OSPF Working Group J. Tantsura
Internet-Draft Nuage Networks
Intended status: Standards Track U. Chunduri
Expires: August 30, 2018 Huawei Technologies
S. Aldrin
Google, Inc
P. Psenak
Cisco Systems
February 26, 2018
Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-09
Abstract
This document defines a way for an OSPF Router to advertise multiple
types of supported Maximum SID Depths (MSDs) at node and/or link
granularity. Such advertisements allow entities (e.g., centralized
controllers) to determine whether a particular SID stack is
supportable in a given network. This document only defines one type
of MSD (maximum label imposition) - but defines an encoding which can
support other MSD types. Here the term OSPF means both OSPFv2 and
OSPFv3.
Status of This Memo
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5
5. Using Node and Link MSD Advertisements . . . . . . . . . . . 5
6. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
When Segment Routing(SR) paths are computed by a centralized
controller, it is critical that the controller learns the Maximum SID
Depth(MSD) which can be imposed at the node/link a given SR path is
applied so as to insure that the SID stack depth of a computed path
doesn't exceed the number of SIDs the node is capable of imposing.
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
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
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
associated attributes and capabilities of the nodes in that topology
to a centralized controller. MSD signaling by BGP-LS has been
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
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necessarily act as head-ends. In order, for BGP-LS to signal MSD for
all the nodes and links in the network MSD is relevant, MSD
capabilites should be advertised to every OSPF router in the network.
Other types of MSD are known to be useful. For example,
[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
appropriate depth, so it could be read by transit nodes.
This document defines an extension to OSPF used to advertise one or
more types of MSD at node and/or link granularity. It also creates
an IANA registry for assigning MSD type identifiers. It also defines
one MSD type called Base MPLS Imposition MSD. In the future it is
expected that new MSD types will be defined to signal additional
capabilities e.g., entropy labels, SIDs that can be imposed through
recirculation, or SIDs associated with another dataplane e.g., IPv6.
1.1. Conventions used in this document
1.1.1. Terminology
BGP-LS: Distribution of Link-State and TE Information using Border
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
MSD: Maximum SID Depth - the number of SIDs a node or a link on a
node can support
PCC: Path Computation Client
PCE: Path Computation Element
PCEP: Path Computation Element Protocol
SID: Segment Identifier
SR: Segment Routing
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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2. Terminology
This memo makes use of the terms defined in [RFC4970].
3. Node MSD TLV
A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD
TLV is defined to carry the provisioned SID depth of the router
originating the RI LSA. Node MSD is the lowest MSD supported by the
node.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type and Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 1: Node MSD TLV
The Type (2 bytes) of this TLV has value of 12.
Length is variable (minimum of 2, multiple of 2 octets) and
represents the total length of value field.
Value field consists of a 1 octet sub-type (IANA Registry) and 1
octet value.
Sub-Type 1 (IANA Section), MSD and the Value field contains maximum
MSD of the router originating the RI LSA. Node Maximum MSD is a
number in the range of 0-254. 0 represents lack of the ability to
impose MSD stack of any depth; any other value represents that of the
node. This value SHOULD represent the lowest value supported by
node.
Other Sub-types other than defined above are reserved for future
extensions.
This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is
optional. The scope of the advertisement is specific to the
deployment.
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4. Link MSD sub-TLV
A new sub-TLV called Link MSD sub-TLV is defined to carry the
provisioned SID depth of the interface associated with the link.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type and Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 2: Link MSD Sub-TLV
The Type (2 bytes) of this TLV:
For OSPFv2, the Link level MSD value is advertised as an optional
Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684], and has
value of 6.
For OSPFv3, the Link level MSD value is advertised as an optional
Sub-TLV of the Router-Link TLV as defined in
[I-D.ietf-ospf-ospfv3-lsa-extend], and has value of 16 (Suggested
value - to be assigned by IANA).
Length is variable and similar to what is defined in Section 3.
Value field consists of a 1 octet sub-type (IANA Registry) and 1
octet value.
Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD
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
represents lack of the ability to impose MSD stack of any depth; any
other value represents that of the particular link MSD value.
Other Sub-types other than defined above are reserved for future
extensions.
5. Using Node and Link MSD Advertisements
When Link MSD is present for a given MSD type, the value of the Link
MSD MUST be used in preference to the Node MSD.
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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
for the new TLV proposed in Section 3 of this document from OSPF
Router Information (RI) TLVs Registry as defined by [RFC4970]. For
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
and from Router-Link TLV defined in OSPFv3 Extend-LSA Sub-TLV
registry.
This document requests creation of a new IANA managed registry under
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
----- --------------------- -------------
0 Reserved This document
1 Base MPLS Imposition MSD This document
2-250 Unassigned This document
251-254 Experimental This document
255 Reserved This document
Figure 3: MSD Types Codepoints Registry
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8. Security Considerations
Security considerations, as specified by [RFC7770] are applicable to
this document
9. Contributors
The following people contributed to this document:
Les Ginsberg
Email: ginsberg@cisco.com
10. Acknowledgements
The authors would like to thank Stephane Litkowski and Bruno Decraene
for their reviews and valuable comments.
11. References
11.1. 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>.
[RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
2007, <https://www.rfc-editor.org/info/rfc4970>.
[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]
Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
"Signaling Maximum SID Depth using Border Gateway Protocol
Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01
(work in progress), October 2017.
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[I-D.ietf-ospf-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability and
Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
mpls-elc-05 (work in progress), January 2018.
[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
lsa-extend-23 (work in progress), January 2018.
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "PCEP Extensions for Segment Routing",
draft-ietf-pce-segment-routing-11 (work in progress),
November 2017.
[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
R. Aggarwal, "Support of Address Families in OSPFv3",
RFC 5838, DOI 10.17487/RFC5838, April 2010,
<https://www.rfc-editor.org/info/rfc5838>.
[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>.
[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
Jeff Tantsura
Nuage Networks
Email: jefftant.ietf@gmail.com
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Uma Chunduri
Huawei Technologies
Email: uma.chunduri@huawei.com
Sam Aldrin
Google, Inc
Email: aldrin.ietf@gmail.com
Peter Psenak
Cisco Systems
Email: ppsenak@cisco.com
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