draft-ietf-isis-segment-routing-msd-16.txt   draft-ietf-isis-segment-routing-msd-17.txt 
IS-IS Working Group J. Tantsura IS-IS 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 27, 2019 Huawei Technologies Expires: March 30, 2019 Huawei Technologies
S. Aldrin S. Aldrin
Google, Inc Google, Inc
L. Ginsberg L. Ginsberg
Cisco Systems Cisco Systems
September 23, 2018 September 26, 2018
Signaling MSD (Maximum SID Depth) using IS-IS Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-16 draft-ietf-isis-segment-routing-msd-17
Abstract Abstract
This document defines a way for an Intermediate System to This document defines a way for an Intermediate System to
Intermediate System (IS-IS) router to advertise multiple types of Intermediate System (IS-IS) router to advertise multiple types of
supported Maximum SID Depths (MSDs) at node and/or link granularity. supported Maximum SID 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 SID stack can be supported in a given determine whether a particular SID stack can be supported in a given
network. This document only defines one type of MSD maximum label network. This document only defines one type of MSD (Base MPLS
imposition, but defines an encoding that can support other MSD types. Imposition), but defines an encoding that can support other MSD
types. This document focuses on MSD use in a Segment Routing enabled
network, but MSD may also be useful when Segment Routing is not
enabled.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 27, 2019. This Internet-Draft will expire on March 30, 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
skipping to change at page 2, line 17 skipping to change at page 2, line 25
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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 . . . . . . . . . . . . . . . . . . 3 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 3 2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 5
4. Procedures for using Node and Link MSD Advertisements . . . . 5 4. Procedures for 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 . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
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 . . . . . . . . . . . . . . . . . 9 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 of a given SR path Depth (MSD) that can be imposed at each node/link of a given SR path
to insure that the Segment Identifier (SID) stack depth of a computed to ensure that the Segment Identifier (SID) stack depth of a computed
path does not exceed the number of SIDs the node is capable of path does not exceed the number of SIDs the node is capable of
imposing. imposing.
[I-D.ietf-pce-segment-routing] defines how to signal MSD in the SR [I-D.ietf-pce-segment-routing] defines how to signal MSD in the Path
Path Computation Element (PCE) Capability TLV and in the METRIC Computation Element Protocol (PCEP). However, if PCEP is not
Object originally defined in [RFC5440]. However, if PCEP is not
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 MSD is relevant, MSD capabilities SHOULD be
advertised by every Intermediate System to Intermediate System(IS-IS) advertised by every Intermediate System to Intermediate System(IS-IS)
router in the network. 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-isis-mpls-elc] defines Readable Label Depth Capability [I-D.ietf-isis-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 could be read by transit nodes. a depth, that could be read by transit nodes.
This document defines an extension to IS-IS used to advertise one or This document defines an extension to IS-IS used to advertise one or
more types of MSD at node and/or link granularity. It also creates more types of MSD at node and/or link granularity. It also creates
an IANA registry for assigning MSD type identifiers. It also defines an IANA registry for assigning MSD-type identifiers. It also defines
the Base MPLS Imposition MSD type. In the future it is expected that the Base MPLS Imposition MSD-type. In the future it is expected that
new MSD types will be defined to signal additional capabilities e.g., new MSD-types will be defined to signal additional capabilities e.g.,
entropy labels, SIDs that can be imposed through recirculation, or entropy labels, SIDs that can be imposed through recirculation, or
SIDs associated with another dataplane e.g., IPv6. SIDs associated with another dataplane e.g., IPv6.
Although MSD advertisements are associated with Segment Routing, the MSD advertisements MAY be useful even if Segment Routing itself is
advertisements MAY be present even if Segment Routing itself is not not enabled. For example, in a non-SR MPLS network, MSD defines the
enabled. Note that in a non-SR MPLS network, label depth is what is maximum label depth.
defined by the MSD advertisements.
1.1. Terminology 1.1. Terminology
BMI: Base MPLS Imposition is the number of MPLS labels which can be BMI: Base MPLS Imposition is the number of MPLS labels which can be
imposed inclusive of all service/transport/special labels imposed inclusive of all service/transport/special labels
MSD: Maximum SID Depth - the number of SIDs supported by a node or a MSD: Maximum SID Depth - the number of SIDs supported by a node or a
link on a node link on a node
SID: Segment Identifier as defined in [RFC8402] SID: Segment Identifier as defined in [RFC8402]
skipping to change at page 4, line 28 skipping to change at page 4, line 37
Figure 1: Node MSD Sub-TLV Figure 1: Node MSD Sub-TLV
Type: 23 (allocated by IANA via the early assignment process) Type: 23 (allocated by IANA via the early assignment process)
Length: variable (multiple of 2 octets) and represents the total Length: variable (multiple of 2 octets) and represents the total
length of value field. length of value field.
Value: field consists of one or more pairs of a 1 octet MSD-Type and Value: field consists of one or more pairs of a 1 octet MSD-Type and
1 octet MSD-Value. 1 octet MSD-Value.
MSD-Type is a value defined in the IGP MSD Types registry created by MSD-Type is a value defined in the IGP MSD-Types registry created by
the IANA Section of this document. the IANA Section of this document.
MSD-Value is a number in the range of 0-255. For all MSD-Types, 0 MSD-Value is a number in the range of 0-255. For all MSD-Types, 0
represents lack of the ability to support SID stack of any depth; any represents lack of the ability to support SID stack of any depth; any
other value represents that of the node. This value MUST represent other value represents that of the node. This value MUST represent
the lowest value supported by any link configured for use by the the lowest value supported by any link configured for use by the
advertising IS-IS instance. advertising IS-IS instance.
This sub-TLV is optional. The scope of the advertisement is specific This sub-TLV is optional. The scope of the advertisement is specific
to the deployment. to the deployment.
skipping to change at page 5, line 28 skipping to change at page 5, line 36
Figure 2: Link MSD Sub-TLV Figure 2: Link MSD Sub-TLV
Type: 15 (allocated by IANA via the early assignment process) Type: 15 (allocated by IANA via the early assignment process)
Length: variable (multiple of 2 octets) and represents the total Length: variable (multiple of 2 octets) and represents the total
length of value field. length of value field.
Value: consists of one or more pairs of a 1 octet MSD-Type and 1 Value: consists of one or more pairs of a 1 octet MSD-Type and 1
octet MSD-Value. octet MSD-Value.
MSD-Type is a value defined in the MSD Types registry created by the MSD-Type is a value defined in the MSD-Types registry created by the
IANA Section of this document. IANA Section of this document.
MSD-Value is a number in the range of 0-255. For all MSD-Types, 0 MSD-Value is a number in the range of 0-255. For all MSD-Types, 0
represents lack of the ability to support SID stack of any depth; any represents lack of the ability to support SID stack of any depth; any
other value represents that of the link. other value represents that of the link.
This sub-TLV is optional. This sub-TLV is optional.
If multiple Link MSD advertisements for the same MSD-Type and the If multiple Link MSD advertisements for the same MSD-Type and the
same link are received, the procedure used to select which copy is same link are received, the procedure used to select which copy is
used is undefined. used is undefined.
4. Procedures for using Node and Link MSD Advertisements 4. Procedures for 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 precedence over the Node MSD. When a Link MSD type is MSD MUST take precedence over the Node MSD. When a Link MSD-type is
not signaled but the Node MSD type is, then the Node MSD type value not signaled but the Node MSD-type is, then the Node MSD-type value
MUST be considered as the MSD value for that link. MUST be considered as the MSD value for that link.
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.
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. Base MPLS Imposition MSD 5. Base MPLS Imposition MSD
Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS
labels which can be imposed, including all service/transport/special labels which can be imposed, including all service/transport/special
labels. labels. The value advertised MUST indicate what can be imposed under
all conditions e.g., if label popping/swapping affects the number of
labels which can be imposed this MUST be accounted for in the value
which is advertised.
If the advertising router performs label imposition in the context of
the ingress interface, it is not possible to meaningfully advertise
per link values. In such a case only the Node MSD SHOULD be
advertised.
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 a sub-TLV type for the new This document requests IANA to allocate a sub-TLV type for the new
sub TLV proposed in Section 2 of this document from IS-IS Router sub TLV proposed in Section 2 of this document from IS-IS Router
Capability TLV Registry as defined by [RFC7981]. Capability TLV Registry as defined by [RFC7981].
skipping to change at page 7, line 13 skipping to change at page 7, line 34
Per TLV information where Link MSD sub-TLV can be part of: Per TLV information where Link MSD sub-TLV can be part of:
TLV 22 23 25 141 222 223 TLV 22 23 25 141 222 223
--- -------------------- --- --------------------
y y y y y y y y y y y y
Figure 5: TLVs where LINK MSD Sub-TLV can be present Figure 5: TLVs where LINK MSD Sub-TLV can be present
This document requests creation of an IANA managed registry under the This document requests creation of an IANA managed registry under the
category of "Interior Gateway Protocol (IGP) Parameters" IANA category of "Interior Gateway Protocol (IGP) Parameters" IANA
registries to identify MSD types as proposed in Section 2 and registries to identify MSD-types as proposed in Section 2 and
Section 3. The registration procedure is "Expert Review" as defined Section 3. The registration procedure is "Expert Review" as defined
in [RFC8126]. Suggested registry name is "IGP MSD Types". Types are in [RFC8126]. Suggested registry name is "IGP MSD-Types". Types are
an unsigned 8 bit number. The following values are defined by this an unsigned 8 bit number. The following values are defined by this
document: document:
Value Name Reference Value Name Reference
----- --------------------- ------------- ----- --------------------- -------------
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 Use This document
255 Reserved This document 255 Reserved This document
Figure 6: MSD Types Codepoints Registry Figure 6: MSD-Types Codepoints Registry
General guidance for the Designated Experts is as defined in General guidance for the Designated Experts is as defined in
[RFC7370] [RFC7370]
7. Security Considerations 7. Security Considerations
Security considerations as specified by [RFC7981] are applicable to Security considerations as specified by [RFC7981] are applicable to
this document. this document.
Advertisement of the additional information defined in this document Advertisement of the additional information defined in this document
skipping to change at page 8, line 21 skipping to change at page 8, line 45
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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC7370] Ginsberg, L., "Updates to the IS-IS TLV Codepoints [RFC7370] Ginsberg, L., "Updates to the IS-IS TLV Codepoints
Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014, Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014,
<https://www.rfc-editor.org/info/rfc7370>. <https://www.rfc-editor.org/info/rfc7370>.
[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
for Advertising Router Information", RFC 7981, for Advertising Router Information", RFC 7981,
DOI 10.17487/RFC7981, October 2016, DOI 10.17487/RFC7981, October 2016,
<https://www.rfc-editor.org/info/rfc7981>. <https://www.rfc-editor.org/info/rfc7981>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
skipping to change at page 9, line 17 skipping to change at page 9, line 31
[I-D.ietf-idr-bgp-ls-segment-routing-msd] [I-D.ietf-idr-bgp-ls-segment-routing-msd]
Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
"Signaling MSD (Maximum SID Depth) using Border Gateway "Signaling MSD (Maximum SID Depth) using Border Gateway
Protocol Link-State", draft-ietf-idr-bgp-ls-segment- Protocol Link-State", draft-ietf-idr-bgp-ls-segment-
routing-msd-02 (work in progress), August 2018. routing-msd-02 (work in progress), August 2018.
[I-D.ietf-isis-mpls-elc] [I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. Xu, X., Kini, S., Sivabalan, S., 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-05 (work in progress), July 2018. elc-06 (work in progress), September 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.
[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,
 End of changes. 26 change blocks. 
43 lines changed or deleted 48 lines changed or added

This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/