Internet-Draft | Inbound BGP Maximum Prefix Limits | February 2023 |
Snijders, et al. | Expires 8 August 2023 | [Page] |
This document describes two threshold types to consider when receiving BGP address prefixes from adjacent systems in order to limit the negative impact of route leaks or resource exhaustion in BGP implementations.¶
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.¶
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This document updates [RFC4271] and describes a revision of the control mechanism which helps limit the negative impact of route leaks [RFC7908] and/or resource exhaustion in Border Gateway Protocol (BGP) implementations. While [RFC4271] described the concept of automatically tearing down BGP sessions or discarding UPDATES after the configured maximum number of prefixes received threshold has been exceeded, operational experience suggests it to be beneficial to recognize two distinct subtypes of this threshold. This document introduces a differentiation between Pre-Policy and Post-Policy maximum prefix limits.¶
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 prefix limit). Limitations on the prefixes accepted from a neighbor can be applied before policy processing (Pre-Policy) and after policy processing (Post-Policy). When one of the two thresholds is reached, the speaker, under control of local configuration, either:¶
Subcode | Symbolic Name |
---|---|
1 | Threshold exceeded: Maximum Number of Prefixes Received |
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:¶
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.¶
Maximum Prefix Limits are an essential tool for routing operations and are RECOMMENDED be used to increase stability for the global routing ecosystem. See [RFC7454] section 8 for more guidance.¶
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.¶
The authors would like to thank Saku Ytti, John Heasley, Jeff Haas, Colby Barth, John Scudder, Martijn Schmidt, Teun Vink, Sabri Berisha, Martin Pels, Steven Bakker, Aftab Siddiqui, Yu Tianpeng, Ruediger Volk, Robert Raszuk, Jakob Heitz, Warren Kumari, Ben Maddison, Randy Bush, Brian Dickson, and Gyan Mishra for their support, insightful reviews, 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 prefix limits. Each table cell shows the applicable configuration keywords if the vendor implemented the feature.¶
Vendor | Type A Pre-Policy | Type B Post-Policy |
---|---|---|
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' |
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 |
TBD¶