BGP Maximum Prefix Limits
draft-sa-grow-maxprefix-01
The information below is for an old version of the document.
| Document | Type | This is an older version of an Internet-Draft whose latest revision is Replaced | |
|---|---|---|---|
| Authors | Job Snijders , Melchior Aelmans | ||
| Last updated | 2018-12-27 | ||
| Replaced by | draft-sa-idr-maxprefix | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-sa-grow-maxprefix-01
Global Routing Operations J. Snijders
Internet-Draft NTT Communications
Intended status: Standards Track M. Aelmans
Expires: June 30, 2019 Juniper Networks
December 27, 2018
BGP Maximum Prefix Limits
draft-sa-grow-maxprefix-01
Abstract
This document describes mechanisms to limit the negative impact of
route leaks [RFC7908] and/or resource exhaustion in BGP-4 [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 June 30, 2019.
Copyright Notice
Copyright (c) 2018 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
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(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Application of Control Theory to BGP-4 Operations . . . . . . 2
3. Inbound Maximum Prefix Limits . . . . . . . . . . . . . . . . 2
3.1. Type A: Pre-Policy Inbound Maximum Prefix Limits . . . . 3
3.2. Type B: Post-Policy Inbound Maximum Prefix Limits . . . . 3
4. Outbound Maximum Prefix Limits . . . . . . . . . . . . . . . 3
5. Considerations for Operations with Multi-Protocol BGP-4 . . . 4
6. Considerations for soft thresholds . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
10. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 5
11. Appendix: Implementation Guidance . . . . . . . . . . . . . . 6
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
12.1. Normative References . . . . . . . . . . . . . . . . . . 6
12.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This document describes mechanisms to reduce the negative impact of
certain types of misconfigurations and/or resource exhaustions in
BGP-4 [RFC4271] operations. While [RFC4271] already described a
method to tear down BGP-4 sessions when certain thresholds are
exceeded, some nuances in this specification were missing resulting
in inconsistencies between BGP-4 implementations. In addition to
clarifying "inbound maximum prefix limits", this document also
introduces a specification for "outbound maximum prefix limits".
2. Application of Control Theory to BGP-4 Operations
3. Inbound Maximum Prefix Limits
An operator MAY configure a BGP speaker to terminate its BGP session
with a neighbor when the number of address prefixes received from
that neighbor exceeds a locally configured 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
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Number of Prefixes Received", and MAY support other actions.
Reporting when thresholds have been exceeded is an implementation
specific consideration, but SHOULD include methods such as Syslog
[RFC5424]. Inbound Maximum Prefix Limits can be applied in two
distinct places in the conceptual model: before or after the
application of routing policy.
3.1. Type A: 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 Type 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 comparisons.
For example, when an operator configures the Type A 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.
Type A 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.
3.2. Type B: 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 Type B 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 Type B 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.
Type B post-policy limits are useful to help prevent FIB exhaustion.
4. 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 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", and MAY support other actions. Reporting
when thresholds have been exceeded is an implementation specific
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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.
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.
5. Considerations for Operations with Multi-Protocol BGP-4
6. Considerations for soft thresholds
describe soft and hard limits (warning vs teardown)
7. Security Considerations
TBD. Maximum Prefix Limits are an essential tool for routing
operations.
8. 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.
This memo requests that IANA assigns a new subcode named "Threshold
exceeded: Maximum Number of Prefixes Send" in the "Cease NOTIFICATION
message subcodes" registry under the "Border Gateway Protocol (BGP)
Parameters" group.
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9. Acknowledgments
The authors would like to thank Saku Ytti and John Heasley (NTT
Communications), 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) and Aftab
Siddiqui (ISOC) for their support, insightful review, and comments.
10. 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 | Type A Pre- | Type B 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 |
+-------------+----------------+-------------------------+----------+
First presented by Snijders at [RIPE77]
Table 1: Maximum prefix limits capabilities per implementation
11. 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
automatictly restart after between 15 and 30 minutes
12. References
12.1. 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>.
12.2. Informative References
[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, "Robust Routing Policy Architecture", May 2018,
<https://ripe77.ripe.net/wp-content/uploads/presentations/
59-RIPE77_Snijders_Routing_Policy_Architecture.pdf>.
Authors' Addresses
Job Snijders
NTT Communications
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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