PCEP extension to support Segment Routing Policy Candidate Paths
draft-ietf-pce-segment-routing-policy-cp-07
| Document | Type | Active Internet-Draft (pce WG) | |
|---|---|---|---|
| Authors | Mike Koldychev , Siva Sivabalan , Colby Barth , Shuping Peng , Hooman Bidgoli | ||
| Last updated | 2022-04-21 | ||
| Replaces | draft-barth-pce-segment-routing-policy-cp | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | plain text html xml htmlized pdfized bibtex | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-pce-segment-routing-policy-cp-07
PCE Working Group M. Koldychev
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Sivabalan
Expires: 21 October 2022 Ciena Corporation
C. Barth
Juniper Networks, Inc.
S. Peng
Huawei Technologies
H. Bidgoli
Nokia
April 2022
PCEP extension to support Segment Routing Policy Candidate Paths
draft-ietf-pce-segment-routing-policy-cp-07
Abstract
This document introduces a mechanism to specify a Segment Routing
(SR) policy, as a collection of SR candidate paths. An SR policy is
identified by <headend, color, endpoint> tuple. An SR policy can
contain one or more candidate paths where each candidate path is
identified in PCEP by its uniquely assigned PLSP-ID. This document
proposes extension to PCEP to support association among candidate
paths of a given SR policy. The mechanism proposed in this document
is applicable to both MPLS and IPv6 data planes of SR.
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.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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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 3 October 2022.
Copyright Notice
Copyright (c) 2022 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Group Candidate Paths belonging to the same SR policy . . 5
3.2. Instantiation of SR policy candidate paths . . . . . . . 5
3.3. Avoid computing lower preference candidate paths . . . . 5
3.4. Minimal signaling overhead . . . . . . . . . . . . . . . 6
4. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1.1. SR Policy Identifiers . . . . . . . . . . . . . . . . 7
4.1.2. SR Policy Candidate Path Identifiers . . . . . . . . 7
4.1.3. SR Policy Candidate Path Attributes . . . . . . . . . 7
4.2. Multiple Optimization Objectives and Constraints . . . . 8
5. SR Policy Association . . . . . . . . . . . . . . . . . . . . 8
5.1. Association Parameters . . . . . . . . . . . . . . . . . 8
5.2. Association Information . . . . . . . . . . . . . . . . . 10
5.2.1. SR Policy Name TLV . . . . . . . . . . . . . . . . . 10
5.2.2. SR Policy Candidate Path Identifiers TLV . . . . . . 11
5.2.3. SR Policy Candidate Path Name TLV . . . . . . . . . . 12
5.2.4. SR Policy Candidate Path Preference TLV . . . . . . . 12
6. Generic Mechanisms . . . . . . . . . . . . . . . . . . . . . 13
6.1. Computation Priority TLV . . . . . . . . . . . . . . . . 13
6.2. Explicit Null Label Policy (ENLP) TLV . . . . . . . . . . 13
6.3. Invalidation TLV . . . . . . . . . . . . . . . . . . . . 14
6.4. Specified-BSID-only . . . . . . . . . . . . . . . . . . . 15
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7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. PCC Initiated SR Policy with single candidate-path . . . 16
7.2. PCC Initiated SR Policy with multiple candidate-paths . . 16
7.3. PCE Initiated SR Policy with single candidate-path . . . 17
7.4. PCE Initiated SR Policy with multiple candidate-paths . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8.1. Association Type . . . . . . . . . . . . . . . . . . . . 18
8.2. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 18
8.3. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 19
8.4. TE-PATH-BINDING TLV Flag field . . . . . . . . . . . . . 19
9. Implementation Status . . . . . . . . . . . . . . . . . . . . 19
9.1. Cisco . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.2. Juniper . . . . . . . . . . . . . . . . . . . . . . . . . 20
10. Security Considerations . . . . . . . . . . . . . . . . . . . 21
11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 21
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
12.1. Normative References . . . . . . . . . . . . . . . . . . 21
12.2. Informative References . . . . . . . . . . . . . . . . . 23
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
Path Computation Element (PCE) Communication Protocol (PCEP)
[RFC5440] enables the communication between a Path Computation Client
(PCC) and a Path Computation Element (PCE), or between two PCEs based
on the PCE architecture [RFC4655].
PCEP Extensions for the Stateful PCE Model [RFC8231] describes a set
of extensions to PCEP to enable active control of Multiprotocol Label
Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS)
tunnels. [RFC8281] describes the setup and teardown of PCE-initiated
LSPs under the active stateful PCE model, without the need for local
configuration on the PCC, thus allowing for dynamic centralized
control of a network.
PCEP Extensions for Segment Routing [RFC8664] specifies extensions to
the Path Computation Element Protocol (PCEP) that allow a stateful
PCE to compute and initiate Traffic Engineering (TE) paths, as well
as a PCC to request a path subject to certain constraint(s) and
optimization criteria in SR networks.
PCEP Extensions for Establishing Relationships Between Sets of LSPs
[RFC8697] introduces a generic mechanism to create a grouping of LSPs
which can then be used to define associations between a set of LSPs
and a set of attributes (such as configuration parameters or
behaviors) and is equally applicable to stateful PCE (active and
passive modes) and stateless PCE.
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Segment Routing Policy for Traffic Engineering
[I-D.ietf-spring-segment-routing-policy] details the concepts of SR
Policy and approaches to steering traffic into an SR Policy.
An SR Policy contains one or more SR Policy Candidate Paths where one
or more such paths can be computed via PCE. This document specifies
PCEP extensions to signal additional information to map candidate
paths to their SR policies. Each candidate path maps to a unique
PLSP-ID in PCEP. By associating multiple candidate paths together, a
PCE becomes aware of the hierarchical structure of an SR policy.
Thus the PCE can take computation and control decisions about the
candidate paths, with the additional knowledge that these candidate
paths belong to the same SR policy. This is accomplished via the use
of the existing PCEP Association object, by defining a new
association type specifically for associating SR candidate paths into
a single SR policy.
2. Terminology
The following terminologies are used in this document:
Endpoint: The IPv4 or IPv6 endpoint address of the SR policy in
question, as described in
[I-D.ietf-spring-segment-routing-policy].
Association Parameters: As described in [RFC8697], the combination
of the mandatory fields Association Type, Association ID and
Association Source in the ASSOCIATION object uniquely identify the
association group. If the optional TLVs - Global Association
Source or Extended Association ID are included, then they MUST be
included in combination with mandatory fields to uniquely identify
the association group.
Association Information: As described in [RFC8697], the ASSOCIATION
object could also include other TLVs based on the association
types, that provides non-key information.
SRPAG: SR Policy Association Group.
SRPAT: SR Policy Association Type.
SRPAT ASSOCIATION: ASSOCIATION object of type SR Policy Association.
PCC: Path Computation Client. Any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application,
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or network node) that is capable of computing a network path or
route based on a network graph and applying computational
constraints.
PCEP: Path Computation Element Protocol.
PCEP Tunnel: The entity identified by the PLSP-ID, as per
[I-D.koldychev-pce-operational].
3. Motivation
The SR Policy Association and its TLVs, defined in this document,
allow PCEP speakers to exchange additional information about SR
Policy Candidate Paths and their container SR Policy.
3.1. Group Candidate Paths belonging to the same SR policy
Since each SR Policy Candidate Path appears as a different Tunnel
(identified via a PLSP-ID) in PCEP, it is useful to group together
all the SR Policy Candidate Paths that belong to the same SR Policy.
Furthermore, it is useful for the PCE to have knowledge of the SR
Policy related information such as color, endpoint, protocol origin,
discriminator, and preference.
3.2. Instantiation of SR policy candidate paths
A PCE needs to instantiate one or more SR Policy Candidate Paths on
the PCC, as specified in [RFC8281]. Each SR Policy Candidate Path is
identified by the tuple <headend, color, endpoint, originator,
discriminator, preference>. This draft provides a mechanism to
signal this information in PCEP.
3.3. Avoid computing lower preference candidate paths
When a PCE knows that a given set of SR Policy Candidate Paths all
belong to the same SR Policy, then path computation MAY be done on
only the highest preference candidate-path(s). Path computation for
lower preference paths is not necessary if one or two higher
preference paths are already computed. Since computing their paths
will not affect traffic steering, it MAY be postponed until the
higher preference paths become invalid.
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3.4. Minimal signaling overhead
When an SR Policy contains multiple SR Policy Candidate Paths
computed by a PCE, such candidate paths can be created, updated and
deleted independently of each other. This is achieved by making each
SR Policy Candidate Path correspond to a unique Tunnel (identified
via PLSP-ID). For example, if an SR Policy has 4 SR Policy Candidate
Paths, then if the PCE wants to update one of those, only one set of
PCUpd and PCRpt messages needs to be exchanged.
4. Procedure
4.1. Overview
As per [RFC8697], LSPs are placed into an association group. As per
[I-D.koldychev-pce-operational], LSPs are contained in PCEP Tunnels
and a PCEP Tunnel is contained in an Association if all of its LSPs
are in that Association. PCEP Tunnels naturally map to SR Policy
Candidate Paths and PCEP Associations naturally map to SR Policies.
The mapping between PCEP Associations and SR Policies is always one-
to-one. However, the mapping between PCEP Tunnels and SR Policy
Candidate Paths may be either one-to-one, or many-to-one, see
Section 4.2.
Each SR Policy Candidate Path contains one or more Segment Lists.
The subject of encoding multiple Segment Lists within an SR Policy
Candidate Path is described in [I-D.koldychev-pce-multipath].
This document defines a new Association Type called "SR Policy
Association", of value 6 based on the generic ASSOCIATION object.
The new Association Type is also called "SRPAT", for "SR Policy
Association Type". We say "SRPAT ASSOCIATION" to mean "ASSOCIATION
object of type SR Policy Association". The group of LSPs that are
part of the SR Policy Association is called "SRPAG", for "SR Policy
Association Group".
As per the processing rules specified in section 6.4 of [RFC8697], if
a PCEP speaker does not support the SRPAT, it MUST return a PCErr
message with Error-Type = 26 "Association Error", Error-Value = 1
"Association-type is not supported".
A given LSP MUST belong to at most one SRPAG, since an SR Policy
Candidate Path cannot belong to multiple SR Policies. If a PCEP
speaker receives a PCEP message with more than one SRPAT ASSOCIATION
for the same LSP, then the PCEP speaker MUST send a PCErr message
with Error-Type = 26 "Association Error", Error-Value = 7 "Cannot
join the association group".
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An SRPAT ASSOCIATION carries three pieces of information: SR Policy
Identifiers, SR Policy Candidate Path Identifiers, and SR Policy
Candidate Path Attributes.
4.1.1. SR Policy Identifiers
SR Policy Identifiers uniquely identify the SR policy within the
context of the headend. SR Policy Identifiers MUST be the same for
all SR Policy Candidate Paths in the same SRPAG. SR Policy
Identifiers MUST NOT change for a given SR Policy Candidate Path
during its lifetime. SR Policy Identifiers MUST be different for
different SRPAGs. SR Policy Identifiers consist of:
* Headend router where the SR Policy originates.
* Color of SR Policy.
* Endpoint of SR Policy.
4.1.2. SR Policy Candidate Path Identifiers
SR Policy Candidate Path Identifiers uniquely identify the SR Policy
Candidate Path within the context of an SR Policy. SR Policy
Candidate Path Identifiers MUST NOT change for a given LSP during its
lifetime. SR Policy Candidate Path Identifiers MUST be different for
different LSPs within the same SRPAG. When these rules are not
satisfied, the PCE MUST send a PCErr message with Error-Type = 26
"Association Error", Error Value = TBD8 "SR Policy Candidate Path
Identifiers Mismatch". SR Policy Candidate Path Identifiers consist
of:
* Protocol Origin.
* Originator.
* Discriminator.
4.1.3. SR Policy Candidate Path Attributes
SR Policy Candidate Path Attributes carry non-key information about
the candidate path and MAY change during the lifetime of the LSP. SR
Policy Candidate Path Attributes consist of:
* Preference.
* Optionally, the SR Policy Candidate Path name.
* Optionally, the SR Policy name.
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4.2. Multiple Optimization Objectives and Constraints
In certain scenarios, it is desired for each SR Policy Candidate Path
to contain multiple sub-candidate paths, each of which has a
different optimization objective and constraints. Traffic is then
sent ECMP or UCMP among these sub-candidate paths.
This is represented in PCEP by a many-to-one mapping between PCEP
Tunnels and SR Policy Candidate Paths. This means that multiple PCEP
Tunnels are allocated for each SR Policy Candidate Path. Each PCEP
Tunnel has its own optimization objective and constraints. When a
single SR Policy Candidate Path contains multiple PCEP Tunnels, each
of these PCEP Tunnels MUST have identical values of Candidate Path
Identifiers, as encoded in SRPOLICY-CPATH-ID TLV, see Section 5.2.2.
5. SR Policy Association
Two ASSOCIATION object types for IPv4 and IPv6 are defined in
[RFC8697]. The ASSOCIATION object includes "Association Type"
indicating the type of the association group. This document adds a
new Association Type (6) "SR Policy Association". This Association
Type is dynamic in nature, thus operator-configured Association Range
MUST NOT be set for this Association type and MUST be ignored.
5.1. Association Parameters
As per [I-D.ietf-spring-segment-routing-policy], an SR Policy is
identified through the tuple <headend, color, endpoint>. the headend
is encoded as the Association Source in the ASSOCIATION object and
the color and endpoint are encoded as part of Extended Association ID
TLV.
The Association Parameters (see Section 2) consist of:
* Association Type: set to 6 "SR Policy Association".
* Association Source (IPv4/IPv6): set to the headend IP address.
* Association ID (16-bit): set to "1".
* Extended Association ID TLV: encodes the Color and Endpoint of the
SR Policy.
The Association Source MUST be set to the headend value of the SR
Policy, as defined in [I-D.ietf-spring-segment-routing-policy]
Section 2.1. If the PCC receives a PCInit message for a non-existent
SR Policy, where the Association Source is set not to the headend
value but to some globally unique IP address that the PCC owns, then
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the PCC SHOULD accept the PCInit message and create the SR Policy
Association with the Association Source that was sent in the PCInit
message.
The 16-bit Association ID field in the ASSOCIATION object MUST be set
to the value of "1".
The Extended Association ID TLV MUST be included and it MUST be in
the following format:
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 = 31 | Length = 8 or 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Endpoint ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended Association ID TLV format
Type: Extended Association ID TLV, type = 31.
Length: Either 8 or 20, depending on whether IPv4 or IPv6 address is
encoded in the Endpoint.
Color: SR Policy color value.
Endpoint: can be either IPv4 or IPv6, depending on whether the policy
endpoint is IPv4 or IPv6. This value MAY be different from the one
contained in the END-POINTS object, or in the LSP IDENTIFIERS TLV of
the LSP object. This value is part of the tuple <color, endpoint>
that identifies the SR Policy on a given headend.
If the PCEP speaker receives an SRPAT ASSOCIATION whose Association
Parameters do not follow the above specification, then the PCEP
speaker MUST send PCErr message with Error-Type = 26 "Association
Error", Error-Value = TBD7 "SR Policy Identifiers Mismatch".
The purpose of choosing the Association Parameters in this way is to
guarantee that there is no possibility of a race condition when
multiple PCEP speakers want to create the same SR Policy at the same
time. By adhering to this format, all PCEP speakers come up with the
same Association Parameters independently of each other. Thus, there
is no chance that different PCEP speakers will come up with different
Association Parameters for the same SR Policy.
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5.2. Association Information
The SRPAT ASSOCIATION contains the following TLVs:
* SRPOLICY-POL-NAME TLV: (optional) encodes SR Policy Name string.
* SRPOLICY-CPATH-ID TLV: (mandatory) encodes SR Policy Candidate
Path Identifiers.
* SRPOLICY-CPATH-NAME TLV: (optional) encodes SR Policy Candidate
Path string name.
* SRPOLICY-CPATH-PREFERENCE TLV: (optional) encodes SR Policy
Candidate Path preference value.
Of these new TLVs, SRPOLICY-CPATH-ID TLV is mandatory. When a
mandatory TLV is missing from the SRPAT ASSOCIATION object, the PCE
MUST send a PCErr message with Error-Type = 6 "Mandatory Object
Missing", Error-Value = TBD6 "Missing Mandatory TLV".
5.2.1. SR Policy Name TLV
The SRPOLICY-POL-NAME TLV is an optional TLV for the SRPAT
ASSOCIATION. At most one SRPOLICY-POL-NAME TLV SHOULD be encoded by
the sender and only the first occurrence is processed and any others
MUST be ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ SR Policy Name ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The SRPOLICY-POL-NAME TLV format
Type: 56 for "SRPOLICY-POL-NAME" TLV.
Length: indicates the length of the value portion of the TLV in
octets and MUST be greater than 0. The TLV MUST be zero-padded so
that the TLV is 4-octet aligned.
SR Policy Name: SR Policy name, as defined in
[I-D.ietf-spring-segment-routing-policy]. It SHOULD be a string of
printable ASCII characters, without a NULL terminator.
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5.2.2. SR Policy Candidate Path Identifiers TLV
The SRPOLICY-CPATH-ID TLV is a mandatory TLV for the SRPAT
ASSOCIATION. Only one SRPOLICY-CPATH-ID TLV SHOULD be encoded by the
sender and only the first occurrence is processed and any others MUST
be ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Proto. Origin | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator ASN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Originator Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The SRPOLICY-CPATH-ID TLV format
Type: 57 for "SRPOLICY-CPATH-ID" TLV.
Length: 28.
Protocol Origin: 8-bit value that encodes the protocol origin, as
specified in [I-D.ietf-spring-segment-routing-policy] Section 2.3.
Note that in PCInit messages, the Protocol Origin is always set to
"PCEP".
Originator ASN: Represented as 4 byte number, part of the originator
identifier, as specified in [I-D.ietf-spring-segment-routing-policy]
Section 2.4.
Originator Address: Represented as 128 bit value where IPv4 address
are encoded in lowest 32 bits, part of the originator identifier, as
specified in [I-D.ietf-spring-segment-routing-policy] Section 2.4.
Discriminator: 32-bit value that encodes the Discriminator of the
candidate path.
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5.2.3. SR Policy Candidate Path Name TLV
The SRPOLICY-CPATH-NAME TLV is an optional TLV for the SRPAT
ASSOCIATION. At most one SRPOLICY-CPATH-NAME TLV SHOULD be encoded
by the sender and only the first occurrence is processed and any
others MUST be ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ SR Policy Candidate Path Name ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The SRPOLICY-CPATH-NAME TLV format
Type: 58 for "SRPOLICY-CPATH-NAME" TLV.
Length: indicates the length of the value portion of the TLV in
octets and MUST be greater than 0. The TLV MUST be zero-padded so
that the TLV is 4-octet aligned.
SR Policy Candidate Path Name: SR Policy Candidate Path Name, as
defined in [I-D.ietf-spring-segment-routing-policy]. It SHOULD be a
string of printable ASCII characters, without a NULL terminator.
5.2.4. SR Policy Candidate Path Preference TLV
The SRPOLICY-CPATH-PREFERENCE TLV is an optional TLV for the SRPAT
ASSOCIATION. Only one SRPOLICY-CPATH-PREFERENCE TLV SHOULD be
encoded by the sender and only the first occurrence is processed and
any others MUST be ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: The SRPOLICY-CPATH-PREFERENCE TLV format
Type: 59 for "SRPOLICY-CPATH-PREFERENCE" TLV.
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Length: 4.
Preference: Numerical preference of the candidate path, as specified
in Section 2.7 of [I-D.ietf-spring-segment-routing-policy].
If the TLV is missing, a default Preference value of 100 is used, as
specified in Section 2.7 of [I-D.ietf-spring-segment-routing-policy].
6. Generic Mechanisms
This section describes various mechanisms that are standardized for
SR Policies in [I-D.ietf-spring-segment-routing-policy], but are
equally applicable to other tunnel types, such as RSVP-TE tunnels.
Hence this section does not make use of the SRPAT ASSOCIATION.
6.1. Computation Priority TLV
The COMPUTATION-PRIORITY TLV is an optional TLV for the LSP object.
It is used to signal the numerical computation priority, as specified
in Section 2.12 of [I-D.ietf-spring-segment-routing-policy]. If the
TLV is absent from the LSP object, a default Priority value of 128 is
used.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: The COMPUTATION-PRIORITY TLV format
Type: TBD1 for "COMPUTATION-PRIORITY" TLV.
Length: 4.
Priority: Numerical priority with which this LSP is to be recomputed
by the PCE upon topology change.
6.2. Explicit Null Label Policy (ENLP) TLV
The ENLP TLV is an optional TLV for the LSP object. It is used to
implement the "Explicit Null Label Policy", as specified in
Section 2.4.5 of [I-D.ietf-idr-segment-routing-te-policy].
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ENLP | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: The Explicit Null Label Policy (ENLP) TLV format
Type: TBD2 for "ENLP" TLV.
Length: 4.
ENLP (Explicit NULL Label Policy): same values as in Section 2.4.5 of
[I-D.ietf-idr-segment-routing-te-policy].
6.3. Invalidation TLV
The INVALIDATION TLV is an optional TLV for the LSP object. It is
used to control traffic streering into the LSP during the time when
the LSP is operationally down/invalid. In the context of SR Policy,
this TLV facilitate the "Drop upon invalid" behavior, specified in
Section 8.2 of [I-D.ietf-spring-segment-routing-policy]. Normally,
if the LSP is down/invalid then traffic that is originally destined
for that LSP is steered somewhere else, such as via IGP or via
another LSP. The "Drop upon invalid" behavior specifies that such
traffic MUST NOT be re-routed and has to be dropped at the head-end.
While in the "Drop upon invalid" state, the LSP operational state is
"UP", as indicated by the O-flag in the LSP object. However the ERO
object is empty, indicating that traffic is being dropped.
In addition to the above, this TLV can also be used by the PCC to
report to the PCE various reasons for LSP being invalidated.
Invalidation reasons are represented by a set of flags.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| |V|P|F|U|
+-+-+-+-+-+-+-+-+
Figure 8: Invalidation Reasons Flags
* U: Unknown - does not fit into any other categories below.
* P: Path computation failure - no path was computed for the LSP.
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* F: First-hop resolution failure - head-end first hop resolution
has failed.
* V: Verification failure - OAM/PM/BFD path verification has
indicated a breakage.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inval Reason | Drop Upon | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: The INVALIDATION TLV format
Type: TBD3 for "INVALIDATION" TLV.
Length: 4.
Inval Reason: contains "Invalidation Reasons Flags" which encode the
reason(s) why the LSP is currently invalidated. This field can be
set to non-zero values only by the PCC, it MUST be set to 0 by the
PCE and ignored by the PCC.
Drop Upon: contains "Invalidation Reasons Flags" for conditions that
SHOULD cause the LSP to drop traffic. This field can be set to non-
zero values by both PCC and PCE. This field MAY be set to all 1's
(0xFF) to indicate that the LSP is to go into Drop upon invalid state
for any reason. I.e., when the PCE does not wish to distinguish any
reason for LSP invalidation and just simply wants it to always "Drop
upon invalid" for any reason.
6.4. Specified-BSID-only
Specified-BSID-only functionality is defined in Section 6.2.3 of
[I-D.ietf-spring-segment-routing-policy]. When specified-BSID-only
is enabled for a particular binding SID, it means that the given
binding SID is required to be allocated and programmed for the LSP to
be operationally up. If the binding SID cannot be allocated or
programmed for some reason, then the LSP must stay down.
To signal specified-BSID-only, a new bit: S (Specified-BSID-only) is
allocated in the "TE-PATH-BINDING TLV Flag field" of the TE-PATH-
BINDING TLV. When this bit is set for a particular BSID, it means
that the BSID follows the Specified-BSID-only behavior. It is
possible to have a mix of BSIDs for the same LSP: some with S=1 and
some with S=0.
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7. Examples
7.1. PCC Initiated SR Policy with single candidate-path
PCReq and PCRep messages are exchanged in the following sequence:
1. PCC sends PCReq message to the PCE, encoding the SRPAT
ASSOCIATION and TLVs in the PCReq message.
2. PCE returns the path in PCRep message, and echoes back the SRPAT
ASSOCIATION.
PCRpt and PCUpd messages are exchanged in the following sequence:
1. PCC sends PCRpt message to the PCE, including the LSP object and
the SRPAT ASSOCIATION.
2. PCE computes path, possibly making use of the Association
Information from the SRPAT ASSOCIATION.
3. PCE updates the SR policy candidate path's ERO using PCUpd
message.
7.2. PCC Initiated SR Policy with multiple candidate-paths
PCRpt and PCUpd messages are exchanged in the following sequence:
1. For each candidate path of the SR Policy, the PCC generates a
different PLSP-ID and symbolic-name and sends multiple PCRpt
messages (or one message with multiple LSP objects) to the PCE.
Each LSP object is followed by SRPAT ASSOCIATION with identical
Color and Endpoint values. The Association Source is set to the
IP address of the PCC and the Association ID is set to a number
that PCC locally chose to represent the SR Policy.
2. PCE takes into account that all the LSPs belong to the same SR
policy. PCE prioritizes computation for the highest preference
LSP and sends PCUpd message(s) back to the PCC.
3. If a new candidate path is added on the PCC by the operator, then
a new PLSP-ID and symbolic name is generated for that candidate
path and a new PCRpt is sent to the PCE.
4. If an existing candidate path is removed from the PCC by the
operator, then that PLSP-ID is deleted from the PCE by sending
PCRpt with the R-flag in the LSP object set.
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7.3. PCE Initiated SR Policy with single candidate-path
A candidate-path is created using the following steps:
1. PCE sends PCInitiate message, containing the SRPAT ASSOCIATION.
The Association Source and the Association ID are set as
described in Section 5.1.
2. PCC uses the color, endpoint and preference from the SRPAT
ASSOCIATION to create a new candidate path. If no SR policy
exists to hold the candidate path, then a new SR policy is
created to hold the new candidate-path. The Originator of the
candidate path is set to be the address of the PCE that is
sending the PCInitiate message.
3. PCC sends a PCRpt message back to the PCE to report the newly
created Candidate Path. The PCRpt message contains the SRPAT
ASSOCIATION.
A candidate-path is deleted using the following steps:
1. PCE sends PCInitiate message, setting the R-flag in the LSP
object.
2. PCC uses the PLSP-ID from the LSP object to find the candidate
path and delete it. If this is the last candidate path under the
SR policy, then the containing SR policy is deleted as well.
7.4. PCE Initiated SR Policy with multiple candidate-paths
A candidate-path is created using the following steps:
1. PCE SHOULD send a separate PCInitiate message for every candidate
path that it wants to create, or it MAY send multiple LSP objects
within a single PCInitiate message. The SRPAT ASSOCIATION is
sent for every LSP in the PCInitiate message. The Association
Source and the Association ID are set as described in
Section 5.1.
2. PCC creates multiple candidate paths under the same SR policy,
identified by Color and Endpoint.
3. PCC sends a PCRpt message back to the PCE to report the newly
created Candidate Path. The PCRpt message contains the SRPAT
ASSOCIATION. The Association Source and the Association ID are
set as described in Section 5.1.
A candidate path is deleted using the following steps:
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1. PCE sends PCInitiate message, setting the R-flag in the LSP
object.
2. PCC uses the PLSP-ID from the LSP object to find the candidate
path and delete it.
8. IANA Considerations
8.1. Association Type
This document defines a new association type: SR Policy Association.
IANA is requested to make the following codepoint assignment in the
"ASSOCIATION Type Field" subregistry [RFC8697] within the "Path
Computation Element Protocol (PCEP) Numbers" registry:
+-----------+-------------------------------------------+-----------+
| Type | Name | Reference |
+-----------+-------------------------------------------+-----------+
| 6 | SR Policy Association | This.I-D |
+-----------+-------------------------------------------+-----------+
8.2. PCEP TLV Type Indicators
This document defines four new TLVs for carrying additional
information about SR policy and SR candidate paths. IANA is
requested to make the assignment of a new value for the existing
"PCEP TLV Type Indicators" registry as follows:
+-----------+-------------------------------------------+-----------+
| Value | Description | Reference |
+-----------+-------------------------------------------+-----------+
| 56 | SRPOLICY-POL-NAME | This.I-D |
+-----------+-------------------------------------------+-----------+
| 57 | SRPOLICY-CPATH-ID | This.I-D |
+-----------+-------------------------------------------+-----------+
| 58 | SRPOLICY-CPATH-NAME | This.I-D |
+-----------+-------------------------------------------+-----------+
| 59 | SRPOLICY-CPATH-PREFERENCE | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD1 | COMPUTATION-PRIORITY | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD2 | EXPLICIT-NULL-LABEL-POLICY | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD3 | INVALIDATION | This.I-D |
+-----------+-------------------------------------------+-----------+
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8.3. PCEP Errors
This document defines one new Error-Value within the "Mandatory
Object Missing" Error-Type and two new Error-Values within the
"Association Error" Error-Type. IANA is requested to allocate new
error values within the "PCEP-ERROR Object Error Types and Values"
sub-registry of the PCEP Numbers registry, as follows:
+------------+------------------+-----------------------+-----------+
| Error-Type | Meaning | Error-value | Reference |
+------------+------------------+-----------------------+-----------+
| 6 | Mandatory Object | | [RFC5440] |
| | Missing | | |
+------------+------------------+-----------------------+-----------+
| | | TBD6: SR Policy | This.I-D |
| | | Missing Mandatory TLV | |
+------------+------------------+-----------------------+-----------+
| 26 | Association | | [RFC8697] |
| | Error | | |
+------------+------------------+-----------------------+-----------+
| | | TBD7: SR Policy | This.I-D |
| | | Identifers Mismatch | |
+------------+------------------+-----------------------+-----------+
| | | TBD8: SR Policy | This.I-D |
| | | Candidate Path | |
| | | Identifiers Mismatch | |
+------------+------------------+-----------------------+-----------+
8.4. TE-PATH-BINDING TLV Flag field
IANA is requested to allocate new bit within the "TE-PATH-BINDING TLV
Flag field" sub-registry of the PCEP Numbers registry, as follows:
+------------+------------------------------------------+-----------+
| Bit position | Description | Reference |
+--------------+----------------------------------------+-----------+
| 1 | Specified-BSID-only | This.I-D |
+--------------+----------------------------------------+-----------+
9. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to RFC 7942.]
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
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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".
9.1. Cisco
* Organization: Cisco Systems
* Implementation: IOS-XR PCC and PCE.
* Description: An experimental code-point is currently used.
* Maturity Level: Proof of concept.
* Coverage: Full.
* Contact: mkoldych@cisco.com
9.2. Juniper
* Organization: Juniper Networks
* Implementation: Head-end and controller.
* Description: An experimental code-point is currently used.
* Maturity Level: Proof of concept.
* Coverage: Partial.
* Contact: cbarth@juniper.net
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10. Security Considerations
This document defines one new type for association, which do not add
any new security concerns beyond those discussed in [RFC5440],
[RFC8231], [RFC8664], [I-D.ietf-pce-segment-routing-ipv6] and
[RFC8697] in itself.
The information carried in the SRPAT ASSOCIATION, as per this
document is related to SR Policy. It often reflects information that
can also be derived from the SR Database, but association provides a
much easier grouping of related LSPs and messages. The SRPAT
ASSOCIATION could provide an adversary with the opportunity to
eavesdrop on the relationship between the LSPs. Thus securing the
PCEP session using Transport Layer Security (TLS) [RFC8253], as per
the recommendations and best current practices in [RFC7525], is
RECOMMENDED.
11. Acknowledgement
Would like to thank Stephane Litkowski, Boris Khasanov, Praveen Kumar
and Tom Petch for review and suggestions.
12. References
12.1. 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>.
[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>.
[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/info/rfc8174>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
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[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[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/info/rfc7942>.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", Work in
Progress, Internet-Draft, draft-ietf-spring-segment-
routing-policy-22, 22 March 2022,
<https://www.ietf.org/archive/id/draft-ietf-spring-
segment-routing-policy-22.txt>.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Jain, D., and S. Lin, "Advertising Segment Routing
Policies in BGP", Work in Progress, Internet-Draft, draft-
ietf-idr-segment-routing-te-policy-17, 14 April 2022,
<https://www.ietf.org/archive/id/draft-ietf-idr-segment-
routing-te-policy-17.txt>.
[RFC8697] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
Dhody, D., and Y. Tanaka, "Path Computation Element
Communication Protocol (PCEP) Extensions for Establishing
Relationships between Sets of Label Switched Paths
(LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
<https://www.rfc-editor.org/info/rfc8697>.
[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/info/rfc8664>.
[I-D.koldychev-pce-operational]
Koldychev, M., Sivabalan, S., Peng, S., Achaval, D., and
H. Kotni, "PCEP Operational Clarification", Work in
Progress, Internet-Draft, draft-koldychev-pce-operational-
05, 19 February 2022, <https://www.ietf.org/archive/id/
draft-koldychev-pce-operational-05.txt>.
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[I-D.koldychev-pce-multipath]
Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
Bidgoli, H., Yadav, B., and S. Peng, "PCEP Extensions for
Signaling Multipath Information", Work in Progress,
Internet-Draft, draft-koldychev-pce-multipath-05, 16
February 2021, <https://www.ietf.org/archive/id/draft-
koldychev-pce-multipath-05.txt>.
12.2. Informative References
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[I-D.ietf-pce-segment-routing-ipv6]
Li, C., Negi, M., Sivabalan, S., Koldychev, M.,
Kaladharan, P., and Y. Zhu, "PCEP Extensions for Segment
Routing leveraging the IPv6 data plane", Work in Progress,
Internet-Draft, draft-ietf-pce-segment-routing-ipv6-13, 1
April 2022, <https://www.ietf.org/internet-drafts/draft-
ietf-pce-segment-routing-ipv6-13.txt>.
Appendix A. Contributors
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Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing, 10095
China
Email: chengli13@huawei.com
Samuel Sidor
Cisco Systems, Inc.
Eurovea Central 3.
Pribinova 10
811 09 Bratislava
Slovakia
Email: ssidor@cisco.com
Authors' Addresses
Mike Koldychev
Cisco Systems, Inc.
2000 Innovation Drive
Kanata Ontario K2K 3E8
Canada
Email: mkoldych@cisco.com
Siva Sivabalan
Ciena Corporation
385 Terry Fox Dr.
Kanata Ontario K2K 0L1
Canada
Email: ssivabal@ciena.com
Colby Barth
Juniper Networks, Inc.
Email: cbarth@juniper.net
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Shuping Peng
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Email: pengshuping@huawei.com
Hooman Bidgoli
Nokia
Email: hooman.bidgoli@nokia.com
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