OSPF Working Group X. Xu
Internet-Draft Alibaba Inc
Intended status: Standards Track S. Kini
Expires: April 27, 2020
P. Psenak
C. Filsfils
S. Litkowski
Cisco Systems, Inc.
M. Bocci
Nokia
October 25, 2019
Signaling Entropy Label Capability and Entropy Readable Label-stack
Depth Using OSPF
draft-ietf-ospf-mpls-elc-12
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 tunnel unless an egress LSR has indicated via signaling that it
has the capability to process ELs, referred to as Entropy Label
Capability (ELC), on that tunnel. In addition, it would be useful
for ingress LSRs to know each LSR's capability of 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 OSPF and OSPFv3.
These mechanism is particularly useful in the environment where
Segment Routing (SR) is used, where label advertisements are done via
protocols like OSPF and OSPFv3.
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 April 27, 2020.
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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 . . . . . . . . . . . . . . 4
3.2. Advertising ELC Using OSPFv3 . . . . . . . . . . . . . . 4
4. Advertising ERLD Using OSPF . . . . . . . . . . . . . . . . . 4
5. Signaling ELC and ERLD in BGP-LS . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5
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 OSPF
[I-D.ietf-ospf-segment-routing-extensions]. In such scenarios, the
signaling mechanisms defined in [RFC6790] are inadequate. This draft
defines a mechanism to signal the ELC using OSPF. This mechanism is
useful when the label advertisement is also done via OSPF.
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In addition, in the cases where stacked LSPs are used for whatever
reasons (e.g., SR-MPLS [I-D.ietf-spring-segment-routing-mpls]), 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 Depth (ERLD) as defined in
[I-D.ietf-mpls-spring-entropy-label] 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 document makes use of the terms defined in [RFC6790], [RFC7770]
and [I-D.ietf-mpls-spring-entropy-label].
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
[BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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 the 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 line cards, the router MUST NOT announce ELC
unless all of its line-cards are capable of processing ELs.
If the router supports ELs on all of its line cards, it SHOULD
advertise the ELC with every local host prefix it advertises in OSPF.
When an OSPF Area Border Router (ABR) advertises the prefix to the
connected area based on the intra-area or inter-area prefix that is
reachable in some other area, it MUST preserve the ELC signalling for
such prefix.
When an OSPF Autonomous System Boundary Router (ASBR) redistributes
the 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
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the ASBR is outside of the scope of this document and is
implementation specific.
3.1. Advertising ELC Using OSPFv2
[RFC7684] defines the OSPFv2 Extended Prefix TLV to advertise
additional attributes associated with a prefix. The OSPFv2 Extended
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 that are advertised along
with the 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
A new MSD (Maximum SID Depth) type of the Node MSD sub-TLV [RFC8476],
called ERLD is defined to advertise the ERLD of a given router. The
scope of the advertisement depends on the application.
Assignment of a MSD-Type for ERLD is defined in
[I-D.ietf-isis-mpls-elc].
If a router has multiple line-cards with different capabilities for
reading the maximum label stack depth, the router MUST advertise the
smallest one.
When the ERLD MSD-Type is received in the OSPFv2 or OSPFv3 Link MSD
Sub-TLV, it MUST be ignored.
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 Flag included in the OSPFv2 Extended Prefix TLV and the
OSPFv3 PrefixOptions, as defined in Section 3, is advertised using
the Prefix Attribute Flags TLV (TLV 1170) of the BGP-LS IPv4/IPv6
Prefix NLRI Attribute as defined in section 2.3.2 of
[I-D.ietf-idr-bgp-ls-segment-routing-ext].
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The ERLD MSD-type introduced for OSPF in Section 4 is advertised
using the Node MSD TLV (TLV 266) of the BGP-LS Node NLRI Attribute as
defined in section 3 of [I-D.ietf-idr-bgp-ls-segment-routing-msd].
6. 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.
7. IANA Considerations
This document requests IANA to allocate one flag from the OSPFv2
Extended Prefix TLV Flags registry:
0x20 - E-Flag (ELC Flag)
This document requests IANA to allocate one flag from the OSPFv3
Prefix Options registry:
0x04 - E-Flag (ELC Flag)
8. Security Considerations
The security considerations as described in [RFC7770] and
[I-D.ietf-mpls-spring-entropy-label] are applicable to this document.
Incorrectly setting the E flag (ELC capable) (during origination,
inter-area advertisement or redistribution) may lead to black-holing
of the traffic on the egress node.
Incorrectly setting of the ERLD value may lead to poor load-balancing
of the traffic.
9. 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
10. References
10.1. Normative References
[BCP14] , <https://tools.ietf.org/html/bcp14>.
[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-09 (work in progress), October
2019.
[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-10 (work in progress), October 2019.
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[I-D.ietf-mpls-spring-entropy-label]
Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
Shakir, R., and J. Tantsura, "Entropy label for SPRING
tunnels", draft-ietf-mpls-spring-entropy-label-12 (work in
progress), July 2018.
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-22
(work in progress), May 2019.
[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>.
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[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>.
10.2. Informative References
[I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-27 (work in progress), December 2018.
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
Clarence Filsfils
Cisco Systems, Inc.
Brussels
Belgium
Email: cfilsfil@cisco.com
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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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