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Versions: (draft-sa-grow-maxprefix) 00

Inter-Domain Routing                                         J. Snijders
Internet-Draft                                                       NTT
Updates: 4271 (if approved)                                   M. Aelmans
Intended status: Standards Track                        Juniper Networks
Expires: March 26, 2020                               September 23, 2019


                   Revised BGP Maximum Prefix Limits
                       draft-sa-idr-maxprefix-00

Abstract

   This document updates RFC4271 by revising control mechanism which
   limit the negative impact of route leaks (RFC7908) and/or 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 March 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
   Provisions Relating to IETF Documents



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   (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
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   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.  BGP Yang Model Considerations - PERHAPS REMOVE BEFORE
       PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Changes to RFC4271 Section 9  . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION   6
   10. Appendix: Implementation Guidance . . . . . . . . . . . . . .   7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     11.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   This document updates [RFC4271] by revising control mechanism which
   limit the negative impact of route leaks [RFC7908] and/or resource
   exhaustion in Border Gateway Protocol (BGP) implementations.  While
   [RFC4271] described methods to tear down BGP sessions or discard
   UPDATES after certain thresholds are exceeded, some nuances in this
   specification were missing resulting in inconsistencies between BGP
   implementations.  In addition to clarifying "inbound maximum prefix
   limits", this document also introduces a specification for "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.

   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.":





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      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 to or from the neighbor (while
          maintaining the BGP connection with the neighbor)

      B.  Terminates the BGP connection with the neighbor

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

   +---------+---------------------------------------------------------+
   | Subcode | Symbolic Name                                           |
   +---------+---------------------------------------------------------+
   | 1       | Maximum Number of Prefixes Reached                      |
   | TBD     | Threshold exceeded: Self-Destructing, Maximum Number of |
   |         | Prefixes Send                                           |
   +---------+---------------------------------------------------------+

      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
      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.








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4.  BGP Yang Model Considerations - PERHAPS REMOVE BEFORE PUBLICATION

   In [I-D.ietf-idr-bgp-model] in container 'prefix-limit', a leaf named
   "max-prefixes" exists.  The authors recommend the BGP Yang Model to
   be revised to contain the following leaves:

      max-prefixes-inbound-pre-policy

      max-prefixes-inbound-post-policy

      max-prefixes-outbound

   In addition to the above, the authors suggest that the BGP Yang Model
   is extended in such a way that per peer per AFI/SAFI pair an operator
   can specify whether to tear down the session or discard sending or
   receiving updates.

5.  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 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







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         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.

         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 Send".  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.



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         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.

6.  Security Considerations

   Maximum Prefix Limits are an essential tool for routing operations
   and SHOULD be used to increase stability.

7.  IANA Considerations

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

8.  Acknowledgments

   The authors would like to thank Saku Ytti and John Heasley (NTT),
   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), and Susan Hares (Hickory Hill Consulting) for their
   support, insightful review, and comments.

9.  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 below table provides an overview (as of the moment of writing) of
   which vendors have produced implementation 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 Pre-  |   Inbound Post-Policy   | Outbound |
   |             |     Policy     |                         |          |
   +-------------+----------------+-------------------------+----------+
   |  Cisco IOS  |                |      maximum-prefix     |          |
   |      XR     |                |                         |          |
   +-------------+----------------+-------------------------+----------+
   |  Cisco IOS  |                |      maximum-prefix     |          |
   |      XE     |                |                         |          |
   +-------------+----------------+-------------------------+----------+
   |   Juniper   |  prefix-limit  |  accepted-prefix-limit, |          |
   |   Junos OS  |                |     or prefix-limit     |          |
   |             |                |   combined with 'keep   |          |
   |             |                |          none'          |          |
   +-------------+----------------+-------------------------+----------+
   | Nokia SR OS |  prefix-limit  |                         |          |
   +-------------+----------------+-------------------------+----------+
   | NIC.CZ BIRD |  'import keep  |    'import limit' or    |  export  |
   |             |   filtered'    |     'receive limit'     |  limit   |
   |             | combined with  |                         |          |
   |             |    'receive    |                         |          |
   |             |     limit'     |                         |          |
   +-------------+----------------+-------------------------+----------+
   |   OpenBSD   |   max-prefix   |                         |          |
   |   OpenBGPD  |                |                         |          |
   +-------------+----------------+-------------------------+----------+
   |  Arista EOS | maximum-routes | maximum-accepted-routes |          |
   +-------------+----------------+-------------------------+----------+
   |    Huawei   |  peer route-   |                         |          |
   |    VRPv5    |     limit      |                         |          |
   +-------------+----------------+-------------------------+----------+
   |    Huawei   |  peer route-   |     peer route-limit    |          |
   |    VRPv8    |     limit      |      accept-prefix      |          |
   +-------------+----------------+-------------------------+----------+

                  First presented by Snijders at [RIPE77]

      Table 1: Maximum prefix limits capabilities per implementation

10.  Appendix: Implementation Guidance

   1) make it clear who does what: if A sends too many prefixes to B A
   should see "ABC" in log B should see "DEF" in log to make it clear
   which of the two parties does what 2) recommended by default
   automatically restart after between 15 and 30 minutes






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11.  References

11.1.  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,
              <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>.

11.2.  Informative References

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., and S. Hares, "BGP YANG Model
              for Service Provider Networks", draft-ietf-idr-bgp-
              model-06 (work in progress), June 2019.

   [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>.

Authors' Addresses







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   Job Snijders
   NTT
   Theodorus Majofskistraat 100
   Amsterdam  1065 SZ
   The Netherlands

   Email: job@ntt.net


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

   Email: maelmans@juniper.net



































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