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Global Routing Operations                                    J. Snijders
Internet-Draft                                        NTT Communications
Intended status: Standards Track                              M. Aelmans
Expires: September 9, 2019                              Juniper Networks
                                                           March 8, 2019


                       BGP Maximum Prefix Limits
                       draft-sa-grow-maxprefix-02

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 September 9, 2019.

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.  Inbound Maximum Prefix Limits . . . . . . . . . . . . . . . .   2
     2.1.  Type A: Pre-Policy Inbound Maximum Prefix Limits  . . . .   3
     2.2.  Type B: Post-Policy Inbound Maximum Prefix Limits . . . .   3
   3.  Outbound Maximum Prefix Limits  . . . . . . . . . . . . . . .   3
   4.  Considerations for Operations with Multi-Protocol BGP . . . .   4
   5.  Considerations for soft thresholds  . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   9.  Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION   5
   10. Appendix: Implementation Guidance . . . . . . . . . . . . . .   6
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     11.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   This document describes mechanisms to reduce the negative impact of
   certain types of misconfigurations and/or resource exhaustions in BGP
   [RFC4271] operations.  While [RFC4271] already described a method to
   tear down BGP sessions when 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.  Inbound Maximum Prefix Limits

   An operator MAY configure a BGP speaker to terminate its BGP session
   with a neighbor when the number of address prefixes received from
   that neighbor exceeds a locally configured 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 Received", and MAY support other actions.
   Reporting when thresholds have been exceeded is an implementation
   specific consideration, but SHOULD include methods such as Syslog



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   [RFC5424].  Inbound Maximum Prefix Limits can be applied in two
   distinct places in the conceptual model: before or after the
   application of routing policy.

2.1.  Type A: 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 Type A 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 Type A 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.

   Type A 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.

2.2.  Type B: 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 Type B 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 Type B 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.

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

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 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", and MAY support other actions.  Reporting
   when thresholds have been exceeded is an implementation specific




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   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.

4.  Considerations for Operations with Multi-Protocol BGP

5.  Considerations for soft thresholds

   describe soft and hard limits (warning vs teardown)

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 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.

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








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8.  Acknowledgments

   The authors would like to thank Saku Ytti and John Heasley (NTT
   Communications), 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) and Yu Tianpeng 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   |  Type A Pre-   |    Type B 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>.

11.2.  Informative References

   [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

   Job Snijders
   NTT Communications
   Theodorus Majofskistraat 100
   Amsterdam  1065 SZ
   The Netherlands

   Email: job@ntt.net









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

   Email: maelmans@juniper.net












































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