Inter-Domain Routing M. Aelmans
Internet-Draft Juniper Networks
Updates: 4271 (if approved) M. Stucchi
Intended status: Standards Track Independent
Expires: October 16, 2021 J. Snijders
Fastly
April 14, 2021
BGP Maximum Prefix Limits Inbound
draft-sas-idr-maxprefix-inbound-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 October 16, 2021.
Copyright Notice
Copyright (c) 2021 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
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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 . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
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 |
+---------+---------------------------------------------------------+
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.
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.
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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
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.
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.
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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
(Bloomberg), Jakob Heitz (Cisco), Warren Kumari (Google), Ben
Maddison (Workonline), Randy Bush, Brian Dickson and Gyan Mishra
(Verizon) 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 IOS XR | | maximum-prefix |
+--------------+----------------------+-----------------------------+
| Cisco IOS XE | | maximum-prefix |
+--------------+----------------------+-----------------------------+
| Juniper | prefix-limit | accepted-prefix-limit, or |
| Junos OS | | prefix-limit combined with |
| | | 'keep none' |
+--------------+----------------------+-----------------------------+
| Nokia SR OS | prefix-limit | |
+--------------+----------------------+-----------------------------+
| NIC.CZ BIRD | 'import keep | 'import limit' or 'receive |
| | filtered' combined | limit' |
| | with 'receive limit' | |
+--------------+----------------------+-----------------------------+
| OpenBSD | max-prefix | |
| OpenBGPD | | |
+--------------+----------------------+-----------------------------+
| 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]
Table 1: Maximum prefix limits capabilities per implementation
9. Appendix: Implementation Guidance
TBD
10. References
10.1. 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>.
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[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
[I-D.ietf-idr-bgp-model]
Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
YANG Model for Service Provider Networks", draft-ietf-idr-
bgp-model-10 (work in progress), November 2020.
[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
Schiphol-Rijk 1119 PZ
The Netherlands
Email: maelmans@juniper.net
Massimiliano Stucchi
Independent
Email: max@stucchi.ch
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Job Snijders
Fastly
Theodorus Majofskistraat 100
Amsterdam 1065 SZ
The Netherlands
Email: job@fastly.com
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