draft-ietf-ospf-segment-routing-msd-08.txt   draft-ietf-ospf-segment-routing-msd-09.txt 
OSPF Working Group J. Tantsura OSPF Working Group J. Tantsura
Internet-Draft Individual Internet-Draft Nuage Networks
Intended status: Standards Track U. Chunduri Intended status: Standards Track U. Chunduri
Expires: June 17, 2018 Huawei Technologies Expires: August 30, 2018 Huawei Technologies
S. Aldrin S. Aldrin
Google, Inc Google, Inc
P. Psenak P. Psenak
Cisco Systems Cisco Systems
December 14, 2017 February 26, 2018
Signaling MSD (Maximum SID Depth) using OSPF Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-08 draft-ietf-ospf-segment-routing-msd-09
Abstract Abstract
This document proposes a way to signal Maximum SID Depth (MSD) This document defines a way for an OSPF Router to advertise multiple
supported by a node at node and/or link granularity by an OSPF types of supported Maximum SID Depths (MSDs) at node and/or link
Router. In a Segment Routing (SR) enabled network a centralized granularity. Such advertisements allow entities (e.g., centralized
controller that programs SR tunnels needs to know the MSD supported controllers) to determine whether a particular SID stack is
by the head-end at node and/or link granularity to impose the SID supportable in a given network. This document only defines one type
stack of an appropriate depth. MSD is relevant to the head-end of a of MSD (maximum label imposition) - but defines an encoding which can
SR tunnel or Binding-SID anchor node where Binding-SID expansions support other MSD types. Here the term OSPF means both OSPFv2 and
might result in creation of a new SID stack. Here the term OSPF OSPFv3.
means both OSPFv2 and OSPFv3.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on June 17, 2018. This Internet-Draft will expire on August 30, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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skipping to change at page 2, line 24 skipping to change at page 2, line 24
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5 4. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5
5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5 5. Using Node and Link MSD Advertisements . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 7 11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
When Segment Routing tunnels are computed by a centralized When Segment Routing(SR) paths are computed by a centralized
controller, it is critical that the controller learns the MSD controller, it is critical that the controller learns the Maximum SID
"Maximum SID Depth" of the node or link SR tunnel exits over, so the Depth(MSD) which can be imposed at the node/link a given SR path is
SID stack depth of a path computed doesn't exceed the number of SIDs applied so as to insure that the SID stack depth of a computed path
the node is capable of imposing. This document describes how to use doesn't exceed the number of SIDs the node is capable of imposing.
OSPF to signal the MSD of a node or link to a centralized controller.
PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD
in SR PCE Capability TLV and METRIC Object. However, if PCEP is not in SR PCE Capability TLV and METRIC Object. However, if PCEP is not
supported/configured on the head-end of a SR tunnel or a Binding-SID supported/configured on the head-end of a SR tunnel or a Binding-SID
anchor node and controller does not participate in IGP routing, it anchor node and controller does not participate in IGP routing, it
has no way to learn the MSD of nodes and links which has been has no way to learn the MSD of nodes and links which has been
configured. BGP-LS [RFC7752] defines a way to expose topology and configured. BGP-LS [RFC7752] defines a way to expose topology and
associated attributes and capabilities of the nodes in that topology associated attributes and capabilities of the nodes in that topology
to a centralized controller. MSD signaling by BGP-LS has been to a centralized controller. MSD signaling by BGP-LS has been
defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically,
BGP-LS is configured on a small number of nodes, that do not BGP-LS is configured on a small number of nodes, that do not
necessarily act as head-ends. In order, for BGP-LS to signal MSD for necessarily act as head-ends. In order, for BGP-LS to signal MSD for
the all nodes and links in the network MSD is relevant, MSD all the nodes and links in the network MSD is relevant, MSD
capabilites SHOULD be distributed to every OSPF router in the capabilites should be advertised to every OSPF router in the network.
network.
Other types of MSD are known to be useful. For example,
[I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability [I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability
(RLDC) that is used by a head-end to insert Entropy Label (EL) at (RLDC) that is used by a head-end to insert Entropy Label (EL) at
appropriate depth, so it could be read by transit nodes. MSD in appropriate depth, so it could be read by transit nodes.
contrary signals ability to impose SID's stack of a particular depth.
MSD of type 1 (IANA Registry), called Base MSD is used to signal the This document defines an extension to OSPF used to advertise one or
total number of SIDs a node is capable of imposing, to be used by a more types of MSD at node and/or link granularity. It also creates
path computation element/controller. In case, there are additional an IANA registry for assigning MSD type identifiers. It also defines
SIDs (e.g. service) that are to be imposed to the stack - this would one MSD type called Base MPLS Imposition MSD. In the future it is
be signaled with an another MSD type (TBD), no adjustment to the Base expected that new MSD types will be defined to signal additional
MSD should be made. In the future, new MSD types could be defined to capabilities e.g., entropy labels, SIDs that can be imposed through
signal additional capabilities: entropy labels, SIDs that can be recirculation, or SIDs associated with another dataplane e.g., IPv6.
imposed thru recirculation, or another dataplane e.g. IPv6.
1.1. Conventions used in this document 1.1. Conventions used in this document
1.1.1. Terminology 1.1.1. Terminology
BGP-LS: Distribution of Link-State and TE Information using Border BGP-LS: Distribution of Link-State and TE Information using Border
Gateway Protocol Gateway Protocol
BMI: Base MPLS Imposition is the number of MPLS labels which can be
imposed inclusive of any service/transport labels
OSPF: Open Shortest Path First OSPF: Open Shortest Path First
MSD: Maximum SID Depth MSD: Maximum SID Depth - the number of SIDs a node or a link on a
node can support
PCC: Path Computation Client PCC: Path Computation Client
PCE: Path Computation Element PCE: Path Computation Element
PCEP: Path Computation Element Protocol PCEP: Path Computation Element Protocol
SID: Segment Identifier SID: Segment Identifier
SR: Segment routing SR: Segment Routing
1.2. Requirements Language 1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Terminology 2. Terminology
This memo makes use of the terms defined in [RFC4970]. This memo makes use of the terms defined in [RFC4970].
skipping to change at page 5, line 46 skipping to change at page 5, line 46
Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD
of the router originating the corresponding LSA as specified for of the router originating the corresponding LSA as specified for
OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0 OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0
represents lack of the ability to impose MSD stack of any depth; any represents lack of the ability to impose MSD stack of any depth; any
other value represents that of the particular link MSD value. other value represents that of the particular link MSD value.
Other Sub-types other than defined above are reserved for future Other Sub-types other than defined above are reserved for future
extensions. extensions.
5. Node MSD vs Link MSD conflict resolution 5. Using Node and Link MSD Advertisements
When both Node MSD and Link MSD are present, the value in the Link When Link MSD is present for a given MSD type, the value of the Link
MSD MUST be used. MSD MUST be used in preference to the Node MSD.
6. IANA Considerations The meaning of the absence of both Node and Link MSD advertisements
for a given MSD type is specific to the MSD type. Generally it can
only be inferred that the advertising node does not support
advertisement of that MSD type. However, in some cases the lack of
advertisement might imply that the functionality associated with the
MSD type is not supported. The correct interpretation MUST be
specified when an MSD type is defined.
6. Base MPLS Imposition MSD
Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS
labels a node is capable of imposing, including any service/transport
labels.
Absence of BMI-MSD advertisements indicates only that the advertising
node does not support advertisement of this capability.
7. IANA Considerations
This document includes a request to IANA to allocate TLV type codes This document includes a request to IANA to allocate TLV type codes
for the new TLV proposed in Section 3 of this document from OSPF for the new TLV proposed in Section 3 of this document from OSPF
Router Information (RI) TLVs Registry as defined by [RFC4970]. For Router Information (RI) TLVs Registry as defined by [RFC4970]. For
the link MSD, we request IANA to allocate new sub-TLV codes as the link MSD, we request IANA to allocate new sub-TLV codes as
proposed in Section 4 from OSPFv2 Extended Link TLV Sub-TLVs registry proposed in Section 4 from OSPFv2 Extended Link TLV Sub-TLVs registry
and from Router-Link TLV defined in OSPFv3 Extend-LSA Sub-TLV and from Router-Link TLV defined in OSPFv3 Extend-LSA Sub-TLV
registry. registry.
This document also requests IANA to create a new Sub-type registry as This document requests creation of a new IANA managed registry under
proposed in Section 3, Section 4. a new category of "Interior Gateway Protocol (IGP) Parameters" IANA
registries to identify MSD types as proposed in Section 3, Section 4.
The registration procedure is "Expert Review" as defined in
[RFC8126]. Suggested registry name is "MSD types". Types are an
unsigned 8 bit number. The following values are defined by this
document
Value Name Reference Value Name Reference
----- --------------------- ------------- ----- --------------------- -------------
0 Reserved This document 0 Reserved This document
1 Base MSD This document 1 Base MPLS Imposition MSD This document
2-250 Unassigned This document 2-250 Unassigned This document
251-254 Experimental This document 251-254 Experimental This document
255 Reserved This document 255 Reserved This document
Figure 3: MSD Sub-type Codepoints Registry Figure 3: MSD Types Codepoints Registry
7. Security Considerations 8. Security Considerations
This document describes a mechanism to signal Segment Routing MSD Security considerations, as specified by [RFC7770] are applicable to
supported at node and/or link granularity through OSPF LSA's and does this document
not introduce any new security issues.
8. Contributors 9. Contributors
The following people contributed to this document: The following people contributed to this document:
Les Ginsberg Les Ginsberg
Email: ginsberg@cisco.com Email: ginsberg@cisco.com
9. Acknowledgements 10. Acknowledgements
The authors would like to thank Stephane Litkowski and Bruno Decraene The authors would like to thank Stephane Litkowski and Bruno Decraene
for their reviews and valuable comments. for their reviews and valuable comments.
10. References 11. References
10.1. Normative References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
2007, <https://www.rfc-editor.org/info/rfc4970>. 2007, <https://www.rfc-editor.org/info/rfc4970>.
10.2. Informative References [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>.
11.2. Informative References
[I-D.ietf-idr-bgp-ls-segment-routing-msd] [I-D.ietf-idr-bgp-ls-segment-routing-msd]
Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
"Signaling Maximum SID Depth using Border Gateway Protocol "Signaling Maximum SID Depth using Border Gateway Protocol
Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01
(work in progress), October 2017. (work in progress), October 2017.
[I-D.ietf-ospf-mpls-elc] [I-D.ietf-ospf-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability Using Litkowski, "Signaling Entropy Label Capability and
OSPF", draft-ietf-ospf-mpls-elc-04 (work in progress), Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
November 2016. mpls-elc-05 (work in progress), January 2018.
[I-D.ietf-ospf-ospfv3-lsa-extend] [I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Roy, A., Goethals, D., Vallem, V., and F. Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3- Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
lsa-extend-18 (work in progress), November 2017. lsa-extend-23 (work in progress), January 2018.
[I-D.ietf-pce-segment-routing] [I-D.ietf-pce-segment-routing]
Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "PCEP Extensions for Segment Routing", and J. Hardwick, "PCEP Extensions for Segment Routing",
draft-ietf-pce-segment-routing-11 (work in progress), draft-ietf-pce-segment-routing-11 (work in progress),
November 2017. November 2017.
[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
R. Aggarwal, "Support of Address Families in OSPFv3", R. Aggarwal, "Support of Address Families in OSPFv3",
RFC 5838, DOI 10.17487/RFC5838, April 2010, RFC 5838, DOI 10.17487/RFC5838, April 2010,
skipping to change at page 8, line 11 skipping to change at page 8, line 38
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>. 2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752, Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016, DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>. <https://www.rfc-editor.org/info/rfc7752>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
Authors' Addresses Authors' Addresses
Jeff Tantsura Jeff Tantsura
Individual Nuage Networks
Email: jefftant.ietf@gmail.com Email: jefftant.ietf@gmail.com
Uma Chunduri Uma Chunduri
Huawei Technologies Huawei Technologies
Email: uma.chunduri@huawei.com Email: uma.chunduri@huawei.com
Sam Aldrin Sam Aldrin
Google, Inc Google, Inc
Email: aldrin.ietf@gmail.com Email: aldrin.ietf@gmail.com
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