies a way to mark routes according to BGP Roles and a way to create double-boundary filters for detection and preventing propagation of route leaks via a new BGP Path Attribute. 2. BGP Role BGP Role is new mandatory configuration option. It reflects the real-world agreement between two BGP speakers about their business relationship. Allowed Role values are: o Provider - sender is a transit provider to neighbor; o Customer - sender is customer of neighbor; o Peer - sender and neighbor are peers; Azimov, et al. Expires September 22, 2016 [Page 3] Internet-Draft Route Leak Detection and Filtering March 2016 o Internal - sender is part of an internal AS of an organization which has multiple ASs, is a confederation, ... Since BGP Role reflects the relationship between two BGP speakers, it could also be used for more than route leak mitigation. 3. Role capability The TLV (type, length, value) of the BGP Role capability are: o Type - ; o Length - 1 (octet); o Value - integer corresponding to speaker' BGP Role. +--------+----------------------+ | Value | Role name | +--------+----------------------+ | 0 | Undefined | | 1 | Sender is Peer | | 2 | Sender is Provider | | 3 | Sender is Customer | | 4 | Sender is Internal | +--------+----------------------+ Table 1: Predefined BGP Role Values 4. Role correctness Section 2 described how BGP Role is a reflection of the relationship between two BGP speakers. But the mere presence of BGP Role doesn't automatically guarantee role agreement between two BGP peers. To enforce correctness, use the BGP Role check with a set of constrains on how speakers' BGP Roles MUST corresponded. Of course, each speaker MUST announce and accept the BGP Role capability in the BGP OPEN message exchange. If a speaker receives a BGP Role capability, it SHOULD check value of the received capability with its own BGP Role. The allowed pairings are (first a sender's Role, second the receiver's Role): Azimov, et al. Expires September 22, 2016 [Page 4] Internet-Draft Route Leak Detection and Filtering March 2016 +--------------+----------------+ | Sender Role | Receiver Role | +--------------+----------------+ | Peer | Peer | | Provider | Customer | | Customer | Provider | | Internal | Internal | +--------------+----------------+ Table 2: Allowed Role Capabilities In all other cases speaker MUST send a Role Mismatch Notification (code 2, sub-code ). 4.1. Strict mode A new BGP configuration option "strict mode" is defined with values of true or false. If set to true, then the speaker MUST refuse to establish a BGP session with peers which do not announce BGP Role capability in their OPEN message. If a speaker rejects a connection, it MUST send a Connection Rejected Notification [RFC4486] (Notification with error code 6, subcode 5). By default strict mode SHOULD be set to false for backward compatibility with BGP speakers, that do not yet support this mechanism. 5. BGP Only To Customer attribute The Only To Customer (OTC) attribute is a new optional, transitive BGP Path attribute with the Type Code . This attribute has zero length as it used only as a flag. 5.1. Attribute usage There are four rules for setting the OTC attribute: 1. The OTC attribute SHOULD be added to all incoming routes if the receiver's Role is Customer or Peer; 2. Routes with the OTC attribute set MUST NOT be announced to a neighbor which is a Provider or a Peer; 3. The OTC attribute SHOULD be added to all outgoing routes if the neighbor has not sent the Role capability in the OPEN message and sender's Role is Provider or Peer; 4. If the receiver's Role is Provider or Peer, incoming routes with the OTC attribute set SHOULD be given a lower local preference, or they MAY be dropped. Azimov, et al. Expires September 22, 2016 [Page 5] Internet-Draft Route Leak Detection and Filtering March 2016 The first two rules avoid creation of route leaks by an AS. The last two rules provide the data to allow detection of route leaks made by some other AS in the AS Path. The OTC attribute will be added automatically if at least one of the speakers correctly sets its role. Additionally, the OTC attribute will be checked if at least one of the speakers set its role correctly. In other words, this double-checks at borders to prevent route leaks. 6. Additional Considerations As BGP Role reflects the relationship between neighbors, it can also have other uses. As an example, BGP Role might affect route priority, or be used to distinguish borders of a network if a network consists of multiple AS. Though such uses may be worthwhile, they are not the goal of this document. Note that such uses would require local policy control. 7. IANA Considerations This document defines a new Capability Codes option [to be removed upon publication: http://www.iana.org/assignments/capability-codes/ capability-codes.xhtml] [RFC5492], named "BGP Role", assigned value . The length of this capability is 1. The BGP Role capability includes a Value field, for which IANA is requested to create and maintain a new sub-registry called "BGP Role Value". Assignments consist of Value and corresponding Role name. Initially this registry is to be populated with the data in Table 1. Future assignments may be made by a standard action procedure [RFC5226]. This document defines new subcode, "Role Mismatch", assigned value in the OPEN Message Error subcodes registry [to be removed upon publication: http://www.iana.org/assignments/bgp-parameters/bgp- parameters.xhtml#bgp-parameters-6] [RFC4271]. This document defines a new optional, transitive BGP Path Attributes option, named "Only To Customer", assigned value [To be removed upon publication: http://www.iana.org/assignments/bgp- parameters/bgp-parameters.xhtml#bgp-parameters-2] [RFC4271]. The length of this attribute is 0. Azimov, et al. Expires September 22, 2016 [Page 6] Internet-Draft Route Leak Detection and Filtering March 2016 8. Security Considerations This document proposes a mechanism for avoiding route leaks, that are the result of BGP policy misconfiguration. That includes preventing route leaks created inside an AS (company), and route leak detection, if a route was leaked by third party. Deliberate sending of a known conflicting BGP Role could be used to sabotage a BGP connection. This is easily detectable. Deliberate mis-marking of the OTC flag could be used to sabotage a route's propagation. BGP Role is disclosed only to an immediate BGP speaker, so it will not itself reveal any sensitive information to third parties. On the other hand, OTC is a transitive BGP AS_PATH attribute which reveals a bit about a BGP speaker's business relationship. It will give a strong hint that some link isn't customer to provider, but will not help to distinguish if it is provider to customer or peer to peer. If OTC is BGPsec signed, it can not be removed for business confidentiality. 9. References 9.1. 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, . [RFC4486] Chen, E. and V. Gillet, "Subcodes for BGP Cease Notification Message", RFC 4486, DOI 10.17487/RFC4486, April 2006, . [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 2009, . Azimov, et al. Expires September 22, 2016 [Page 7] Internet-Draft Route Leak Detection and Filtering March 2016 9.2. Informative References [I-D.ietf-grow-route-leak-problem-definition] Sriram, K., Montgomery, D., McPherson, D., Osterweil, E., and B. Dickson, "Problem Definition and Classification of BGP Route Leaks", draft-ietf-grow-route-leak-problem- definition-03 (work in progress), October 2015. [I-D.ietf-idr-route-leak-detection-mitigation] Sriram, K., Montgomery, D., Dickson, B., Patel, K., and A. Robachevsky, "Methods for Detection and Mitigation of BGP Route Leaks", draft-ietf-idr-route-leak-detection- mitigation-01 (work in progress), October 2015. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008, . Authors' Addresses Alexander Azimov Qrator Labs Email: aa@qrator.net Eugene Bogomazov Qrator Labs Email: eb@qrator.net Randy Bush Internet Initiative Japan Email: randy@psg.com Azimov, et al. Expires September 22, 2016 [Page 8]