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Versions: (draft-tantsura-ospf-segment-routing-msd)
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24 25 RFC 8476
OSPF Working Group J. Tantsura
Internet-Draft Individual
Intended status: Standards Track U. Chunduri
Expires: December 6, 2017 Huawei Technologies
S. Aldrin
Google, Inc
P. Psenak
Cisco Systems
June 04, 2017
Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-05
Abstract
This document proposes a way to signal Maximum SID Depth (MSD)
supported by a node at node and/or link granularity by an OSPF
Router. In a Segment Routing (SR) enabled network a centralized
controller that programs SR tunnels needs to know the MSD supported
by the head-end at node and/or link granularity to push the SID stack
of an appropriate depth. MSD is relevant to the head-end of a SR
tunnel or Binding-SID anchor node where Binding-SID expansions might
result in creation of a new SID stack. Here the term OSPF means both
OSPFv2 and OSPFv3.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 6, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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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. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
When Segment Routing tunnels are computed by a centralized
controller, it is critical that the controller learns the MSD
"Maximum SID Depth" of the node or link SR tunnel exits over, so the
SID stack depth of a path computed doesn't exceed the number of SIDs
the node is capable of imposing. This document describes how to use
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
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.tantsura-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
the all nodes and links in the network MSD is relevant, MSD
capabilites SHOULD be distributed to every OSPF router in the
network.
[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. MSD in
contrary signals ability to push SID's stack of a particular depth.
MSD of type 1 (IANA Registry), called Base MSD is used to signal the
total number of SIDs a node is capable of imposing, to be used by a
path computation element/controller. In case, there are additional
labels (e.g. service) that are to be pushed to the stack - this would
be signaled with an another MSD type (TBD), no adjustment to the Base
MSD should be made. In the future, new MSD types could be defined to
signal additional capabilities: entropy labels, labels that can be
pushed thru recirculation, or 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
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].
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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 is 12 (Suggested value - to be
assigned by IANA).
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
push MSD 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 the
value is 5 (Suggested value - to be assigned by IANA)
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 the value is 3 (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 push MSD 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. Node MSD vs Link MSD conflict resolution
When both Node MSD and Link MSD are present, the value in the Link
MSD MUST be used.
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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.
This document also request IANA to create a new Sub-type registry as
proposed in Section 3, Section 4.
Value Name Reference
----- --------------------- -------------
0 Reserved This document
1 Base MSD This document
2-250 Unassigned This document
251-254 Experimental This document
255 Reserved This document
Figure 3: MSD Sub-type Codepoints Registry
7. Security Considerations
This document describes a mechanism to signal Segment Routing MSD
supported at node and/or link granularity through OSPF LSA's and does
not introduce any new security issues.
8. Contributors
The following people contributed to this document:
Les Ginsberg
Email: ginsberg@cisco.com
9. Acknowledgements
The authors would like to thank Stephane Litkowski and Bruno Decraene
for their reviews and valuable comments.
10. References
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10.1. 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>.
10.2. Informative References
[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-04 (work in progress),
November 2016.
[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-14 (work in progress), April 2017.
[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-09 (work in progress),
April 2017.
[I-D.tantsura-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-tantsura-idr-bgp-ls-segment-routing-
msd-04 (work in progress), March 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,
<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>.
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[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,
<http://www.rfc-editor.org/info/rfc7752>.
Authors' Addresses
Jeff Tantsura
Individual
Email: jefftant.ietf@gmail.com
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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