Inter-Domain Routing J. Snijders
Internet-Draft NTT
Updates: 4271 (if approved) M. Aelmans
Intended status: Standards Track Juniper Networks
Expires: March 27, 2020 September 24, 2019

Revised BGP Maximum Prefix Limits


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

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This Internet-Draft will expire on March 27, 2020.

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Table of Contents

1. Introduction

This document updates [RFC4271] by revising control mechanism which limit the negative impact of route leaks 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.":

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

3. Changes to RFC4271 Section 8

This section updates Section 8, 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:


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:


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.

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 (, 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.


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.

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

First presented by Snijders at [RIPE77]

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

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.
[RFC4271] Rekhter, Y., Li, T. and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[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.

11.2. Informative References

[I-D.ietf-idr-bgp-model] Jethanandani, M., Patel, K. and S. Hares, "BGP YANG Model for Service Provider Networks", Internet-Draft draft-ietf-idr-bgp-model-06, June 2019.
[RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, DOI 10.17487/RFC5424, March 2009.
[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.
[RIPE77] Snijders, J., "Robust Routing Policy Architecture", May 2018.

Authors' Addresses

Job Snijders NTT Theodorus Majofskistraat 100 Amsterdam, 1065 SZ The Netherlands EMail:
Melchior Aelmans Juniper Networks Boeing Avenue 240 Schiphol-Rijk, 1119 PZ The Netherlands EMail: