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Versions: (draft-ietf-idr-route-leak-detection-mitigation) 00 01

IDR and SIDR                                              K. Sriram, Ed.
Internet-Draft                                                  USA NIST
Intended status: Standards Track                          A. Azimov, Ed.
Expires: January 26, 2020                                         Yandex
                                                           July 25, 2019


        Methods for Detection and Mitigation of BGP Route Leaks
           draft-ietf-grow-route-leak-detection-mitigation-01

Abstract

   Problem definition for route leaks and enumeration of types of route
   leaks are provided in [RFC7908].  This document describes a new well-
   known Large Community that provides a way for route leak prevention,
   detection, and mitigation.  The configuration process for this
   Community can be automated with the methodology for setting BGP roles
   that is described in ietf-idr-bgp-open-policy draft.

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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   This Internet-Draft will expire on January 26, 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
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   include Simplified BSD License text as described in Section 4.e of



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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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Peering Relationships . . . . . . . . . . . . . . . . . . . .   2
   3.  Community vs Attribute  . . . . . . . . . . . . . . . . . . .   3
   4.  Down Only Community . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Route Leak Mitigation . . . . . . . . . . . . . . . . . .   5
     4.2.  Only Marking  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Implementation Considerations . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   7
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   [RFC7908] provides a definition of the route leak problem and
   enumerates several types of route leaks.  For this document, the
   definition that is applied is that a route leak occurs when a route
   received from a transit provider or a lateral peer is forwarded
   (against commonly used policy) to another transit provider or a
   lateral peer.  The commonly used policy is that a route received from
   a transit provider or a lateral peer MAY be forwarded only to
   customers.

   This document describes a solution for prevention, detection and
   mitigation route leaks which is based on conveying route-leak
   detection information in a well-known BGP Large Community.  The
   configuration process for the Large Community MUST be defined
   according to peering relations between ISPs.  This process can be
   automated with the methodology for setting BGP roles that is
   described in [I-D.ietf-idr-bgp-open-policy].

   The techniques described in this document can be incrementally
   deployed.  If a group of big ISPs and/or Internet Exchanges (IXes)
   deploy the proposed techniques, then they would be helping each other
   by blocking route leaks that can happen between them.

2.  Peering Relationships

   As described in [I-D.ietf-idr-bgp-open-policy] there are several
   common peering relations between eBGP neighbors:




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   o  Provider - sender is a transit provider of the neighbor;

   o  Customer - sender is a customer of the neighbor;

   o  Route Server (RS) - sender is route server at an internet exchange
      (IX)

   o  RS-client - sender is client of an RS at an IX

   o  Peer - sender and neighbor are lateral (non-transit) peers;

   If a route is received from a provider, peer or RS-client, it MUST
   follow the 'down only' rule, i.e., it MAY be advertised only to
   customers.  If a route is sent to a customer, peer or RS-client, it
   also MUST follow the 'down only' rule at each subsequent AS in the AS
   path.

   A standardized transitive route-leak detection signal is needed that
   will prevent Autonomous Systems (ASes) from leaking and also inform a
   remote ISP (or AS) in the AS path that a received route violates
   'down only' policy.  This signal would facilitate a way to stop the
   propagation of leaked prefixes.

   To improve reliability and cover for non-participating preceding
   neighbor, the signal should be set on both receiver and sender sides.

3.  Community vs Attribute

   This section presents a brief discussion of the advantages and
   disadvantages of communities and BGP path attributes for the purpose
   of route leak detection.

   A transitive path attribute is a native way to implement the route-
   leak detection signal.  Based on the way BGP protocol works, the use
   of a transitive attribute makes it more certain that the route-leak
   detection signal would pass unaltered through non-participating
   (i.e., not updated) BGP routers.  The main disadvantage of this
   approach is that the deployment of a new BGP attribute requires a
   software update in router OS which may delay wide adoption for years.

   On the other hand, BGP communities do not require a router OS update.
   The potential disadvantage of using a Community for the route-leak
   detection signal is that it is more likely to be dropped somewhere
   along the way in the AS path.  Currently, the use of BGP Communities
   is somewhat overloaded.  BGP Communities are already used for
   numerous applications: different types of route marking, route policy
   control, black-holing, etc.  It is observed that some ASes seem to
   purposefully or accidentally remove transitive communities on



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   receipt, sometimes well-known ones.  Perhaps this issue may be
   mitigated with strong policy guidance related to the handling of
   Communities.

   Due to frequently occurring regional and global disruptions in
   Internet connectivity, it is critical to move forward with a solution
   that is viable in the near term.  That solution would be route leak
   detection using BGP Community.

   Large Communities have much higher capacity, and therefore they are
   likely to be less overloaded.  Hence, Large Community is proposed to
   be used for route-leak detection.  This document suggests reserving
   <TBD1> class for the purpose of transitive well-known Large
   Communities that MUST not be stripped on ingress or egress.

   While it is not part of this document, the route-leak detection
   signal described here can also be carried in a BGP path attribute,
   and the same prevention and mitigation techniques as described here
   would apply.  The authors are pursuing a separate internet draft in
   the IDR WG on that approach.

4.  Down Only Community

   This section specifies the semantics of route-leak-detection
   Community and its usage.  This Community is given the specific name
   Down Only (DO) Community.  The DO Community is carried in a BGP Large
   Community with a format as shown in Figure 1.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        TBD1 (class for well-known transit communities)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   TBD2 (subclass for DO)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             ASN                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



       Figure 1: Format of the DO Community using a Large Community
                                [RFC8092].

   The authors studied different options for route leak mitigation.  The
   main options considered are (1) drop detected route leaks and (2)
   deprioritize detected route leaks.  It can be demonstrated that the
   loose mode that uses deprioritization is not safe.  Traffic



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   Engineering (TE) technique which limit prefix visibility are quite
   common.  It may happen that a more specific TE prefix is sent only to
   downstream ASes or to IX(es)/selected peers, and a control Community
   is used to restrict its propagation.  If such a more specific prefix
   is leaked, deprioritization will not stop such a route leak from
   propagating.  In addition, propagation of leaked prefixes based on
   deprioritization may result in priority loops leading to BGP wedgies
   [RFC4264] or even persistent route oscillations.

   So, the only truly safe way to implement route leak mitigation is to
   drop detected route leaks.  The ingress and egress policies
   corresponding to 'drop detected route leaks' is described in
   Section 4.1.  This policy SHOULD be used as a default behavior.

   Nevertheless, early adopters might want to deploy only the signaling
   and perhaps use it only for diagnostics before applying any route
   leak mitigation policy.  They are also encouraged to use slightly
   limited marking, which is described in Section 4.2.

4.1.  Route Leak Mitigation

   This section describes the eBGP ingress and egress policies that MUST
   be used to perform route leak prevention, detection and mitigation
   using the DO Community.

   The ingress policy MUST use the following procedure:

   1.  If a route with DO Community set (i.e., DO is attached) is
       received from a Customer or RS-client, then it is a route leak
       and MUST be rejected.  The procedure halts.

   2.  If a route with DO Community set is received from Peer (non-
       transit) and DO value is not equal to the sending neighbor's ASN,
       then it is a route leak and MUST be rejected.  The procedure
       halts.

   3.  If a route is received from a Provider, Peer or RS, then the DO
       Community MUST be added with a value equal to the sending
       neighbor's ASN.

   The egress policy MUST use the following procedure:

   1.  A route with DO Community set MUST not be sent to Providers,
       Peers, and RS.

   2.  If a route is sent to a Customer or Peer, then the DO Community
       MUST be added with a value equal to the ASN of the sender.




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   The above procedures comprehensively provide route-leak prevention,
   detection and mitigation.  Policy consisting of these procedures
   SHOULD be used as a default behavior.

4.2.  Only Marking

   This section describes eBGP ingress and egress marking policies that
   MUST be used if an AS is not performing route-leak mitigation (i.e.,
   dropping detected route leaks) as described in Section 4.1, but wants
   to use only marking with DO Community.  The slightly limited DO
   marking (compared to that in Section 4.1) described below guarantees
   that this DO marking will not limit the leak detection opportunities
   for subsequent ASes in the AS path.

   The ingress policy MUST use the following procedure:

   1.  If a route with DO Community set is received from a Customer or
       RS-client, then it is a route leak.  The procedure halts.

   2.  If a route with DO Community set is received from a Peer and DO
       value is not equal to the sending neighbor's ASN, then it is a
       route leak.  The procedure halts.

   3.  If a route is received from a Provider, Peer or RS, then the DO
       Community MUST be added with value equal to the sending
       neighbor's ASN.

   The egress policy MUST use the following procedure:

   1.  If a route is sent to a Customer or RS-client, then the DO
       Community MUST be added with value equal to the ASN of the
       sender.

   2.  If DO Community is not set and the route is sent to a Peer, then
       the DO Community MUST be added with value equal to the ASN of the
       sender.

   These above procedures specify setting DO signal in a way that can be
   used to evaluate the potential impact of route leak mitigation policy
   before deploying strict dropping of detected route leaks.

5.  Implementation Considerations

   It was observed that the majority of BGP implementations does not
   support negative match for communities like a:b:!c.  Considering that
   it is suggested to replace the second rule from ingress policy with
   the following:




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   If a route with DO Community set is received from a Peer and DO value
   is equal to the sending neighbor's ASN, then it is a valid route,
   otherwise it is a route leak.  The procedure halts.

   This rule is based on a weaker assumption that a peer that is doing
   marking is also doing filtering (dropping detected leaks).  That is
   why networks that do not follow the route leak mitigation policy in
   Section 4.1 MUST carefully follow marking rules described in
   Section 4.2.

6.  Security Considerations

   In specific circumstances in a state of partial adoption, route leak
   mitigation mechanism can result in Denial of Service (DoS) for the
   victim prefix.  Such a scenario may happen only for a prefix that has
   a single path from the originator to a Tier-1 ISP and only when the
   prefix is not covered with a less specific prefix with multiple paths
   to the Tier-1 ISP.  If, in such unreliable topology, route leak is
   injected somewhere inside this single path, then it may be rejected
   by upper layer providers in the path, thus limiting prefix
   visibility.  While such anomaly is unlikely to happen, such an issue
   should be easy to debug, since it directly affects the sequence of
   originator's providers.

   With the use of BGP Community, there is often a concern that the
   Community propagates beyond its intended perimeter and causes harm
   [streibelt].  However, that concern does not apply to the DO
   Community because it is a transitive Community that must propagate as
   far as the update goes.

7.  IANA Considerations

   The draft suggests to reserve a Global Administrator ID <TBD1> for
   transitive well-known Large Community registry.  IANA is requested to
   register a subclass <TBD2> for DO Community in this registry.

8.  Informative References

   [I-D.ietf-idr-bgp-open-policy]
              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-06 (work in
              progress), July 2019.

   [RFC4264]  Griffin, T. and G. Huston, "BGP Wedgies", RFC 4264,
              DOI 10.17487/RFC4264, November 2005,
              <https://www.rfc-editor.org/info/rfc4264>.




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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, <https://www.rfc-editor.org/info/rfc7908>.

   [RFC8092]  Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas,
              I., and N. Hilliard, "BGP Large Communities Attribute",
              RFC 8092, DOI 10.17487/RFC8092, February 2017,
              <https://www.rfc-editor.org/info/rfc8092>.

   [streibelt]
              Streibelt et al., F., "BGP Communities: Even more Worms in
              the Routing Can",  ACM IMC, October 2018,
              <https://archive.psg.com//181101.imc-communities.pdf>.

Acknowledgements

   The authors wish to thank John Scudder, Susan Hares, Ruediger Volk,
   Mat Ford, Greg Skinner for their review and comments.

Contributors

   The following people made significant contributions to this document
   and should be considered co-authors:

   Brian Dickson
   Independent
   Email: brian.peter.dickson@gmail.com

   Doug Montgomery
   USA National Institute of Standards and Technology
   Email: dougm@nist.gov

   Keyur Patel
   Arrcus
   Email: keyur@arrcus.com

   Andrei Robachevsky
   Internet Society
   Email: robachevsky@isoc.org

   Eugene Bogomazov
   Qrator Labs
   Email: eb@qrator.net

   Randy Bush
   Internet Initiative Japan
   Email: randy@psg.com



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Authors' Addresses

   Kotikalapudi Sriram (editor)
   USA National Institute of Standards and Technology
   100 Bureau Drive
   Gaithersburg, MD  20899
   United States of America

   Email: ksriram@nist.gov


   Alexander Azimov (editor)
   Yandex
   Ulitsa Lva Tolstogo 16
   Moscow  119021
   Russia

   Email: a.e.azimov@gmail.com

































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