Internet DRAFT - draft-decraene-lsr-lag-indication
draft-decraene-lsr-lag-indication
Network Working Group B. Decraene
Internet-Draft Orange
Intended status: Standards Track S. Hegde
Expires: 2 February 2023 Juniper Networks Inc.
J. Halpern
Ericsson
1 August 2022
LAG indication
draft-decraene-lsr-lag-indication-03
Abstract
This document defines a new link flag to advertise that a layer-three
link is composed of multiple layer-two sub-links, such as when this
link is a Link Aggregation Group (LAG). This allows a large single
flow (an elephant flow) to be aware that the link capacity will be
lower than expected as this single flow is not load-balanced across
the multiple layer-two sub-links. A path computation logic may use
that information to route that elephant flow along a different path.
Status of This Memo
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This Internet-Draft will expire on 2 February 2023.
Copyright Notice
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Please review these documents carefully, as they describe your rights
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and restrictions with respect to this document. Code Components
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Protocol extensions . . . . . . . . . . . . . . . . . . . . . 3
2.1. IS-IS extension . . . . . . . . . . . . . . . . . . . . . 3
2.2. OSPF extension . . . . . . . . . . . . . . . . . . . . . 3
3. Operational considerations . . . . . . . . . . . . . . . . . 3
3.1. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Changes / Author Notes . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
An IP link may be composed a multiple layer two sub-links not visible
to the IGP routing topology. When traffic crossing that IP link is
load-balanced on a per flow basis, a large elephant flow will only
benefit from the capacity of a single sub-link. This is an issue for
the routing logic which only see the aggregated bandwidth of the IP
link, and hence may incorrectly route a large flow over a link which
is incapable of transporting that flow.
This document defines a new link flag to signal that an IP link is a
Link Aggregate Group composed of multiple layer two sub-links. This
flag may be automatically be set by routing nodes connected to such
links, without requiring manual tagging by the network operator. A
path computation logic such as a PCE or a CSPF computation on the
ingress, may use that information to avoid such links for elephant
flows.
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1.1. 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 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
appear in all capitals, as shown here.
2. Protocol extensions
2.1. IS-IS extension
To advertise that a layer-three link is composed of multiple layer-
two sub-components this document defines a new bit in the IS-IS link-
attribute sub-TLV RFC 5029 [RFC5029] .
L2 LAG (Link Aggregation Group) TBD1. When set, this layer-three
link is composed of multiple layer-two sub-components performing per
flow load balancing.
2.2. OSPF extension
To advertise that a layer-three link is composed of multiple layer-
two sub-components this document defines a new bit in the OSPF Link
Attributes Bits TLV [I-D.ietf-lsr-dynamic-flooding] .
L2 LAG (Link Aggregation Group) TBD2. When set, this layer-three
link is composed of multiple layer-two sub-components performing per
flow load balancing.
3. Operational considerations
A node supporting this extension SHOULD automatically advertise the
L2 LAG flag for IP links composed of multiple layer-two sub-
components. Configuration knob MAY be provided to override this
default.
In order to handle nodes not supporting this extension, network
operator may need to use an admin group (color) [RFC5305] [RFC7308]
in order to flag those links on legacy nodes.
3.1. Usage
The information provided by this flag can be used in several
different ways, depending upon the technology choices and needs of
the operator.
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If the operator's usage of LAGs is fairly consistent, one could have
a variation on a bandwidth limited flex-algo that specifies minimum
bandwidth and the LAG flag not being set. This could then be
selected by encapsulating head ends for streams which are judged to
need to avoid the LAGs. Likely this would be coupled with a
configured value representing the likely limit of LAG components for
selecting when to use this flex-algo instance. Note that extending
flex-algo requires every node to upgrade.
Another option is if the operator is using traffic engineering
(either with a PCE or the head end doing the path selection). The
path selector can select points in e.g. a segment routed path so as
to avoid links marked as being LAGs for elephant flows. This can be
coupled with a more flexible heuristic for limits than the above.
The path selector can look at the advertised link bandwidth, and the
presence of the LAG flag, and frequently reliably infer the LAG
component size. Thus, it would only need to avoid LAGs where the
component is expected to be too small for the large flow being
placed.
[Editor's note: This does suggest a possible extension if the working
group is interested. We could add a new sub-TLV indicating the
lowest bandwidth of the LAG components of a given LAG. This is
additional complexity and the question is whether the use cases where
this would give noticeably more accurate path estimates and better
elephant flow placement are likely.]
4. IANA Considerations
4.1. IS-IS
IANA is requested to allocate one bit value from the registry: link-
attribute bit values for sub-TLV 19 of TLV 22 (Extended IS
reachability TLV).
Value Name
---- --------------------------------
TBD1 L2 LAG (Link Aggregation Group)
Figure 1: IS-IS IANA registration
4.2. OSPF
IANA is requested to allocate one bit number from the registry: OSPF
Link Attributes Sub-TLV Bit Values.
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Bit Number Description
---------- --------------------------------
TBD2 L2 LAG (Link Aggregation Group)
Figure 2: OSPF IANA registration
5. Security Considerations
This extension advertises additional information and capabilities
about a link.
An attacker having access to this information would gain knowledge
that this link has sub components and that sending a large amount of
traffic via a single flow (hence not a DOS) is more likely to
overload that sub-component. On the other hand, this overloading
would be limited to this specific sub-component and hence not affect
other sub-component.
An attacker been capable of adding this information may gain ability
to change the routing of some flow crossing the links, typically
large elephant flows specifically configured to avoid such link.
An attacker been capable of removing this information may gain the
ability to change the routing and direct a large elephant flow on
this link, which would overload a sub component of this link and
likely create packet drop for this specific flow.
However, in those two cases, the attacker would equally have the
capability to change other routing information such as the link
metric, link usability and any link characteristics. Hence this new
information does not add new security considerations. Besides, as
with others TLV advertisements, the use of a cryptographic
authentication as defined in [RFC5304] or [RFC5310] allows the
authentication of the peer and the integrity of the message and
remove the ability for an attacker to modify such information.
.
6. Acknowledgments
TBD.
7. References
7.1. Normative References
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[I-D.ietf-lsr-dynamic-flooding]
Li, T., Przygienda, T., Psenak, P., Ginsberg, L., Chen,
H., Cooper, D., Jalil, L., Dontula, S., and G. S. Mishra,
"Dynamic Flooding on Dense Graphs", Work in Progress,
Internet-Draft, draft-ietf-lsr-dynamic-flooding-11, June
2022, <https://www.ietf.org/archive/id/draft-ietf-lsr-
dynamic-flooding-11.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", DOI 10.17487/RFC2119, BCP 14,
RFC 2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link
Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029,
September 2007, <https://www.rfc-editor.org/info/rfc5029>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", DOI 10.17487/RFC8174, RFC 8174, BCP 14,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", DOI 10.17487/RFC5305, RFC 5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC7308] Osborne, E., "Extended Administrative Groups in MPLS
Traffic Engineering (MPLS-TE)", RFC 7308,
DOI 10.17487/RFC7308, July 2014,
<https://www.rfc-editor.org/info/rfc7308>.
Appendix A. Changes / Author Notes
[RFC Editor: Please remove this section before publication]
00: Initial version.
01: Refresh.
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02: New section "Usage".
03: Refresh.
Authors' Addresses
Bruno Decraene
Orange
Email: bruno.decraene@orange.com
Shraddha Hegde
Juniper Networks Inc.
Exora Business Park
Bangalore 560103
KA
India
Email: shraddha@juniper.net
Joel Halpern
Ericsson
Email: joel.halpern@ericsson.com
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