Route Leak Detection and Filtering using Roles in Update and Open messages
draft-ymbk-idr-bgp-open-policy-02

Network Working Group                                          A. Azimov
Internet-Draft                                              E. Bogomazov
Intended status: Standards Track                             Qrator Labs
Expires: May 18, 2017                                            R. Bush
                                               Internet Initiative Japan
                                                                K. Patel
                                                            Arrcus, Inc.
                                                               K. Sriram
                                                                 US NIST
                                                       November 14, 2016

   Route Leak Detection and Filtering using Roles in Update and Open
                                messages
                   draft-ymbk-idr-bgp-open-policy-02

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 without
   any 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, internal) relationship of two
   neighboring BGP speakers to enforce appropriate configuration on both
   sides.  Propagated routes are then marked with a eOTC and iOTC
   attributes according to agreed relationship allowing 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.

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

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   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
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   This Internet-Draft will expire on May 18, 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Role Definitions  . . . . . . . . . . . . . . . . . . . . . .   4
   3.  BGP Role  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Role capability . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Role correctness  . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Strict mode . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Restrictions on the Complex role  . . . . . . . . . . . . . .   6
   7.  BGP Internal Only To Customer attribute . . . . . . . . . . .   6
   8.  BGP External Only To Customer attribute . . . . . . . . . . .   7
   9.  Compatibility with BGPsec . . . . . . . . . . . . . . . . . .   8
   10. Additional Considerations . . . . . . . . . . . . . . . . . .   8
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   12. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     14.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     14.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

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1.  Introduction

   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
   [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
   markings.  Unfortunately, in most cases, a leaking router will likely
   also be misconfigured to mark incorrectly.  The mechanism proposed in
   that draft provides the opportunity to detect route leaks made by
   third parties but provides no support to strongly prevent route leak
   creation.  The leak prevention 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 peer's customer cone as import filtering, in
   order to detect route leaks.  Unfortunately, a large number of
   incidents in medium transit operators use a single prefix list as
   only the ACL for export filtering, without community tagging and
   without 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 established in Open and a way to create double-boundary filters
   for prevention and detection of route leaks via a two new BGP Path
   Attributes.

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2.  Role Definitions

   As many of these terms are used differently in various contexts, it
   is worth being explicit.

   A Provider:  sends their own routes and (possibly) a subset of routes
      learned from their other customers, peers, and transit providers
      to their customer.

   A Customer:  accepts 'transit routes' from its provider(s) and
      announces their own routes and the routes they have learned from
      the transitive closure of their customers (AKA their 'customer
      cone') to their provider(s).

   A Peer:  announces their routes and the routes from their customer
      cone to other Peers.

   An Internal  BGP Neighbor has one of the above relationships to
      another internal BGP AS.

   A Complex  BGP relationship is an attempt to allow those whose policy
      may vary by prefix.  It is aptly named and the authors question
      its real utility.

   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.

3.  BGP Role

   BGP Role is new mandatory configuration option which must be set per
   each address family.  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;

   o  Internal - sender is part of an internal AS of an organization
      which has multiple ASs, or is a confederation, etc.

   o  Complex - sender has a non-standard relationship and wants to use
      manual per-prefix based role policies.

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   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 - <TBD1>;

   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   |
                     |   5    | Sender is Complex    |
                     +--------+----------------------+

                    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
   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 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):

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                     +--------------+----------------+
                     | Sender Role  | Receiver Role  |
                     +--------------+----------------+
                     | Peer         | Peer           |
                     | Provider     | Customer       |
                     | Customer     | Provider       |
                     | Internal     | Internal       |
                     | Complex      | Complex        |
                     +--------------+----------------+

                    Table 2: Allowed Role Capabilities

   In all other cases speaker MUST send a Role Mismatch Notification
   (code 2, sub-code <TBD2>).

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 peers which do not announce the 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.

6.  Restrictions on the Complex role

   The Complex role should be set only if the relationship between BGP
   neighbors can not be described using simple Customer/Provider/Peer
   roles.  For a example, if neighbor is literal peer, but for some
   prefixes it provides full transit; the complex role SHOULD be set on
   both sides.  In this case roles Customer/Provider/Peer should be set
   on per-prefix basis, keeping the abstraction from detection and
   filtering mechanisms (Section 7 and Section 8).

   If role is not Complex all per-prefix role settings MUST be ignored.

7.  BGP Internal Only To Customer attribute

   The Internal Only To Customer (iOTC) attribute is a new optional,
   non-transitive BGP Path attribute with the Type Code <TBD3>.  This
   attribute has zero length as it is used only as a flag.

   There are four rules for setting the iOTC attribute:

   1.  The iOTC attribute MUST be added to all incoming routes if the
       receiver's Role is Customer or Peer;

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   2.  The iOTC attribute MUST be added to all incoming routes if the
       receiver's Role is Complex and the prefix Role is Customer or
       Peer;

   3.  Routes with the iOTC attribute set MUST NOT be announced by a
       sender whose Role is Customer or Peer;

   4.  Routes with the iOTC attribute set MUST NOT be announced if by a
       sender whose Role is Complex and the prefix Role is Customer or
       Peer;

   These four rules provide mechanism that strongly prevents route leak
   creation by an AS.

8.  BGP External Only To Customer attribute

   The External Only To Customer (eOTC) attribute is a new optional,
   transitive BGP Path attribute with the Type Code <TBD4>.  This
   attribute is four bytes and contains an AS number of the AS that
   added the attribute to the route.

   There are four rules for setting the eOTC attribute:

   1.  If eOTC is not set and the sender's Role is Provider or Peer, the
       eOTC attribute MUST be added with value equal to the sender's AS
       number

   2.  If eOTC is not set and the sender's Role is Complex and the
       prefix role is Provider or Peer, the eOTC attribute MUST be added
       with value equal to to the sender's AS number.

   3.  If eOTC is set, the receiver's Role is Provider or Peer, and its
       value is not the neighbor's AS number then the incoming route is
       route leak and MUST be given a lower local preference, or MAY be
       dropped.

   4.  If eOTC is set, the receiver's Role is Complex, the prefix role
       Role is Provider or Peer, and the eOTC value is not equal to the
       neighbor's AS number, then the incoming route is a route leak and
       MUST be given a lower local preference, or they MAY be dropped.

   These four rules provide mechanism for route leak detection that is
   created by an distant party in the AS_Path.

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9.  Compatibility with BGPsec

   For BGPsec [I-D.ietf-sidr-bgpsec-protocol] enabled routers, the Flags
   field will have a bit added to indicate that an eOTC attribute
   exists.  The eOTC value will be automatically carried in AS field of
   the added Secure_Path Segment.

   When a route is translated from a BGPsec enabled router to a non-
   BGPsec router, in addition to AS_PATH reconstruction, reconstruction
   MUST be performed for the eOTC attribute.. If Flag bit was set in one
   of Secure_Path Segments, the eOTC attribute SHOULD be added with the
   AS number of the segment in which it appears for the first time.

10.  Additional Considerations

   As the 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.

   This document doesn't provide any security measures to check
   correctness of per-prefix roles, so the Complex role should be used
   with great caution.  It is as dangerous as current BGP peering.

11.  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
   <TBD1> . 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
   <TBD2> 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

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   <TBD3> [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 "External Only To Customer", assigned value <TBD4> [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 4.

12.  Security Considerations

   This document proposes a mechanism for prevention and detection of
   route leaks that are the result of BGP policy misconfiguration.  This
   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 eOTC flag could be used to affect the
   BGP decision process, but could not sabotage a route's propagation.

   BGP Role is disclosed only to an immediate BGP neighbor, so it will
   not itself reveal any sensitive information to third parties.

   On the other hand, eOTC 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 eOTC is BGPsec signed, it can not be removed for business
   confidentiality.

13.  Acknowledgments

   The authors wish to thank Douglas Montgomery, Brian Dickson, and
   Andrei Robachevsky for their contributions to a variant of this work.

14.  References

14.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

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   [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,
              <http://www.rfc-editor.org/info/rfc4271>.

   [RFC4486]  Chen, E. and V. Gillet, "Subcodes for BGP Cease
              Notification Message", RFC 4486, DOI 10.17487/RFC4486,
              April 2006, <http://www.rfc-editor.org/info/rfc4486>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <http://www.rfc-editor.org/info/rfc5492>.

14.2.  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-06 (work in progress), May 2016.

   [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-03 (work in progress), May 2016.

   [I-D.ietf-sidr-bgpsec-protocol]
              Lepinski, M. and K. Sriram, "BGPsec Protocol
              Specification", draft-ietf-sidr-bgpsec-protocol-15 (work
              in progress), March 2016.

   [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,
              <http://www.rfc-editor.org/info/rfc5226>.

Authors' Addresses

   Alexander Azimov
   Qrator Labs

   Email: aa@qrator.net

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   Eugene Bogomazov
   Qrator Labs

   Email: eb@qrator.net

   Randy Bush
   Internet Initiative Japan

   Email: randy@psg.com

   Keyur Patel
   Arrcus, Inc.

   Email: keyurpat@yahoo.com

   Kotikalapudi Sriram
   US NIST

   Email: ksriram@nist.gov

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