draft-ietf-ospf-segment-routing-msd-18.txt   draft-ietf-ospf-segment-routing-msd-19.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: March 1, 2019 Huawei Technologies Expires: March 4, 2019 Huawei Technologies
S. Aldrin S. Aldrin
Google, Inc Google, Inc
P. Psenak P. Psenak
Cisco Systems Cisco Systems
August 28, 2018 August 31, 2018
Signaling MSD (Maximum SID Depth) using OSPF Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-18 draft-ietf-ospf-segment-routing-msd-19
Abstract Abstract
This document defines a way for an Open Shortest Path First (OSPF) This document defines a way for an Open Shortest Path First (OSPF)
Router to advertise multiple types of supported Maximum SID Depths Router to advertise multiple types of supported Maximum SID Depths
(MSDs) at node and/or link granularity. Such advertisements allow (MSDs) at node and/or link granularity. Such advertisements allow
entities (e.g., centralized controllers) to determine whether a entities (e.g., centralized controllers) to determine whether a
particular SID stack can be supported in a given network. This particular SID stack can be supported in a given network. This
document defines only one type of MSD, but defines an encoding that document defines only one type of MSD, but defines an encoding that
can support other MSD types. Here the term OSPF means both OSPFv2 can support other MSD types. Here the term OSPF means both OSPFv2
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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-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
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 March 1, 2019. This Internet-Draft will expire on March 4, 2019.
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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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 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. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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.
Path Computation Element Protocol(PCEP) SR draft Path Computation Element Protocol(PCEP) SR draft
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supported/configured on the head-end of an SR tunnel or a Binding-SID 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 anchor node and controller does not participate in IGP routing, it
has no way to learn the MSD of nodes and links. BGP-LS (Distribution has no way to learn the MSD of nodes and links. BGP-LS (Distribution
of Link-State and TE Information using Border Gateway Protocol) of Link-State and TE Information using Border Gateway Protocol)
[RFC7752] defines a way to expose topology and associated attributes [RFC7752] defines a way to expose topology and associated attributes
and capabilities of the nodes in that topology to a centralized and capabilities of the nodes in that topology to a centralized
controller. MSD signaling by BGP-LS has been defined in controller. MSD signaling by BGP-LS has been defined in
[I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is
configured on a small number of nodes that do not necessarily act as configured on a small number of nodes that do not necessarily act as
head-ends. In order for BGP-LS to signal MSD for all the nodes and head-ends. In order for BGP-LS to signal MSD for all the nodes and
links in the network MSD is relevant, MSD capabilities should be links in the network where MSD is relevant, MSD capabilities should
advertised by every OSPF router in the network. be advertised by every OSPF router in the network.
Other types of MSD are known to be useful. For example, Other types of MSD are known to be useful. For example,
[I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability [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 (RLDC) that is used by a head-end to insert an Entropy Label (EL) at
a depth that can be read by transit nodes. a depth that can be read by transit nodes.
This document defines an extension to OSPF used to advertise one or This document defines an extension to OSPF used to advertise one or
more types of MSD at node and/or link granularity. In the future it more types of MSD at node and/or link granularity. In the future it
is expected, that new MSD types will be defined to signal additional is expected, that new MSD types will be defined to signal additional
capabilities e.g., entropy labels, SIDs that can be imposed through capabilities e.g., entropy labels, SIDs that can be imposed through
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Information LSA. If the Node MSD TLV appears in multiple Router Information LSA. If the Node MSD TLV appears in multiple Router
Information LSAs that have different flooding scopes, the Node MSD Information LSAs that have different flooding scopes, the Node MSD
TLV in the Router Information LSA with the area-scoped flooding scope TLV in the Router Information LSA with the area-scoped flooding scope
MUST be used. If the Node MSD TLV appears in multiple Router MUST be used. If the Node MSD TLV appears in multiple Router
Information LSAs that have the same flooding scope, the Node MSD TLV Information LSAs that have the same flooding scope, the Node MSD TLV
in the Router Information (RI) LSA with the numerically smallest in the Router Information (RI) LSA with the numerically smallest
Instance ID MUST be used and subsequent instances of the Node MSD TLV 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 MUST be ignored. The RI LSA can be advertised at any of the defined
opaque flooding scopes (link, area, or Autonomous System (AS)). For opaque flooding scopes (link, area, or Autonomous System (AS)). For
the purpose of Node MSD TLV advertisement, area-scoped flooding is the purpose of Node MSD TLV advertisement, area-scoped flooding is
REQUIRED. RECOMMENDED.
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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If this sub-TLV is advertised multiple times in the same OSPFv2 If this sub-TLV is advertised multiple times in the same OSPFv2
Extended Link Opaque LSA/E-Router-LSA, only the first instance of the Extended Link Opaque LSA/E-Router-LSA, only the first instance of the
TLV MUST be used by receiving OSPF routers. This situation SHOULD be TLV MUST be used by receiving OSPF routers. This situation SHOULD be
logged as an error. logged as an error.
If this sub-TLV is advertised multiple times for the same link in If this sub-TLV is advertised multiple times for the same link in
different OSPF Extended Link Opaque LSAs/E-Router-LSAs originated by different OSPF Extended Link Opaque LSAs/E-Router-LSAs originated by
the same OSPF router, the OSPFv2 Extended Link TLV in the OSPFv2 the same OSPF router, the OSPFv2 Extended Link TLV in the OSPFv2
Extended Link Opaque LSA with the smallest Opaque ID or in the OSPFv3 Extended Link Opaque LSA with the smallest Opaque ID or in the OSPFv3
E-Router-LSA with the smallest Link State ID is used by receiving E-Router-LSA with the smallest Link State ID MUSR be used by
OSPF routers. This situation MAY be logged as a warning. receiving OSPF 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 Node not signalled but the Node MSD type is, then the value of that Node
MSD type MUST be considered as the corresponding Link MSD type value. MSD type MUST be considered as the corresponding Link 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.
Information received in an MSD advertisements is to to ensure that
the controller learns the Maximum SID Depth (MSD) that can be imposed
at each node/link on a given SR path so that the SID stack depth of a
computed path doesn't exceed the number of SIDs the node is capable
of imposing
The meaning of the absence of both Node and Link MSD advertisements 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 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. IANA Considerations 5. IANA Considerations
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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. IANA Considerations 5. 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 [RFC7770]. IANA Router Information (RI) TLVs Registry as defined by [RFC7770]. 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)
from the OSPFv2 Extended Link TLV Sub-TLVs registry. IANA has from the OSPFv2 Extended Link TLV Sub-TLVs registry. IANA has
allocated the value 6 through the early assignment process. Finally, allocated the value 6 through the early assignment process. Finally,
this document requests IANA to allocate a sub-TLV type (TBD3) from this document requests IANA to allocate a sub-TLV type (TBD3) from
the OSPFv3 Extended-LSA Sub-TLV registry. the OSPFv3 Extended-LSA Sub-TLV registry.
6. Security Considerations 6. Security Considerations
Security concerns for OSPF are addressed in [RFC7474]. Further Security concerns for OSPF are addressed in [RFC7474], [RFC4552] and
security analysis for OSPF protocol is done in [RFC6863] Security [RFC7166]. Further security analysis for OSPF protocol is done in
considerations, as specified by [RFC7770], [RFC7684] and [RFC8362] [RFC6863]. Security considerations, as specified by [RFC7770],
are applicable to this document. [RFC7684] and [RFC8362] are applicable to this document.
Advertisement of an incorrect MSD value may result: in a path Implementations MUST assure that malformed TLV and Sub-TLV defined in
computation failing and the service unavailable or instantiation of a this document are detected and do not provide a vulnerability for
path that can't be supported by the head-end (the node performing the attackers to crash the OSPF router or routing process. Reception of
malformed TLV or Sub-TLV SHOULD be counted and/or logged for further
analysis. Logging of malformed TLVs and Sub-TLVs SHOULD be rate-
limited to prevent a Denial of Service (DoS) attack (distributed or
otherwise) from overloading the OSPF control plane.
Advertisement of an incorrect MSD value may result:
If the value is smaller than supported - path computation failing to
compute a viable path.
If the value is larger than supported - instantiation of a path that
can't be supported by the head-end (the node performing the SID
imposition). imposition).
The MSD discloses capabilities of the nodes (how many SIDs it
supports), which could provide an indication of the abilities or even
types of the nodes being used. This information could be used to
gain intelligence about devices in the network.
There's no Denial of Service risk specific to this extension, and it
is not vulnerable to replay attacks.
7. Contributors 7. 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
8. Acknowledgments 8. Acknowledgments
The authors would like to thank Acee Lindem, Ketan Talaulikar, Tal The authors would like to thank Acee Lindem, Ketan Talaulikar, Tal
Mizrahi, Stephane Litkowski and Bruno Decraene for their reviews and Mizrahi, Stephane Litkowski and Bruno Decraene for their reviews and
valuable comments. valuable comments.
9. References 9. References
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Litkowski, "Signaling Entropy Label Capability and Entropy Litkowski, "Signaling Entropy Label Capability and Entropy
Readable Label-stack Depth Using OSPF", draft-ietf-ospf- Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
mpls-elc-06 (work in progress), August 2018. mpls-elc-06 (work in progress), August 2018.
[I-D.ietf-pce-segment-routing] [I-D.ietf-pce-segment-routing]
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-12 (work in progress), June draft-ietf-pce-segment-routing-12 (work in progress), June
2018. 2018.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>.
[RFC6863] Hartman, S. and D. Zhang, "Analysis of OSPF Security [RFC6863] Hartman, S. and D. Zhang, "Analysis of OSPF Security
According to the Keying and Authentication for Routing According to the Keying and Authentication for Routing
Protocols (KARP) Design Guide", RFC 6863, Protocols (KARP) Design Guide", RFC 6863,
DOI 10.17487/RFC6863, March 2013, DOI 10.17487/RFC6863, March 2013,
<https://www.rfc-editor.org/info/rfc6863>. <https://www.rfc-editor.org/info/rfc6863>.
[RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting
Authentication Trailer for OSPFv3", RFC 7166,
DOI 10.17487/RFC7166, March 2014,
<https://www.rfc-editor.org/info/rfc7166>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key "Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<https://www.rfc-editor.org/info/rfc7474>. <https://www.rfc-editor.org/info/rfc7474>.
[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>.
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