OSPF Working Group J. Tantsura
Internet-Draft Nuage Networks
Intended status: Standards Track U. Chunduri
Expires: October 7, 2018 Huawei Technologies
S. Aldrin
Google, Inc
P. Psenak
Cisco Systems
April 05, 2018
Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-10
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 can be
supported 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) that can be imposed at each node/link a given SR path to
insure that the SID stack depth of a computed path doesn't exceed the
number of SIDs the node is capable of imposing.
The 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 an 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
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not 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 an Entropy Label (EL) at
a depth that can 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 laso defines
the Base MPLS Imposition MSD type. 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 that 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 one of its
links 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", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
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BCP14 [RFC2119], [RFC8174] when, and only when they appear in all
capitals, as shown here .
2. Terminology
This memo makes use of the terms defined in [RFC4970].
3. Node MSD TLV
The node MSD TLV within the body of the OSPF RI Opaque LSA is defined
to carry the provisioned SID depth of the router originating the RI
LSA. Node MSD is the minimum 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: TBD1
Length: variable (minimum of 2, multiple of 2 octets) and represents
the total length of value field.
Value: 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 minimum value supported by a
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
Type:
For OSPFv2, the Link level MSD value is advertised as an optional
Sub-TLV of the OSPFv2 Extended Link TLV as defined in [RFC7684], and
has value of TBD2.
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 TBD3.
Length: variable and similar to what is defined in Section 3.
Value: 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 take preference over the Node MSD.
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
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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
The 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 solely that the
advertising node does not support advertisement of this capability.
7. IANA Considerations
This document requests IANA to allocate TLV type (TBD1) from the OSPF
Router Information (RI) TLVs Registry as defined by [RFC4970]. IANA
has allocated the value 12 through the early assignment process.
Also, this document requests IANA to allocate a sub-TLV type (TBD2)
from the OSPFv2 Extended Link TLV Sub-TLVs registry. IANA has
allocated the the value 6 through the early assignment process.
Finally, this document requests IANA to allocate a sub-TLV type
(TBD3) from the OSPFv3 Extended-LSA Sub-TLV registry.
This document requests creation of an 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]. The 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 Acee Lindem, 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>.
[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>.
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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