Internet DRAFT - draft-sas-idr-maxprefix-inbound
draft-sas-idr-maxprefix-inbound
Inter-Domain Routing J. Snijders
Internet-Draft Fastly
Updates: 4271 (if approved) M. Aelmans
Intended status: Standards Track Juniper Networks
Expires: 8 August 2023 M. Stucchi
Independent
4 February 2023
Inbound BGP Maximum Prefix Limits
draft-sas-idr-maxprefix-inbound-05
Abstract
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.
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 8 August 2023.
Copyright Notice
Copyright (c) 2023 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
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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 . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
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.
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.":
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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:
a. Discards new address prefixes from the neighbor, while
maintaining the BGP connection in Established state. Note
that as these prefixes are discarded, their reachability
information is not stored on the local router, which might
lead to inconsistent routing behaviour;
b. Continues to receives new prefixes while exceeding the
threshold and generates a log of the event;
c. Terminates the BGP connection with the neighbor. This is the
safest option.
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 threshold, 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:
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Possible reasons for an AutomaticStop event are: A BGP speaker
receives an UPDATE messages with a number of prefixes from 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.
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]. 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
calculation, without having applied any policies from the
Policy Information Base. For example, when an operator
configures the local system to terminate a given EBGP session
when more than 50 IPv4 Unicast NLRIs exist in the Adj-RIB-In,
and a given adjacent system announces the 51st IPv4 Unicast
NLRI, the session MUST be terminated.
Pre-policy limits are particularly useful to help prevent
memory exhaustion during full Internet routing table leaks on
systems which store all 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 -
none of which 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.
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 from the PIB
are applied, and one after. This is to prevent exhaustion of
control plane resources. A Pre-Policy maximum prefix limit
SHOULD equal to or higher than a Post-Policy maximum prefix
limit.
5. Security Considerations
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.
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, 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.
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
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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 | | 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]
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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>.
[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
[RFC7454] Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations
and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454,
February 2015, <https://www.rfc-editor.org/info/rfc7454>.
[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
Fastly
Amsterdam
Netherlands
Email: job@fastly.com
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Melchior Aelmans
Juniper Networks
Boeing Avenue 240
1119 PZ Schiphol-Rijk
Netherlands
Email: maelmans@juniper.net
Massimiliano Stucchi
Independent
Email: max@stucchi.ch
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