Network Working Group                                          A. Azimov
Internet-Draft                                              E. Bogomazov
Intended status: Standards Track                             Qrator Labs
Expires: December 20, 2017 January 4, 2018                                         R. Bush
                                               Internet Initiative Japan
                                                                K. Patel
                                                            Arrcus, Inc.
                                                               K. Sriram
                                                                 US NIST
                                                           June 18,
                                                            July 3, 2017

     Route Leak Prevention using Roles in Update and Open messages


   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 an iOTC attribute
   according to agreed relationship allowing prevention of route leaks.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 20, 2017. January 4, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

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

1.  Preamble

1.1.  Peering Relationships

   Despite uses of words such as "Customer," "Peer." etc. the intent is
   not business relationships, who pays whom, etc.  These are common
   terms to represent restrictions on BGP route propagation, some times sometimes
   known as Gao/Rexford. Gao-Rexford model.  E.g. if A is a "peer" of B and C, A does
   not propagate B's prefixes to C.  If D is a "customer" of E and F, D
   does not propagate prefixes learned from E to F.

   As the whole point of route leak detection and prevention is to
   prevent vioation of these relationships, they are inescapable.

2.  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 via new BGP Path Attribute.

   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] 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

   Also, route tagging which relies on operator maintained policy
   configuration is too easily and too often misconfigured.

3.  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:  announces all routes, accepts all routes.

   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.

4.  BGP Role

   BGP Role is new mandatory configuration option. option that SHOULD be configured at
   each BGP session.  It reflects the real-world agreement between two
   BGP speakers about their peering 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  Peer - sender and neighbor are peers;

   o  Internal - sender and neighbor is part of same organization.  This
      includes but is not limited to situation when sender and neighbor
      are in same AS.

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

   For iBGP sessions only Internal role policies. MAY be configured.

   Since BGP Role reflects the relationship between two BGP speakers, it
   could also be used for more than route leak mitigation.

5.  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

6.  Role correctness

   Section 4 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 MUST check value of
   the received capability with its own BGP Role. Role (if it is set).  The
   allowed pairings are (first a sender's Role, second the receiver's

                     | 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>).

6.1.  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.

7.  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 filtering
   mechanisms (Section 8).

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

8.  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 three rules for setting the of iOTC attribute: attribute usage:

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

   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

   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

   3.  A sender MUST NOT be announced include this attribute in UPDATE messages if by a
       sender whose
       its Role is Complex Customer, Provider or Peer.  If it is contained in an
       UPDATE message from eBGP speaker and the prefix receiver's Role is Customer Customer,
       Provider, Peer or
       Peer; unspecified, then this attribute MUST be

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

8.  Attribute or Community

   Having the relationship hard set by agreement between the two peers
   in BGP OPEN is critical; the routers enforce the relationship
   irrespective of operator configuration errors.

   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 misconfiguration.  There is a question
   whether the iOTC marking should be an attribute or a well-known

   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.

   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.

9.  Compatibility with BGPsec

   As the iOTC field is non-transitive, it is not seen by or signed by
   BGPsec [I-D.ietf-sidr-bgpsec-protocol].

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.

   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.  [I-D.ietf-grow-bgp-reject]

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

11.  IANA Considerations

   This document defines a new Capability Codes option [to be removed
   upon publication:
   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

   This document defines new subcode, "Role Mismatch", assigned value
   <TBD2> in the OPEN Message Error subcodes registry [to be removed
   upon publication:
   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
   <TBD3> [To be removed upon publication:
   parameters.xhtml#bgp-parameters-2] [RFC4271].  The length of this
   attribute is 0.

12.  Security Considerations

   This document proposes a mechanism for prevention of route leaks that
   are the result of BGP policy misconfiguration.

   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.

13.  Acknowledgments

   The authors wish to thank Douglas Montgomery, Brian Dickson, and Andrei
   Robachevsky and Daniel Ginsburg 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,

   [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, <>.

14.2.  Informative References

              Mauch, J., Snijders, J., and G. Hankins, "Default EBGP
              Route Propagation Behavior Without Policies", draft-ietf-
              grow-bgp-reject-08 (work in progress), May 2017.

              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.

              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.

              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,

Authors' Addresses

   Alexander Azimov
   Qrator Labs


   Eugene Bogomazov
   Qrator Labs


   Randy Bush
   Internet Initiative Japan


   Keyur Patel
   Arrcus, Inc.

   Kotikalapudi Sriram