Internet DRAFT - draft-tantsura-ospf-segment-routing-msd
draft-tantsura-ospf-segment-routing-msd
OSPF Working Group J. Tantsura
Internet-Draft U. Chunduri
Intended status: Standards Track Ericsson
Expires: September 9, 2016 March 8, 2016
Signaling MSD (Maximum SID Depth) using OSPF
draft-tantsura-ospf-segment-routing-msd-00
Abstract
This document proposes a way to expose Maximum SID Depth (MSD)
supported by a node at node and/or link level by an OSPF Router. In
a Segment Routing (SR) enabled network a centralized controller that
programs SR tunnels at the head-end node needs to know the MSD
information at node level and/or link level to push the label stack
of an appropriate depth . Here the term OSPF means both OSPFv2 and
OSPFv3.
Status of This Memo
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 3
4. LINK MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
When Segment Routing tunnels are computed by a centralized
controller, it is crucial that the controller knows the MSD "Maximum
SID Depth" of the node or link SR tunnel exits over, so it doesn't
download a path with SID (label stack) of a depth more than the node
or link used is capable of imposing. This document describes how to
use OSPF to expose the MSD of the node or link to a centralized
controller.
PCEP SR extensions [I-D.ietf-pce-segment-routing] has defined MSD, to
signal in SR PCE Capability TLV, METRIC Object. However, If PCEP is
not supported by a node (head-end of the SR tunnel) and controller
does not participate in IGP routing it has no way to learn the MSD of
the node or link configured. BGP-LS [I-D.ietf-idr-ls-distribution]
defines a way to expose topology and associated different attributes,
capabilities of the nodes in that topology to a centralized
controller and MSD has been defined in
[I-D.tantsura-bgp-ls-segment-routing-msd]. For this information to
be advertised by BGP for the all nodes and links of the network,
where this is provisioned, OSPF module should have this information
in the LSDB.
[I-D.ietf-ospf-mpls-elc] defines, RLSDC which indicates how many
labels a node can read to take a decision to insert an Entropy Label
(EL) and is different than how many labels a node can push as defined
by MSD in this draft.
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1.1. Conventions used in this document
1.1.1. Terminology
BGP-LS: Distribution of Link-State and TE Information using Border
Gateway Protocol
OSPF: Open Shortest Path First
MSD: Maximum SID Depth
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].
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.
The Type (2 bytes) of this TLV is TBD.
Length is 2 bytes, and
the Value field contains MSD of the router originating the RI LSA.
Node MSD is a number in the range of 0-254. 0 represents lack of the
ability to push MSD of any depth; any other value represents that of
the node. This value SHOULD represent the lowest value supported by
node.
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This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is
optional. The scope of the advertisement is specific to the
deployment.
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.
The Type (2 bytes) of this TLV is TBD.
Length is 2 bytes, and
the Value field contains Link MSD of the router originating the
corresponding LSA as specified for OSPFv3 and OSPFv3. Link MSD is a
number in the range of 0-254. 0 represents lack of the ability to
push MSD of any depth; any other value represents that of the
particular link MSD value.
For OSPFv2, the Link level MSD value is advertised as an optional
Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684].
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].
5. Acknowledgements
TBD
6. 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]. Also
for link MSD, we request IANA to allocate new sub-TLV codes as
proposed in Section 4 from OSPFv2 Extended Link Opaque LSAs Extended
Link TLV registry and from Router-Link TLV defined in OSPFv3 Extend-
LSA Sub-TLV registry.
7. Security Considerations
This document describes a mechanism for advertising Segment Routing
SID depth supported at node and link level information through OSPF
LSAs and does not introduce any new security issues.
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8. References
8.1. 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,
<http://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, <http://www.rfc-editor.org/info/rfc4970>.
8.2. Informative References
[I-D.ietf-idr-ls-distribution]
Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
Ray, "North-Bound Distribution of Link-State and TE
Information using BGP", draft-ietf-idr-ls-distribution-13
(work in progress), October 2015.
[I-D.ietf-ospf-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability Using
OSPF", draft-ietf-ospf-mpls-elc-01 (work in progress),
November 2015.
[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-09
(work in progress), November 2015.
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,
Lopez, V., Tantsura, J., Henderickx, W., and J. Hardwick,
"PCEP Extensions for Segment Routing", draft-ietf-pce-
segment-routing-06 (work in progress), August 2015.
[I-D.tantsura-bgp-ls-segment-routing-msd]
Tantsura, J., Mirsky, G., Sivabalan, S., and U. Chunduri,
"Signaling Maximum SID Depth using Border Gateway Protocol
Link-State", draft-tantsura-bgp-ls-segment-routing-msd-02
(work in progress), January 2016.
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[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,
<http://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, <http://www.rfc-editor.org/info/rfc7684>.
Authors' Addresses
Jeff Tantsura
Ericsson
Email: jeff.tantsura@ericsson.com
Uma Chunduri
Ericsson
Email: uma.chunduri@ericsson.com
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