Internet Engineering Task Force (IETF) D. Dhody
Request for Comments: 8637 Huawei Technologies
Category: Informational Y. Lee
ISSN: 2070-1721 Futurewei Technologies
D. Ceccarelli
Ericsson
July 2019
Applicability of the Path Computation Element (PCE)
to the Abstraction and Control of TE Networks (ACTN)
Abstract
Abstraction and Control of TE Networks (ACTN) refers to the set of
virtual network (VN) operations needed to orchestrate, control, and
manage large-scale multidomain TE networks so as to facilitate
network programmability, automation, efficient resource sharing, and
end-to-end virtual service-aware connectivity and network function
virtualization services.
The Path Computation Element (PCE) is a component, application, or
network node that is capable of computing a network path or route
based on a network graph and applying computational constraints. The
PCE serves requests from Path Computation Clients (PCCs) that
communicate with it over a local API or using the Path Computation
Element Communication Protocol (PCEP).
This document examines the applicability of PCE to the ACTN
framework.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8637.
Dhody, et al. Informational [Page 1]RFC 8637 PCE-ACTN July 2019
Copyright Notice
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document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Background Information . . . . . . . . . . . . . . . . . . . 3
2.1. Path Computation Element (PCE) . . . . . . . . . . . . . 3
2.1.1. Role of PCE in SDN . . . . . . . . . . . . . . . . . 4
2.1.2. PCE in Multidomain and Multilayer Deployments . . . . 4
2.1.3. Relationship to PCE-Based Central Control . . . . . . 5
2.2. Abstraction and Control of TE Networks (ACTN) . . . . . . 5
3. Architectural Considerations . . . . . . . . . . . . . . . . 7
3.1. Multidomain Coordination via Hierarchy . . . . . . . . . 7
3.2. Abstraction . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Customer Mapping . . . . . . . . . . . . . . . . . . . . 9
3.4. Virtual Service Coordination . . . . . . . . . . . . . . 10
4. Interface Considerations . . . . . . . . . . . . . . . . . . 10
5. Realizing ACTN with PCE (and PCEP) . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Normative References . . . . . . . . . . . . . . . . . . 16
8.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Additional Information . . . . . . . . . . . . . . . 21
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
Abstraction and Control of TE Networks (ACTN) [RFC8453] refers to the
set of virtual network (VN) operations needed to orchestrate,
control, and manage large-scale multidomain TE networks so as to
facilitate network programmability, automation, efficient resource
sharing, and end-to-end virtual service-aware connectivity and
network function virtualization services.
Dhody, et al. Informational [Page 2]RFC 8637 PCE-ACTN July 2019
The Path Computation Element (PCE) [RFC4655] is a component,
application, or network node that is capable of computing a network
path or route based on a network graph and applying computational
constraints. The PCE serves requests from Path Computation Clients
(PCCs) that communicate with it over a local API or using the Path
Computation Element Communication Protocol (PCEP).
This document examines the PCE and ACTN architecture and describes
how PCE architecture is applicable to ACTN. It also lists the PCEP
extensions that are needed to use PCEP as an ACTN interface. This
document also identifies any gaps in PCEP that exist at the time of
publication of this document.
Further, ACTN, stateful Hierarchical PCE (H-PCE) [PCE-HPCE], and PCE
as a central controller (PCECC) [RFC8283] are based on the same basic
hierarchy framework and are thus compatible with each other.
2. Background Information
2.1. Path Computation Element (PCE)
The Path Computation Element Communication Protocol (PCEP) [RFC5440]
provides mechanisms for Path Computation Clients (PCCs) to request a
Path Computation Element (PCE) [RFC4655] to perform path
computations.
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.
A stateful PCE [RFC8231] 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
Dhody, et al. Informational [Page 3]
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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 a PCC to delegate control of
specific LSPs to a new PCE.
2.1.1. Role of PCE in SDN
Software-Defined Networking (SDN) [RFC7149] 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 component as performing
specific computations to place 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. It is concluded in [RFC7399] that this is the same function
that a PCE might offer in a network operated using a dynamic control
plane. This is the function and purpose of a PCE, and the way that a
PCE integrates into a wider network control system including SDN is
presented in Application-Based Network Operation (ABNO) [RFC7491].
2.1.2. PCE in Multidomain and Multilayer Deployments
Computing paths across large multidomain environments requires
special computational components and cooperation between entities in
different domains capable of complex path computation. The PCE
provides an architecture and a set of functional components to
address this problem space. A PCE may be used to compute end-to-end
paths across multidomain environments using a per-domain path
computation technique [RFC5152]. The Backward-Recursive PCE-based
path computation (BRPC) mechanism [RFC5441] defines a PCE-based path
computation procedure to compute interdomain-constrained MPLS and
GMPLS TE networks. However, per-domain technique assumes that the
sequence of domains to be crossed from source to destination is
known, either fixed by the network operator or obtained by other
means. BRPC can work best with a known domain sequence, and it will
also work nicely with a small set of interconnected domains.
However, it doesn't work well for a large set of interconnected
domains.
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[RFC6805] describes a Hierarchical PCE (H-PCE) architecture that can
be used for computing end-to-end paths for interdomain MPLS Traffic
Engineering (TE) and GMPLS Label Switched Paths (LSPs) when the
domain sequence is not known. Within the Hierarchical PCE (H-PCE)
architecture, the Parent PCE (P-PCE) is used to compute a multidomain
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 intradomain path based on its domain
topology information.
[PCE-HPCE] states the considerations for stateful PCEs in
Hierarchical PCE architecture. In particular, the behavior changes
and adds to the existing stateful PCE mechanisms (including PCE-
initiated LSP setup and active PCE usage) in the context of networks
using the H-PCE architecture.
[RFC5623] describes a framework for applying the PCE-based
architecture to interlayer (G)MPLS TE. It provides suggestions for
the deployment of PCE in support of multilayer networks. It also
describes the relationship between PCE and a functional component in
charge of the control and management of the Virtual Network Topology
(VNT) [RFC5212] called the VNT Manager (VNTM).
2.1.3. Relationship to PCE-Based Central Control
[RFC8283] introduces the architecture for PCE as a central controller
(PCECC); it further examines the motivations and applicability for
PCEP as a southbound interface (SBI) and introduces the implications
for the protocol. Section 2.1.3 of [RFC8283] describes a hierarchy
of PCE-based controllers as per the PCE Hierarchy Framework defined
in [RFC6805].
2.2. Abstraction and Control of TE Networks (ACTN)
[RFC8453] describes the high-level ACTN requirements and the
architecture model for ACTN, including the entities Customer Network
Controller (CNC), Multidomain Service Coordinator (MDSC), and
Provisioning Network Controller (PNC) and their interfaces.
The ACTN reference architecture is shown in Figure 1, which is
reproduced here from [RFC8453] for convenience. [RFC8453] remains
the definitive reference for the ACTN architecture. As depicted in
Figure 1, the ACTN architecture identifies a three-tier hierarchy.
Dhody, et al. Informational [Page 5]
RFC 8637 PCE-ACTN July 2019
+---------+ +---------+ +---------+
| CNC | | CNC | | CNC |
+---------+ +---------+ +---------+
\ | /
\ | /
Boundary =============\==============|==============/============
Between \ | /
Customer & ------- | CMI -------
Network Operator \ | /
+---------------+
| MDSC |
+---------------+
/ | \
------------ | MPI -------------
/ | \
+-------+ +-------+ +-------+
| PNC | | PNC | | PNC |
+-------+ +-------+ +-------+
| SBI / | / \
| / | SBI / \
--------- ----- | / \
( ) ( ) | / \
- Control - ( Phys. ) | / -----
( Plane ) ( Net ) | / ( )
( Physical ) ----- | / ( Phys. )
( Network ) ----- ----- ( Net )
- - ( ) ( ) -----
( ) ( Phys. ) ( Phys. )
--------- ( Net ) ( Net )
----- -----
CMI - (CNC-MDSC Interface)
MPI - (MDSC-PNC Interface)
SBI - (Southbound Interface)
Figure 1: ACTN Hierarchy
There are two interfaces with respect to the MDSC: one north of the
MDSC (the CNC-MDSC Interface (CMI)), and one south (the MDSC-PNC
Interface (MPI)). A hierarchy of MDSCs is possible with a recursive
MPI interface.
[RFC8454] provides an information model for ACTN interfaces.
Dhody, et al. Informational [Page 6]RFC 8637 PCE-ACTN July 2019
3. Architectural Considerations
The ACTN architecture [RFC8453] is based on the hierarchy and
recursiveness of controllers. It defines three types of controllers
(depending on the functionalities they implement). The main
functionalities are:
o Multidomain coordination
o Abstraction
o Customer mapping/translation
o Virtual service coordination
Section 3 of [RFC8453] describes these functions.
It should be noted that this document lists all possible ways in
which PCE could be used for each of the above functions, but all
functions are not required to be implemented via PCE. Similarly,
this document presents the ways in which PCEP could be used as the
communications medium between functional components. Operators may
choose to use the PCEP for multidomain coordination via stateful
H-PCE but alternatively use Network Configuration Protocol (NETCONF)
[RFC6241], RESTCONF [RFC8040], or BGP - Link State (BGP-LS) [RFC7752]
to get access to the topology and support abstraction function.
3.1. Multidomain Coordination via Hierarchy
With the definition of domain being everything that is under the
control of the single logical controller, as per [RFC8453], it is
needed both to have a control entity that oversees the specific
aspects of the different domains and to build a single abstracted
end-to-end network topology in order to coordinate end-to-end path
computation and path/service provisioning.
The MDSC in ACTN framework realizes this function by coordinating the
per-domain PNCs in a hierarchy of controllers. It also needs to
detach from the underlying network technology and express customer
concerns by business needs.
[RFC6805] and [PCE-HPCE] describe a hierarchy of PCEs with the Parent
PCE coordinating multidomain path computation function between Child
PCEs. It is easy to see how these principles align, and thus how the
stateful H-PCE architecture can be used to realize ACTN.
Dhody, et al. Informational [Page 7]
RFC 8637 PCE-ACTN July 2019
The per-domain stitched LSP in the Hierarchical stateful PCE
architecture, described in Section 3.3.1 of [PCE-HPCE], is well
suited for multidomain coordination function. This includes domain
sequence selection, End-to-End (E2E) path computation, and
controller-initiated (PCE-initiated) path setup and reporting. This
is also applicable to multilayer coordination in case of IP+optical
networks.
[PCE-STATE-SYNC] describes the procedures to allow a stateful
communication between PCEs for various use cases. The procedures and
extensions are also applicable to Child and Parent PCE communication
and are thus useful for ACTN as well.
3.2. Abstraction
To realize ACTN, an abstracted view of the underlying network
resources needs to be built. This includes global network-wide
abstracted topology based on the underlying network resources of each
domain. This also includes abstract topology created as per the
customer service connectivity requests and represented as a VN slice
allocated to each customer.
In order to compute and provide optimal paths, PCEs require an
accurate and timely Traffic Engineering Database (TED).
Traditionally, this TED has been obtained from a link-state (LS)
routing protocol supporting traffic engineering extensions. PCE may
construct its TED by participating in the IGP ([RFC3630] and
[RFC5305] for MPLS-TE; [RFC4203] and [RFC5307] for GMPLS). An
alternative is offered by BGP-LS [RFC7752].
In case of H-PCE [RFC6805], the Parent PCE needs to build the domain
topology map of the child domains and their interconnectivity.
[RFC6805] and [PCE-INTER-AREA] suggest that BGP-LS could be used as a
"northbound" TE advertisement from the Child PCE to the Parent PCE.
[PCEP-LS] proposes another approach for learning and maintaining the
Link-State and TE information as an alternative to IGPs and BGP
flooding, using PCEP itself. The Child PCE can use this mechanism to
transport Link-State and TE information from Child PCE to a Parent
PCE using PCEP.
In ACTN, there is a need to control the level of abstraction based on
the deployment scenario and business relationship between the
controllers. The mechanism used to disseminate information from the
PNC (Child PCE) to the MDSC (Parent PCE) should support abstraction.
[RFC8453] describes a few alternative approaches of abstraction. The
resulting abstracted topology can be encoded using the PCEP-LS
mechanisms [PCEP-LS] and its optical network extension
Dhody, et al. Informational [Page 8]
RFC 8637 PCE-ACTN July 2019
[PCEP-OPTICAL]. PCEP-LS is an attractive option when the operator
would wish to have a single control-plane protocol (PCEP) to achieve
ACTN functions.
[RFC8453] discusses two ways to build abstract topology from an MDSC
standpoint with interaction with PNCs. The primary method is called
automatic generation of abstract topology by configuration. With
this method, automatic generation is based on the abstraction/
summarization of the whole domain by the PNC and its advertisement on
the MPI. The secondary method is called on-demand generation of
supplementary topology via Path Compute Request/Reply. This method
may be needed to obtain further complementary information such as
potential connectivity from Child PCEs in order to facilitate an end-
to-end path provisioning. PCEP is well suited to support both
methods.
3.3. Customer Mapping
In ACTN, there is a need to map customer virtual network (VN)
requirements into a network provisioning request to the PNC. That
is, the customer requests/commands are mapped by the MDSC into
network provisioning requests that can be sent to the PNC.
Specifically, the MDSC provides mapping and translation of a
customer's service request into a set of parameters that are specific
to a network type and technology such that the network configuration
process is made possible.
[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. As described in [PCE-HPCE], for
interdomain LSP in Hierarchical PCE architecture, the initiation
operations can be carried out at the Parent PCE. In this case, after
Parent PCE finishes the E2E path computation, it can send the
PCInitiate message to the Child PCE; the Child PCE further propagates
the initiate request to the Label Switching Router (LSR). The
customer request is received by the MDSC (Parent PCE), and, based on
the business logic, global abstracted topology, network conditions,
and local policy, the MDSC (Parent PCE) translates this into a per-
domain LSP initiation request that a PNC (Child PCE) can understand
and act on. This can be done via the PCInitiate message.
PCEP extensions for associating opaque policy between PCEP peer
[ASSOC-POLICY] can be used.
Dhody, et al. Informational [Page 9]
RFC 8637 PCE-ACTN July 2019
3.4. Virtual Service Coordination
Virtual service coordination function in ACTN incorporates customer
service-related information into the virtual network service
operations in order to seamlessly operate virtual networks while
meeting customers' service requirements.
[PCEP-VN] describes the need for associating a set of LSPs with a VN
"construct" to facilitate VN operations in PCE architecture. This
association allows the PCEs to identify which LSPs belong to a
certain VN.
This association based on VN is useful for various optimizations at
the VN level, which can be applied to all the LSPs that are part of
the VN slice. During path computation, the impact of a path for an
LSP is compared against the paths of other LSPs in the VN. This is
to ensure optimization and SLA attainment for the VN rather than for
a single LSP. Similarly, during reoptimization, advanced path
computation algorithms and optimization techniques can be considered
for all the LSPs belonging to a VN/customer and optimize them all
together.
4. Interface Considerations
As per [RFC8453], to allow virtualization and multidomain
coordination, the network has to provide open, programmable
interfaces in which customer applications can create, replace, and
modify virtual network resources and services in an interactive,
flexible, and dynamic fashion while having no impact on other
customers. The two ACTN interfaces are as follows:
o The CNC-MDSC Interface (CMI) is an interface between a Customer
Network Controller and a Multidomain Service Coordinator. It
requests the creation of the network resources, topology, or
services for the applications. The MDSC may also report potential
network topology availability if queried for current capability
from the Customer Network Controller.
o The MDSC-PNC Interface (MPI) is an interface between a Multidomain
Service Coordinator and a Provisioning Network Controller. It
communicates the creation request, if required, of new
connectivity of bandwidth changes in the physical network via the
PNC. In multidomain environments, the MDSC needs to establish
multiple MPIs, one for each PNC, as there are multiple PNCs
responsible for its domain control.
Dhody, et al. Informational [Page 10]RFC 8637 PCE-ACTN July 2019
In the case of a hierarchy of MDSCs, the MPI is applied recursively.
From an abstraction point of view, the top-level MDSC, which
interfaces the CNC, operates on a higher level of abstraction (i.e.,
less granular level) than the lower-level MDSCs.
PCEP is especially suitable on the MPI as it meets the requirement
and the functions as set out in the ACTN framework [RFC8453]. Its
recursive nature is well suited via the multilevel hierarchy of PCE.
PCEP can also be applied to the CMI as the CNC can be a path
computation client while the MDSC can be a path computation server.
Section 5 describes how PCE and PCEP could help realize ACTN on the
MPI.
5. Realizing ACTN with PCE (and PCEP)
As per the example in Figure 2, there are 4 domains, each with their
own PNC and MDSC on top. The PNC and MDSC need PCE as an important
function. The PNC (or Child PCE) already uses PCEP to communicate to
the network device. It can utilize the PCEP as the MPI to
communicate between controllers too.
Dhody, et al. Informational [Page 11]
RFC 8637 PCE-ACTN July 2019
******
..........*MDSC*..............................
. ****** .. MPI .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
v v v .
****** ****** ****** .
*PNC1* *PNC2* *PNC4* .
****** ****** ****** .
+---------------+ +---------------+ +---------------+ .
|A |----| |----| C| .
| | | | | | .
|DOMAIN 1 |----|DOMAIN 2 |----|DOMAIN 4 | .
+------------B13+ +---------------+ +B43------------+ .
\ / .
\ ****** / .
\ *PNC3*<............/.....................
\ ****** /
\+---------------+/
B31 B34
| |
|DOMAIN 3 B|
+---------------+
MDSC -> Parent PCE
PNC -> Child PCE
MPI -> PCEP
Figure 2: ACTN with PCE
o Building Domain Topology at MDSC: PNC (or Child PCE) needs to have
the TED to compute the path in its domain. As described in
Section 3.2, it can learn the topology via IGP or BGP-LS. PCEP-LS
is also a proposed mechanism to carry link state and traffic
engineering information within PCEP. A mechanism to carry
abstracted topology while hiding technology-specific information
between PNC and MDSC is described in [PCEP-LS]. At the end of
this step, the MDSC (or Parent PCE) has the abstracted topology
from each of its PNCs (or Child PCE). This could be as simple as
a domain topology map as described in [RFC6805], or it can have
full topology information of all domains. The latter is not
scalable, and thus, an abstracted topology of each domain
interconnected by interdomain links is the most common case.
Dhody, et al. Informational [Page 12]RFC 8637 PCE-ACTN July 2019
* Topology Change: When the PNC learns of any topology change,
the PNC needs to decide if the change needs to be notified to
the MDSC. This is dependent on the level of abstraction
between the MDSC and the PNC.
o VN Instantiate: When an MDSC is requested to instantiate a VN, the
minimal information that is required would be a VN identifier and
a set of end points. Various path computation, setup constraints,
and objective functions may also be provided. In PCE terms, a VN
Instantiate can be considered as a set of paths belonging to the
same VN. As described in Section 3.4 and [PCEP-VN], the VN
association can help in identifying the set of paths that belong
to a VN. The rest of the information, like the endpoints,
constraints, and objective function (OF), is already defined in
PCEP in terms of a single path.
* Path Computation: As per the example in Figure 2, the VN
instantiate requires two end-to-end paths between (A in Domain
1 to B in Domain 3) and (A in Domain 1 to C in Domain 4). The
MDSC (or Parent PCE) triggers the end-to-end path computation
for these two paths. MDSC can do path computation based on the
abstracted domain topology that it already has, or it may use
the H-PCE procedures (Section 3.1) using the PCReq and PCRep
messages to get the end-to-end path with the help of the Child
PCEs (PNC). Either way, the resultant E2E paths may be broken
into per-domain paths.
* A-B: (A-B13,B13-B31,B31-B)
* A-C: (A-B13,B13-B31,B31-B34,B34-B43,B43-C)
* Per-Domain Path Instantiation: Based on the above path
computation, MDSC can issue the path instantiation request to
each PNC via PCInitiate message (see [PCE-HPCE] and [PCEP-VN]).
A suitable stitching mechanism would be used to stitch these
per-domain LSPs. One such mechanism is described in
[PCE-INTERDOMAIN], where PCEP is extended to support stitching
in stateful H-PCE context.
* Per-Domain Path Report: Each PNC should report the status of
the per-domain LSP to the MDSC via PCRpt message, as per the
hierarchy of stateful PCEs ([PCE-HPCE]). The status of the
end-to-end LSP (A-B and A-C) is made up when all the per-domain
LSPs are reported up by the PNCs.
* Delegation: It is suggested that the per-domain LSPs are
delegated to respective PNCs so that they can control the path
and attributes based on the conditions of each domain network.
Dhody, et al. Informational [Page 13]RFC 8637 PCE-ACTN July 2019
* State Synchronization: The state needs to be synchronized
between the Parent PCE and Child PCE. The mechanism described
in [PCE-STATE-SYNC] can be used.
o VN Modify: MDSC is requested to modify a VN, for example, the
bandwidth for VN is increased. This may trigger path computation
at MDSC as described in the previous step and can trigger an
update to an existing per-intradomain path (via PCUpd message) or
the creation (or deletion) of a per-domain path (via PCInitiate
message). As described in [PCE-HPCE], this should be done in
make-before-break fashion.
o VN Delete: MDSC is requested to delete a VN, in this case, based
on the E2E paths, and the resulting per-domain paths need to be
removed (via PCInitiate message).
o VN Update (based on network changes): Any change in the per-domain
LSP is reported to the MDSC (via PCRpt message) as per [PCE-HPCE].
This may result in changes in the E2E path or VN status. This may
also trigger a reoptimization leading to a new per-domain path, an
update to an existing path, or the deletion of the path.
o VN Protection: The VN protection/restoration requirements need to
be applied to each E2E path as well as each per-domain path. The
MDSC needs to play a crucial role in coordinating the right
protection/restoration policy across each PNC. The existing
protection/restoration mechanism of PCEP can be applied on each
path.
o In case a PNC generates an abstract topology towards the MDSC, the
PCInitiate/PCUpd messages from the MDSC to a PNC will contain a
path with abstract nodes and links. A PNC would need to take that
as an input for path computation to get a path with physical nodes
and links. Similarly, a PNC would convert the path received from
the device (with physical nodes and links) into an abstract path
(based on the abstract topology generated before with abstract
nodes and links) and report it to the MDSC.
6. IANA Considerations
This document has no IANA actions.
Dhody, et al. Informational [Page 14]RFC 8637 PCE-ACTN July 2019
7. Security Considerations
Various security considerations for PCEP are described in [RFC5440]
and [RFC8253]. Security considerations as stated in Sections 10.1,
10.6, and 10.7 of [RFC5440] continue to apply on PCEP when used as an
ACTN interface. Further, this document lists various extensions of
PCEP that are applicable; each of them specify various security
considerations that continue to apply here.
The ACTN framework described in [RFC8453] defines key components and
interfaces for managed traffic-engineered networks. It also lists
various security considerations such as request and control of
resources, confidentially of the information, and availability of
function, which should be taken into consideration.
As per [RFC8453], securing the request and control of resources,
confidentiality of the information, and availability of function
should all be critical security considerations when deploying and
operating ACTN platforms. From a security and reliability
perspective, ACTN may encounter many risks such as malicious attack
and rogue elements attempting to connect to various ACTN components
(with PCE being one of them). Furthermore, some ACTN components
represent a single point of failure and threat vector, and must also
manage policy conflicts and eavesdropping of communication between
different ACTN components. [RFC8453] further states that all
protocols used to realize the ACTN framework should have rich
security features, and customer, application, and network data should
be stored in encrypted data stores. When PCEP is used as an ACTN
interface, the security of PCEP provided by Transport Layer Security
(TLS) [RFC8253], as per the recommendations and best current
practices in [RFC7525] (unless explicitly set aside in [RFC8253]), is
used.
As per [RFC8453], regarding the MPI, a PKI-based mechanism is
suggested, such as building a TLS or HTTPS connection between the
MDSC and PNCs, to ensure trust between the physical network layer
control components and the MDSC. Which MDSC the PNC exports topology
information to, and the level of detail (full or abstracted), should
also be authenticated, and specific access restrictions and topology
views should be configurable and/or policy based. When PCEP is used
in MPI, the security functions, as per [RFC8253], are used to fulfill
these requirements.
As per [RFC8453], regarding the CMI, suitable authentication and
authorization of each CNC connecting to the MDSC will be required.
If PCEP is used in CMI, the security functions, as per [RFC8253], can
be used to support peer authentication, message encryption, and
integrity checks.
Dhody, et al. Informational [Page 15]
RFC 8637 PCE-ACTN July 2019
8. References
8.1. Normative 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>.
[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>.
[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,
<https://www.rfc-editor.org/info/rfc6805>.
[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>.
8.2. Informative References
[ASSOC-POLICY]
Litkowski, S., Sivabalan, S., Tantsura, J., Hardwick, J.,
and M. Negi, "Path Computation Element communication
Protocol extension for associating Policies and LSPs",
Work in Progress, draft-ietf-pce-association-policy-05,
February 2019.
[EXP] Casellas, R., Vilalta, R., Martinez, R., Munoz, R., Zheng,
H., and Y. Lee, "Experimental Validation of the ACTN
architecture for flexi-grid optical networks using Active
Stateful Hierarchical PCEs", 19th International Conference
on Transparent Optical Networks (ICTON),
DOI 10.5281/zenodo.832904, July 2017,
<https://zenodo.org/record/832904>.
[PCE-HPCE]
Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., and D. King,
"Hierarchical Stateful Path Computation Element (PCE).",
Work in Progress, draft-ietf-pce-stateful-hpce-10, June
2019.
Dhody, et al. Informational [Page 16]RFC 8637 PCE-ACTN July 2019
[PCE-INTER-AREA]
King, D. and H. Zheng, "Applicability of the Path
Computation Element to Interarea and Inter-AS MPLS and
GMPLS Traffic Engineering", Work in Progress,
draft-ietf-pce-inter-area-as-applicability-07, December
2018.
[PCE-INTERDOMAIN]
Dugeon, O., Meuric, J., Lee, Y., and D. Ceccarelli, "PCEP
Extension for Stateful Interdomain Tunnels", Work in
Progress, draft-dugeon-pce-stateful-interdomain-02, March
2019.
[PCE-STATE-SYNC]
Litkowski, S., Sivabalan, S., Li, C., and H. Zheng, "Inter
Stateful Path Computation Element (PCE) Communication
Procedures.", Work in Progress,
draft-litkowski-pce-state-sync-05, March 2019.
[PCEP-LS] Dhody, D., Lee, Y., and D. Ceccarelli, "PCEP Extension for
Distribution of Link-State and TE Information.", Work in
Progress, draft-dhodylee-pce-pcep-ls-13, February 2019.
[PCEP-OPTICAL]
Lee, Y., Zheng, H., Ceccarelli, D., Wang, W., Park, P.,
and B. Yoon, "PCEP Extension for Distribution of Link-
State and TE information for Optical Networks", Work in
Progress, draft-lee-pce-pcep-ls-optical-07, March 2019.
[PCEP-VN] Lee, Y., Zhang, X., and D. Ceccarelli, "Path Computation
Element communication Protocol (PCEP) extensions for
Establishing Relationships between sets of LSPs and
Virtual Networks", Work in Progress,
draft-leedhody-pce-vn-association-08, June 2019.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<https://www.rfc-editor.org/info/rfc3630>.
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
<https://www.rfc-editor.org/info/rfc4203>.
Dhody, et al. Informational [Page 17]RFC 8637 PCE-ACTN July 2019
[RFC5152] Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A
Per-Domain Path Computation Method for Establishing Inter-
Domain Traffic Engineering (TE) Label Switched Paths
(LSPs)", RFC 5152, DOI 10.17487/RFC5152, February 2008,
<https://www.rfc-editor.org/info/rfc5152>.
[RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux,
M., and D. Brungard, "Requirements for GMPLS-Based Multi-
Region and Multi-Layer Networks (MRN/MLN)", RFC 5212,
DOI 10.17487/RFC5212, July 2008,
<https://www.rfc-editor.org/info/rfc5212>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008,
<https://www.rfc-editor.org/info/rfc5307>.
[RFC5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
"A Backward-Recursive PCE-Based Computation (BRPC)
Procedure to Compute Shortest Constrained Inter-Domain
Traffic Engineering Label Switched Paths", RFC 5441,
DOI 10.17487/RFC5441, April 2009,
<https://www.rfc-editor.org/info/rfc5441>.
[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>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC7149] Boucadair, M. and C. Jacquenet, "Software-Defined
Networking: A Perspective from within a Service Provider
Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
<https://www.rfc-editor.org/info/rfc7149>.
[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>.
Dhody, et al. Informational [Page 18]RFC 8637 PCE-ACTN July 2019
[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>.
[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>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[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>.
[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>.
[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>.
[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>.
Dhody, et al. Informational [Page 19]RFC 8637 PCE-ACTN July 2019
[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>.
[RFC8454] Lee, Y., Belotti, S., Dhody, D., Ceccarelli, D., and B.
Yoon, "Information Model for Abstraction and Control of TE
Networks (ACTN)", RFC 8454, DOI 10.17487/RFC8454,
September 2018, <https://www.rfc-editor.org/info/rfc8454>.
Dhody, et al. Informational [Page 20]RFC 8637 PCE-ACTN July 2019
Appendix A. Additional Information
In the paper [EXP], the application of the ACTN architecture is
presented to demonstrate the control of a multidomain flexi-grid
optical network by proposing, adopting, and extending:
o the Hierarchical active stateful PCE architectures and protocols
o the PCEP protocol to support efficient and incremental link-state
topological reporting, known as PCEP-LS
o the per-link partitioning of the optical spectrum based on
variable-sized allocated frequency slots enabling network sharing
and virtualization
o the use of a model-based interface to dynamically request the
instantiation of virtual networks for specific clients/tenants.
The design and implementation of the test bed are reported in order
to validate the approach.
Acknowledgments
The authors would like to thank Jonathan Hardwick for the inspiration
behind this document. Further thanks to Avantika for her comments
with suggested text.
Thanks to Adrian Farrel and Daniel King for their substantial
reviews.
Thanks to Yingzhen Qu for RTGDIR review.
Thanks to Rifaat Shekh-Yusef for SECDIR review.
Thanks to Meral Shirazipour for GENART review.
Thanks to Roman Danyliw and Barry Leiba for IESG review comments.
Thanks to Deborah Brungard for being the responsible AD.
Dhody, et al. Informational [Page 21]RFC 8637 PCE-ACTN July 2019
Authors' Addresses
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Young Lee
Futurewei Technologies
5340 Legacy Drive, Suite 173
Plano, TX 75024
United States of America
Email: younglee.tx@gmail.com
Daniele Ceccarelli
Ericsson
Torshamnsgatan,48
Stockholm
Sweden
Email: daniele.ceccarelli@ericsson.com
Dhody, et al. Informational [Page 22]
