--- 1/draft-ietf-idr-bgp-open-policy-05.txt 2019-07-08 11:14:19.676488843 -0700 +++ 2/draft-ietf-idr-bgp-open-policy-06.txt 2019-07-08 11:14:19.752490777 -0700 @@ -1,427 +1,418 @@ Network Working Group A. Azimov Internet-Draft E. Bogomazov Intended status: Standards Track Qrator Labs -Expires: August 19, 2019 R. Bush - Internet Initiative Japan +Expires: January 9, 2020 R. Bush + Internet Initiative Japan & Arrcus K. Patel Arrcus, Inc. K. Sriram US NIST - February 15, 2019 + July 8, 2019 Route Leak Prevention using Roles in Update and Open messages - draft-ietf-idr-bgp-open-policy-05 + draft-ietf-idr-bgp-open-policy-06 Abstract Route Leaks are the 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 operator configuration options, with no - check that 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, RS, RS-client, internal) relationship of two + marking routes by operator configuration, with no check that 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, Route Server, Route Server client) relationship of two neighboring BGP speakers to enforce appropriate configuration on both - sides. Propagated routes are then marked with an iOTC attribute - according to agreed relationship allowing prevention of route leaks. + sides. Propagated routes are then marked with an OTC attribute + according to the agreed relationship, allowing both prevention and + detection 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. + "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and + "OPTIONAL" in this document are to be interpreted as described in + BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all + capitals, as shown here. 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 August 19, 2019. + This Internet-Draft will expire on January 9, 2020. Copyright Notice Copyright (c) 2019 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 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 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Peering Relationships . . . . . . . . . . . . . . . . . . . . 3 3. BGP Role . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Role capability . . . . . . . . . . . . . . . . . . . . . . . 4 5. Role correctness . . . . . . . . . . . . . . . . . . . . . . 5 - 5.1. Strict mode . . . . . . . . . . . . . . . . . . . . . . . 6 - 6. BGP Internal Only To Customer attribute . . . . . . . . . . . 6 - 7. Attribute or Community . . . . . . . . . . . . . . . . . . . 6 - 8. Compatibility with BGPsec . . . . . . . . . . . . . . . . . . 7 - 9. Additional Considerations . . . . . . . . . . . . . . . . . . 7 - 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 - 11. Security Considerations . . . . . . . . . . . . . . . . . . . 8 - 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 - 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 - 13.1. Normative References . . . . . . . . . . . . . . . . . . 8 - 13.2. Informative References . . . . . . . . . . . . . . . . . 9 + 5.1. Strict mode . . . . . . . . . . . . . . . . . . . . . . . 5 + 6. BGP Only To Customer attribute . . . . . . . . . . . . . . . 6 + 7. Enforcement . . . . . . . . . . . . . . . . . . . . . . . . . 6 + 8. Additional Considerations . . . . . . . . . . . . . . . . . . 7 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 + 10. Security Considerations . . . . . . . . . . . . . . . . . . . 8 + 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 + 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 + 12.1. Normative References . . . . . . . . . . . . . . . . . . 8 + 12.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction - 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 established in OPEN message and a way to create double-boundary - filters for prevention of route leaks using the new BGP Path - Attribute. + BGP route leaks are BGP route(s) which were learned from transit + provider or peer and then announced to another provider or peer. See + [RFC7908]. These are usually the result of misconfigured or absent + BGP route filtering or lack of coordination between two BGP speakers. - For the purpose 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[RFC7908]. These are usually the - result of misconfigured or absent BGP route filtering or lack of - coordination between two BGP speakers. + The mechanism proposed in + [I-D.ietf-idr-route-leak-detection-mitigation] uses large-communities + to attempt detection of route leaks. While signaling using + communities is easy to implement, ut relies on operator maintained + policy configuration which is too easily, and too often, + misconfigured. Another problem may occur if the community signal is + stripped, accidentally or maliciously. - [I-D.ietf-idr-route-leak-detection-mitigation] The mechanism proposed - in that draft provides the opportunity to detect route leaks made by - third parties but provides no mechanism to strongly prevent route - leak creation. + This document provides configuration automation using 'BGP roles', + which are negotiated using a new BGP Capability Code in OPEN message, + [RFC5492] Sec 4. Either or both BGP speakers MAY be configured to + require that this capability be agreed for the BGP OPEN to succeed. - Also, route tagging which relies on operator maintained policy - configuration is too easily, and too often, misconfigured. + A new BGP Path Attribute is specified that SHOULD be automatically + configured using BGP roles. This attribute prevents networks from + creating leaks, and detects leaks created by third-parties. 2. Peering Relationships - Despite uses of words such as "Customer," "Peer." etc. described - above are not business relationships, who pays whom, etc. These are - common terms to represent restrictions on BGP route propagation, - sometimes known as the Gao-Rexford model. + Despite uses of words such as "Customer," "Peer." etc.; these are not + business relationships, who pays whom, etc. These are common terms + to represent restrictions on BGP route propagation, sometimes known + as the Gao-Rexford model [cite]. A Provider: MAY send to a customer all available prefixes. A Customer: MAY send to a provider their own prefixes and prefixes learned from any of their customers. A customer MUST NOT send to - a provider prefixes learned from peers, other providers, or RS. + a provider prefixes learned from its peers, from other providers, + or from Route Servers. - A Route Server (RS) MAY send to a RS client all available prefixes. + A Route Server (RS) MAY send to a RS Client all available prefixes. A Route Server Client (RS-client) MAY send to an RS its own prefixes and prefixes learned from its customers. A RS-client MUST NOT - send to an RS prefixes learned from peers, providers, or other RS. + send to an RS prefixes learned from peers, from its providers, or + from other RS(s). A Peer: MAY send to a peer its own prefixes and prefixes learned from its customers. A peer MUST NOT send to a peer prefixes - learned from other peers, providers, or RS. - - An Internal: MAY send all available prefixes through internal link. + learned from other peers, from its providers, or from RS(s). Of course, any BGP speaker may apply policy to reduce what is announced, and a recipient may apply policy to reduce the set of - routes they accept. But violation of rules marked MUST NOT may - result in route leaks. While these peering relations cover 99% of - possible scenarios, their configuration isn't part of the BGP itself, - thus requiring configuration of communities and corresponding egress - prefix filters. The automation of this process may significantly - decrease number of configuration mistakes. + routes they accept. Violation of the above rules may result in route + leaks so MUST not be allowed. Automatic enforment of these rules + should significantly reduce configuration mistakes. While these + enforcing the above rules will address most BGP peering scenarios, + their configuration isn't part of BGP itself; therefore requiring + configuration of ingress and egress prefix filters is still strongly + advised. 3. BGP Role BGP Role is new configuration option that SHOULD be configured on each BGP session. It reflects the real-world agreement between two - BGP speakers about their peering relationship. + BGP speakers about their relationship. Allowed Role values for eBGP sessions are: o Provider - sender is a transit provider to neighbor; - o Customer - sender is customer of neighbor; + o Customer - sender is transit customer of neighbor; - o RS - sender is route server at internet exchange point (IX) + o RS - sender is a Route Server, usually at internet exchange point + (IX) - o RS-client - sender is client of RS at internet exchange point (IX) + o RS-Client - sender is client of RS o Peer - sender and neighbor are peers; - o Internal - sender and neighbor are part of the same organization. - - For iBGP sessions, only the Internal role MAY be configured. - Since BGP Role reflects the relationship between two BGP speakers, it could also be used for more than route leak mitigation. 4. 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 | Sender is Internal | - | 1 | Sender is Provider | - | 2 | Sender is RS | - | 3 | Sender is RS-Client | - | 4 | Sender is Customer | - | 5 | Sender is Peer | + | 0 | Sender is Provider | + | 1 | Sender is RS | + | 2 | Sender is RS-Client | + | 3 | Sender is Customer | + | 4 | Sender is Peer | +-------+---------------------+ Table 1: Predefined BGP Role Values 5. Role correctness - Section 3 described how BGP Role is a reflection of the relationship - between two BGP speakers. But the mere presence of BGP Role doesn't + Section 3 described how BGP Role encodes 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, the BGP Role check is used with a set of constrains on how speakers' BGP Roles MUST correspond. 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 MUST check the value of the received capability with its own BGP Role (if it is set). The allowed pairings are (first a sender's Role, second the receiver's Role): +-------------+---------------+ | Sender Role | Receiver Role | +-------------+---------------+ - | Internal | Internal | | Provider | Customer | | Customer | Provider | | RS | RS-Client | | RS-Client | RS | | Peer | Peer | +-------------+---------------+ Table 2: Allowed Role Capabilities - In case of any other pairs of roles, a speaker MUST send a Role - Mismatch Notification (code 2, sub-code ). + If the Role pair is not in the above table, a speaker MUST send a + Role Mismatch Notification (code 2, sub-code ). 5.1. 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 a neighbor which does not announce the - BGP Role capability in their OPEN message. If a speaker rejects a + BGP Role capability in the 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. -6. BGP Internal Only To Customer attribute +6. BGP Only To Customer attribute - The Internal Only To Customer (iOTC) attribute is a new optional, - non-transitive BGP Path attribute with the Type Code . This - attribute has zero length as it is used only as a flag. + The Only To Customer (OTC) BGP Attribute is a new optional, + transitive BGP Path attribute with the Type Code . - There are four rules of iOTC attribute usage: + This four byte attribute MUST apply the following policy: - 1. The iOTC attribute MUST be added to all incoming routes if the - receiver's Role is Customer, Peer, or RS-client; + 1. If a route with OTC attribute is received from Customer or RS- + client - it's a route leak and MUST be rejected. - 2. Routes with the iOTC attribute set MUST NOT be announced by a - sender whose Role is Customer, Peer, or RS-client; + 2. If a route with OTC attribute is received from Peer and its value + isn't equal to the neighbor's ASN - it's a route leak and MUST be + rejected. - 3. A sender MUST NOT include iOTC in UPDATE messages advertised to - eBGP neighbor if its Role isn't Internal. + 3. If a route is received from a Provider, Peer or RS and the OTC + attribute has not been set it MUST be added with value equal to + AS number of the neighbor (sender). - 4. If iOTC is contained in an UPDATE message from eBGP speaker and - receiver's Role isn't Internal then this attribute MUST be - removed. + The egress policy MUST be: - These rules provide mechanism to strongly prevent route leak creation - by an AS. + 1. A route with the OTC attribute set MUST NOT be sent to providers, + peers, or RS(s). -7. Attribute or Community + 2. If route is sent to customer or peer and the OTC attribute is not + set it MUST be added with value equal to AS number of the sender. - Having the relationship hard set by agreement between the two peers - in BGP OPEN is critical; the routers enforce the relationship - irrespective of operator policy configuration errors. + Once the OTC attribute has been set, it MUST be preserved unchanged. - Similarly, it is critical that the application of that relationship - on prefix propagation using iOTC is enforced by the router(s), and - minimally exposed to user mis-configuration. There is a question - whether the iOTC marking should be an attribute or a well-known - community. +7. Enforcement - There is a long and sordid history of mis-configurations inserting - incorrect communities, deleting communities, ignoring well-known - community markings etc. In this mechanism's case, an operator could, - for example, accidentally strip the well-known community on receipt. + Having the relationship unequivocally agreed between the two peers in + BGP OPEN is critical; the BGP implementations enforce the + relationship irrespective of operator policy configuration errors. + + Similarly, the application of that relationship on prefix propagation + using OTC MUST BE enforced by the BGP implementations, and not + exposed to user mis-configuration. As opposed to communities, BGP attributes may not be generally modified or filtered by the operator. The router(s) enforce them. - This is the desired property for the iOTC marking. Hence, this - document specifies iOTC as an attribute. - -8. Compatibility with BGPsec - - As the iOTC attribute is non-transitive, it is not seen by or signed - by BGPsec [RFC8205]. + This is the desired property for the OTC marking. Hence, this + document specifies OTC as an attribute. -9. Additional Considerations +8. Additional Considerations As the BGP Role reflects the peering 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 ASs. - - Though such uses may be worthwhile, they are not the goal of this - document. Note that such uses would require local policy control. + it might have other uses. For example, BGP Role might affect route + priority, or be used to distinguish borders of a network if a network + consists of multiple ASs. Though such uses may be worthwhile, they + are not the goal of this document. Note that such uses would require + local policy control. As BGP role configuration results in automatic creation of inbound/ outbound filters, existence of roles should be treated as existence of Import and Export policy. [RFC8212] - This document doesn't provide any security measures to check - correctness of iOTC usage if role isn't configured. + There are peering relationships which are 'complex'; e.g. when both + parties are intentionally sending prefixes received from each other + to their peers and/or upstreams. If multiple BGP peerings can + segregate the 'complex' parts of the relationship, the complex + peering roles can be segregated into different BGP sessions, and + normal BGP Roles MUST be used on the non-complex sessions. No Roles + SHOULD be configured on 'complex' BGP sessions, and OTC MUST be set + by configuration on a per-prefix basis. There can be no measures to + check correctness of OTC use if Role is not configured. -10. IANA Considerations +9. 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, non-transitive BGP Path - Attributes option, named "Internal 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. + 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. -11. Security Considerations +10. Security Considerations This document proposes a mechanism for prevention of route leaks that are the result of BGP policy mis-configuration. Deliberate sending of a known conflicting BGP Role could be used to sabotage a BGP connection. This is easily detectable. - BGP Role is disclosed only to an immediate BGP neighbor, so it will - not itself reveal any sensitive information to third parties. + A misconfiguration in OTC setup may affect prefix propagation. But + the automation that is provided by BGP roles should make such + misconfiguration unlikely. -12. Acknowledgments +11. Acknowledgments The authors wish to thank Douglas Montgomery, Brian Dickson, Andrei - Robachevsky and Daniel Ginsburg for their contributions to a variant + Robachevsky, and Daniel Ginsburg for their contributions to a variant of this work. -13. References +12. References -13.1. Normative References +12.1. 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, . -13.2. Informative References + [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC + 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, + May 2017, . + +12.2. Informative References [I-D.ietf-idr-route-leak-detection-mitigation] Sriram, K. and A. Azimov, "Methods for Detection and Mitigation of BGP Route Leaks", draft-ietf-idr-route-leak- detection-mitigation-10 (work in progress), October 2018. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008, . [RFC7908] Sriram, K., Montgomery, D., McPherson, D., Osterweil, E., and B. Dickson, "Problem Definition and Classification of BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June 2016, . - [RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol - Specification", RFC 8205, DOI 10.17487/RFC8205, September - 2017, . - [RFC8212] Mauch, J., Snijders, J., and G. Hankins, "Default External BGP (EBGP) Route Propagation Behavior without Policies", RFC 8212, DOI 10.17487/RFC8212, July 2017, . Authors' Addresses Alexander Azimov Qrator Labs Email: a.e.azimov@gmail.com Eugene Bogomazov Qrator Labs Email: eb@qrator.net Randy Bush - Internet Initiative Japan + Internet Initiative Japan & Arrcus Email: randy@psg.com + Keyur Patel Arrcus, Inc. Email: keyur@arrcus.com - Kotikalapudi Sriram US NIST Email: ksriram@nist.gov