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


   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",
   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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any

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   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
   ( 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

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   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

   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

   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;

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   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 - <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   |

                    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):

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                     | 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 <TBD2>).

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 <TBD3>.  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.

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   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:
   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, transitive BGP Path Attributes
   option, named "Only To Customer", assigned value <TBD3> [To be
   removed upon publication:
   parameters/bgp-parameters.xhtml#bgp-parameters-2] [RFC4271].  The
   length of this attribute is 0.

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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

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, <>.

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9.2.  Informative References

              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.

              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


   Eugene Bogomazov
   Qrator Labs


   Randy Bush
   Internet Initiative Japan


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