PCE Working Group D. Dhody
Internet-Draft Y. Lee
Intended status: Informational Huawei Technologies
Expires: October 26, 2019 D. Ceccarelli
Ericsson
J. Shin
SK Telecom
D. King
Lancaster University
O. Gonzalez de Dios
Telefonica I+D
April 24, 2019
Hierarchical Stateful Path Computation Element (PCE).
draft-ietf-pce-stateful-hpce-07
Abstract
A Stateful Path Computation Element (PCE) maintains information on
the current network state, including: computed Label Switched Path
(LSPs), reserved resources within the network, and pending path
computation requests. This information may then be considered when
computing new traffic engineered LSPs, and for associated
and dependent LSPs, received from Path Computation Clients (PCCs).
The Hierarchical Path Computation Element (H-PCE) architecture,
provides an architecture to allow the optimum sequence of
inter-connected domains to be selected, and network policy to be
applied if applicable, via the use of a hierarchical relationship
between PCEs.
Combining the capabilities of Stateful PCE and the Hierarchical PCE
would be advantageous. This document describes general considerations
and use cases for the deployment of Stateful PCE(s) using the
Hierarchical PCE architecture.
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/.
Internet-Drafts are draft documents valid for a maximum of six months
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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."
Copyright Notice
Copyright (c) 2019 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 and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
1.2. Use-cases and Applicability of Hierarchical Stateful PCE . 5
1.2.1 Applicability to ACTN . . . . . . . . . . . . . . . . . 6
1.2.2 End-to-End Contiguous LSP . . . . . . . . . . . . . . . 6
1.2.3 Applicability of a Stateful P-PCE . . . . . . . . . . . 7
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Hierarchical Stateful PCE . . . . . . . . . . . . . . . . . . 7
3.1. Passive Operations . . . . . . . . . . . . . . . . . . . . 9
3.2. Active Operations . . . . . . . . . . . . . . . . . . . . 11
3.3. PCE Initiation Operation . . . . . . . . . . . . . . . . . 12
3.3.1. Per Domain Stitched LSP . . . . . . . . . . . . . . . 13
4. Other Considerations . . . . . . . . . . . . . . . . . . . . . 15
4.1. Applicability to Inter-Layer . . . . . . . . . . . . . . . 15
5. Other Considerations . . . . . . . . . . . . . . . . . . . . . 16
5.1. Scalability Considerations . . . . . . . . . . . . . . . . 16
5.2. Confidentiality . . . . . . . . . . . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. Manageability Considerations . . . . . . . . . . . . . . . . . 17
7.1. Control of Function and Policy . . . . . . . . . . . . . . 17
7.2. Information and Data Models . . . . . . . . . . . . . . . 17
7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 17
7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 17
7.5. Requirements On Other Protocols . . . . . . . . . . . . . 18
7.6. Impact On Network Operations . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Contributor Addresses . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
The Path Computation Element communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path
computations in response to Path Computation Clients' (PCCs)
requests.
A stateful PCE is capable of considering, for the purposes of
path computation, not only the network state in terms of links and
nodes (referred to as the Traffic Engineering Database or TED) but
also the status of active services (previously computed paths,
and currently reserved resources, stored in the Label Switched
Paths Database (LSP-DB).
[RFC8051] describes general considerations for a stateful PCE
deployment and examines its applicability and benefits, as well as
its challenges and limitations through a number of use cases.
[RFC8231] describes a set of extensions to PCEP to provide stateful
control. A stateful PCE has access to not only the information
carried by the network's Interior Gateway Protocol (IGP), but also
the set of active paths and their reserved resources for its
computations. The additional state allows the PCE to compute
constrained paths while considering individual LSPs and their
interactions. [RFC8281] describes the setup, maintenance and
teardown of PCE-initiated LSPs under the stateful PCE model.
[RFC8231] also describes the active stateful PCE. The active PCE
functionality allows a PCE to reroute an existing LSP or make changes
to the attributes of an existing LSP, or delegate control of specific
LSPs to a new PCE.
The ability to compute shortest constrained TE LSPs in Multiprotocol
Label Switching (MPLS) and Generalized MPLS (GMPLS) networks across
multiple domains has been identified as a key motivation for PCE
development. [RFC6805] describes a Hierarchical PCE (H-PCE)
architecture which can be used for computing end-to-end paths for
inter-domain MPLS Traffic Engineering (TE) and GMPLS Label Switched
Paths (LSPs). Within the Hierarchical PCE (H-PCE) architecture
[RFC6805], the Parent PCE (P-PCE) is used to compute a multi-domain
path based on the domain connectivity information. A Child PCE
(C-PCE) may be responsible for a single domain or multiple domains,
it is used to compute the intra-domain path based on its domain
topology information.
This document presents general considerations for stateful PCE(s) in
hierarchical PCE architecture. In particular, the behavior changes
and additions to the existing stateful PCE mechanisms (including PCE-
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initiated LSP setup and active PCE usage) in the context of networks
using the H-PCE architecture.
The initial section of the document focuses on end to end (E2E)
inter-domain TE LSP. Section 3.3.1 describe the operations for the
Per Domain LSP that could be stitched.
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. Use-cases and Applicability of Hierarchical Stateful PCE
As per [RFC6805], in the hierarchical PCE architecture, a P-PCE
maintains a domain topology map that contains the child domains and
their interconnections. Usually, the P-PCE has no information about
the content of the child domains. But if the PCE is applied to the
Abstraction and Control of TE Networks (ACTN) [RFC8453] as described
in [I-D.ietf-pce-applicability-actn], the Provisioning Network
Controller (PNC) can provide an abstract topology to the Multi-Domain
Service Coordinator (MDSC). Thus the P-PCE in MDSC could be aware of
topology information in much more detail than just the domain
topology.
In a PCEP session between a PCC (Ingress) and a C-PCE, the C-PCE acts
as per the stateful PCE operations described in [RFC8231] and
[RFC8281]. The same C-PCE behaves as a PCC on the PCEP session
towards the P-PCE. The P-PCE is stateful in nature and thus maintains
the state of the inter-domain LSPs that are reported to it. The
inter-domain LSP could also be delegated by the C-PCE to the P-PCE,
so that the P-PCE could update the inter-domain path. The trigger for
this update could be the LSP state change reported for this LSP or
any other LSP. It could also be a change in topology at the P-PCE
such as inter-domain link status change. In case of use of stateful
H-PCE in ACTN, a change in abstract topology learned by the P-PCE
could also trigger the update. Some other external factors (such as a
measurement probe) could also be a trigger at the P-PCE. Any such
update would require an inter-domain path recomputation as described
in [RFC6805].
The inter-domain LSP could be set up using the end-to-end signaling
as described in [RFC6805]. Additionally a per-domain stitched LSP
model is also applicable in a P-PCE initiation model. Section 3.1,
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Section 3.2, and Section 3.3 describe the end-to-end Contiguous LSP
setup, whereas Section 3.3.1 describe the per-domain stitching.
1.2.1 Applicability to ACTN
[RFC8453] describes the framework for ACTN, where each PNC is
equivalent to a C-PCE, and the P-PCE is the MDSC. In this case the
P-PCE (MDSC) receives the request for inter-domain path setup as part
of the Virtual Network (VN) operations. The per-domain stitched LSP
for a P-PCE initiated model is well suited for ACTN. This is
described in Section 3.3.1 and Section 4.1 of this document.
[I-D.ietf-pce-applicability-actn] examines the applicability of PCE
to the ACTN framework. To support the function of multi domain
coordination via hierarchy, the hierarchy of stateful PCEs play a
crucial role.
In the ACTN framework, the Customer Network Controller (CNC) can
request the MDSC to check if there is a possibility to meet VN
requirements (before requesting for VN provisioning). The H-PCE
architecture as described in [RFC6805] can support VN compute
function via the use of Path Computation Request (PCReq) and Path
Computation Reply (PCRep) messages between the P-PCE and C-PCEs. When
the CNC requests for VN provisioning, the MDSC decompose this request
into multiple inter-domain LSP provisioning requests, which might be
further decomposed to per-domain path segments. This is described in
Section 3.3.1. The MDSC uses the LSP Initiate Request (PCInitiate)
message from the P-PCE towards the C-PCE, and the C-PCE reports the
state back to the P-PCE via a Path Computation State Report (PCRpt)
message. The P-PCE could make changes to the LSP via the use of a
Path Computation Update Request (PCUpd) message.
In this case, the P-PCE (as MDSC) interacts with multiple C-PCEs (as
PNCs) along the inter-domain path of the LSP.
1.2.2 End-to-End Contiguous LSP
Different signaling methods for inter-domain RSVP-TE signaling are
identified in [RFC4726]. Contiguous LSPs are achieved using the
procedures of [RFC3209] and [RFC3473] to create a single end-to-end
LSP that spans all domains. [RFC6805] describes the technique to
establish the optimum path when the sequence of domains is not known
in advance. It shows how the PCE architecture can be extended to
allow the optimum sequence of domains to be selected, and the optimum
end-to-end path to be derived.
In case of a stateful P-PCE, the stateful P-PCE has to be aware of
the inter-domain LSPs for it to consider them during path
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computation. For example, a domain diverse path from another LSP.
This is the Passive Stateful P-PCE as described in Section 3.1.
Additionally, the inter-domain LSP could be delegated to the P-PCE,
so that P-PCE could trigger an update via a PCUpd message. The update
could be triggered on receipt of the PCRpt message that indicates a
status change of this LSP or some other LSP. The other LSP could be
an associated LSP (such as protection) or an unrelated LSP whose
resource change leads to re-optimization at the P-PCE. This is the
Active Stateful Operation as described in Section 3.2. Further, the
P-PCE could be instructed to create an inter-domain LSP on its own
using the PCInitiate message for an E2E contiguous LSP. The P-PCE
would send the PCInitiate message to the Ingress domain C-PCE, which
would further instruct the Ingress PCC.
In this document, for the Contiguous LSP, the above interactions are
only between the ingress domain C-PCE and the P-PCE. The use of
stateful operations for an inter-domain LSP between the
transit/egress domain C-PCEs towards the P-PCE is out of scope of
this document.
1.2.3 Applicability of a Stateful P-PCE
[RFC8051] describes general considerations for a stateful PCE
deployment and examines its applicability and benefits, as well as
its challenges and limitations, through a number of use cases. These
are also applicable to the stateful P-PCE when used for the inter-
domain LSP path computation and setup. It should be noted that though
the stateful P-PCE has limited direct visibility inside the child
domain, it could still trigger re-optimization with the help of child
PCEs based on LSP state changes, abstract topology changes, or some
other external factors.
The C-PCE would delegate control of the inter-domain LSP to the P-PCE
so that the P-PCE can make changes to it. Note that, if the C-PCE
becomes aware of a topology change that is hidden from the P-PCE, it
could take back the delegation from the P-PCE to act on it itself.
Similarly, a P-PCE could also request for delegation if it needs to
make a change to the LSP (refer to
[I-D.ietf-pce-lsp-control-request]).
2. Terminology
The terminology is as per [RFC4655], [RFC5440], [RFC6805], [RFC8231],
and [RFC8281].
3. Hierarchical Stateful PCE
As described in [RFC6805], in the hierarchical PCE architecture, a
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P-PCE maintains a domain topology map that contains the child domains
(seen as vertices in the topology) and their interconnections (links
in the topology). The P-PCE has no information about the content of
the child domains. Each child domain has at least one PCE capable of
computing paths across the domain. These PCEs are known as C-PCEs
and have a direct relationship with the P-PCE. The P-PCE builds the
domain topology map either via direct configuration (allowing network
policy to also be applied) or from learned information received from
each C-PCE.
Note that, in the scope of this document, both the C-PCEs and the P-
PCE are stateful in nature.
[RFC8231] specifies new functions to support a stateful PCE. It also
specifies that a function can be initiated either from a PCC towards
a PCE (C-E) or from a PCE towards a PCC (E-C).
This document extends these functions to support H-PCE Architecture
from a C-PCE towards a P-PCE (CE-PE) or from a P-PCE towards a C-PCE
(PE-CE). All PCE types herein (i.e., PE or CE) are assumed to be
'stateful PCE'.
A number of interactions are expected in the Hierarchical Stateful
PCE architecture, these include:
LSP State Report (CE-PE): a child stateful PCE sends an LSP state
report to a Parent Stateful PCE whenever the state of a LSP
changes.
LSP State Synchronization (CE-PE): after the session between the
Child and Parent stateful PCEs is initialized, the P-PCE must
learn the state of C-PCE's TE LSPs.
LSP Control Delegation (CE-PE,PE-CE): a C-PCE grants to the P-PCE
the right to update LSP attributes on one or more LSPs; the C-PCE
may withdraw the delegation or the P-PCE may give up the
delegation at any time.
LSP Update Request (PE-CE): a stateful P-PCE requests modification
of attributes on a C-PCE's TE LSP.
PCE LSP Initiation Request (PE-CE): a stateful P-PCE requests C-PCE
to initiate a TE LSP.
Note that this hierarchy is recursive and thus a Label Switching
Router (LSR), as a PCC could delegate the control to a PCE, which may
delegate to its parent, which may further delegate it to its parent
(if it exist or needed). Similarly update operations could also be
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applied recursively.
[I-D.ietf-pce-hierarchy-extensions] defines the H-PCE capability TLV
that should be used in the OPEN message to advertise the H-PCE
capability. [RFC8231] defines the stateful PCE capability TLV. The
presence of both TLVs represent the support for stateful H-PCE
operations as described in this document.
[I-D.litkowski-pce-state-sync] describes the procedures to allow a
stateful communication between PCEs for various use-cases. The
procedures and extensions as described in Section 3 of
[I-D.litkowski-pce-state-sync] are also applicable to Child and
Parent PCE communication. The SPEAKER-IDENTITY-TLV (defined in
[RFC8232]) is included in the LSP object to identify the Ingress
(PCC). The PLSP-ID used in the forwarded PCRpt by the C-PCE to P-PCE
is same as the original one used by the PCC.
3.1. Passive Operations
Procedures as described in [RFC6805] are applied, where the ingress
C-PCE sends a request to the P-PCE. The P-PCE selects a set of
candidate domain paths based on the domain topology and the state of
the inter-domain links. It then sends computation requests to the C-
PCEs responsible for each of the domains on the candidate domain
paths. Each C-PCE computes a set of candidate path segments across
its domain and sends the results to the P-PCE. The P-PCE uses this
information to select path segments and concatenate them to derive
the optimal end-to-end inter-domain path. The end-to-end path is
then sent to the C-PCE that received the initial path request, and
this C-PCE passes the path on to the PCC that issued the original
request.
As per [RFC8231], PCC sends an LSP State Report carried on a PCRpt
message to the C-PCE, indicating the LSP's status. The C-PCE MAY
further propagate the State Report to the P-PCE. A local policy at
C-PCE MAY dictate which LSPs to be reported to the P-PCE. The PCRpt
message is sent from C-PCE to P-PCE.
State synchronization mechanism as described in [RFC8231] and
[RFC8232] are applicable to PCEP session between C-PCE and P-PCE as
well.
Taking the sample hierarchical domain topology example from [RFC6805]
as the reference topology for the entirety of this document.
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-----------------------------------------------------------------
| Domain 5 |
| ----- |
| |PCE 5| |
| ----- |
| |
| ---------------- ---------------- ---------------- |
| | Domain 1 | | Domain 2 | | Domain 3 | |
| | | | | | | |
| | ----- | | ----- | | ----- | |
| | |PCE 1| | | |PCE 2| | | |PCE 3| | |
| | ----- | | ----- | | ----- | |
| | | | | | | |
| | ----| |---- ----| |---- | |
| | |BN11+---+BN21| |BN23+---+BN31| | |
| | - ----| |---- ----| |---- - | |
| | |S| | | | | |D| | |
| | - ----| |---- ----| |---- - | |
| | |BN12+---+BN22| |BN24+---+BN32| | |
| | ----| |---- ----| |---- | |
| | | | | | | |
| | ---- | | | | ---- | |
| | |BN13| | | | | |BN33| | |
| -----------+---- ---------------- ----+----------- |
| \ / |
| \ ---------------- / |
| \ | | / |
| \ |---- ----| / |
| ----+BN41| |BN42+---- |
| |---- ----| |
| | | |
| | ----- | |
| | |PCE 4| | |
| | ----- | |
| | | |
| | Domain 4 | |
| ---------------- |
| |
-----------------------------------------------------------------
Figure 1: Sample Hierarchical Domain Topology
Steps 1 to 11 are exactly as described in section 4.6.2 (Hierarchical
PCE End-to-End Path Computation Procedure) of [RFC6805], the
following additional steps are added for stateful PCE:
(1) The Ingress LSR initiates the setup of the LSP as per the path
and reports to the PCE1 the LSP status ("GOING-UP").
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(2) The PCE1 further reports the status of the LSP to the P-PCE
(PCE5).
(3) The Ingress LSR notifies the LSP state to PCE1 when the state is
"UP".
(4) The PCE1 further reports the status of the LSP to the P-PCE
(PCE5).
The Ingress LSR could trigger path re-optimization by sending the
path computation request as described in [RFC6805], at this time it
can include the LSP object in the PCReq message as described in
[RFC8231].
3.2. Active Operations
[RFC8231] describes the case of active stateful PCE. The active PCE
functionality uses two specific PCEP messages:
o Update Request (PCUpd)
o State Report (PCRpt)
The first is sent by the PCE to a Path Computation Client (PCC) for
modifying LSP attributes. The PCC sends back a PCRpt to acknowledge
the requested operation or report any change in LSP's state.
As per [RFC8051], Delegation is an operation to grant a PCE,
temporary rights to modify a subset of LSP parameters on one or more
PCC's LSPs. The C-PCE may further choose to delegate to P-PCE based
on a local policy. The PCRpt message with "D" (delegate) flag is
sent from C-PCE to P-PCE.
To update an LSP, a PCE send to the PCC, an LSP Update Request using
a PCUpd message. For LSP delegated to the P-PCE via the child PCE,
the P-PCE can use the same PCUpd message to request change to the C-
PCE (the Ingress domain PCE), the PCE further propagates the update
request to the PCC.
The P-PCE uses the same mechanism described in Section 3.1 to compute
the end to end path using PCReq and PCRep messages.
The following additional steps are also initially performed, for
active operations, again using the reference architecture described
in Figure 1 (Sample Hierarchical Domain Topology).
(1) The Ingress LSR delegates the LSP to the PCE1 via PCRpt message
with D flag set.
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(2) The PCE1 further delegates the LSP to the P-PCE (PCE5).
Steps 4 to 10 of section 4.6.2 of [RFC6805] are executed to determine
the end to end path.
(3) The P-PCE (PCE5) sends the update request to the C-PCE
(PCE1) via PCUpd message.
(4) The PCE1 further updates the LSP to the Ingress LSR (PCC).
(5) The Ingress LSR initiates the setup of the LSP as per the path
and reports to the PCE1 the LSP status ("GOING-UP").
(6) The PCE1 further reports the status of the LSP to the P-PCE
(PCE5).
(7) The Ingress LSR notifies the LSP state to PCE1 when the state is
"UP".
(8) The PCE1 further reports the status of the LSP to the P-PCE
(PCE5).
3.3. PCE Initiation Operation
[RFC8281] describes the setup, maintenance and teardown of PCE-
initiated LSPs under the stateful PCE model, without the need for
local configuration on the PCC, thus allowing for a dynamic network
that is centrally controlled and deployed. To instantiate or delete
an LSP, the PCE sends the Path Computation LSP Initiate Request
(PCInitiate) message to the PCC. In case of inter-domain LSP in
Hierarchical PCE architecture, the initiation operations can be
carried out at the P-PCE. In which case after P-PCE finishes the E2E
path computation, it can send the PCInitiate message to the C-PCE
(the Ingress domain PCE), the PCE further propagates the initiate
request to the PCC.
The following additional steps are also initially performed, for PCE
initiated operations, again using the reference architecture
described in Figure 1 (Sample Hierarchical Domain Topology):
(1) The P-PCE (PCE5) is requested to initiate a LSP.
Steps 4 to 10 of section 4.6.2 of [RFC6805] are executed to determine
the end to end path.
(2) The P-PCE (PCE5) sends the initiate request to the child
PCE (PCE1) via PCInitiate message.
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(3) The PCE1 further propagates the initiate message to the Ingress
LSR (PCC).
(4) The Ingress LSR initiates the setup of the LSP as per the path
and reports to the PCE1 the LSP status ("GOING-UP").
(5) The PCE1 further reports the status of the LSP to the P-PCE
(PCE5).
(6) The Ingress LSR notifies the LSP state to PCE1 when the state is
"UP".
(7) The PCE1 further reports the status of the LSP to the P-PCE
(PCE5).
The Ingress LSR (PCC) generates the PLSP-ID for the LSP and inform
the C-PCE, which is propagated to the P-PCE as described in
[I-D.litkowski-pce-state-sync]
3.3.1. Per Domain Stitched LSP
The Hierarchical PCE architecture as per [RFC6805] is primarily used
for E2E LSP. With PCE-Initiated capability, another mode of
operation is possible, where multiple intra-domain LSPs are initiated
in each domain which are further stitched to form an E2E LSP. The
P-PCE sends PCInitiate message to each C-PCE separately to initiate
individual LSP segments along the domain path. These individual per
domain LSP are stitched together by some mechanism, which is out of
scope of this document (Refer [I-D.dugeon-pce-stateful-
interdomain]).
The following additional steps are also initially performed, for the
Per Domain stitched LSP operation, again using the reference
architecture described in Figure 1 (Sample Hierarchical Domain
Topology):
(1) The P-PCE (PCE5) is requested to initiate a LSP.
Steps 4 to 10 of section 4.6.2 of [RFC6805] are executed to determine
the end to end path, which are broken into per-domain LSPs say -
o S-BN41
o BN41-BN33
o BN33-D
It should be noted that the P-PCE MAY use other mechanisms to
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determine the suitable per-domain LSPs (apart from [RFC6805]).
For LSP (BN33-D)
(2) The P-PCE (PCE5) sends the initiate request to the child
PCE (PCE3) via PCInitiate message for LSP (BN33-D).
(3) The PCE3 further propagates the initiate message to BN33.
(4) BN33 initiates the setup of the LSP as per the path and reports
to the PCE3 the LSP status ("GOING-UP").
(5) The PCE3 further reports the status of the LSP to the P-PCE
(PCE5).
(6) The node BN33 notifies the LSP state to PCE3 when the state is
"UP".
(7) The PCE3 further reports the status of the LSP to the P-PCE
(PCE5).
For LSP (BN41-BN33)
(8) The P-PCE (PCE5) sends the initiate request to the child PCE
(PCE4) via PCInitiate message for LSP (BN41-BN33).
(9) The PCE4 further propagates the initiate message to BN41.
(10) BN41 initiates the setup of the LSP as per the path and reports
to the PCE4 the LSP status ("GOING-UP").
(11) The PCE4 further reports the status of the LSP to the P-PCE
(PCE5).
(l2) The node BN41 notifies the LSP state to PCE4 when the state is
"UP".
(13) The PCE4 further reports the status of the LSP to the P-PCE
(PCE5).
For LSP (S-BN41)
(14) The P-PCE (PCE5) sends the initiate request to the child
PCE (PCE1) via PCInitiate message for LSP (S-BN41).
(15) The PCE1 further propagates the initiate message to node S.
(16) S initiates the setup of the LSP as per the path and reports to
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the PCE1 the LSP status ("GOING-UP").
(17) The PCE1 further reports the status of the LSP to the P-PCE
(PCE5).
(18) The node S notifies the LSP state to PCE1 when the state is
"UP".
(19) The PCE1 further reports the status of the LSP to the P-PCE
(PCE5).
Additionally:
(20) Once P-PCE receives report of each per-domain LSP, it
should use suitable stitching mechanism, which is out of scope
of this document. In this step, P-PCE (PCE5) could also
initiate an E2E LSP (S-D) by sending the PCInitiate message to
Ingress C-PCE (PCE1). It is also possible to stitch the per-
domain LSP at the same time as the per-domain LSPs are
initiated as defined in [I-D.dugeon-pce-stateful-interdomain].
4. Other Considerations
4.1. Applicability to Inter-Layer
[RFC5623] describes a framework for applying the PCE-based
architecture to inter-layer (G)MPLS traffic engineering. The H-PCE
Stateful architecture with stateful P-PCE coordinating with the
stateful C-PCEs of higher and lower layer is shown in the figure
below.
+----------+
/| Parent |
/ | PCE |
/ +----------+
/ / Stateful
/ /
/ /
/ /
Stateful +---+/ /
Child + PCE + /
PCE Hi + Hi + /
+---+ /
+---+ +---+ / +---+ +---+
+ LSR +--+ LSR +........................+ LSR +--+ LSR +
+ H1 + + H2 + / + H3 + + H4 +
+---+ +---+\ +---+/ /+---+ +---+
\ + PCE + /
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\ + Lo + /
Stateful \ +---+ /
C-PCE \ /
Lo \+---+ +---+/
+ LSR +--+ LSR +
+ L1 + + L2 +
+---+ +---+
Figure 2: Sample Inter-Layer Topology
All procedures described in Section 3 are applicable to inter-layer
path setup as well.
5. Other Considerations
5.1. Scalability Considerations
It should be noted that if all the C-PCEs would report all the LSPs
in their domain, it could lead to scalability issues for the P-PCE.
Thus it is recommended to only report the LSPs which are involved in
H-PCE, i.e. the LSPs which are either delegated to the P-PCE or
initiated by the P-PCE. Scalability considerations for PCEP as per
[RFC8231] continue to apply for the PCEP session between child and
parent PCE.
5.2. Confidentiality
As described in section 4.2 of [RFC6805], information about the
content of child domains is not shared for both scaling and
confidentiality reasons. Along with the confidentiality during path
computation, the child PCE could also conceal the path information, a
C-PCE may replace a path segment with a path-key [RFC5520],
effectively hiding the content of a segment of a path.
6. Security Considerations
The security considerations listed in [RFC8231],[RFC6805] and
[RFC5440] apply to this document as well. As per [RFC6805], it is
expected that the parent PCE will require all child PCEs to use full
security when communicating with the parent.
Any multi-domain operation necessarily involves the exchange of
information across domain boundaries. This is bound to represent a
significant security and confidentiality risk especially when the
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child domains are controlled by different commercial concerns. PCEP
allows individual PCEs to maintain confidentiality of their domain
path information using path-keys [RFC5520], and the hierarchical PCE
architecture is specifically designed to enable as much isolation of
domain topology and capabilities information as is possible. The LSP
state in the PCRpt message SHOULD continue to use this.
The security consideration for PCE-Initiated LSP as per [RFC8281] is
also applicable from P-PCE to C-PCE.
Thus securing the PCEP session (between the P-PCE and the C-PCE)
using mechanism like TCP Authentication Option (TCP-AO) [RFC5925] or
Transport Layer Security (TLS) [RFC8253] is RECOMMENDED.
7. Manageability Considerations
All manageability requirements and considerations listed in
[RFC5440], [RFC6805], [RFC8231], and [RFC8281] apply to Stateful H-
PCE defined in this document. In addition, requirements and
considerations listed in this section apply.
7.1. Control of Function and Policy
Support of the hierarchical procedure will be controlled by the
management organization responsible for each child PCE. The parent
PCE must only accept path computation requests from authorized child
PCEs. If a parent PCE receives report from an unauthorized child
PCE, the report should be dropped. All mechanism as described in
[RFC8231] and [RFC8281] continue to apply.
7.2. Information and Data Models
An implementation SHOULD allow the operator to view the stateful and
H-PCE capabilities advertised by each peer. The PCEP YANG module
[I-D.ietf-pce-pcep-yang] can be extended to include details stateful
H-PCE.
7.3. 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].
7.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
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[RFC5440] and [RFC8231].
7.5. Requirements On Other Protocols
Mechanisms defined in this document do not imply any new requirements
on other protocols.
7.6. Impact On Network Operations
Mechanisms defined in [RFC5440] and [RFC8231] also apply to PCEP
extensions defined in this document.
The stateful H-PCE technique brings the applicability of stateful PCE
as described in [RFC8051], for the LSP traversing multiple domains.
8. IANA Considerations
There are no IANA considerations.
9. Acknowledgments
Thanks to Manuela Scarella, Haomian Zheng, Sergio Marmo, Stefano
Parodi, Giacomo Agostini, Jeff Tantsura and Rajan Rao for
suggestions.
10. References
10.1. 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,
<http://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,
<http://www.rfc-editor.org/info/rfc5440>.
[RFC6805] King, D., Ed. and A. Farrel, Ed., "The Application of the
Path Computation Element Architecture to the Determination
of a Sequence of Domains in MPLS and GMPLS", RFC 6805, DOI
10.17487/RFC6805, November 2012,
<http://www.rfc-editor.org/info/rfc6805>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
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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>.
[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>.
10.2. Informative References
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC3473, January 2003,
<https://www.rfc-editor.org/info/rfc3473>.
[RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for
Inter-Domain Multiprotocol Label Switching Traffic
Engineering", RFC 4726, DOI 10.17487/RFC4726, November
2006, <https://www.rfc-editor.org/info/rfc4726>.
[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>.
[RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel,
"Preserving Topology Confidentiality in Inter-Domain Path
Computation Using a Path-Key-Based Mechanism", RFC 5520,
DOI 10.17487/RFC5520, April 2009,
<https://www.rfc-editor.org/info/rfc5520>.
[RFC5623] Oki, E., Takeda, T., Le Roux, JL., and A. Farrel,
"Framework for PCE-Based Inter-Layer MPLS and GMPLS
Traffic Engineering", RFC 5623, DOI 10.17487/RFC5623,
September 2009, <https://www.rfc-editor.org/info/rfc5623>.
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[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
Stateful Path Computation Element (PCE)", RFC 8051,
DOI 10.17487/RFC8051, January 2017,
<https://www.rfc-editor.org/info/rfc8051>.
[RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
and D. Dhody, "Optimizations of Label Switched Path State
Synchronization Procedures for a Stateful PCE", RFC 8232,
DOI 10.17487/RFC8232, September 2017,
<https://www.rfc-editor.org/info/rfc8232>.
[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>.
[RFC8453] Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
Abstraction and Control of TE Networks (ACTN)", RFC 8453,
DOI 10.17487/RFC8453, August 2018,
<https://www.rfc-editor.org/info/rfc8453>.
[I-D.ietf-pce-applicability-actn]
Dhody, D., Lee, Y., and D. Ceccarelli, "Applicability of
Path Computation Element (PCE) for Abstraction and
Control of TE Networks (ACTN)", draft-ietf-pce-
applicability-actn-11 (work in progress), April 2019.
[I-D.litkowski-pce-state-sync]
Litkowski, S., Sivabalan, S., and D. Dhody, "Inter
Stateful Path Computation Element communication
procedures", draft-litkowski-pce-state-sync-05 (work in
progress), March 2019.
[I-D.ietf-pce-hierarchy-extensions]
Zhang, F., Zhao, Q., Dios, O., Casellas, R., and D. King,
"Extensions to Path Computation Element Communication
Protocol (PCEP) for Hierarchical Path Computation Elements
(PCE)", draft-ietf-pce-hierarchy-extensions-10 (work in
progress), March 2019.
[I-D.ietf-pce-pcep-yang]
Dhody, D., Hardwick, J., Beeram, V., and j.
jefftant@gmail.com, "A YANG Data Model for Path
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Computation Element Communications Protocol (PCEP)",
draft-ietf-pce-pcep-yang-11 (work in progress),
March 2019.
[I-D.dugeon-pce-stateful-interdomain]
Dugeon, O., Meuric, J., Lee, Y., Dhody, D., and D.
Ceccarelli, "PCEP Extension for Stateful Inter-Domain
Tunnels", draft-dugeon-pce-stateful-interdomain-02 (work
in progress), March 2019.
[I-D.ietf-pce-lsp-control-request]
Raghuram, A., Goddard, A., Yadlapalli, C., Karthik, J.,
Sivabalan, S., Parker, J., and M. Negi, "Ability for a
stateful Path Computation Element (PCE) to request and
obtain control of a LSP", draft-ietf-pce-lsp-control-
request-03 (work in progress), February 2019.
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Appendix A. Contributor Addresses
Avantika
ECI Telecom
India
EMail: avantika.srm@gmail.com
Xian Zhang
Huawei Technologies
Bantian, Longgang District
Shenzhen, Guangdong 518129
P.R.China
EMail: zhang.xian@huawei.com
Udayasree Palle
EMail: udayasreereddy@gmail.com
Authors' Addresses
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: dhruv.ietf@gmail.com
Young Lee
Huawei Technologies
5340 Legacy Drive, Building 3
Plano, TX 75023
USA
EMail: leeyoung@huawei.com
Daniele Ceccarelli
Ericsson
Torshamnsgatan,48
Stockholm
Sweden
EMail: daniele.ceccarelli@ericsson.com
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Jongyoon Shin
SK Telecom
6 Hwangsaeul-ro, 258 beon-gil, Bundang-gu, Seongnam-si,
Gyeonggi-do 463-784
Republic of Korea
EMail: jongyoon.shin@sk.com
Daniel King
Lancaster University
UK
EMail: d.king@lancaster.ac.uk
Oscar Gonzalez de Dios
Telefonica I+D
Don Ramon de la Cruz 82-84
Madrid, 28045
Spain
Phone: +34913128832
Email: oscar.gonzalezdedios@telefonica.com
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