Paths Limit for Multiple Paths in BGP
draft-abraitis-idr-addpath-paths-limit-00
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| Authors | Donatas Abraitis , Alvaro Retana , Jeffrey Haas | ||
| Last updated | 2024-01-17 | ||
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draft-abraitis-idr-addpath-paths-limit-00
Inter-Domain Routing D. Abraitis
Internet-Draft NetDef
Intended status: Standards Track A. Retana
Expires: 20 July 2024 Futurewei Technologies, Inc.
J. Haas
Juniper Networks
17 January 2024
Paths Limit for Multiple Paths in BGP
draft-abraitis-idr-addpath-paths-limit-00
Abstract
This document specifies a BGP capability that complements the ADD-
PATH Capability by indicating the maximum number of paths a BGP
speaker can receive from a peer, optimizing the transmission of BGP
routes by selectively relaying pertinent routes instead of the entire
set.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 20 July 2024.
Copyright Notice
Copyright (c) 2024 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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . 3
3. PATHS-LIMIT Capability . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
BGP ADD-PATH [RFC7911] defines a BGP extension that allows the
advertisement of multiple paths for the same address prefix without
the new paths implicitly replacing any previous ones.
Multiple paths for a large number of prefixes may be received by a
BGP speaker, potentially depleting memory resources or even causing
network-wide instability. Such instability could be considered a
denial-of-service attack. Without knowing the maximum number of
paths the receiver wants to receive, the sender may send more than
that number of paths. [I-D.ietf-idr-add-paths-guidelines] provides
recommendations for the use of BGP ADD-PATH while implementing
specific applications.
This document specifies a BGP capability [RFC5492] that complements
the ADD-PATH Capability [RFC7911] by indicating the maximum number of
paths a BGP speaker can receive from a peer. This indication allows
the sender to optimize the transmission of BGP routes by selectively
relaying pertinent routes instead of the entire set.
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2. Specification of Requirements
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.
3. PATHS-LIMIT Capability
The PATHS-LIMIT Capability is a BGP capability [RFC5492], with
Capability Code TBD. The Capability Length field of this capability
is variable. The Capability Value field consists of one or more of
the following tuples:
+------------------------------------------------+
| Address Family Identifier (2 octets) |
+------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+------------------------------------------------+
| Paths Limit (2 octet) |
+------------------------------------------------+
Figure 1
The meaning and use of the fields are as follows:
Address Family Identifier (AFI):
This field is the same as the one used in [RFC4760].
Subsequent Address Family Identifier (SAFI):
This field is the same as the one used in [RFC4760].
Paths Limit:
This field indicates the maximum paths limit the receiver wants
to receive from its peer. If the received Paths Limit is zero
(0), the tuple SHOULD be ignored.
A BGP speaker that wishes to indicate support for multiple AFI/SAFIs
MUST do so by including the information in a single instance of the
PATHS-LIMIT capability.
The PATHS-LIMIT capability MUST be ignored if the ADD-PATH capability
is not present.
If the PATHS-LIMIT capability is empty (i.e. the Capability Length
field is set to 0), it means that the sender doesn't have any
specific limits to communicate.
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An AFI/SAFI tuple MUST be ignored if the same tuple was not received
in the ADD-PATH capability.
If more than one tuple is received for the same AFI/SAFI pair, only
the first tuple should be considered. All others MUST be ignored.
A sender advertising multiple paths for the same prefix SHOULD send
only the specified maximum number of paths indicated in the PATHS-
LIMIT capability.
An implementation SHOULD provide a configuration knob to specify the
maximum number of paths to accept from a sender.
4. IANA Considerations
IANA is requested to assign a value (TBD) for the PATHS-LIMIT
Capability from the "Capability Codes" registry.
5. Security Considerations
This document defines a BGP extension that allows a receiver to
better control the number of routes it receives when using BGP ADD-
PATH [RFC7911]. Use of the PATHS-LIMIT capability can then mitigate
some of the security-related concerns expressed in [RFC7911].
A rogue node or misconfiguration can result in the advetisement of a
Paths Limit value that is too low for the application being used.
This can result in inconsistent forwarding. Describing applications
for BGP ADD-PATH is outside the scope of this document. Users of the
PATHS-LIMIT Capability are encouraged to examine the behavior and
potential impact by studying the best practices described in
[I-D.ietf-idr-add-paths-guidelines].
6. References
6.1. 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>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
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[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
[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>.
6.2. Informative References
[I-D.ietf-idr-add-paths-guidelines]
Uttaro, J., Francois, P., Patel, K., Haas, J., Simpson,
A., and R. Fragassi, "Best Practices for Advertisement of
Multiple Paths in IBGP", Work in Progress, Internet-Draft,
draft-ietf-idr-add-paths-guidelines-08, 25 April 2016,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-add-
paths-guidelines-08>.
Acknowledgements
TBD
Authors' Addresses
Donatas Abraitis
NetDef
Email: donatas@opensourcerouting.org
Alvaro Retana
Futurewei Technologies, Inc.
Email: aretana@futurewei.com
Jeffrey Haas
Juniper Networks
1133 Innovation Way
Sunnyvale, CA 94089
United States of America
Email: jhaas@juniper.net
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