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draft-sa-idr-maxprefix.txt
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Inter-Domain Routing J. Snijders
Internet-Draft NTT
Updates: 4271 (if approved) M. Aelmans
Intended status: Standards Track Juniper Networks
Expires: September 30, 2020 March 29, 2020
Revised BGP Maximum Prefix Limits
draft-sa-idr-maxprefix-00
Abstract
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
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 30, 2020.
Copyright Notice
Copyright (c) 2020 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
Snijders & Aelmans Expires September 30, 2020 [Page 1]
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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
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Changes to RFC4271 Section 6 . . . . . . . . . . . . . . . . 2
3. Changes to RFC4271 Section 8 . . . . . . . . . . . . . . . . 3
4. BGP Yang Model Considerations - PERHAPS REMOVE BEFORE
PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Changes to RFC4271 Section 9 . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
9. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 6
10. Appendix: Implementation Guidance . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . 8
11.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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. 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.":
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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) or send to a neighbor (outbound 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). Outbound prefix limits MUST be measured after
policy since the Policy (even a policy of "send all") is run
before determining what can be sent. When the upper bound is
reached, the speaker, under control of local configuration,
either:
A. Discards new address prefixes to or from the neighbor (while
maintaining the BGP connection with the neighbor)
B. Terminates the BGP connection with the neighbor
If the BGP peer uses option (b) where the limit causes a CEASE
Notification, then the CEASE error codes should use:
+---------+---------------------------------------------------------+
| Subcode | Symbolic Name |
+---------+---------------------------------------------------------+
| 1 | Maximum Number of Prefixes Reached |
| TBD | Threshold exceeded: Self-Destructing, Maximum Number of |
| | Prefixes Send |
+---------+---------------------------------------------------------+
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"), or announces more prefixes than through local
configuration allowed to. The local system automatically
disconnects the peer.
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4. BGP Yang Model Considerations - PERHAPS REMOVE BEFORE PUBLICATION
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:
max-prefixes-inbound-pre-policy
max-prefixes-inbound-post-policy
max-prefixes-outbound
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.
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
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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.
9.5.3 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
post-policy 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". Implementations MAY support additional
actions. The Hard Cease action is defined in [RFC8538].
Reporting when thresholds have been exceeded is an
implementation specific 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.
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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.
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 (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), and Susan Hares (Hickory Hill Consulting) 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 | Inbound Pre- | Inbound 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>.
[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,
<https://www.rfc-editor.org/info/rfc8538>.
11.2. 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-08 (work in progress), February 2020.
[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
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Job Snijders
NTT
Theodorus Majofskistraat 100
Amsterdam 1065 SZ
The Netherlands
Email: job@ntt.net
Melchior Aelmans
Juniper Networks
Boeing Avenue 240
Schiphol-Rijk 1119 PZ
The Netherlands
Email: maelmans@juniper.net
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