Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-08
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8491.
|
|
|---|---|---|---|
| Authors | Jeff Tantsura , Uma Chunduri , Sam Aldrin , Les Ginsberg | ||
| Last updated | 2018-01-05 | ||
| Replaces | draft-tantsura-isis-segment-routing-msd | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | In WG Last Call | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 8491 (Proposed Standard) | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-isis-segment-routing-msd-08
IS-IS Working Group J. Tantsura
Internet-Draft Individual
Intended status: Standards Track U. Chunduri
Expires: July 8, 2018 Huawei Technologies
S. Aldrin
Google, Inc
L. Ginsberg
Cisco Systems
January 04, 2018
Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-08
Abstract
This document proposes a way to signal Maximum SID Depth (MSD)
supported by a node and/or link granularity by an IS-IS 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 impose 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.
Status of This Memo
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This Internet-Draft will expire on July 8, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
4. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. 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 SID's
the node is capable of imposing. This document describes how to use
IS-IS 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.ietf-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
all the nodes and links in the network MSD is relevant, MSD
capabilites should be advertised to every IS-IS router in the
network.
[I-D.ietf-isis-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 impose SID's stack of a particular depth.
MSD of type 1 (IANA Registry), called Base MSD, is used to signal the
total number of SID's a node is capable of imposing, to be used by a
path computation element/controller. In case, there are additional
SID's (e.g. service) that are to be imposed 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, SID's that can be
imposed 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
IS-IS: Intermediate System to Intermediate System
MSD: Maximum SID Depth - a number of SID's a node or a link on a node
is capable of imposing
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. Node MSD Advertisement
A new sub-TLV "Node MSD sub-TLV" is defined within the body of IS-IS
Router Capability TLV [RFC7981], to carry the provisioned MSD of the
router originating the Router Capability TLV. Node MSD is the lowest
MSD supported by the node of any interface and if not known throught
an API, can be provisioned in IS-IS instance.
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 pair |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Node MSD Sub-TLV
The Type (1 byte) of this sub-TLV has value of 23.
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. There could be one or more of the Sub-Type/Value pairs.
Sub-Type 1 (IANA Section), MSD and the Value field associated with
the Sub-Type contains maximum MSD of the router originating the
Router Capability TLV.
Node MSD value is a number in the range of 0-254. 0 represents lack
of the ability to impose SID stack 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 sub-TLV is optional. The scope of the advertisement is specific
to the deployment.
3. Link MSD Advertisement
A new sub-TLV - Link MSD sub-TLV is defined for TLVs 22, 23, 141,
222, and 223 to carry the provisioned MSD of the interface associated
with the link.
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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 pair |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Link MSD Sub-TLV
The Type (1 byte) of this sub-TLV has value of 15.
Length is variable and similar to what is defined in Section 2.
Value field consists of a 1 octet sub-type (IANA Registry) and 1
octet value. There could be one or more of the Sub-Type/Value pairs.
Sub-Type 1 (IANA Section), MSD and the Value field associated with
the Sub-Type contains Link MSD of the router originating the
corresponding TLV's 22, 23, 141, 222, and 223.
The value of Link MSD represents MSD on the outgoing link. Link MSD
is a number in the range of 0-254. 0 represents lack of the ability
to impose SID stack of any depth; any other value represents that of
the particular link MSD value.
4. Node MSD vs Link MSD conflict resolution
When both Node MSD and Link MSD are present, the value of the Link
MSD MUST be used.
5. IANA Considerations
This document includes a request to IANA to allocate sub-TLV type
codes for the new sub TLV proposed in Section 2 of this document from
IS-IS Router Capability TLV Registry as defined by [RFC7981].
Following values have been allocated by IANA:
Value Description Reference
----- --------------- -------------
23 Node MSD This document
Figure 3: Node MSD
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For the Link MSD, we request IANA to allocate new sub-TLV codes as
defined in Section 3 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223
registry.
Value Description Reference
----- --------------- -------------
15 Link MSD This document
Figure 4: Link MSD
Per TLV information where Link MSD sub-TLV can be part of:
TLV 22 23 25 141 222 223
--- --------------------
y y y y y y
Figure 5: TLVs where LINK MSD Sub-TLV can be present
This document requests creation of a new IANA managed registry under
a new category of "Interior Gateway Protocol (IGP) Parameters" IANA
registries to identify MSD types as proposed in Section 2, Section 3.
The registration procedure is "Expert Review" as defined in
[RFC8126]. Suggested registry name is "MSD Sub-types". Types are an
unsigned 8 bit number. The following values are defined by this
document
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 6: MSD Sub-type Codepoints Registry
6. Security Considerations
Security considerations, as specified by [RFC7981] are applicable to
this document
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7. Contributors
The following people contributed to this document:
Peter Psenak
Email: ppsenak@cisco.com
8. Acknowledgements
The authors would like to thank Stephane Litkowski and Bruno Decraene
for their reviews and valuable comments.
9. References
9.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
for Advertising Router Information", RFC 7981,
DOI 10.17487/RFC7981, October 2016,
<https://www.rfc-editor.org/info/rfc7981>.
9.2. Informative References
[I-D.ietf-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-ietf-idr-bgp-ls-segment-routing-msd-01
(work in progress), October 2017.
[I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability and
Readable Label-stack Depth Using IS-IS", draft-ietf-isis-
mpls-elc-03 (work in progress), January 2018.
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[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-11 (work in progress),
November 2017.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[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,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
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
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Les Ginsberg
Cisco Systems
Email: ginsberg@cisco.com
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