< draft-ietf-isis-segment-routing-msd-08.txt   draft-ietf-isis-segment-routing-msd-09.txt >
IS-IS Working Group J. Tantsura IS-IS Working Group J. Tantsura
Internet-Draft Individual Internet-Draft Individual
Intended status: Standards Track U. Chunduri Intended status: Standards Track U. Chunduri
Expires: July 8, 2018 Huawei Technologies Expires: July 14, 2018 Huawei Technologies
S. Aldrin S. Aldrin
Google, Inc Google, Inc
L. Ginsberg L. Ginsberg
Cisco Systems Cisco Systems
January 04, 2018 January 10, 2018
Signaling MSD (Maximum SID Depth) using IS-IS Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-08 draft-ietf-isis-segment-routing-msd-09
Abstract Abstract
This document proposes a way to signal Maximum SID Depth (MSD) This document defines a way for an IS-IS Router to advertise multiple
supported by a node and/or link granularity by an IS-IS Router. In a types of supported Maximum SID Depths (MSDs) at node and/or link
Segment Routing (SR) enabled network a centralized controller that granularity. Such advertisements allow entities (e.g., centralized
programs SR tunnels needs to know the MSD supported by the head-end controllers) to determine whether a particular SID stack is
at node and/or link granularity to impose the SID stack of an supportable in a given network. This document only defines one type
appropriate depth. MSD is relevant to the head-end of a SR tunnel or of MSD (maximum label imposition) - but defines an encoding which can
Binding-SID anchor node where Binding-SID expansions might result in support other MSD types.
creation of a new SID stack.
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
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This Internet-Draft will expire on July 8, 2018. This Internet-Draft will expire on July 14, 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.
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skipping to change at page 2, line 23 skipping to change at page 2, line 20
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. 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 . . . . . . . . . . . . . . . . . . 3 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
4. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5 4. Using Node and Link MSD Advertisements . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7 10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
When Segment Routing tunnels are computed by a centralized When Segment Routing(SR) paths are computed by a centralized
controller, it is critical that the controller learns the MSD controller, it is critical that the controller learns the Maximum SID
"Maximum SID Depth" of the node or link SR tunnel exits over, so the Depth(MSD) which can be imposed at the node/link a given SR path is
SID stack depth of a path computed doesn't exceed the number of SID's applied so as to insure that the SID stack depth of a computed path
the node is capable of imposing. This document describes how to use doesn't exceed the number of SIDs the node is capable of imposing.
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 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 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 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 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 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 configured. BGP-LS [RFC7752] defines a way to expose topology and
associated attributes and capabilities of the nodes in that topology associated attributes and capabilities of the nodes in that topology
to a centralized controller. MSD signaling by BGP-LS has been to a centralized controller. MSD signaling by BGP-LS has been
defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, 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 BGP-LS is configured on a small number of nodes, that do not
necessarily act as head-ends. In order, for BGP-LS to signal MSD for 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 all the nodes and links in the network MSD is relevant, MSD
capabilites should be advertised to every IS-IS router in the capabilites should be advertised to every IS-IS router in the
network. network.
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 Entropy Label (EL) at (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 appropriate depth, so it could be read by transit nodes.
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 This document defines an extension to IS-IS used to advertise one or
total number of SID's a node is capable of imposing, to be used by a more types of MSD at node and/or link granularity. It also creates
path computation element/controller. In case, there are additional an IANA registry for assigning MSD type identifiers. It also defines
SID's (e.g. service) that are to be imposed to the stack - this would one MSD type called Base MPLS Imposition MSD. In the future it is
be signaled with an another MSD type (TBD), no adjustment to the Base expected that new MSD types will be defined to signal additional
MSD should be made. In the future, new MSD types could be defined to capabilities e.g., entropy labels, SIDs that can be imposed through
signal additional capabilities: entropy labels, SID's that can be recirculation, or SIDs associated with another dataplane e.g., IPv6.
imposed thru recirculation, or another dataplane e.g IPv6.
1.1. Conventions used in this document 1.1. Conventions used in this document
1.1.1. Terminology 1.1.1. Terminology
BGP-LS: Distribution of Link-State and TE Information using Border BGP-LS: Distribution of Link-State and TE Information using Border
Gateway Protocol Gateway Protocol
BMI: Base MPLS Imposition is the number of MPLS labels which can be
imposed inclusive of any service/transport labels
IS-IS: Intermediate System to Intermediate System IS-IS: Intermediate System to Intermediate System
MSD: Maximum SID Depth - a number of SID's a node or a link on a node MSD: Maximum SID Depth - the number of SIDs a node or a link on a
is capable of imposing node can support
PCC: Path Computation Client PCC: Path Computation Client
PCE: Path Computation Element PCE: Path Computation Element
PCEP: Path Computation Element Protocol PCEP: Path Computation Element Protocol
SID: Segment Identifier SID: Segment Identifier
SR: Segment Routing SR: Segment Routing
1.2. Requirements Language 1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Node MSD Advertisement 2. Node MSD Advertisement
A new sub-TLV "Node MSD sub-TLV" is defined within the body of IS-IS A new sub-TLV "Node MSD sub-TLV" is defined within the body of the
Router Capability TLV [RFC7981], to carry the provisioned MSD of the IS-IS Router Capability TLV [RFC7981], to carry the provisioned
router originating the Router Capability TLV. Node MSD is the lowest MSD(s) of the router originating the Router Capability TLV. Node MSD
MSD supported by the node of any interface and if not known throught is the lowest MSD supported by the node on any interface. MSD values
an API, can be provisioned in IS-IS instance. may be learned via a hardware API or may be provisioned.
0 1 2 3 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Type and Value pair | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ................... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Node MSD Sub-TLV Figure 1: Node MSD Sub-TLV
The Type (1 byte) of this sub-TLV has value of 23. The Type (1 byte) of this sub-TLV has value of 23.
Length is variable (minimum of 2, multiple of 2 octets) and Length is variable (minimum of 2, multiple of 2 octets) and
represents the total length of value field. represents the total length of value field.
Value field consists of a 1 octet Sub-Type (IANA Registry) and 1 Value field consists of one or more pairs of a 1 octet MSD-Type (IANA
octet Value. There could be one or more of the Sub-Type/Value pairs. Registry) and 1 octet Value.
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 Node MSD value is a number in the range of 0-255. 0 represents lack
extensions. of the ability to support SID stack of any depth; any other value
represents that of the node. This value MUST represent the lowest
value supported by any link associated with the node.
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.
3. Link MSD Advertisement 3. Link MSD Advertisement
A new sub-TLV - Link MSD sub-TLV is defined for TLVs 22, 23, 141, 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 222, and 223 to carry the MSD of the interface associated with the
with the link. link. MSD values may be learned via a hardware API or may be
provisioned.
0 1 2 3 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Type and Value pair | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ................... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Link MSD Sub-TLV Figure 2: Link MSD Sub-TLV
The Type (1 byte) of this sub-TLV has value of 15. The Type (1 byte) of this sub-TLV has value of 15.
Length is variable and similar to what is defined in Section 2. 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 Value field consists of one or more pairs of a 1 octet MSD-Type (IANA
octet value. There could be one or more of the Sub-Type/Value pairs. Registry) and 1 octet Value.
Sub-Type 1 (IANA Section), MSD and the Value field associated with Link MSD value is a number in the range of 0-255. 0 represents lack
the Sub-Type contains Link MSD of the router originating the of the ability to support SID stack of any depth; any other value
corresponding TLV's 22, 23, 141, 222, and 223. represents that of the link when used as an outgoing link.
The value of Link MSD represents MSD on the outgoing link. Link MSD This sub-TLV is optional. The scope of the advertisement is specific
is a number in the range of 0-254. 0 represents lack of the ability to the deployment.
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 4. Using Node and Link MSD Advertisements
When both Node MSD and Link MSD are present, the value of the Link When Link MSD is present for a given MSD type, the value of the Link
MSD MUST be used. MSD MUST be used in preference to the Node MSD.
5. IANA Considerations 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
only be inferred that the advertising node does not support
advertisement of that MSD type. However, in some cases the lack of
advertisement might imply that the functionality associated with the
MSD type is not supported. The correct interpretation MUST be
specified when an MSD type is defined.
This document includes a request to IANA to allocate sub-TLV type 5. Base MPLS Imposition MSD
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: Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS
labels a node is capable of imposing, including any service/transport
labels.
Absence of BMI-MSD advertisements indicates only that the advertising
node does not support advertisement of this capability.
6. IANA Considerations
This document requests IANA to allocate a sub-TLV type code for the
new sub TLV proposed in Section 2 of this document from IS-IS Router
Capability TLV Registry as defined by [RFC7981].
The following value has been allocated by IANA:
Value Description Reference Value Description Reference
----- --------------- ------------- ----- --------------- -------------
23 Node MSD This document 23 Node MSD This document
Figure 3: Node MSD Figure 3: Node MSD
For the Link MSD, we request IANA to allocate new sub-TLV codes as This document requests IANA to allocate a sub-TLV type code as
defined in Section 3 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223 defined in Section 3 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223
registry. registry.
The following value has been allocated by IANA:
Value Description Reference Value Description Reference
----- --------------- ------------- ----- --------------- -------------
15 Link MSD This document 15 Link MSD This document
Figure 4: Link MSD Figure 4: Link MSD
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 a new IANA managed registry under This document requests creation of a new IANA managed registry under
a new category of "Interior Gateway Protocol (IGP) Parameters" IANA a new category of "Interior Gateway Protocol (IGP) Parameters" IANA
registries to identify MSD types as proposed in Section 2, Section 3. registries to identify MSD types as proposed in Section 2 and
The registration procedure is "Expert Review" as defined in Section 3. The registration procedure is "Expert Review" as defined
[RFC8126]. Suggested registry name is "MSD Sub-types". Types are an in [RFC8126]. Suggested registry name is "MSD types". Types are an
unsigned 8 bit number. The following values are defined by this 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 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 6: MSD Sub-type Codepoints Registry Figure 6: MSD Types Codepoints Registry
6. 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
7. Contributors 8. Contributors
The following people contributed to this document: The following people contributed to this document:
Peter Psenak Peter Psenak
Email: ppsenak@cisco.com Email: ppsenak@cisco.com
8. Acknowledgements 9. Acknowledgements
The authors would like to thank Stephane Litkowski and Bruno Decraene The authors would like to thank Stephane Litkowski and Bruno Decraene
for their reviews and valuable comments. for their reviews and valuable comments.
9. References 10. References
9.1. 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>.
[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 [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>.
9.2. Informative References 10.2. Informative References
[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 Maximum SID Depth using Border Gateway Protocol "Signaling Maximum SID Depth using Border Gateway Protocol
Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01
(work in progress), October 2017. (work in progress), October 2017.
[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 Litkowski, "Signaling Entropy Label Capability and
Readable Label-stack Depth Using IS-IS", draft-ietf-isis- Readable Label-stack Depth Using IS-IS", draft-ietf-isis-
mpls-elc-03 (work in progress), January 2018. mpls-elc-03 (work in progress), January 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-11 (work in progress), draft-ietf-pce-segment-routing-11 (work in progress),
November 2017. 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 [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,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
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