OSPF Working Group X. Xu
Internet-Draft Alibaba Inc
Intended status: Standards Track S. Kini
Expires: October 19, 2020
P. Psenak
C. Filsfils
S. Litkowski
Cisco Systems, Inc.
M. Bocci
Nokia
April 17, 2020
Signaling Entropy Label Capability and Entropy Readable Label Depth
Using OSPF
draft-ietf-ospf-mpls-elc-13
Abstract
Multiprotocol Label Switching (MPLS) has defined a mechanism to load-
balance traffic flows using Entropy Labels (EL). An ingress Label
Switching Router (LSR) cannot insert ELs for packets going into a
given Label Switched Path (LSP) unless an egress LSR has indicated
via signaling that it has the capability to process ELs, referred to
as the Entropy Label Capability (ELC), on that tunnel. In addition,
it would be useful for ingress LSRs to know each LSR's capability for
reading the maximum label stack depth and performing EL-based load-
balancing, referred to as Entropy Readable Label Depth (ERLD). This
document defines a mechanism to signal these two capabilities using
OSPFv2 and OSPFv3.
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 October 19, 2020.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Advertising ELC Using OSPF . . . . . . . . . . . . . . . . . 3
3.1. Advertising ELC Using OSPFv2 . . . . . . . . . . . . . . 3
3.2. Advertising ELC Using OSPFv3 . . . . . . . . . . . . . . 4
4. Advertising ERLD Using OSPF . . . . . . . . . . . . . . . . . 4
5. Signaling ELC and ERLD in BGP-LS . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
[RFC6790] describes a method to load-balance Multiprotocol Label
Switching (MPLS) traffic flows using Entropy Labels (EL). It also
introduces the concept of Entropy Label Capability (ELC) and defines
the signaling of this capability via MPLS signaling protocols.
Recently, mechanisms have been defined to signal labels via link-
state Interior Gateway Protocols (IGP) such as OSPFv2 [RFC8665] and
OSPFv3 [RFC8666]. This draft defines a mechanism to signal the ELC
using OSPFv2 and OSPFv3.
In cases where LSPs are used (e.g., SR-MPLS [RFC8660], it would be
useful for ingress LSRs to know each intermediate LSR's capability of
reading the maximum label stack depth and performing EL-based load-
balancing. This capability, referred to as Entropy Readable Label
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Depth (ERLD) as defined in [RFC8662] may be used by ingress LSRs to
determine the position of the EL label in the stack, and whether it's
necessary to insert multiple ELs at different positions in the label
stack.
2. Terminology
This memo makes use of the terms defined in [RFC6790], and [RFC8662].
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.
The key word OSPF is used throughout the document to refer to both
OSPFv2 and OSPFv3.
3. Advertising ELC Using OSPF
Even though ELC is a property of the node, in some cases it is
advantageous to associate and advertise the ELC with a prefix. In
multi-area networks, routers may not know the identity of the prefix
originator in a remote area, or may not know the capabilities of such
originator. Similarly, in a multi domain network, the identity of
the prefix originator and its capabilities may not be known to the
ingress LSR.
If a router has multiple interfaces, the router MUST NOT announce ELC
unless all of its interfaces are capable of processing ELs.
If the router supports ELs on all of its interfaces, it SHOULD
advertise the ELC with every local host prefix it advertises in OSPF.
When an OSPF Area Border Router (ABR) distributes information between
connected areas it MUST preserve the ELC setting.
When an OSPF Autonomous System Boundary Router (ASBR) redistributes a
prefix from another instance of the OSPF or from some other protocol,
it SHOULD preserve the ELC signaling for the prefix. The exact
mechanism used to exchange ELC between protocol instances on the ASBR
is outside of the scope of this document.
3.1. Advertising ELC Using OSPFv2
[RFC7684] defines the OSPFv2 Extended Prefix TLV to advertise
additional attributes associated with a prefix. The OSPFv2 Extended
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Prefix TLV includes a one octet Flags field. A new flag in the Flags
field is used to signal the ELC for the prefix:
0x20 - E-Flag (ELC Flag): Set by the advertising router to
indicate that the prefix originator is capable of processing ELs.
3.2. Advertising ELC Using OSPFv3
[RFC5340] defines the OSPFv3 PrefixOptions field to indicate
capabilities associated with a prefix. A new bit in the OSPFv3
PrefixOptions is used to signal the ELC for the prefix:
0x04 - E-Flag (ELC Flag): Set by the advertising router to
indicate that the prefix originator is capable of processing ELs.
4. Advertising ERLD Using OSPF
The ERLD is advertised in a Node MSD sub-TLV [RFC8476] using the
ERLD-MSD type defined in [I-D.ietf-isis-mpls-elc].
If a router has multiple interfaces with different capabilities of
reading the maximum label stack depth, the router MUST advertise the
smallest one.
The absence of ERLD-MSD advertisements indicates only that the
advertising node does not support advertisement of this capability.
When the ERLD MSD-Type is received in the OSPFv2 or OSPFv3 Link MSD
Sub-TLV, it MUST be ignored.
The considerations for advertising the ERLD are specified in
[RFC8662].
5. Signaling ELC and ERLD in BGP-LS
The OSPF extensions defined in this document can be advertised via
BGP-LS [RFC7752] using existing BGP-LS TLVs.
The ELC is advertised using the Prefix Attribute Flags TLV as defined
in [I-D.ietf-idr-bgp-ls-segment-routing-ext].
The ERLD-MSD is advertised using the Node MSD TLV as defined in
[I-D.ietf-idr-bgp-ls-segment-routing-msd].
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6. IANA Considerations
Early allocation has been done by IANA for this document as follows:
- Flag 0x20 in the OSPFv2 Extended Prefix TLV Flags registry has
been assigned to the E-Flag (ELC Flag). IANA is asked to update
the registry to reflect the name used in this document: E-Flag
(ELC Flag).
- Bit 0x04 in the "OSPFv3 Prefix Options (8 bits)" registry has
been assigned to the E-Flag (ELC Flag). IANA is asked to update
the registry to reflect the name used in this document: E-Flag
(ELC Flag).
7. Security Considerations
This document specifies the ability to advertise additional node
capabilities using OSPF and BGP-LS. As such, the security
considerations as described in [RFC5340], [RFC7770], [RFC7752],
[RFC7684], [RFC8476], [RFC8662],
[I-D.ietf-idr-bgp-ls-segment-routing-ext] and
[I-D.ietf-idr-bgp-ls-segment-routing-msd] are applicable to this
document.
Incorrectly setting the E flag during origination, propagation or
redistribution may lead to black-holing of the traffic on the egress
node.
Incorrectly setting of the ERLD value may lead to poor or no load-
balancing of the traffic.
8. Contributors
The following people contributed to the content of this document and
should be considered as co-authors:
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Gunter Van de Velde (editor)
Nokia
Antwerp
BE
Email: gunter.van_de_velde@nokia.com
Wim Henderickx
Nokia
Belgium
Email: wim.henderickx@nokia.com
Keyur Patel
Arrcus
USA
Email: keyur@arrcus.com
9. Acknowledgements
The authors would like to thank Yimin Shen, George Swallow, Acee
Lindem, Les Ginsberg, Ketan Talaulikar, Jeff Tantsura , Bruno
Decraene and Carlos Pignataro for their valuable comments.
10. References
10.1. Normative References
[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
(work in progress), June 2019.
[I-D.ietf-idr-bgp-ls-segment-routing-msd]
Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G.,
and N. Triantafillis, "Signaling MSD (Maximum SID Depth)
using Border Gateway Protocol - Link State", draft-ietf-
idr-bgp-ls-segment-routing-msd-16 (work in progress),
March 2020.
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[I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using IS-IS", draft-ietf-
isis-mpls-elc-11 (work in progress), March 2020.
[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>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[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>.
[RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
DOI 10.17487/RFC8476, December 2018,
<https://www.rfc-editor.org/info/rfc8476>.
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[RFC8662] Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
Shakir, R., and J. Tantsura, "Entropy Label for Source
Packet Routing in Networking (SPRING) Tunnels", RFC 8662,
DOI 10.17487/RFC8662, December 2019,
<https://www.rfc-editor.org/info/rfc8662>.
10.2. Informative References
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
December 2019, <https://www.rfc-editor.org/info/rfc8666>.
Authors' Addresses
Xiaohu Xu
Alibaba Inc
Email: xiaohu.xxh@alibaba-inc.com
Sriganesh Kini
Email: sriganeshkini@gmail.com
Peter Psenak
Cisco Systems, Inc.
Eurovea Centre, Central 3
Pribinova Street 10
Bratislava 81109
Slovakia
Email: ppsenak@cisco.com
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Clarence Filsfils
Cisco Systems, Inc.
Brussels
Belgium
Email: cfilsfil@cisco.com
Stephane Litkowski
Cisco Systems, Inc.
La Rigourdiere
Cesson Sevigne
France
Email: slitkows@cisco.com
Matthew Bocci
Nokia
Shoppenhangers Road
Maidenhead, Berks
UK
Email: matthew.bocci@nokia.com
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