Internet DRAFT - draft-ietf-spring-mpls-path-segment
draft-ietf-spring-mpls-path-segment
SPRING Working Group W. Cheng, Ed.
Internet-Draft H. Li
Intended status: Standards Track China Mobile
Expires: 2 June 2024 C. Li, Ed.
Huawei Technologies
R. Gandhi
Cisco Systems, Inc.
R. Zigler
Broadcom
30 November 2023
Path Segment Identifier in MPLS Based Segment Routing Network
draft-ietf-spring-mpls-path-segment-22
Abstract
A Segment Routing (SR) path is identified by an SR segment list. A
sub-set of segments from the segment list cannot be leveraged to
distinguish one SR path from another as they may be partially
congruent. SR path identification is a pre-requisite for various
use-cases such as Performance Measurement, and end-to-end 1+1 path
protection.
In SR for MPLS data plane (SR-MPLS), an Egress node cannot determine
on which SR path a packet traversed the network from the label stack
because the segment identifiers are removed from the label stack as
the packet transits the network.
This document defines Path Segment Identifier(PSID) to identify an SR
path on the egress node of the path.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 2 June 2024.
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Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Abbreviations and Terms . . . . . . . . . . . . . . . . . 3
2. Path Segment . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Equal-Cost Multipath(ECMP) Considerations . . . . . . . . 5
3. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. PSID for Performance Measurement . . . . . . . . . . . . 6
3.2. PSID for Bidirectional SR Path . . . . . . . . . . . . . 7
3.3. PSID for End-to-end Path Protection . . . . . . . . . . . 7
3.4. Nesting of PSIDs . . . . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 9
5.1. Huawei Technologies . . . . . . . . . . . . . . . . . . . 10
5.2. ZTE Corp . . . . . . . . . . . . . . . . . . . . . . . . 10
5.3. New H3C Technologies . . . . . . . . . . . . . . . . . . 11
5.4. Spirent Communications . . . . . . . . . . . . . . . . . 11
5.5. Fiberhome . . . . . . . . . . . . . . . . . . . . . . . . 12
5.6. Interoperability Test . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . 13
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 16
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
Segment Routing (SR) [RFC8402] leverages the source-routing paradigm
to steer packets from a source node through a controlled set of
instructions, called segments, by prepending the packet with an SR
header. In the MPLS data plane SR-MPLS [RFC8660] the SR header is
instantiated through a label stack.
In an SR-MPLS network, when a packet is transmitted along an SR path,
the labels in the MPLS label stack will be swapped or popped. The
result of this is that no label or only the last label may be left in
the MPLS label stack when the packet reaches the egress node. Thus,
the egress node cannot use the SR label stack to determine along
which SR path the packet came.
However, identifying a path on the egress node is a pre-requisite for
various use-cases in SR-MPLS networks, such as Performance
Measurement (Section 3.1), bidirectional path (Section 3.2), and end-
to-end 1+1 path protection (Live-Live case) (Section 3.3).
Therefore, this document defines a new segment type, referred to
herein as a Path Segment. A Path Segment is defined to uniquely
identify an SR path on the egress node of the path. It MAY be used
by the egress node for path identification. Note that, per-path
state will be maintained in the egress node due to the requirements
in the aforementioned use cases, though in normal cases that the per-
path state will be maintained in the ingress node only.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Abbreviations and Terms
MPLS: Multiprotocol Label Switching.
SR: Segment Routing.
SID: Segment Identifier.
SR-MPLS: Instantiation of SR on the MPLS data plane.
SR path: A SR path is a path described by a Segment-List.
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Sub-Path: A sub-path is a part of a path, which contains a sub-set of
the nodes and links of the path.
PSID: Path Segment Identifier.
2. Path Segment
A Path Segment is a Local Segment [RFC8402] which uniquely identifies
an SR path on the egress node. A Path Segment Identifier(PSID) is a
single label that is assigned from the Segment Routing Local Block
(SRLB) [RFC8402] of the egress node of an SR path.
A PSID is used to identify a Segment List. However, one PSID can be
used to identify multiple Segment Lists in some use cases if needed.
For example, one single PSID MAY be used to identify some or all
Segment lists in a Candidate path or an SR policy, if an operator
would like to aggregate these Segment Lists in operation.
When a PSID is used, the PSID can be inserted at the ingress node and
MUST immediately follow the last label of the SR path, in other
words, inserted after the routing segment (adjacency/node/prefix
segment) pointing to the egress node of the SR path. Therefore, a
PSID will not be the top label in the label stack when received on an
intermediate node of the associated path, but it can be the top label
in the label stack on the penultimate node.
The value of the TTL field in the MPLS label stack entry containing a
PSID can be set to any value except 0. If a PSID is the bottom
label, the S bit MUST be set, and if the PSID is NOT the bottom
label, the S bit MUST be 0.
The egress node MUST pop the PSID. The egress node MAY use the PSID
for further processing. For example, when performance measurement is
enabled on the SR path, it can trigger packet counting or
timestamping.
The addition of the PSID will require the egress to read and process
the PSID label in addition to the regular processing. This
additional processing may have an impact on forwarding performance.
Behavior relating to the use of explicit null directly preceding the
PSID is undefined in this document.
Generic Associated Channel Label (GAL) MAY be used for Operations,
Administration and Maintenance (OAM) in MPLS networks. As per
[RFC5586], when GAL is used, the ACH appears immediately after the
bottom of the label stack.
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The SR path computation needs to know the Maximum SID Depth (MSD)
that can be imposed at the ingress node of a given SR path [RFC8664].
This ensures that the SID stack depth of a computed path does not
exceed the number of SIDs the node is capable of imposing. As per
[RFC8491] the MSD signals the total number of MPLS labels that can be
imposed, where the total number of MPLS labels includes the PSID.
An example label stack with PSID is shown in Figure 1:
+--------------------+
| ... |
+--------------------+
| Label 1 |
+--------------------+
| Label 2 |
+--------------------+
| ... |
+--------------------+
| Label n |
+--------------------+
| PSID |
+--------------------+
~ Payload ~
+--------------------+
Figure 1: Label Stack with PSID
Where:
* The Labels 1 to n are the segment label stack used to direct how
to steer the packets along the SR path.
* The PSID identifies the SR path in the context of the egress node
of the SR path.
Signaling of the PSID between the egress node, the ingress node and
possibly a centralized controller is out of the scope of this
document.
2.1. Equal-Cost Multipath(ECMP) Considerations
If Entropy Label(EL) is also used on the egress node, as per
[RFC6790] the Entropy label Indicator (ELI) and Entropy Label (EL)
would be placed before the tunnel label and hence does not interfere
with the PSID which is placed below.
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It is worthy to note that in case of ECMP, with or without the use of
EL, the SR packets may be forwarded over multiple paths. In this
case, the SID list cannot directly reflect the actual forwarding path
and the PSID can only identify the SID list rather than the actual
forwarding path.
Also, similar to Synonymous Flow Labels(SFL) [RFC8957], the
introduction of an PSID to an existing flow may cause that flow to
take a different path through the network under conditions of Equal-
Cost Multipath. This, in turn, may invalidate certain uses of the
PSID, such as performance measurement applications. Therefore, the
considerations as per section 5 in [RFC8957] of SFL also apply to
PSID in implementation.
3. Use cases
This section describes use cases which can leverage the PSID. The
content is for informative purpose, and the detailed solutions might
be defined in other documents in the future.
3.1. PSID for Performance Measurement
As defined in [RFC7799], performance measurement can be classified
into Passive, Active, and Hybrid measurement. Since a PSID is
encoded in the SR-MPLS Label Stack as shown in Figure 1, existing
implementation on the egress node can leverage PSID for measuring
packet counts.
For Passive performance measurement, path identification at the
measuring points is the pre-requisite. PSID can be used by the
measuring points (e.g., the ingress and egress nodes of the SR path
or a centralized controller) to correlate the packet counts and
timestamps from the ingress and egress nodes for a specific SR path,
then packet loss and delay can be calculated for the end-to-end path,
respectively.
Furthermore, PSID can also be used for:
* Active Performance Measurement for an SR path in SR-MPLS networks
for collecting packet counters and timestamps from the egress node
using probe messages.
* In-situ OAM[RFC9197] for SR-MPLS to identify the SR Path
associated with the in-situ data fields in the data packets on the
egress node.
* In-band Performance Measurement for SR-MPLS to identify the SR
Path associated with the collected performance metrics.
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3.2. PSID for Bidirectional SR Path
In some scenarios, for example, mobile backhaul transport networks,
there are requirements to support bidirectional paths[RFC6965], and
the path is normally treated as a single entity. Forward and reverse
directions of the path have the same fate, for example, failure in
one direction will result in switching traffic at both directions.
MPLS supports this by introducing the concepts of co-routed
bidirectional LSP and associated bidirectional LSP [RFC5654].
In the current SR architecture, an SR path is a unidirectional path
[RFC8402]. In order to support bidirectional SR paths, a
straightforward way is to bind two unidirectional SR paths to a
single bidirectional SR path. PSIDs can be used to identify and
correlate the traffic for the two unidirectional SR paths at both
ends of the bidirectional path.
The mechanism of constructing bidirectional path using PSID is out of
the scope of this document and has been described in several
documents, such as [I-D.ietf-pce-sr-bidir-path] and
[I-D.ietf-idr-sr-policy-path-segment].
3.3. PSID for End-to-end Path Protection
For end-to-end 1+1 path protection (i.e., Live-Live case), the egress
node of the path needs to know the set of paths that constitute the
primary and the secondaries, in order to select the primary path
packets for onward transmission, and to discard the packets from the
secondaries [RFC4426].
To do this in Segment Routing, each SR path needs a path identifier
that is unique at the egress node. For SR-MPLS, this can be the Path
Segment label allocated by the egress node.
The detailed solution of using PSID in end-to-end 1+1 path protection
is out of the scope of this document.
3.4. Nesting of PSIDs
Binding SID (BSID) [RFC8402] can be used for SID list compression.
With BSID, an end-to-end SR path in a trusted domain can be split
into several sub-paths, each sub-path is identified by a BSID. Then
an end-to-end SR path can be identified by a list of BSIDs,
therefore, it can provide better scalability.
BSID and PSID can be combined to achieve both sub-path and end-to-end
path monitoring. A reference model for such a combination in
(Figure 2) shows an end-to-end path (A->D) in a trusted domain that
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spans three subdomains (Access, Aggregation and Core domain) and
consists of three sub-paths, one in each subdomain (sub-path (A->B),
sub-path (B->C) and sub-path (C->D)).
The SID list of a sub-path can be expressed as <SID1, SID2, ...SIDn,
s-PSID>, where the s-PSID is the PSID of the sub-path. Each sub-path
is associated with a BSID and an s-PSID.
The SID list of the end-to-end path can be expressed as <BSID1,
BSID2, ..., BSIDn, e-PSID>, where the e-PSID is the PSID of the end-
to-end path.
Figure 2 shows the details of the label stacks when PSID and BSID are
used to support both sub-path and end-to-end path monitoring in a
multi-domain scenario.
/--------\ /--------\ /--------\
/ \ / \ / \
A{ Access }B{ Aggregation }C{ Core }D
\ / \ / \ /
\--------/ \--------/ \--------/
Sub-path(A->B) Sub-path(B->C) Sub-path(C->D)
|<--------------->|<-------------->|<-------------->|
E2E Path(A->D)
|<------------------------------------------------->|
+------------+
~A->B SubPath~
+------------+ +------------+
|s-PSID(A->B)| ~B->C SubPath~
+------------+ +------------+ +------------+
| BSID(B->C) | |s-PSID(B->C)| ~C->D SubPath~
+------------+ +------------+ +------------+
| BSID(C->D) | | BSID(C->D) | |s-PSID(C->D)|
+------------+ +------------+ +------------+ +------------+
|e-PSID(A->D)| |e-PSID(A->D)| |e-PSID(A->D)| |e-PSID(A->D)|
+------------+ +------------+ +------------+ +------------+
Figure 2: Nesting of PSIDs
4. Security Considerations
A PSID in SR-MPLS is a local label similar to other labels/Segment,
such as a VPN label, defined in MPLS and SR-MPLS. The data plane
processing of a PSID is a local implementation of an ingress node, or
an egress node, which follows the same logic of existing MPLS
dataplane. As per definition of PSID, only the egress node and the
ingress node of the associated path will learn the information of
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PSID. The intermediate nodes of this path will not learn it.
A PSID may be used on an ingress node that is not the ingress of the
associated path, if the associated label stack with PSID is part of a
deeper label stack which represents a longer path. For example the
case described in Section 3.4 and the related BSID is not used while
the original label stack of sub-path is inserted as a part of the
whole label stack. In this case, the PSID must be distributed in a
trusted domain under the considerations defined in Section 8.1 of
[RFC8402].
A PSID is used within an SR-MPLS trusted domain [RFC8402] and must
not leak outside the domain, therefore no new security threats are
introduced comparing to current SR-MPLS. As per [RFC8402], SR domain
boundary routers MUST filter any external traffic destined to a label
associated with a segment within the trusted domain, this applies to
PSID as well. Other security considerations of SR-MPLS, described in
Section 8.1 of [RFC8402] applies to this document.
The distribution of a PSID from an egress node to an ingress nodes is
performed within an SR trusted domain, and it is out of the scope of
this document. The details of the mechanism and related security
considerations will be described in other documents.
5. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942].
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
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5.1. Huawei Technologies
* Organization: Huawei Technologies.
* Implementation: Huawei PTN7900 Series Routers implementation of
SR-TP[HW-IMP].
* Description: SR-TP is a feature of Huawei PTN7900 series Routers,
which uses PSIDs to associate with paths and build up
bidirectional paths. Huawei PTN7900 Series Routers with version
V100R018C00 and above have commercially implemented the definition
of PSID and use cases which is defined in section 2 and
Section 3.2 in this document, including all the "MUST" and
"SHOULD" clauses, while other use cases for PSID in section 3 are
not yet implemented. For control plane, PTN7900 Series Routers
support configuring PSID using NETCONF.
* Maturity Level: Product
* Coverage: Partial, section 2 and use case section 3.2.
* Version: Draft-12
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: li.fan@huawei.com
* Last updated: September 14, 2023
5.2. ZTE Corp
* Organization: ZTE Corporation.
* Implementation: ZTE's SPN implementation of PSID[ZTE-IMP].
* Description: The feature of SR-MPLS PSID has been implemented in
ZTE SPN products and follows the definition and mechanism as
defined in section 2 and Section 3.2 including all the "MUST" and
"SHOULD" clauses while other use cases for PSID in section 3 are
not yet implemented.
* Maturity Level: Product
* Coverage: Partial,section 2 and use case section 3.2.
* Version: Draft-12
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* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: liu.aihua@zte.com.cn
* Last updated: September 21, 2023
5.3. New H3C Technologies
* Organization: New H3C Technologies.
* Implementation: H3C CR16000, CR19000 series routers implementation
of PSID.
* Description: Section 2 and Section 3.2 including all the "MUST"
and "SHOULD" clauses have been implemented in above-mentioned New
H3C Products(running Version 7.1.086 and above) for testing, while
other use cases for PSID in section 3 are not yet implemented.
* Maturity Level: Beta
* Coverage: Partial, section 2 and use case section 3.2.
* Version: Draft-12
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: linchangwang.04414@h3c.com
* Last updated: September 13, 2023
5.4. Spirent Communications
* Organization: Spirent Communications
* Implementation: Spirent Testcenter Product Family implementation
of SR-TP test capability[SP-IMP].
* Description: Spirent Testcenter product family implements SR-MPLS
PSID test capabilities on the versions above Spirent Testcenter
4.85. Spirent Testcenter fully support testing all clauses
defined in section 2 and Section 3.1,3.2,3.4 , including all the
"MUST" and "SHOULD" clauses, and partially support the test of
clauses in section 3.3.
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* Maturity Level: Production
* Coverage: fully cover section 2 and use case section 3.1,3.2, 3.4,
partially cover section 3.3
* Version: Draft-12
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: junqi.zhao@spirent.com
* Last updated: September 21, 2023
5.5. Fiberhome
* Organization: Fiberhome Corporation.
* Implementation: Fiberhome SPN series of products (Citrans
650/690E) implementation of PSID[FH-IMP].
* Description: SR-TP is a feature of SPN products, which realizes a
controllable L3 tunnel, builds the end-to-end L3 deployment
business model. The PSID follows the definition and mechanism as
defined in section 2 and Section 3.2 including all the "MUST" and
"SHOULD" clauses had been implemented, while other use cases for
PSID in section 3 are not yet implemented.
* Maturity Level: Product
* Coverage: Partial,section 2 and use case section 3.2.
* Version: Draft-12
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: zhhan@fiberhome.com
* Last updated: September 21, 2023
5.6. Interoperability Test
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942].
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The Interoperability test of PSID had been done among products from
several vendors, including Huawei(PTN7900, V100R018C00), ZTE(ZXCTN
6180, Ver 4.00.00), FiberHome(Citrans 650/690E) , Spirent (Chassis:
SPT-N4U-220.Test. Module: PX3-QSFP28-12-225A. Version: 4.86) and
Nokia in 2018[INTEROP-TEST]. Note that PSID is a key feature of
Layer3 in SPN architecture [SPN-L3]. This is reported by Weiqiang
Cheng from China Mobile at September, 21, 2023.
6. IANA Considerations
This document does not require any IANA actions.
7. References
7.1. 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/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/rfc/rfc8402>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/rfc/rfc8660>.
7.2. Informative References
[FH-IMP] "Fiberhome Routers", 21 September 2021,
<https://www.fiberhome.com/operator/product/
products/294.aspx.html>.
[HW-IMP] "Huawei PTN7900 Routers", 21 September 2021,
<https://carrier.huawei.com/en/products/fixed-network/
carrier-ip/router/ptn/ptn7900>.
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[I-D.ietf-idr-sr-policy-path-segment]
Li, C., Li, Z., Yin, Y., Cheng, W., and K. Talaulikar, "SR
Policy Extensions for Path Segment and Bidirectional
Path", Work in Progress, Internet-Draft, draft-ietf-idr-
sr-policy-path-segment-08, 16 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-path-segment-08>.
[I-D.ietf-pce-sr-bidir-path]
Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
"Path Computation Element Communication Protocol (PCEP)
Extensions for Associated Bidirectional Segment Routing
(SR) Paths", Work in Progress, Internet-Draft, draft-ietf-
pce-sr-bidir-path-12, 9 September 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-sr-
bidir-path-12>.
[INTEROP-TEST]
China Mobile, "Adhering to Innovation-Driven Development
and Focusing on Technological Breakthroughs--China Mobile
Research Institute Accelerates 5G R&D and Tests", 30 May
2019, <http://www.cww.net.cn/web/news/channel/
articleinfo.action?id=452789>.
[RFC4426] Lang, J., Ed., Rajagopalan, B., Ed., and D. Papadimitriou,
Ed., "Generalized Multi-Protocol Label Switching (GMPLS)
Recovery Functional Specification", RFC 4426,
DOI 10.17487/RFC4426, March 2006,
<https://www.rfc-editor.org/rfc/rfc4426>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/rfc/rfc5586>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
September 2009, <https://www.rfc-editor.org/rfc/rfc5654>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/rfc/rfc6790>.
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[RFC6965] Fang, L., Ed., Bitar, N., Zhang, R., Daikoku, M., and P.
Pan, "MPLS Transport Profile (MPLS-TP) Applicability: Use
Cases and Design", RFC 6965, DOI 10.17487/RFC6965, August
2013, <https://www.rfc-editor.org/rfc/rfc6965>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/rfc/rfc7799>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/rfc/rfc7942>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/rfc/rfc8491>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/rfc/rfc8664>.
[RFC8957] Bryant, S., Chen, M., Swallow, G., Sivabalan, S., and G.
Mirsky, "Synonymous Flow Label Framework", RFC 8957,
DOI 10.17487/RFC8957, January 2021,
<https://www.rfc-editor.org/rfc/rfc8957>.
[RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
Ed., "Data Fields for In Situ Operations, Administration,
and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
May 2022, <https://www.rfc-editor.org/rfc/rfc9197>.
[SP-IMP] "Spirent Devices", 21 September 2021,
<https://www.spirent.com/assets/u/flexe-test-solution-for-
5g-backhaul>.
[SPN-L3] China Mobile, "The-transport-network-consi-deration-for-
5G-in-CMCC", 1 December 2018, <https://opennetworking.org/
wp-content/uploads/2018/12/The-transport-network-consi-
deration-for-5G-in-CMCC.pdf>.
[ZTE-IMP] "ZTE ZXCTN-6700 Routers", 21 September 2021,
<https://www.zte.com.cn/china/product_index/ip_network/
item01/zxctn-6700/zxctn_6700.html>.
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Acknowledgements
The authors would like to thank Adrian Farrel, Stewart Bryant,
Shuangping Zhan, Alexander Vainshtein, Andrew G. Malis, Ketan
Talaulikar, Shraddha Hegde, Xinyue Zhang, Loa Andersson and Bruno
Decraene for their review, suggestions, comments and contributions to
this document.
The authors would like to acknowledge the contribution from Alexander
Vainshtein on "Nesting of PSIDs".
Contributors
The following people have substantially contributed to this document.
Mach(Guoyi) Chen
Huawei Technologies Co., Ltd
Email: mach.chen@huawei.com
Lei Wang
China Mobile
Email: wangleiyj@chinamobile.com
Aihua Liu
ZTE Corp
Email: liu.aihua@zte.com.cn
Greg Mirsky
ZTE Corp
Email: gregimirsky@gmail.com
Gyan S. Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
Authors' Addresses
Weiqiang Cheng (editor)
China Mobile
Email: chengweiqiang@chinamobile.com
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Han Li
China Mobile
Email: lihan@chinamobile.com
Cheng Li (editor)
Huawei Technologies
China
Email: c.l@huawei.com
Rakesh Gandhi
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
Royi Zigler
Broadcom
Email: royi.zigler@broadcom.com
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