PCE Working Group Q. Zhao
Internet-Draft Z. Li
Intended status: Standards Track D. Dhody
Expires: December 20, 2018 S. Karunanithi
Huawei Technologies
A. Farrel
Juniper Networks, Inc
C. Zhou
Cisco Systems
June 18, 2018
PCEP Procedures and Protocol Extensions for Using PCE as a Central
Controller (PCECC) of LSPs
draft-zhao-pce-pcep-extension-for-pce-controller-08
Abstract
The Path Computation Element (PCE) is a core component of Software-
Defined Networking (SDN) systems. It can compute optimal paths for
traffic across a network and can also update the paths to reflect
changes in the network or traffic demands.
PCE was developed to derive paths for MPLS Label Switched Paths
(LSPs), which are supplied to the head end of the LSP using the Path
Computation Element Communication Protocol (PCEP). But SDN has a
broader applicability than signaled (G)MPLS traffic-engineered (TE)
networks, and the PCE may be used to determine paths in a range of
use cases. PCEP has been proposed as a control protocol for use in
these environments to allow the PCE to be fully enabled as a central
controller.
A PCE-based central controller (PCECC) can simplify the processing of
a distributed control plane by blending it with elements of SDN and
without necessarily completely replacing it. Thus, the LSP can be
calculated/setup/initiated and the label forwarding entries can also
be downloaded through a centralized PCE server to each network
devices along the path while leveraging the existing PCE technologies
as much as possible.
This document specifies the procedures and PCEP protocol extensions
for using the PCE as the central controller.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Basic PCECC Mode . . . . . . . . . . . . . . . . . . . . . . 5
4. PCEP Requirements . . . . . . . . . . . . . . . . . . . . . . 5
5. Procedures for Using the PCE as the Central Controller
(PCECC) . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Stateful PCE Model . . . . . . . . . . . . . . . . . . . 6
5.2. New LSP Functions . . . . . . . . . . . . . . . . . . . . 6
5.3. PCECC Capability Advertisement . . . . . . . . . . . . . 7
5.4. LSP Operations . . . . . . . . . . . . . . . . . . . . . 8
5.4.1. Basic PCECC LSP Setup . . . . . . . . . . . . . . . . 8
5.4.2. Central Control Instructions . . . . . . . . . . . . 10
5.4.2.1. Label Download . . . . . . . . . . . . . . . . . 10
5.4.2.2. Label Cleanup . . . . . . . . . . . . . . . . . . 11
5.4.3. PCE Initiated PCECC LSP . . . . . . . . . . . . . . . 12
5.4.4. PCECC LSP Update . . . . . . . . . . . . . . . . . . 14
5.4.5. Re Delegation and Cleanup . . . . . . . . . . . . . . 16
5.4.6. Synchronization of Central Controllers Instructions . 16
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5.4.7. PCECC LSP State Report . . . . . . . . . . . . . . . 16
6. PCEP messages . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. The PCInitiate message . . . . . . . . . . . . . . . . . 17
6.2. The PCRpt message . . . . . . . . . . . . . . . . . . . . 18
7. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1. OPEN Object . . . . . . . . . . . . . . . . . . . . . . . 19
7.1.1. PCECC Capability sub-TLV . . . . . . . . . . . . . . 19
7.2. PATH-SETUP-TYPE TLV . . . . . . . . . . . . . . . . . . . 20
7.3. CCI Object . . . . . . . . . . . . . . . . . . . . . . . 20
7.3.1. Address TLVs . . . . . . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8.1. Malicious PCE . . . . . . . . . . . . . . . . . . . . . . 23
9. Manageability Considerations . . . . . . . . . . . . . . . . 23
9.1. Control of Function and Policy . . . . . . . . . . . . . 23
9.2. Information and Data Models . . . . . . . . . . . . . . . 23
9.3. Liveness Detection and Monitoring . . . . . . . . . . . . 23
9.4. Verify Correct Operations . . . . . . . . . . . . . . . . 23
9.5. Requirements On Other Protocols . . . . . . . . . . . . . 23
9.6. Impact On Network Operations . . . . . . . . . . . . . . 24
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
10.1. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 24
10.2. New Path Setup Type Registry . . . . . . . . . . . . . . 24
10.3. PCEP Object . . . . . . . . . . . . . . . . . . . . . . 24
10.4. CCI Object Flag Field . . . . . . . . . . . . . . . . . 24
10.5. PCEP-Error Object . . . . . . . . . . . . . . . . . . . 25
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
12.1. Normative References . . . . . . . . . . . . . . . . . . 25
12.2. Informative References . . . . . . . . . . . . . . . . . 26
Appendix A. Contributor Addresses . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
The Path Computation Element (PCE) [RFC4655] was developed to offload
path computation function from routers in an MPLS traffic-engineered
network. Since then, the role and function of the PCE has grown to
cover a number of other uses (such as GMPLS [RFC7025]) and to allow
delegated control [RFC8231] and PCE-initiated use of network
resources [RFC8281].
According to [RFC7399], Software-Defined Networking (SDN) refers to a
separation between the control elements and the forwarding components
so that software running in a centralized system, called a
controller, can act to program the devices in the network to behave
in specific ways. A required element in an SDN architecture is a
component that plans how the network resources will be used and how
the devices will be programmed. It is possible to view this
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component as performing specific computations to place traffic flows
within the network given knowledge of the availability of network
resources, how other forwarding devices are programmed, and the way
that other flows are routed. This is the function and purpose of a
PCE, and the way that a PCE integrates into a wider network control
system (including an SDN system) is presented in [RFC7491].
In early PCE implementations, where the PCE was used to derive paths
for MPLS Label Switched Paths (LSPs), paths were requested by network
elements (known as Path Computation Clients (PCCs)), and the results
of the path computations were supplied to network elements using the
Path Computation Element Communication Protocol (PCEP) [RFC5440].
This protocol was later extended to allow a PCE to send unsolicited
requests to the network for LSP establishment [RFC8281].
[RFC8283] introduces the architecture for PCE as a central controller
as an extension of the architecture described in [RFC4655] and
assumes the continued use of PCEP as the protocol used between PCE
and PCC. [RFC8283] further examines the motivations and
applicability for PCEP as a Southbound Interface (SBI), and
introduces the implications for the protocol.
[I-D.ietf-teas-pcecc-use-cases] describes the use cases for the PCECC
architecture.
A PCE-based central controller (PCECC) can simplify the processing of
a distributed control plane by blending it with elements of SDN and
without necessarily completely replacing it. Thus, the LSP can be
calculated/setup/initiated and the label forwarding entries can also
be downloaded through a centralized PCE server to each network
devices along the path while leveraging the existing PCE technologies
as much as possible.
This draft specify the procedures and PCEP protocol extensions for
using the PCE as the central controller for static LSPs, where LSPs
can be provisioned as explicit label instructions at each hop on the
end-to-end path. Each router along the path must be told what label-
forwarding instructions to program and what resources to reserve.
The PCE-based controller keeps a view of the network and determines
the paths of the end-to-end LSPs, and the controller uses PCEP to
communicate with each router along the path of the end-to-end LSP.
The extension for PCECC in Segment Routing (SR) is specified in a
separate draft [I-D.zhao-pce-pcep-extension-pce-controller-sr].
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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.
2. Terminology
Terminologies used in this document is same as described in the draft
[RFC8283] and [I-D.ietf-teas-pcecc-use-cases].
3. Basic PCECC Mode
In this mode LSPs are provisioned as explicit label instructions at
each hop on the end-to-end path. Each router along the path must be
told what label forwarding instructions to program and what resources
to reserve. The controller uses PCEP to communicate with each router
along the path of the end-to-end LSP.
Note that the PCE-based controller will take responsibility for
managing some part of the MPLS label space for each of the routers
that it controls, and may taker wider responsibility for partitioning
the label space for each router and allocating different parts for
different uses. This is also described in section 3.1.2. of
[RFC8283]. For the purpose of this document, it is assumed that
label range to be used by a PCE is known and set on both PCEP peers.
A future extension could add this capability to advertise the range
via possible PCEP extensions as well. The rest of processing is
similar to the existing stateful PCE mechanism.
4. PCEP Requirements
Following key requirements associated PCECC should be considered when
designing the PCECC based solution:
1. PCEP speaker supporting this draft MUST have the capability to
advertise its PCECC capability to its peers.
2. PCEP speaker not supporting this draft MUST be able to reject
PCECC related extensions with a error reason code that indicates
that this feature is not supported.
3. PCEP speaker MUST provide a means to identify PCECC based LSP in
the PCEP messages.
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4. PCEP procedures SHOULD provide a means to update (or cleanup) the
label- download entry to the PCC.
5. PCEP procedures SHOULD provide a means to synchronize the labels
between PCE to PCC in PCEP messages.
5. Procedures for Using the PCE as the Central Controller (PCECC)
5.1. Stateful PCE Model
Active stateful PCE is described in [RFC8231]. PCE as a central
controller (PCECC) reuses existing Active stateful PCE mechanism as
much as possible to control the LSP.
5.2. New LSP Functions
This document defines the following new PCEP messages and extends the
existing messages to support PCECC:
(PCRpt): a PCEP message described in [RFC8231]. PCRpt message is
used to send PCECC LSP Reports. It is also extended to report the
set of Central Controller's Instructions (CCI) (label forwarding
instructions in the context of this document) received from the
PCE. See Section 5.4.6 for more details.
(PCInitiate): a PCEP message described in [RFC8281]. PCInitiate
message is used to setup PCE-Initiated LSP based on PCECC
mechanism. It is also extended for Central Controller's
Instructions (CCI) (download or cleanup the Label forwarding
instructions in the context of this document) on all nodes along
the path.
(PCUpd): a PCEP message described in [RFC8231]. PCUpd message is
used to send PCECC LSP Update.
The new LSP functions defined in this document are mapped onto the
messages as shown in the following table.
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+----------------------------------------+--------------------------+
| Function | Message |
+----------------------------------------+--------------------------+
| PCECC Capability advertisement | Open |
| Label entry Add | PCInitiate |
| Label entry Cleanup | PCInitiate |
| PCECC Initiated LSP | PCInitiate |
| PCECC LSP Update | PCUpd |
| PCECC LSP State Report | PCRpt |
| PCECC LSP Delegation | PCRpt |
| PCECC Label Report | PCRpt |
+----------------------------------------+--------------------------+
This document specify a new object CCI (see Section 7.3) for the
encoding of central controller's instructions. In the scope of this
document this is limited to Label forwarding instructions. The CC-ID
is the unique identifier for the central controller's instructions in
PCEP. The PCEP messages are extended in this document to handle the
PCECC operations.
5.3. PCECC Capability Advertisement
During PCEP Initialization Phase, PCEP Speakers (PCE or PCC)
advertise their support of PCECC extensions.
This document defines a new Path Setup Type (PST)
[I-D.ietf-pce-lsp-setup-type] for PCECC, as follows:
o PST = TBD: Path is setup via PCECC mode.
A PCEP speaker MUST indicate its support of the function described in
this document by sending a PATH-SETUP-TYPE-CAPABILITY TLV in the OPEN
object with this new PST included in the PST list.
This document also defines the PCECC Capability sub-TLV
Section 7.1.1. PCEP speakers use this sub-TLV to exchange
information about their PCECC capability. If a PCEP speaker includes
PST=TBD in the PST List of the PATH-SETUP-TYPE-CAPABILITY TLV then it
MUST also include the PCECC Capability sub-TLV inside the PATH-SETUP-
TYPE-CAPABILITY TLV.
The presence of the PST and PCECC Capability sub-TLV in PCC's OPEN
Object indicates that the PCC is willing to function as a PCECC
client.
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The presence of the PST and PCECC Capability sub-TLV in PCE's OPEN
message indicates that the PCE is interested in function as a PCECC
server.
The PCEP protocol extensions for PCECC MUST NOT be used if one or
both PCEP Speakers have not included the PST or the PCECC Capability
sub-TLV in their respective OPEN message. If the PCEP Speakers
support the extensions of this draft but did not advertise this
capability then a PCErr message with Error-Type=19(Invalid Operation)
and Error-Value=TBD (Attempted PCECC operations when PCECC capability
was not advertised) will be generated and the PCEP session will be
terminated.
A PCC or a PCE MUST include both PCECC-CAPABILITY sub-TLV and
STATEFUL-PCE-CAPABILITY TLV ([RFC8231]) (with I flag set [RFC8281])
in OPEN Object to support the extensions defined in this document.
If PCECC-CAPABILITY sub-TLV is advertised and STATEFUL-PCE-CAPABILITY
TLV is not advertised in OPEN Object, it SHOULD send a PCErr message
with Error-Type=19 (Invalid Operation) and Error-value=TBD (stateful
PCE capability was not advertised) and terminate the session.
5.4. LSP Operations
The PCEP messages pertaining to PCECC MUST include PATH-SETUP-TYPE
TLV [I-D.ietf-pce-lsp-setup-type] in the SRP object to clearly
identify the PCECC LSP is intended.
5.4.1. Basic PCECC LSP Setup
In order to setup a LSP based on PCECC mechanism, a PCC MUST delegate
the LSP by sending a PCRpt message with PST set for PCECC (see
Section 7.2) and D (Delegate) flag (see [RFC8231]) set in the LSP
object.
LSP-IDENTIFIER TLV MUST be included for PCECC LSP, the tuple uniquely
identifies the LSP in the network. The LSP object is included in
central controller's instructions (label download) to identify the
PCECC LSP for this instruction. The PLSP-ID is the original
identifier used by the ingress PCC, so the transit LSR could have
multiple central controller instructions that have the same PLSP-ID.
The PLSP-ID in combination with the source (in LSP-IDENTIFIER TLV)
MUST be unique. The PLSP-ID is included for maintainability reasons.
As per [RFC8281], the LSP object could include SPEAKER-ENTITY-ID TLV
to identify the PCE that initiated these instructions. Also the CC-
ID is unique on the PCEP session as described in Section 7.3.
When a PCE receives PCRpt message with D flags and PST Type set, it
calculates the path and assigns labels along the path; and set up the
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path by sending PCInitiate message to each node along the path of the
LSP. The PCC generates a Path Computation State Report (PCRpt) and
include the central controller's instruction (CCI) and the identified
LSP. The CC-ID is uniquely identify the central controller's
instruction within PCEP. The PCC further responds with the PCRpt
messages including the CCI and LSP objects.
Once the central controller's instructions (label operations) are
completed, the PCE SHOULD send the PCUpd message to the Ingress PCC.
The PCUpd message is as per [RFC8231] SHOULD include the path
information as calculated by the PCE.
Note that the PCECC LSPs MUST be delegated to a PCE at all times.
LSP deletion operation for PCECC LSP is same as defined in [RFC8231].
If the PCE receives PCRpt message for LSP deletion then it does Label
cleanup operation as described in Section 5.4.2.2 for the
corresponding LSP.
The Basic PCECC LSP setup sequence is as shown below.
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+-------+ +-------+
|PCC | | PCE |
|Ingress| +-------+
+------| | |
| PCC +-------+ |
| Transit| | |
+------| | |-- PCRpt,PLSP-ID=1, PST=TBD, D=1---->| PCECC LSP
|PCC +--------+ | |
|Egress | | | |
+--------+ | | |
| | | |
|<------ PCInitiate,CC-ID=X,PLSP-ID=1 ------------ | Label
| | | | download
|------- PCRpt,CC-ID=X,PLSP-ID=1 ----------------->|
| | | |
| |<----- PCInitiate,CC-ID=Y,PLSP-ID=1 ----- | Label
| | | | download
| |----- PCRpt,CC-ID=Y,PLSP-ID=1 ---------->|
| | | |
| | |<--- PCInitiate,CC-ID=Z,PLSP-ID=1 - | Label
| | | | download
| | |---- PCRpt,CC-ID=Z,PLSP-ID=1 ------>|
| | | |
| | |<-- PCUpd,PLSP-ID=1,PST=TBD, D=1-----| PCECC LSP
| | | | Update
| | | |
Figure 2: Basic PCECC LSP setup
The PCECC LSP are considered to be 'up' by default (on receipt of
PCUpd message from PCE). The Ingress MAY further choose to deploy a
data plane check mechanism and report the status back to the PCE via
PCRpt message.
5.4.2. Central Control Instructions
The new central controller's instructions (CCI) for the label
operations in PCEP is done via the PCInitiate message, by defining a
new PCEP Objects for CCI operations. Local label range of each PCC
is assumed to be known at both the PCC and the PCE.
5.4.2.1. Label Download
In order to setup an LSP based on PCECC, the PCE sends a PCInitiate
message to each node along the path to download the Label instruction
as described in Section 5.4.1.
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The CCI object MUST be included, along with the LSP object in the
PCInitiate message. The LSP-IDENTIFIER TLV MUST be included in LSP
object. The SPEAKER-ENTITY-ID TLV SHOULD be included in LSP object.
If a node (PCC) receives a PCInitiate message which includes a Label
to download as part of CCI, that is out of the range set aside for
the PCE, it MUST send a PCErr message with Error-type=TBD (PCECC
failure) and Error-value=TBD (Label out of range) and MUST include
the SRP object to specify the error is for the corresponding label
update via PCInitiate message. If a PCC receives a PCInitiate
message but failed to download the Label entry, it MUST send a PCErr
message with Error-type=TBD (PCECC failure) and Error-value=TBD
(instruction failed) and MUST include the SRP object to specify the
error is for the corresponding label update via PCInitiate message.
New PCEP object for central control instructions (CCI) is defined in
Section 7.3.
5.4.2.2. Label Cleanup
In order to delete an LSP based on PCECC, the PCE sends a central
controller instructions via a PCInitiate message to each node along
the path of the LSP to cleanup the Label forwarding instruction.
If the PCC receives a PCInitiate message but does not recognize the
label in the CCI, the PCC MUST generate a PCErr message with Error-
Type 19(Invalid operation) and Error-Value=TBD, "Unknown Label" and
MUST include the SRP object to specify the error is for the
corresponding label cleanup (via PCInitiate message).
The R flag in the SRP object defined in [RFC8281] specifies the
deletion of Label Entry in the PCInitiate message.
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+-------+ +-------+
|PCC | | PCE |
|Ingress| +-------+
+------| | |
| PCC +-------+ |
| Transit| | |
+------| | |-- PCRpt,PLSP-ID=1,PST=TBD,D=1,R=1--->| PCECC LSP
|PCC +--------+ | | remove
|Egress | | | |
+--------+ | | |
| | | |
|<------ PCInitiate,CC-ID=X,PLSP-ID=1 ------------ | Label
| | | R=1 | cleanup
|------- PCRpt,CC-ID=X,PLSP-ID=1 ------------------>|
| | | |
| |<----- PCInitiate,CC-ID=Y,PLSP-ID=1 ------ | Label
| | | R=1 | cleanup
| |----- PCRpt,CC-ID=Y,PLSP-ID=1 ----------->|
| | | |
| | |<--- PCInitiate,CC-ID=Z,PLSP-ID=1 -- | Label
| | | R=1 | cleanup
| | |---- PCRpt,CC-ID=Z,PLSP-ID=1 ------->|
| | | |
As per [RFC8281], following the removal of the Label forwarding
instruction, the PCC MUST send a PCRpt message. The SRP object in
the PCRpt MUST include the SRP-ID-number from the PCInitiate message
that triggered the removal. The R flag in the SRP object MUST be
set.
5.4.3. PCE Initiated PCECC LSP
The LSP Instantiation operation is same as defined in [RFC8281].
In order to setup a PCE Initiated LSP based on the PCECC mechanism, a
PCE sends PCInitiate message with Path Setup Type set for PCECC (see
Section 7.2) to the Ingress PCC.
The Ingress PCC MUST also set D (Delegate) flag (see [RFC8231]) and C
(Create) flag (see [RFC8281]) in LSP object of PCRpt message. The
PCC responds with first PCRpt message with the status as "GOING-UP"
and assigned PLSP-ID.
Note that the label forwarding instructions from PCECC are send after
the initial PCInitiate and PCRpt exchange. This is done so that the
PLSP-ID and other LSP identifiers can be obtained from the ingress
and can be included in the label forwarding instruction in the next
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PCInitiate message. The rest of the PCECC LSP setup operations are
same as those described in Section 5.4.1.
The LSP deletion operation for PCE Initiated PCECC LSP is same as
defined in [RFC8281]. The PCE should further perform Label entry
cleanup operation as described in Section 5.4.2.2 for the
corresponding LSP.
The PCE Initiated PCECC LSP setup sequence is shown below -
+-------+ +-------+
|PCC | | PCE |
|Ingress| +-------+
+------| | |
| PCC +-------+ |
| Transit| | |
+------| | |<--PCInitiate,PLSP-ID=0,PST=TBD,D=1---| PCECC LSP
|PCC +--------+ | | Initiate
|Egress | | |--- PCRpt,PLSP-ID=2,P=1,D=1,C=1---> | PCECC LSP
+--------+ | | (GOING-UP) |
| | | |
|<------ PCInitiate,CC-ID=X,PLSP-ID=2 -------------- | Label
| | | | download
|------- PCRpt,CC-ID=X,PLSP-ID=2 ------------------>|
| | | |
| |<----- PCInitiate,CC-ID=Y,PLSP-ID=2 ------- | Label
| | | | download
| |----- PCRpt,CC-ID=Y,PLSP-ID=2 ----------->|
| | | |
| | |<--- PCInitiate,CC-ID=Z,PLSP-ID=2 --- | Label
| | | | download
| | |---- PCRpt,CC-ID=Z,PLSP-ID=2 ------->|
| | | |
| | |<-- PCUpd, PLSP-ID=2, PST=TBD, D=1--- | PCECC LSP
| | | (UP) | Update
| | |--- PCRpt,PLSP-ID=2,P=1,D=1,C=1---> |
| | | (UP) |
Once the label operations are completed, the PCE SHOULD send the
PCUpd message to the Ingress PCC. The PCUpd message is as per
[RFC8231].
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5.4.4. PCECC LSP Update
In case of a modification of PCECC LSP with a new path, a PCE sends a
PCUpd message to the Ingress PCC. But to follow the make-before-
break procedures, the PCECC first update new instructions based on
the updated LSP and then update to ingress to switch traffic, before
cleaning up the old instructions. A new CC-ID is used to identify
the updated instruction, the existing identifiers in the LSP object
identify the existing LSP. Once new instructions are downloaded, the
PCE further updates the new path at the ingress which triggers the
traffic switch on the updated path. The Ingress PCC acknowledges
with a PCRpt message, on receipt of PCRpt message, the PCE does
cleanup operation for the old LSP as described in Section 5.4.2.2.
The PCECC LSP Update sequence is shown below -
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+-------+ +-------+
|PCC | | PCE |
|Ingress| +-------+
+------| | |
| PCC +-------+ |
| Transit| | |
+------| | | |
|PCC +--------+ | |
|Egress | | | |
+--------+ | | |
| | | | New Path for
|<------ PCInitiate,CC-ID=XX,PLSP-ID=1 ----------- | LSP trigger
| | | | new instruct
|------- PCRpt,CC-ID=XX,PLSP-ID=1 ---------------->|
| | | |
| |<----- PCInitiate,CC-ID=YY,PLSP-ID=1------ | Label
| | | | download
| |----- PCRpt,CC-ID=YY,PLSP-ID=1 --------->|
| | | |
| | |<--- PCInitiate,CC-ID=ZZ,PLSP-ID=1 - | Label
| | | | download
| | |---- PCRpt,CC-ID=ZZ,PLSP-ID=1 ----->|
| | | |
| | |<-- PCUpd, PLSP-ID=1, PST=TBD, D=1-- | PCECC
| | | SRP=S | LSP Update
| | | |
| | |-- PCRpt,PLSP-ID=1,PST=TBD,D=1 -->| Trigger
| | | (SRP=S) | Delete old
| | | | instruct
| | | |
|<------ PCInitiate,CC-ID=X, PLSP-ID=1 ----------- | Label
| | | R=1 | cleanup
|------- PCRpt,CC-ID=X, PLSP-ID=1 ---------------->|
| | | |
| |<----- PCInitiate,CC-ID=Y, PLSP-ID=1 ----- | Label
| | | R=1 | cleanup
| |----- PCRpt,CC-ID=Y, PLSP-ID=1 --------->|
| | | |
| | |<--- PCInitiate,CC-ID=Z, PLSP-ID=1 - | Label
| | | R=1 | cleanup
| | |---- PCRpt,CC-ID=Z, PLSP-ID=1 ----->|
| | | |
The modified PCECC LSP are considered to be 'up' by default. The
Ingress MAY further choose to deploy a data plane check mechanism and
report the status back to the PCE via PCRpt message.
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5.4.5. Re Delegation and Cleanup
As described in [RFC8281], a new PCE can gain control over the
orphaned LSP. In case of PCECC LSP, the new PCE MUST also gain
control over the central controllers instructions in the same way by
sending a PCInitiate message that includes the SRP, LSP and CCI
objects and carries the CC-ID and PLSP-ID identifying the
instruction, it wants to take control of.
Further, as described in [RFC8281], the State Timeout Interval timer
ensures that a PCE crash does not result in automatic and immediate
disruption for the services using PCE-initiated LSPs. Similarly the
central controller instructions are not removed immediately upon PCE
failure. Instead, they are cleaned up on the expiration of this
timer. This allows for network cleanup without manual intervention.
The PCC MUST support removal of CCI as one of the behaviors applied
on expiration of the State Timeout Interval timer.
5.4.6. Synchronization of Central Controllers Instructions
The purpose of Central Controllers Instructions synchronization
(labels in the context of this document) is to make sure that the
PCE's view of CCI (Labels) matches with the PCC's Label allocation.
This synchronization is performed as part of the LSP state
synchronization as described in [RFC8231] and [RFC8233].
As per LSP State Synchronization [RFC8231], a PCC reports the state
of its LSPs to the PCE using PCRpt messages and as per [RFC8281], PCE
would initiate any missing LSPs and/or remove any LSPs that are not
wanted. The same PCEP messages and procedure is also used for the
Central Controllers Instructions synchronization. The PCRpt message
includes the CCI and the LSP object to report the label forwarding
instructions. The PCE would further remove any unwanted instructions
or initiate any missing instructions.
5.4.7. PCECC LSP State Report
As mentioned before, an Ingress PCC MAY choose to apply any OAM
mechanism to check the status of LSP in the Data plane and MAY
further send its status in PCRpt message to the PCE.
6. PCEP messages
As defined in [RFC5440], a PCEP message consists of a common header
followed by a variable-length body made of a set of objects that can
be either mandatory or optional. An object is said to be mandatory
in a PCEP message when the object must be included for the message to
be considered valid. For each PCEP message type, a set of rules is
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defined that specify the set of objects that the message can carry.
An implementation MUST form the PCEP messages using the object
ordering specified in this document.
LSP-IDENTIFIERS TLV MUST be included in the LSP object for PCECC LSP.
6.1. The PCInitiate message
The PCInitiate message [RFC8281] can be used to download or remove
the labels, the message has been extended as shown below -
<PCInitiate Message> ::= <Common Header>
<PCE-initiated-lsp-list>
Where:
<Common Header> is defined in [RFC5440]
<PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
[<PCE-initiated-lsp-list>]
<PCE-initiated-lsp-request> ::=
(<PCE-initiated-lsp-instantiation>|
<PCE-initiated-lsp-deletion>|
<PCE-initiated-lsp-central-control>)
<PCE-initiated-lsp-central-control> ::= <SRP>
<LSP>
<cci-list>
<cci-list> ::= <CCI>
[<cci-list>]
Where:
<PCE-initiated-lsp-instantiation> and
<PCE-initiated-lsp-deletion> are as per
[RFC8281].
The LSP and SRP object is defined in [RFC8231].
When PCInitiate message is used for central controller's instructions
(labels), the SRP, LSP and CCI objects MUST be present. The SRP
object is defined in [RFC8231] and if the SRP object is missing, the
receiving PCC MUST send a PCErr message with Error-type=6 (Mandatory
Object missing) and Error-value=10 (SRP object missing). The LSP
object is defined in [RFC8231] and if the LSP object is missing, the
receiving PCC MUST send a PCErr message with Error-type=6 (Mandatory
Object missing) and Error-value=8 (LSP object missing). The CCI
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object is defined in Section 7.3 and if the CCI object is missing,
the receiving PCC MUST send a PCErr message with Error-type=6
(Mandatory Object missing) and Error-value=TBD (CCI object missing).
More than one CCI object MAY be included in the PCInitiate message
for the transit LSR.
To cleanup the SRP object must set the R (remove) bit.
At max two instances of CCI object would be included in case of
transit LSR to encode both in-coming and out-going label forwarding
instructions. Other instances MUST be ignored.
6.2. The PCRpt message
The PCRpt message can be used to report the labels that were
allocated by the PCE, to be used during the state synchronization
phase.
<PCRpt Message> ::= <Common Header>
<state-report-list>
Where:
<state-report-list> ::= <state-report>[<state-report-list>]
<state-report> ::= (<lsp-state-report>|
<central-control-report>)
<lsp-state-report> ::= [<SRP>]
<LSP>
<path>
<central-control-report> ::= [<SRP>]
<LSP>
<cci-list>
<cci-list> ::= <CCI>
[<cci-list>]
Where:
<path> is as per [RFC8231] and the LSP and SRP object are
also defined in [RFC8231].
When PCRpt message is used to report the central controller's
instructions (labels), the LSP and CCI objects MUST be present. The
LSP object is defined in [RFC8231] and if the LSP object is missing,
the receiving PCE MUST send a PCErr message with Error-type=6
(Mandatory Object missing) and Error-value=8 (LSP object missing).
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The CCI object is defined in Section 7.3 and if the CCI object is
missing, the receiving PCC MUST send a PCErr message with Error-
type=6 (Mandatory Object missing) and Error-value=TBD (CCI object
missing). Two CCI object can be included in the PCRpt message for
the transit LSR.
7. PCEP Objects
The PCEP objects defined in this document are compliant with the PCEP
object format defined in [RFC5440].
7.1. OPEN Object
This document defines a new optional TLVs for use in the OPEN Object.
7.1.1. PCECC Capability sub-TLV
The PCECC-CAPABILITY sub-TLV is an optional TLV for use in the OPEN
Object for PCECC capability advertisement in PATH-SETUP-TYPE-
CAPABILITY TLV. Advertisement of the PCECC capability implies
support of LSPs that are setup through PCECC as per PCEP extensions
defined in this document.
Its format is shown in the following figure:
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=TBD | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The type of the TLV is TBD and it has a fixed length of 4 octets.
The value comprises a single field - Flags (32 bits).
No flags are assigned right now.
Unassigned bits are considered reserved. They MUST be set to 0 on
transmission and MUST be ignored on receipt.
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7.2. PATH-SETUP-TYPE TLV
The PATH-SETUP-TYPE TLV is defined in [I-D.ietf-pce-lsp-setup-type];
this document defines a new PST value:
o PST = TBD: Path is setup via PCECC mode.
On a PCRpt/PCUpd/PCInitiate message, the PST=TBD in PATH-SETUP-TYPE
TLV in SRP object indicates that this LSP was setup via a PCECC based
mechanism.
7.3. CCI Object
The Central Control Instructions (CCI) Object is used by the PCE to
specify the forwarding instructions (Label information in the context
of this document) to the PCC, and MAY be carried within PCInitiate or
PCRpt message for label download.
CCI Object-Class is TBD.
CCI Object-Type is 1 for the MPLS Label.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CC-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |O|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields in the CCI object are as follows:
CC-ID: A PCEP-specific identifier for the CCI information. A PCE
creates an CC-ID for each instruction, the value is unique within
the scope of the PCE and is constant for the lifetime of a PCEP
session. The values 0 and 0xFFFFFFFF are reserved and MUST NOT be
used.
Flags: is used to carry any additional information pertaining to the
CCI. Currently, the following flag bit is defined:
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* O bit(Out-label) : If the bit is set, it specifies the label is
the OUT label and it is mandatory to encode the next-hop
information (via IPV4-ADDRESS TLV or IPV6-ADDRESS TLV or
UNNUMBERED-IPV4-ID-ADDRESS TLV in the CCI object). If the bit
is not set, it specifies the label is the IN label and it is
optional to encode the local interface information (via
IPV4-ADDRESS TLV or IPV6-ADDRESS TLV or UNNUMBERED-IPV4-ID-
ADDRESS TLV in the CCI object).
Label (20-bit): The Label information.
Reserved (12 bit): Set to zero while sending, ignored on receive.
7.3.1. Address TLVs
This document defines the following TLVs for the CCI object to
associate the next-hop information in case of an outgoing label and
local interface information in case of an incoming label.
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IPV4-ADDRESS TLV:
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=TBD | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPV6-ADDRESS TLV:
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=TBD | Length = 16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// IPv6 address (16 bytes) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
UNNUMBERED-IPV4-ID-ADDRESS TLV:
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=TBD | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The address TLVs are as follows:
IPV4-ADDRESS TLV: an IPv4 address.
IPV6-ADDRESS TLV: an IPv6 address.
UNNUMBERED-IPV4-ID-ADDRESS TLV: a pair of Node ID / Interface ID
tuples.
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8. Security Considerations
The security considerations described in [RFC8231] and [RFC8281]
apply to the extensions described in this document. Additional
considerations related to a malicious PCE are introduced.
8.1. Malicious PCE
PCE has complete control over PCC to update the labels and can cause
the LSP's to behave inappropriate and cause cause major impact to the
network. As a general precaution, it is RECOMMENDED that these PCEP
extensions only be activated on authenticated and encrypted sessions
across PCEs and PCCs belonging to the same administrative authority,
using Transport Layer Security (TLS) [RFC8253], as per the
recommendations and best current practices in [RFC7525].
9. Manageability Considerations
9.1. Control of Function and Policy
A PCE or PCC implementation SHOULD allow to configure to enable/
disable PCECC capability as a global configuration.
9.2. Information and Data Models
[RFC7420] describes the PCEP MIB, this MIB can be extended to get the
PCECC capability status.
The PCEP YANG module [I-D.ietf-pce-pcep-yang] could be extended to
enable/disable PCECC capability.
9.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
9.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440] and [RFC8231].
9.5. Requirements On Other Protocols
PCEP extensions defined in this document do not put new requirements
on other protocols.
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9.6. Impact On Network Operations
PCEP extensions defined in this document do not put new requirements
on network operations.
10. IANA Considerations
10.1. PCEP TLV Type Indicators
IANA is requested to confirm the early allocation of the following
TLV Type Indicator values within the "PCEP TLV Type Indicators" sub-
registry of the PCEP Numbers registry, and to update the reference in
the registry to point to this document, when it is an RFC:
Value Meaning Reference
TBD PCECC-CAPABILITY This document
TBD IPV4-ADDRESS TLV This document
TBD IPV6-ADDRESS TLV This document
TBD UNNUMBERED-IPV4-ID-ADDRESS TLV This document
10.2. New Path Setup Type Registry
IANA is requested to allocate new PST Field in PATH- SETUP-TYPE TLV.
The allocation policy for this new registry should be by IETF
Consensus. The new registry should contain the following value:
Value Description Reference
TBD Traffic engineering path is This document
setup using PCECC mode
10.3. PCEP Object
IANA is requested to allocate new registry for CCI PCEP object.
Object-Class Value Name Reference
TBD CCI Object-Type This document
1 MPLS Label
10.4. CCI Object Flag Field
IANA is requested to create a registry to manage the Flag field of
the CCI object.
One bit to be defined for the CCI Object flag field in this document:
Codespace of the Flag field (CCI Object)
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Bit Description Reference
7 Specifies label This document
is out label
10.5. PCEP-Error Object
IANA is requested to allocate new error types and error values within
the "PCEP-ERROR Object Error Types and Values" sub-registry of the
PCEP Numbers registry for the following errors:
Error-Type Meaning
---------- -------
19 Invalid operation.
Error-value = TBD : Attempted PCECC
operations when
PCECC capability
was not advertised
Error-value = TBD : Stateful PCE
capability was not
advertised
Error-value = TBD : Unknown Label
6 Mandatory Object missing.
Error-value = TBD : CCI object missing
TBD PCECC failure.
Error-value = TBD : Label out of range.
Error-value = TBD : Instruction failed.
11. Acknowledgments
We would like to thank Robert Tao, Changjing Yan, Tieying Huang and
Avantika for their useful comments 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>.
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[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>.
[RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
Hardwick, "Path Computation Element Communication Protocol
(PCEP) Management Information Base (MIB) Module",
RFC 7420, DOI 10.17487/RFC7420, December 2014,
<https://www.rfc-editor.org/info/rfc7420>.
[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>.
[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>.
[RFC8233] Dhody, D., Wu, Q., Manral, V., Ali, Z., and K. Kumaki,
"Extensions to the Path Computation Element Communication
Protocol (PCEP) to Compute Service-Aware Label Switched
Paths (LSPs)", RFC 8233, DOI 10.17487/RFC8233, September
2017, <https://www.rfc-editor.org/info/rfc8233>.
[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>.
12.2. Informative References
[RFC4655] Farrel, A., Vasseur, J., 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>.
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[RFC7025] Otani, T., Ogaki, K., Caviglia, D., Zhang, F., and C.
Margaria, "Requirements for GMPLS Applications of PCE",
RFC 7025, DOI 10.17487/RFC7025, September 2013,
<https://www.rfc-editor.org/info/rfc7025>.
[RFC7399] Farrel, A. and D. King, "Unanswered Questions in the Path
Computation Element Architecture", RFC 7399,
DOI 10.17487/RFC7399, October 2014,
<https://www.rfc-editor.org/info/rfc7399>.
[RFC7491] King, D. and A. Farrel, "A PCE-Based Architecture for
Application-Based Network Operations", RFC 7491,
DOI 10.17487/RFC7491, March 2015,
<https://www.rfc-editor.org/info/rfc7491>.
[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>.
[RFC8283] Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
Architecture for Use of PCE and the PCE Communication
Protocol (PCEP) in a Network with Central Control",
RFC 8283, DOI 10.17487/RFC8283, December 2017,
<https://www.rfc-editor.org/info/rfc8283>.
[I-D.ietf-teas-pcecc-use-cases]
Zhao, Q., Li, Z., Khasanov, B., Ke, Z., Fang, L., Zhou,
C., Communications, T., and A. Rachitskiy, "The Use Cases
for Using PCE as the Central Controller(PCECC) of LSPs",
draft-ietf-teas-pcecc-use-cases-01 (work in progress), May
2017.
[I-D.ietf-pce-lsp-setup-type]
Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
Hardwick, "Conveying path setup type in PCEP messages",
draft-ietf-pce-lsp-setup-type-10 (work in progress), May
2018.
[I-D.ietf-pce-pcep-yang]
Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", draft-ietf-pce-pcep-
yang-07 (work in progress), March 2018.
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[I-D.zhao-pce-pcep-extension-pce-controller-sr]
Zhao, Q., Li, Z., Dhody, D., Karunanithi, S., Farrel, A.,
and C. Zhou, "PCEP Procedures and Protocol Extensions for
Using PCE as a Central Controller (PCECC) of SR-LSPs",
draft-zhao-pce-pcep-extension-pce-controller-sr-02 (work
in progress), March 2018.
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Appendix A. Contributor Addresses
Udayasree Palle
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: udayasreereddy@gmail.com
Mahendra Singh Negi
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: mahendrasingh@huawei.com
Katherine Zhao
Huawei Technologies
2330 Central Expressway
Santa Clara, CA 95050
USA
EMail: katherine.zhao@huawei.com
Boris Zhang
Telus Ltd.
Toronto
Canada
EMail: boris.zhang@telus.com
Authors' Addresses
Quintin Zhao
Huawei Technologies
125 Nagog Technology Park
Acton, MA 01719
USA
EMail: quintin.zhao@huawei.com
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Zhenbin Li
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
EMail: lizhenbin@huawei.com
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: dhruv.ietf@gmail.com
Satish Karunanithi
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: satishk@huawei.com
Adrian Farrel
Juniper Networks, Inc
UK
EMail: adrian@olddog.co.uk
Chao Zhou
Cisco Systems
EMail: choa.zhou@cisco.com
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