draft-ietf-ospf-segment-routing-msd-11.txt   draft-ietf-ospf-segment-routing-msd-12.txt 
OSPF Working Group J. Tantsura OSPF Working Group J. Tantsura
Internet-Draft Nuage Networks Internet-Draft Nuage Networks
Intended status: Standards Track U. Chunduri Intended status: Standards Track U. Chunduri
Expires: November 8, 2018 Huawei Technologies Expires: November 10, 2018 Huawei Technologies
S. Aldrin S. Aldrin
Google, Inc Google, Inc
P. Psenak P. Psenak
Cisco Systems Cisco Systems
May 07, 2018 May 09, 2018
Signaling MSD (Maximum SID Depth) using OSPF Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-11 draft-ietf-ospf-segment-routing-msd-12
Abstract Abstract
This document defines a way for an OSPF Router to advertise multiple This document defines a way for an OSPF Router to advertise multiple
types of supported Maximum SID Depths (MSDs) at node and/or link types of supported Maximum SID Depths (MSDs) at node and/or link
granularity. Such advertisements allow entities (e.g., centralized granularity. Such advertisements allow entities (e.g., centralized
controllers) to determine whether a particular SID stack can be controllers) to determine whether a particular SID stack can be
supported in a given network. This document defines only one type of supported in a given network. This document defines only one type of
MSD, but defines an encoding that can support other MSD types. Here MSD, but defines an encoding that can support other MSD types. Here
the term OSPF means both OSPFv2 and OSPFv3. the term OSPF means both OSPFv2 and OSPFv3.
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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
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 8, 2018. This Internet-Draft will expire on November 10, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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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 . . . . . . . . . . . . . . . . . . 4 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
3. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5 3. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5
4. Using Node and Link MSD Advertisements . . . . . . . . . . . 6 4. Using Node and Link MSD Advertisements . . . . . . . . . . . 6
5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6 5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 7 10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 8 10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
When Segment Routing(SR) paths are computed by a centralized When Segment Routing(SR) paths are computed by a centralized
controller, it is critical that the controller learns the Maximum SID controller, it is critical that the controller learns the Maximum SID
Depth(MSD) that can be imposed at each node/link on a given SR path Depth(MSD) that can be imposed at each node/link on a given SR path
to insure that the SID stack depth of a computed path doesn't exceed 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 number of SIDs the node is capable of imposing.
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| MSD Type and Value ... | MSD Type and Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 1: Node MSD TLV Figure 1: Node MSD TLV
The Type: TBD1 The Type: TBD1
Length: variable (minimum of 2, multiple of 2 octets) and represents Length: variable (minimum of 2, multiple of 2 octets) and represents
the total length of value field. the total length of value field.
Value: consists of one or more pairs of a 1 octet sub-type (IANA Value: consists of one or more pairs of a 1 octet type (IANA
Registry) and 1 octet value. Registry) and 1 octet value.
MSD Type 1 (IANA Section), MSD and the Value field contains the MSD MSD Type 1 (IANA Section), MSD and the Value field contains the MSD
of the originating router. Node MSD is a number in the range of of the originating router. Node MSD is a number in the range of
0-255. 0 represents lack of the ability to impose MSD stack of any 0-255. 0 represents lack of the ability to impose MSD stack of any
depth; any other value represents that of the node. This value depth; any other value represents that of the node. This value
SHOULD represent the minimum value supported by a node. SHOULD represent the minimum value supported by a node.
Other MSD Types are reserved for future extensions. Other MSD Types are reserved for future extensions.
This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is
optional. The scope of the advertisement is specific to the optional. The scope of the advertisement is specific to the
deployment. deployment.
When multiple Node MSD TLVs are received from a given router, the
receiver MUST use the first occurrence of the TLV in the Router
Information LSA. If the Node MSD TLV appears in multiple Router
Information LSAs that have different flooding scopes, the Node MSD
TLV in the Router Information LSA with the area-scoped flooding scope
MUST be used. If the Node MSD TLV appears in multiple Router
Information LSAs that have the same flooding scope, the Node MSD TLV
in the Router Information (RI) LSA with the numerically smallest
Instance ID MUST be used and subsequent instances of the Node MSD TLV
MUST be ignored. The RI LSA can be advertised at any of the defined
opaque flooding scopes (link, area, or Autonomous System (AS)). For
the purpose of Node MSD TLV advertisement, area-scoped flooding is
REQUIRED.
3. Link MSD sub-TLV 3. Link MSD sub-TLV
The link sub-TLV is defined to carry the MSD of the interface The link sub-TLV is defined to carry the MSD of the interface
associated with the link. MSD values may be learned via a hardware associated with the link. MSD values may be learned via a hardware
API or may be provisioned. API or may be provisioned.
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Registry) and 1 octet value. Registry) and 1 octet value.
MSD Type 1 (IANA Section), MSD and the Value field contains Link MSD MSD 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 0-255. 0 OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-255. 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 MSD Types are reserved for future extensions. Other MSD Types are reserved for future extensions.
If these TLVs are advertised multiple times, only the first instance If this TLV is advertised multiple times in the same OSPFv2 Extended
of the TLV is used by receiving OSPF routers. This situation SHOULD Link Opaque LSA, only the first instance of the TLV is used by
be logged as an error. receiving OSPFv2 routers. This situation SHOULD be logged as an
error.
If these TLV is advertised multiple times for the same link in If this TLV is advertised multiple times for the same link in
different LSAs originated by the same OSPF router, the TLV with the different OSPFv2 Extended Link Opaque LSAs originated by the same
smallest Opaque ID/Link State ID is used by receiving OSPF routers. OSPFv2 router, the OSPFv2 Extended Link TLV in the OSPFv2 Extended
This situation MAY be logged as a warning. Link Opaque LSA with the smallest Opaque ID is used by receiving
OSPFv2 routers. This situation may be logged as a warning.
4. Using Node and Link MSD Advertisements 4. Using Node and Link MSD Advertisements
When Link MSD is present for a given MSD type, the value of the Link When Link MSD is present for a given MSD type, the value of the Link
MSD MUST take preference over the Node MSD. When a Link MSD type is MSD MUST take preference over the Node MSD. When a Link MSD type is
not signalled but the Node MSD type is, then the value of that Link not signalled but the Node MSD type is, then the value of that Link
MSD type MUST be considered as the corresponding Node MSD type value. MSD type MUST be considered as the corresponding Node MSD type value.
In order to increase flooding efficiency, it is RECOMMENDED, that In order to increase flooding efficiency, it is RECOMMENDED, that
routers with homogenous link MSD values advertise just the Node MSD routers with homogenous link MSD values advertise just the Node MSD
value. value.
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for a given MSD type is specific to the MSD type. Generally it can for a given MSD type is specific to the MSD type. Generally it can
only be inferred that the advertising node does not support only be inferred that the advertising node does not support
advertisement of that MSD type. However, in some cases the lack of advertisement of that MSD type. However, in some cases the lack of
advertisement might imply that the functionality associated with the advertisement might imply that the functionality associated with the
MSD type is not supported. The correct interpretation MUST be MSD type is not supported. The correct interpretation MUST be
specified when an MSD type is defined. specified when an MSD type is defined.
5. Base MPLS Imposition MSD 5. Base MPLS Imposition MSD
The Base MPLS Imposition MSD (BMI-MSD) signals the total number of The Base MPLS Imposition MSD (BMI-MSD) signals the total number of
MPLS labels a node is capable of imposing, including any service/ MPLS labels a node is capable of imposing, including all
transport labels. service/transport/special labels.
Absence of BMI-MSD advertisements indicates solely that the Absence of BMI-MSD advertisements indicates solely that the
advertising node does not support advertisement of this capability. advertising node does not support advertisement of this capability.
6. IANA Considerations 6. IANA Considerations
This document requests IANA to allocate TLV type (TBD1) from the OSPF This document requests IANA to allocate TLV type (TBD1) from the OSPF
Router Information (RI) TLVs Registry as defined by [RFC4970]. IANA Router Information (RI) TLVs Registry as defined by [RFC4970]. IANA
has allocated the value 12 through the early assignment process. has allocated the value 12 through the early assignment process.
Also, this document requests IANA to allocate a sub-TLV type (TBD2) Also, this document requests IANA to allocate a sub-TLV type (TBD2)
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0 Reserved This document 0 Reserved This document
1 Base MPLS Imposition 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 Types Codepoints Registry Figure 3: MSD Types Codepoints Registry
7. Security Considerations 7. Security Considerations
Security concerns for OSPF are addressed in [RFC7474] and [RFC5310]. Security concerns for OSPF are addressed in [RFC7474]. Further
Further security analysis for OSPF protocol is done in [RFC6853] security analysis for OSPF protocol is done in [RFC6863] including
including analysis of both the above documents. Security analysis of both the above documents. Security considerations, as
considerations, as specified by [RFC7770] are applicable to this specified by [RFC7770], [RFC7684] and [RFC8362] are applicable to
document. this document.
Advertisement of the additional information defined in this document Advertisement of an incorrect MSD value may result: in a path
that is false, e.g. MSD that is incorrect may result: in a path
computation failing and the service unavailable or instantiation of a computation failing and the service unavailable or instantiation of a
path that can't be supported by the head-end (the node performing the path that can't be supported by the head-end (the node performing the
imposition). imposition).
8. Contributors 8. 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 9. Acknowledgements
The authors would like to thank Acee Lindem, Stephane Litkowski and The authors would like to thank Acee Lindem, Ketan Talaulikar,
Bruno Decraene for their reviews and valuable comments. Stephane Litkowski and Bruno Decraene for their reviews and valuable
comments.
10. References 10. References
10.1. Normative References 10.1. 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>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<https://www.rfc-editor.org/info/rfc7474>.
[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>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and [RFC7770] 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 7770, DOI 10.17487/RFC7770, Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>. February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
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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,
<https://www.rfc-editor.org/info/rfc5838>. <https://www.rfc-editor.org/info/rfc5838>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., [RFC6863] Hartman, S. and D. Zhang, "Analysis of OSPF Security
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute According to the Keying and Authentication for Routing
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November Protocols (KARP) Design Guide", RFC 6863,
2015, <https://www.rfc-editor.org/info/rfc7684>. DOI 10.17487/RFC6863, March 2013,
<https://www.rfc-editor.org/info/rfc6863>.
[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 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
 End of changes. 17 change blocks. 
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