Inter-Domain Routing                                          M. Aelmans
Internet-Draft                                          Juniper Networks
Updates: 4271 (if approved)                                   M. Stucchi
Intended status: Standards Track                             Independent
Expires: 23 July 2022                                        J. Snijders
                                                                  Fastly
                                                         19 January 2022


                   BGP Maximum Prefix Limits Inbound
                   draft-sas-idr-maxprefix-inbound-04

Abstract

   This document describes mechanisms to limit the negative impact of
   route leaks [RFC7908] and/or resource exhaustion in BGP [RFC4271]
   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 23 July 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised 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 . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Implementation status - RFC EDITOR: REMOVE BEFORE
           PUBLICATION . . . . . . . . . . . . . . . . . . . . . . .   5
   9.  Appendix: Implementation Guidance . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

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.

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.":

      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



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      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).  When the upper bound is reached,
      the speaker, under control of local configuration, either:

      a.  Discards new address prefixes from the neighbor, while
          maintaining the BGP connection.  As these prefixes are
          discared, their reachability information is not stored on the
          local router, which might lead to inconsistent routing
          behaviour;

      b.  Receives all the new prefixes exceeding the threshold, accepts
          them and generates a log of the event;

      c.  Terminates the BGP connection with the neighbor.

      If the BGP speaker decides to terminate its BGP connection with a
      neighbor because the number of address prefixes received from the
      neighbor exceeds the locally-configured, upper bound, then the
      speaker MUST send the neighbor a NOTIFICATION message with the
      Error Code Cease.

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

                                  Table 1

      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").  The local system automatically disconnects the peer.







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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 AutomaticStop (Event 8) in the BGP FSM.

      9.5 Maximum Prefix Limits

      9.5.1 Pre-Policy Inbound Maximum Prefix Limits

         The Adj-RIB-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.

         Operators SHOULD take special care when utilizing methods where
         the router maintains a table of all the received updates pre-
         policy, as this could still expose control plane to exhaustion
         if no pre-policy limits are available or are not configured.
         Implementations SHOULD provide means to configure two
         thresholds for inbound limits, one before policies are applied,
         and one after.  This is to prevent exhaustion of control plane
         resources.  The threshold before policy SHOULD be higher than
         or equal to the limit configured after policy.

      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.

5.  Security Considerations

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

6.  IANA Considerations

   This memo requests that IANA updates the name of subcode "Maximum
   Number of Prefixes Reached" to "Threshold exceeded: Maximum Number of
   Prefixes Received" 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 (NTT),
   Jakob Heitz (Cisco), Warren Kumari (Google), Ben Maddison
   (Workonline), Randy Bush, Brian Dickson, Gyan Mishra (Verizon) and
   John John Heasley (NTTA) 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 below table provides an overview (as of the moment of writing) of
   which vendors have produced implementation of inbound prefix limits.
   Each table cell shows the applicable configuration keywords if the
   vendor implemented the feature.



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

      Table 2: Maximum prefix limits capabilities per implementation

   First presented by Snijders at [RIPE77]

9.  Appendix: Implementation Guidance

   TBD

10.  References

10.1.  Normative References







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   [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>.

10.2.  Informative References

   [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

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

   Email: maelmans@juniper.net


   Massimiliano Stucchi
   Independent

   Email: max@stucchi.ch


   Job Snijders
   Fastly
   Theodorus Majofskistraat 100
   1065 SZ Amsterdam
   Netherlands




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   Email: job@fastly.com


















































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