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Versions: (draft-sa-idr-maxprefix) 00 01

Inter-Domain Routing                                          M. Aelmans
Internet-Draft                                          Juniper Networks
Updates: 4271 (if approved)                                   M. Stucchi
Intended status: Standards Track                             Independent
Expires: April 19, 2021                                      J. Snijders
                                                                     NTT
                                                        October 16, 2020


               Revised BGP Maximum Prefix Limits Outbound
                  draft-sas-idr-maxprefix-outbound-01

Abstract

   This document updates RFC4271 by adding a control mechanism which
   limits the negative impact of outbound route leaks (RFC7908) in order
   to prevent resource exhaustion in Border Gateway Protocol (BGP)
   implementations.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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 https://datatracker.ietf.org/drafts/current/.

   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 April 19, 2021.








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Copyright Notice

   Copyright (c) 2020 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
   (https://trustee.ietf.org/license-info) 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.  Changes to RFC4271 Section 6  . . . . . . . . . . . . . . . .   2
   3.  Changes to RFC4271 Section 8  . . . . . . . . . . . . . . . .   3
   4.  Changes to RFC4271 Section 9  . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   This document updates [RFC4271] by adding a control mechanism which
   limits the negative impact of outbound route leaks [RFC7908] in order
   to prevent resource exhaustion in Border Gateway Protocol (BGP)
   implementations.  [RFC4271] describes methods to tear down BGP
   sessions or discard UPDATES after certain inbound thresholds are
   exceeded.  In addition to "inbound maximum prefix limits", this
   document introduces a specification for "outbound maximum prefix
   limits".  [I-D.sas-idr-maxprefix-inbound] updates sections in
   [RFC4271] to clarify "inbound maximum prefix limits".  This documents
   updates those sections again to add "outbound maximum prefix limits".

2.  Changes to RFC4271 Section 6

   This section updates [RFC4271] to specify what events can result in
   AutomaticStop (Event 8) in the BGP FSM.




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   The following paragraph replaces the second paragraph of Section 6.7
   (Cease), which starts with "A BGP speaker MAY support" and ends with
   "The speaker MAY also log this locally.":

      A BGP speaker MAY support the ability to impose a locally-
      configured, upper bound on the number of address prefixes the
      speaker is willing to accept from a neighbor (inbound maximum
      prefix limit) or send to a neighbor (outbound prefix limit).  The
      limit on the prefixes accepted from a neighbor can be applied
      before policy processing (Pre-Policy) or after policy processing
      (Post-Policy).  Outbound prefix limits MUST be measured after
      policy since the Policy (even a policy of "send all") is run,
      before determining what can be sent.  When the upper bound is
      reached, the speaker, under control of local configuration,
      either:

      A.  Discards new address prefixes being sent to the neighbor while
          maintaining the BGP connection with the neighbor.  As these
          prefixes are discared and their reachability information is
          not sent to the neighbor it might lead to inconsistent routing
          behaviour;

      B.  Sent all prefixes exceeding the threshold and generates a log;

      C.  Terminates the BGP session with the neighbor.  This should be
          done using a Hard Reset according to [RFC8538].

      If the BGP speaker uses option (b), where the limit causes a CEASE
      Notification, then the CEASE error codes should use:

   +---------+---------------------------------------------------------+
   | Subcode | Symbolic Name                                           |
   +---------+---------------------------------------------------------+
   | 1       | Threshold exceeded: Maximum Number of Prefixes Received |
   | TBD     | Threshold exceeded: Maximum Number of Prefixes Sent     |
   +---------+---------------------------------------------------------+

      The speaker MAY also log this locally.

3.  Changes to RFC4271 Section 8

   This section updates Section 8 [RFC4271], the paragraph that starts
   with "One reason for an AutomaticStop event is" and ends with "The
   local system automatically disconnects the peer." is replaced with:

      Possible reasons for an AutomaticStop event are: A BGP speaker
      receives an UPDATE messages with a number of prefixes for a given
      peer such that the total prefixes received exceeds the maximum



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      number of prefixes configured (either "Pre-Policy" or "Post-
      Policy"), or announces more prefixes than through local
      configuration allowed to.  The local system automatically
      disconnects the peer.

4.  Changes to RFC4271 Section 9

   This section updates [RFC4271] by adding a subsection after
   Section 9.4 (Originating BGP routes) to specify various events that
   can lead up to an AutomaticStop (Event 8) in the BGP FSM.

      9.5 Maximum Prefix Limits

      9.5.1 Pre-Policy Inbound Maximum Prefix Limits



         The Adj-RIBs-In stores routing information learned from inbound
         UPDATE messages that were received from another BGP speaker
         Section 3.2 [RFC4271].  The pre-policy limit uses the number of
         NLRIs per Address Family Identifier (AFI) per Subsequent
         Address Family Identifier (SAFI) as input into its threshold
         comparisons.  For example, when an operator configures the pre-
         policy limit for IPv4 Unicast to be 50 on a given EBGP session,
         and the other BGP speaker announces its 51st IPv4 Unicast NLRI,
         the session MUST be terminated.

         Pre-policy limits are particularly useful to help dampen the
         effects of full table route leaks and memory exhaustion when
         the implementation stores rejected routes.

      9.5.2 Post-Policy Inbound Maximum Prefix Limits



         [RFC4271] describes a Policy Information Base (PIB) that
         contains local policies that can be applied to the information
         in the Routing Information Base (RIB).  The post-policy limit
         uses the number of NLRIs per Address Family Identifier (AFI)
         per Subsequent Address Family Identifier (SAFI), after
         application of the Import Policy as input into its threshold
         comparisons.  For example, when an operator configures the
         post-policy limit for IPv4 Unicast to be 50 on a given EBGP
         session, and the other BGP speaker announces a hundred IPv4
         Unicast routes of which none are accepted as a result of the
         local import policy (and thus not considered for the Loc-RIB by
         the local BGP speaker), the session is not terminated.




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         Post-policy limits are useful to help prevent FIB exhaustion
         and prevent accidental BGP session teardown due to prefixes not
         accepted by policy anyway.

      9.5.3 Outbound Maximum Prefix Limits



         An operator MAY configure a BGP speaker to terminate its BGP
         session with a neighbor when the number of address prefixes to
         be advertised to that neighbor exceeds a locally configured
         post-policy upper limit.  The BGP speaker then MUST send the
         neighbor a NOTIFICATION message with the Error Code "Cease" and
         the Error Subcode "Threshold reached: Maximum Number of
         Prefixes Sent".  Implementations MAY support additional
         actions.  The Hard Cease action is defined in [RFC8538].

         Reporting when thresholds have been exceeded is an
         implementation specific consideration, but SHOULD include
         methods such as Syslog [RFC5424].  By definition, Outbound
         Maximum Prefix Limits are Post-Policy.

         The Adj-RIBs-Out stores information selected by the local BGP
         speaker for advertisement to its neighbors.  The routing
         information stored in the Adj-RIBs-Out will be carried in the
         local BGP speaker's UPDATE messages and advertised to its
         neighbors Section 3.2 [RFC4271].  The Outbound Maximum Prefix
         Limit uses the number of NLRIs per Address Family Identifier
         (AFI) per Subsequent Address Family Identifier (SAFI), after
         application of the Export Policy, as input into its threshold
         comparisons.  For example, when an operator configures the
         Outbound Maximum Prefix Limit for IPv4 Unicast to be 50 on a
         given EBGP session, and were about to announce its 51st IPv4
         Unicast NLRI to the other BGP speaker as a result of the local
         export policy, the session MUST be terminated.

         Outbound Maximum Prefix Limits are useful to help dampen the
         negative effects of a misconfiguration in local policy.  In
         many cases, it would be more desirable to tear down a BGP
         session rather than causing or propagating a route leak.

5.  Security Considerations

   Maximum Prefix Limits are an essential tool for routing operations
   and SHOULD be used to increase stability.  They provide a first-line
   mechanism to avoid route leaks and to avoid unintended routing
   suggestions to happen between neighbors.  Implementing this measures




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   is only one of the building blocks you need to provide full security,
   but it is important to build a modular defense system.

   Stability for the routing table is also an important aspect for
   implementing the measures included in this draft.  Ensuring that
   neighbors will not receive an amount of routes that would overload
   their routing platform contributes to the stability of
   interconnections and of the Internet as a whole.

6.  IANA Considerations

   This memo requests that IANA assigns a new subcode named "Threshold
   exceeded: Maximum Number of Prefixes Sent" in the "Cease NOTIFICATION
   message subcodes" registry under the "Border Gateway Protocol (BGP)
   Parameters" group.

7.  Acknowledgments

   The authors would like to thank Saku Ytti and John Heasley (NTT
   Ltd.), Jeff Haas, Colby Barth and John Scudder (Juniper Networks),
   Martijn Schmidt (i3D.net), Teun Vink (BIT), Sabri Berisha (eBay),
   Martin Pels (Quanza), Steven Bakker (AMS-IX), Aftab Siddiqui (ISOC),
   Yu Tianpeng, Ruediger Volk (Deutsche Telekom), Robert Raszuk
   (Bloomberg), Jakob Heitz (Cisco), Warren Kumari (Google), Ben
   Maddison (Workonline), Randy Bush, Brian Dickson and Gyan Mishra
   (Verizon) for their support, insightful reviews, and comments.

8.  Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in RFC7942.  The
   description of implementations in this section is intended to assist
   the IETF in its decision processes in progressing drafts to RFCs.
   Please note that the listing of any individual implementation here
   does not imply endorsement by the IETF.  Furthermore, no effort has
   been spent to verify the information presented here that was supplied
   by IETF contributors.  This is not intended as, and must not be
   construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   The table below provides an overview (as of the moment of writing) of
   which vendors have produced implementations of inbound or outbound
   maximum prefix limits.  Each table cell shows the applicable
   configuration keywords if the vendor implemented the feature.





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   +----------+-------------+---------------------+--------------------+
   |  Vendor  |   Inbound   | Inbound Post-Policy |      Outbound      |
   |          |  Pre-Policy |                     |                    |
   +----------+-------------+---------------------+--------------------+
   |  Cisco   |             |    maximum-prefix   |                    |
   |  IOS XR  |             |                     |                    |
   +----------+-------------+---------------------+--------------------+
   |  Cisco   |             |    maximum-prefix   |                    |
   |  IOS XE  |             |                     |                    |
   +----------+-------------+---------------------+--------------------+
   | Juniper  |   prefix-   |   accepted-prefix-  | advertise-prefix-  |
   | Junos OS |    limit    |  limit, or prefix-  |      limit *       |
   |          |             | limit combined with |                    |
   |          |             |     'keep none'     |                    |
   +----------+-------------+---------------------+--------------------+
   | Nokia SR |   prefix-   |                     |                    |
   |    OS    |    limit    |                     |                    |
   +----------+-------------+---------------------+--------------------+
   |  NIC.CZ  |   'import   |  'import limit' or  |    export limit    |
   |   BIRD   |     keep    |   'receive limit'   |                    |
   |          |  filtered'  |                     |                    |
   |          |   combined  |                     |                    |
   |          |     with    |                     |                    |
   |          |   'receive  |                     |                    |
   |          |    limit'   |                     |                    |
   +----------+-------------+---------------------+--------------------+
   | OpenBSD  |  max-prefix |                     |                    |
   | OpenBGPD |             |                     |                    |
   +----------+-------------+---------------------+--------------------+
   |  Arista  |   maximum-  |  maximum-accepted-  |                    |
   |   EOS    |    routes   |        routes       |                    |
   +----------+-------------+---------------------+--------------------+
   |  Huawei  | peer route- |                     |                    |
   |  VRPv5   |    limit    |                     |                    |
   +----------+-------------+---------------------+--------------------+
   |  Huawei  | peer route- |   peer route-limit  |                    |
   |  VRPv8   |    limit    |    accept-prefix    |                    |
   +----------+-------------+---------------------+--------------------+

                First presented by Job Snijders at [RIPE77]

      Table 1: Maximum prefix limits capabilities per implementation

   *In testing stage







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9.  References

9.1.  Normative References

   [I-D.sas-idr-maxprefix-inbound]
              Snijders, J., Aelmans, M., and s. stucchi-
              lists@glevia.com, "BGP Maximum Prefix Limits Inbound",
              draft-sas-idr-maxprefix-inbound-00 (work in progress),
              April 2020.

   [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-editor.org/info/rfc2119>.

   [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-editor.org/info/rfc4271>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8538]  Patel, K., Fernando, R., Scudder, J., and J. Haas,
              "Notification Message Support for BGP Graceful Restart",
              RFC 8538, DOI 10.17487/RFC8538, March 2019,
              <https://www.rfc-editor.org/info/rfc8538>.

9.2.  Informative References

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", draft-ietf-idr-
              bgp-model-09 (work in progress), June 2020.

   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424,
              DOI 10.17487/RFC5424, March 2009,
              <https://www.rfc-editor.org/info/rfc5424>.

   [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>.

   [RIPE77]   Snijders, J., "Robust Routing Policy Architecture", May
              2018, <https://ripe77.ripe.net/wp-content/uploads/presenta
              tions/59-RIPE77_Snijders_Routing_Policy_Architecture.pdf>.



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Authors' Addresses

   Melchior Aelmans
   Juniper Networks
   Boeing Avenue 240
   Schiphol-Rijk  1119 PZ
   The Netherlands

   Email: maelmans@juniper.net


   Massimiliano Stucchi
   Independent

   Email: max@stucchi.ch


   Job Snijders
   NTT Ltd.
   Theodorus Majofskistraat 100
   Amsterdam  1065 SZ
   The Netherlands

   Email: job@ntt.net



























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