draft-ietf-idr-bgp-ls-segment-routing-msd-06.txt   draft-ietf-idr-bgp-ls-segment-routing-msd-07.txt 
IDR Working Group J. Tantsura IDR Working Group J. Tantsura
Internet-Draft Apstra, Inc. Internet-Draft Apstra, Inc.
Intended status: Standards Track U. Chunduri Intended status: Standards Track U. Chunduri
Expires: March 8, 2020 Futurewei Technologies Expires: March 14, 2020 Futurewei Technologies
K. Talaulikar K. Talaulikar
Cisco Systems Cisco Systems
G. Mirsky G. Mirsky
ZTE Corp. ZTE Corp.
N. Triantafillis N. Triantafillis
Apstra, Inc. Apstra, Inc.
September 5, 2019 September 11, 2019
Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link- Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link-
State State
draft-ietf-idr-bgp-ls-segment-routing-msd-06 draft-ietf-idr-bgp-ls-segment-routing-msd-07
Abstract Abstract
This document defines a way for a Border Gateway Protocol Link-State This document defines a way for a Border Gateway Protocol Link-State
(BGP-LS) speaker to advertise multiple types of supported Maximum SID (BGP-LS) speaker to advertise multiple types of supported Maximum SID
Depths (MSDs) at node and/or link granularity. Depths (MSDs) at node and/or link granularity.
Such advertisements allow entities (e.g., centralized controllers) to Such advertisements allow entities (e.g., centralized controllers) to
determine whether a particular Segment Identifier (SID) stack can be determine whether a particular Segment Identifier (SID) stack can be
supported in a given network. supported in a given network.
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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 8, 2020. This Internet-Draft will expire on March 14, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 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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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
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4
2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4 2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4
3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Manageability Considerations . . . . . . . . . . . . . . . . 6 6. Manageability Considerations . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8 10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 8 10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
When Segment Routing (SR) [RFC8402] paths are computed by a When Segment Routing (SR) [RFC8402] paths are computed by a
centralized controller, it is critical that the controller learns the centralized controller, it is critical that the controller learns the
Maximum SID Depth (MSD) that can be imposed at each node/link on a Maximum SID Depth (MSD) that can be imposed at each node/link on a
given SR path. This ensures that the Segment Identifier (SID) stack given SR path. This ensures that the Segment Identifier (SID) stack
depth of a computed path doesn't exceed the number of SIDs the node depth of a computed path doesn't exceed the number of SIDs the node
is capable of imposing. is capable of imposing.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here . capitals, as shown here .
2. Advertisement of MSD via BGP-LS 2. Advertisement of MSD via BGP-LS
This document describes extensions that enable BGP-LS speakers to This document describes extensions that enable BGP-LS speakers to
signal the MSD capabilities of nodes and their links in a network to signal the MSD capabilities (described in [RFC8491] ) of nodes and
a BGP-LS consumer of network topology such as a centralized their links in a network to a BGP-LS consumer of network topology
controller. The centralized controller can leverage this information such as a centralized controller. The centralized controller can
in computation of SR paths and their instantiation on network nodes leverage this information in computation of SR paths and their
based on their MSD capabilities. When a BGP-LS speaker is instantiation on network nodes based on their MSD capabilities. When
originating the topology learnt via link-state routing protocols like a BGP-LS speaker is originating the topology learnt via link-state
OSPF or IS-IS, the MSD information for the nodes and their links is routing protocols like OSPF or IS-IS, the MSD information for the
sourced from the underlying extensions as defined in [RFC8476] and nodes and their links is sourced from the underlying extensions as
[RFC8491] respectively. The BGP-LS speaker may also advertise the defined in [RFC8476] and [RFC8491] respectively. The BGP-LS speaker
MSD information for the local node and its links when not running any may also advertise the MSD information for the local node and its
link-state IGP protocol e.g. when running BGP as the only routing links when not running any link-state IGP protocol e.g. when running
protocol. BGP as the only routing protocol.
The extensions introduced in this document allow for advertisement of The extensions introduced in this document allow for advertisement of
different MSD-Types. This document does not define these MSD-Types different MSD-Types. This document does not define these MSD-Types
but leverages the definition, guidelines and the code-point registry but leverages the definition, guidelines and the code-point registry
specified in [RFC8491]. This enables sharing of MSD-Types that may specified in [RFC8491]. This enables sharing of MSD-Types that may
be defined in the future by the IGPs in BGP-LS. be defined in the future by the IGPs in BGP-LS.
3. Node MSD TLV 3. Node MSD TLV
Node MSD is encoded in a new Node Attribute TLV [RFC7752] using the Node MSD is encoded in a new Node Attribute TLV [RFC7752] using the
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PCE to perform path computations taking into consideration the size PCE to perform path computations taking into consideration the size
of SID Stack that the specific headend node may be able to impose. of SID Stack that the specific headend node may be able to impose.
Errors in the encoding or decoding of the MSD information may result Errors in the encoding or decoding of the MSD information may result
in the unavailability of such information to the SR PCE or incorrect in the unavailability of such information to the SR PCE or incorrect
information being made available to it. This may result in the information being made available to it. This may result in the
headend node not being able to instantiate the desired SR path in its headend node not being able to instantiate the desired SR path in its
forwarding and provide the SR based optimization functionality. The forwarding and provide the SR based optimization functionality. The
handling of such errors by applications like SR PCE may be handling of such errors by applications like SR PCE may be
implementation specific and out of scope of this document. implementation specific and out of scope of this document.
The extensions, specified in this document, do not introduce any new The extensions specified in this document, do not specify any new
configuration or monitoring aspects in BGP or BGP-LS other than as configuration or monitoring aspects in BGP or BGP-LS. The
discussed in [RFC7752]. The manageability aspects of the MSD specification of BGP models BGP and BGP-LS models is an ongoing work
features are covered by [I-D.ietf-spring-sr-yang]. based on the [I-D.ietf-idr-bgp-model]. The management of the MSD
features within an ietf segment-routing stack is also an ongoing work
based on the [I-D.ietf-spring-sr-yang]. Management of the segment
routing in IGPs is ongoing work for ISIS [I-D.ietf-isis-sr-yang] ,
and OSPF [I-D.ietf-ospf-sr-yang].
7. Security Considerations 7. Security Considerations
The advertisement of an incorrect MSD value may have negative The advertisement of an incorrect MSD value may have negative
consequences. If the value is smaller than supported, path consequences. If the value is smaller than supported, path
computation may fail to compute a viable path. If the value is computation may fail to compute a viable path. If the value is
larger than supported, an attempt to instantiate a path that can't be larger than supported, an attempt to instantiate a path that can't be
supported by the head-end (the node performing the SID imposition) supported by the head-end (the node performing the SID imposition)
may occur. The presence of this information may also inform an may occur. The presence of this information may also inform an
attacker of how to induce any of the aforementioned conditions. attacker of how to induce any of the aforementioned conditions.
This document does not introduce security issues beyond those The document does not introduce additional security issues beyond
discussed in [RFC7752], [RFC8476] and [RFC8491] discussed in [RFC7752], [RFC8476] and [RFC8491]. However, [RFC7752]
is being revised in [I-D.ietf-idr-rfc7752bis] to provide additional
clarification in several portions of the specification after
receiving feedback from implementers. One of the places that is
being clarified is the error handling and security. It is expected
that after [I-D.ietf-idr-rfc7752bis] is released that implementers
will update all BGP-LS base implementations improving the error
handling for protocol work (including this document) that depend on
this function.
8. Contributors 8. Contributors
Siva Sivabalan Siva Sivabalan
Cisco Systems Inc. Cisco Systems Inc.
Canada Canada
Email: msiva@cisco.com Email: msiva@cisco.com
9. Acknowledgements 9. Acknowledgements
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DOI 10.17487/RFC8476, December 2018, DOI 10.17487/RFC8476, December 2018,
<https://www.rfc-editor.org/info/rfc8476>. <https://www.rfc-editor.org/info/rfc8476>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018, DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>. <https://www.rfc-editor.org/info/rfc8491>.
10.2. Informative References 10.2. Informative References
[I-D.ietf-idr-bgp-model]
Jethanandani, M., Patel, K., and S. Hares, "BGP YANG Model
for Service Provider Networks", draft-ietf-idr-bgp-
model-06 (work in progress), June 2019.
[I-D.ietf-idr-rfc7752bis]
Talaulikar, K., Gredler, H., Medved, J., Previdi, S.,
Farrel, A., and S. Ray, "Distribution of Link-State and
Traffic Engineering Information Using BGP", draft-ietf-
idr-rfc7752bis-00 (work in progress), September 2019.
[I-D.ietf-isis-mpls-elc] [I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., and S. Xu, X., Kini, S., Psenak, P., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability and Entropy Litkowski, "Signaling Entropy Label Capability and Entropy
Readable Label Depth Using IS-IS", draft-ietf-isis-mpls- Readable Label Depth Using IS-IS", draft-ietf-isis-mpls-
elc-08 (work in progress), September 2019. elc-08 (work in progress), September 2019.
[I-D.ietf-isis-sr-yang]
Litkowski, S., Qu, Y., Sarkar, P., Chen, I., and J.
Tantsura, "YANG Data Model for IS-IS Segment Routing",
draft-ietf-isis-sr-yang-06 (work in progress), July 2019.
[I-D.ietf-ospf-mpls-elc] [I-D.ietf-ospf-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., and S. Xu, X., Kini, S., Psenak, P., Filsfils, C., and S.
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-08 (work in progress), May 2019. mpls-elc-09 (work in progress), September 2019.
[I-D.ietf-ospf-sr-yang]
Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem,
"YANG Data Model for OSPF SR (Segment Routing) Protocol",
draft-ietf-ospf-sr-yang-10 (work in progress), August
2019.
[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-16 (work in progress), draft-ietf-pce-segment-routing-16 (work in progress),
March 2019. March 2019.
[I-D.ietf-spring-sr-yang] [I-D.ietf-spring-sr-yang]
Litkowski, S., Qu, Y., Lindem, A., Sarkar, P., and J. Litkowski, S., Qu, Y., Lindem, A., Sarkar, P., and J.
Tantsura, "YANG Data Model for Segment Routing", draft- Tantsura, "YANG Data Model for Segment Routing", draft-
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