Network Working Group                                          A. Azimov
Internet-Draft                                              E. Bogomazov
Intended status: Standards Track                             Qrator Labs
Expires: September 18, 2018                                      R. Bush
                                               Internet Initiative Japan
                                                                K. Patel
                                                            Arrcus, Inc.
                                                          March 17, 2018

   Route Leak Detection and Filtering using Roles in Update and Open


   [draft-ietf-idr-bgp-open-policy] defines a BGP OPEN capability and
   consequent route marking which enforces a valley-free peering
   relationship.  This document defines an eOTC (external Only To
   Customer) transitive BGP attribute which propagates the specific
   marking to automatically detect route leaks.  The goal is to allow a
   distant AS to determine a violation of valley-free peering.

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
   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 18, 2018.

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Copyright Notice

   Copyright (c) 2018 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 External Only To Customer attribute . . . . . . . . . . .   3
   3.  Compatibility with BGPsec . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   For the purpose of this document, BGP route leaks are when a BGP
   route was learned from transit provider or peer 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.

   [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.

   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 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

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   misconfiguration affects a limited number of prefixes; but such route
   leaks will obviously bypass customer cone import filtering made by
   upper level upstream providers.

   This document specifies a way to to create automatic filters for
   detection of route leaks via new BGP Path Attribute which is set
   according to BGP Roles ([I-D.ietf-idr-bgp-open-policy]) .  While iOTC
   provides strong vendor-code-based enforcement of route leak
   prevention, route leaks could still exist as result of misconfigured
   old BGP implementations.  Route leaks could also be result of
   malicious activity such as MITM attacks or DoS.  The goal of this
   proposal is to allow a distant AS to determine a violation of valley-
   free peering that is made by mistake or by purpose.

2.  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 <TBD1>.  This
   attribute is four bytes and contains an AS number of the AS that
   added the attribute to the route.

   There are two 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

   2.  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

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

3.  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.

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4.  IANA Considerations

   This document defines a new optional, transitive BGP Path Attributes
   option, named "External Only To Customer", assigned value <TBD1> [To
   be removed upon publication:
   parameters/bgp-parameters.xhtml#bgp-parameters-2] [RFC4271].  The
   length of this attribute is 4.

5.  Security Considerations

   This document proposes a mechanism for detection of route leaks that
   are the result of BGP policy misconfiguration.  If BGPSec is enabled
   it will also provide mechanism to detect leaks that are result of
   malicious activity.

   Deliberate mis-marking of the eOTC flag could be used to affect the
   BGP decision process, but could not sabotage a route's propagation.

   eOTC is a transitive BGP AS_PATH attribute which reveals a
   information about a BGP speaker's peering 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.
   In addition it could reveal sequence of p2c to downstream ISPs.  If
   eOTC is BGPsec signed, it can not be removed for peering

   Still, any Tier-1 number in AS_PATH could be used in the same way to
   reveal possible p2c sequence.

6.  References

6.1.  Normative References

              Azimov, A., Bogomazov, E., Bush, R., Patel, K., and K.
              Sriram, "Route Leak Prevention using Roles in Update and
              Open messages", draft-ietf-idr-bgp-open-policy-02 (work in
              progress), January 2018.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997, <https://www.rfc-

   [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, <https://www.rfc-

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   [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, <>.

6.2.  Informative References

              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.

Authors' Addresses

   Alexander Azimov
   Qrator Labs


   Eugene Bogomazov
   Qrator Labs


   Randy Bush
   Internet Initiative Japan


   Keyur Patel
   Arrcus, Inc.


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