Use Cases for a PCE as a Central Controller (PCECC)
draft-ietf-teas-pcecc-use-cases-18
| Document | Type | Active Internet-Draft (teas WG) | |
|---|---|---|---|
| Authors | Zhenbin Li , Dhruv Dhody , Quintin Zhao , Zekung Ke, Boris Khasanov | ||
| Last updated | 2024-05-31 | ||
| Replaces | draft-zhao-teas-pcecc-use-cases | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
| Formats | |||
| Reviews |
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by Susan Hares
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Vishnu Pavan Beeram | ||
| Shepherd write-up | Show Last changed 2023-03-25 | ||
| IESG | IESG state | RFC Ed Queue | |
| Action Holders |
(None)
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| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Jim Guichard | ||
| Send notices to | vishnupavan@gmail.com | ||
| IANA | IANA review state | IANA OK - No Actions Needed | |
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| Details |
draft-ietf-teas-pcecc-use-cases-18
TEAS Working Group Z. Li
Internet-Draft D. Dhody
Intended status: Informational Huawei Technologies
Expires: 2 December 2024 Q. Zhao
Etheric Networks
K. He
Tencent Holdings Ltd.
B. Khasanov
Yandex LLC
31 May 2024
Use Cases for a PCE as a Central Controller (PCECC)
draft-ietf-teas-pcecc-use-cases-18
Abstract
The PCE is a core component of a Software-Defined Networking (SDN)
system. It can be used to compute optimal paths for network traffic
and update existing paths to reflect changes in the network or
traffic demands. PCE was developed to derive traffic-engineered
paths in MPLS networks, which are supplied to the head end of the
paths using the Path Computation Element Communication Protocol
(PCEP).
SDN has much broader applicability than signaled MPLS traffic-
engineered (TE) networks, and the PCE may be used to determine paths
in a range of use cases including static LSPs, Segment Routing (SR),
Service Function Chaining (SFC), and most forms of a routed or
switched network. It is, therefore, reasonable to consider PCEP as a
control protocol for use in these environments to allow the PCE to be
fully enabled as a central controller.
A PCE as a Central Controller (PCECC) can simplify the processing of
a distributed control plane by blending it with elements of SDN
without necessarily completely replacing it. This document describes
general considerations for PCECC deployment and examines its
applicability and benefits, as well as its challenges and
limitations, through a number of use cases. PCEP extensions which
are required for the PCECC use cases are covered in separate
documents.
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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This Internet-Draft will expire on 2 December 2024.
Copyright Notice
Copyright (c) 2024 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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. PCECC for Label Management . . . . . . . . . . . . . . . 5
3.2. PCECC and Segment Routing . . . . . . . . . . . . . . . . 7
3.2.1. PCECC SID Allocation for SR-MPLS . . . . . . . . . . 8
3.2.2. PCECC for SR-MPLS Best Effort (BE) Path . . . . . . . 9
3.2.3. PCECC for SR-MPLS TE Path . . . . . . . . . . . . . . 9
3.2.4. PCECC for SRv6 . . . . . . . . . . . . . . . . . . . 12
3.3. PCECC for Static TE LSP . . . . . . . . . . . . . . . . . 14
3.4. PCECC for Load Balancing (LB) . . . . . . . . . . . . . . 16
3.5. PCECC and Inter-AS TE . . . . . . . . . . . . . . . . . . 18
3.6. PCECC for Multicast LSPs . . . . . . . . . . . . . . . . 21
3.6.1. PCECC for P2MP/MP2MP LSPs' Setup . . . . . . . . . . 21
3.6.2. PCECC for the End-to-End Protection of P2MP/MP2MP
LSPs . . . . . . . . . . . . . . . . . . . . . . . . 24
3.6.3. PCECC for the Local Protection of the P2MP/MP2MP
LSPs . . . . . . . . . . . . . . . . . . . . . . . . 25
3.7. PCECC for Traffic Classification . . . . . . . . . . . . 26
3.8. PCECC for SFC . . . . . . . . . . . . . . . . . . . . . . 27
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3.9. PCECC for Native IP . . . . . . . . . . . . . . . . . . . 28
3.10. PCECC for BIER . . . . . . . . . . . . . . . . . . . . . 29
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
5. Security Considerations . . . . . . . . . . . . . . . . . . . 29
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.1. Normative References . . . . . . . . . . . . . . . . . . 30
7.2. Informative References . . . . . . . . . . . . . . . . . 31
Appendix A. Other Use Cases of PCECC . . . . . . . . . . . . . . 38
A.1. PCECC for Network Migration . . . . . . . . . . . . . . . 38
A.2. PCECC for L3VPN and PWE3 . . . . . . . . . . . . . . . . 39
A.3. PCECC for Local Protection (RSVP-TE) . . . . . . . . . . 40
A.4. Using reliable P2MP TE based multicast delivery for
distributed computations (MapReduce-Hadoop) . . . . . . . 41
Appendix B. Contributor Addresses . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44
1. Introduction
The PCE [RFC4655] was developed to offload the path computation
function from routers in an MPLS traffic-engineered (TE) network. 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. The role and function of PCE have grown to cover several
other uses (such as GMPLS [RFC7025] or Multicast), and to allow
delegated stateful 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
component as performing specific computations to place traffic flows
within the network given knowledge of the availability of the 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].
[RFC8283] introduces the architecture for the PCE as a central
controller as an extension to the architecture described in [RFC4655]
and assumes the continued use of PCEP as the protocol used between
the PCE and PCC. [RFC8283] further examines the motivations and
applicability of PCEP as a Southbound Interface (SBI) and introduces
the implications for the protocol.
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[RFC9050] introduces the procedures and extensions for PCEP to
support the PCECC architecture [RFC8283].
This document describes the various use cases for the PCECC
architecture.
2. Terminology
The following terminology is used in this document.
BGP-LS: Border Gateway Protocol - Link State [RFC9552].
LSP: Label Switched Path.
IGP: Interior Gateway Protocol. In the document, we assume either
Open Shortest Path First (OSPF) [RFC2328][RFC5340] or Intermediate
System to Intermediate System (IS-IS) [RFC1195] as IGP.
PCC: Path Computation Client. As per [RFC4655], any client
application requesting a path computation to be performed by a Path
Computation Element.
PCE: Path Computation Element. As per [RFC4655], an entity
(component, application, or network node) that is capable of
computing a network path or route based on a network graph and
applying computational constraints.
PCECC: PCE as a Central Controller. Extension of PCE to support SDN
functions as per [RFC8283].
PST: Path Setup Type [RFC8408].
RR: Route Reflector [RFC4456].
SID: Segment Identifier [RFC8402].
SR: Segment Routing [RFC8402].
SRGB: Segment Routing Global Block [RFC8402].
SRLB: Segment Routing Local Block [RFC8402].
TE: Traffic Engineering [RFC9522].
3. Use Cases
[RFC8283] describes various use cases for PCECC such as:
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* Use of PCECC to set up Static TE LSPs. The PCEP extension for
this use case is in [RFC9050].
* Use of PCECC in Segment Routing [RFC8402].
* Use of PCECC to set up Multicast Point-to-Multipoint (P2MP) LSP.
* Use of PCECC to set up Service Function Chaining (SFC) [RFC7665].
* Use of PCECC in Optical Networks.
Section 3.1 describes the general case of PCECC being in charge of
managing MPLS label space which is a prerequisite for further use
cases. Further, various use cases (SR, Multicast etc) are described
in the following sections to showcase scenarios that can benefit from
the use of PCECC.
It is interesting to note that some of the use cases listed can also
be supported via BGP instead of PCEP. However, within the scope of
this document, the focus is on the use of PCEP.
3.1. PCECC for Label Management
As per [RFC8283], in some cases, the PCE-based controller can take
responsibility for managing some part of the MPLS label space for
each of the routers that it controls, and it may take wider
responsibility for partitioning the label space for each router and
allocating different parts for different uses, communicating the
ranges to the router using PCEP.
[RFC9050] describes a mode where 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.
For this to work, the PCE-based controller will take responsibility
for managing some part of the MPLS label space for each of the
routers that it controls. An extension to PCEP could be done to
allow a PCC to inform the PCE of such a label space to control. (See
[I-D.li-pce-controlled-id-space] for a possible PCEP extension to
support the advertisement of the MPLS label space to the PCE to
control.)
[RFC8664] specifies extensions to PCEP that allow a stateful PCE to
compute, update or initiate SR-TE paths.
[I-D.ietf-pce-pcep-extension-pce-controller-sr] describes the
mechanism for PCECC to allocate and provision the node/prefix/
adjacency label (Segment Routing Identifier (SID)) via PCEP. To make
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such an allocation PCE needs to be aware of the label space from the
Segment Routing Global Block (SRGB) or Segment Routing Local Block
(SRLB) [RFC8402] of the node that it controls. A mechanism for a PCC
to inform the PCE of such a label space to control is needed within
the PCEP. The full SRGB/SRLB of a node could be learned via existing
IGP or BGP-LS [RFC9552] mechanisms.
Further, there have been proposals for a global label range in MPLS,
the PCECC architecture could be used as a means to learn the label
space of nodes, and could also be used to determine and provision the
global label range.
+------------------------------+ +------------------------------+
| PCE DOMAIN 1 | | PCE DOMAIN 2 |
| +--------+ | | +--------+ |
| | | | | | | |
| | PCECC1 | ---------PCEP---------- | PCECC2 | |
| | | | | | | |
| | | | | | | |
| +--------+ | | +--------+ |
| ^ ^ | | ^ ^ |
| / \ PCEP | | PCEP / \ |
| V V | | V V |
| +--------+ +--------+ | | +--------+ +--------+ |
| |NODE 11 | | NODE 1n| | | |NODE 21 | | NODE 2n| |
| | | ...... | | | | | | ...... | | |
| | PCECC | | PCECC | | | | PCECC | |PCECC | |
| |Enabled | | Enabled| | |Enabled | |Enabled | |
| +--------+ +--------+ | | +--------+ +--------+ |
| | | |
+------------------------------+ +------------------------------+
Figure 1: PCECC for MPLS Label Management
* As shown in Figure 1, PCC will advertise the PCECC capability to
the PCE central controller (PCECC) [RFC9050].
* The PCECC could also learn the label range set aside by the PCC
(via [I-D.li-pce-controlled-id-space]).
* Optionally, the PCECC could determine the shared MPLS global label
range for the network.
- In the case that the shared global label range needs to be
negotiated across multiple domains, the central controllers of
these domains will also need to negotiate a common global label
range across domains.
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- The PCECC will need to set the shared global label range to all
PCC nodes in the network.
As per [RFC9050], PCECC could also rely on the PCC to make label
allocations initially and use PCEP to distribute it to where it is
needed.
3.2. PCECC and Segment Routing
Segment Routing (SR) [RFC8402] leverages the source routing paradigm.
Using SR, a source node steers a packet through a path without
relying on hop-by-hop signalling protocols such as LDP [RFC5036] or
RSVP-TE [RFC3209]. Each path is specified as an ordered list of
instructions called "segments". Each segment is an instruction to
route the packet to a specific place in the network, or to perform a
specific service on the packet. A database of segments can be
distributed through the network using a intra-domain routing protocol
(such as IS-IS or OSPF) or an inter-domain protocol (BGP), or by any
other means. PCEP could also be one of other protocols.
[RFC8664] specifies the SR-specific PCEP extension for SR-MPLS.
PCECC may further use PCEP protocol for SR SIDs (Segment Identifiers)
distribution to the SR nodes (PCC) with some benefits. If the PCECC
allocates and maintains the SIDs in the network for the nodes and
adjacencies; and further distributes them to the SR nodes directly
via the PCEP session then it is more advantageous over the
configurations on each SR node and flooding them via IGP, especially
in an SDN environment.
When the PCECC is used for the distribution of the Node-SID and Adj-
SID for SR-MPLS, the Node-SID is allocated from the SRGB of the node.
For the allocation of Adj-SID, the allocation is from the SRLB of the
node as described in [I-D.ietf-pce-pcep-extension-pce-controller-sr].
[RFC8355] identifies various protection and resiliency usecases for
SR. Path protection lets the ingress node be in charge of the
failure recovery (used for SR-TE [RFC8664]). Also, protection can be
performed by the node adjacent to the failed component, commonly
referred to as local protection techniques or fast-reroute (FRR)
techniques. In the case of PCECC, the protection paths can be pre-
computed and set up by the PCE.
The Figure 2 illustrates the use case where the Node-SID and Adj-SID
are allocated by the PCECC for SR-MPLS.
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192.0.2.1/32
+----------+
| R1(1001) |
+----------+
|
+----------+
| R2(1002) | 192.0.2.2/32
+----------+
* | * *
* | * *
*link1| * *
192.0.2.4/32 * | *link2 * 192.0.2.5/32
+-----------+ 9001| * +-----------+
| R4(1004) | | * | R5(1005) |
+-----------+ | * +-----------+
* | *9003 * +
* | * * +
* | * * +
+-----------+ +-----------+
192.0.2.3/32 | R3(1003) | |R6(1006) |192.0.2.6/32
+-----------+ +-----------+
|
+-----------+
| R8(1008) | 192.0.2.8/32
+-----------+
Figure 2: SR Topology
3.2.1. PCECC SID Allocation for SR-MPLS
Each node (PCC) is allocated a Node-SID by the PCECC. The PCECC
needs to update the label mapping of each node to all the other nodes
in the domain. After receiving the label mapping, each node (PCC)
uses the local routing information to determine the nexthop and
download the label forwarding instructions accordingly. The
forwarding behaviour and the end result are the same as IGP shortest-
path SR forwarding based on Node-SID. Thus, from anywhere in the
domain, it enforces the ECMP-aware shortest-path forwarding of the
packet towards the related node.
For each adjacency in the network, a PCECC can allocate an Adj-SID.
The PCECC sends a PCInitiate message to update the label mapping of
each adjacency to the corresponding nodes in the domain. Each node
(PCC) downloads the label forwarding instructions accordingly. The
forwarding behaviour and the end result are similar to IGP-based Adj-
SID allocation and usage in SR.
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These mechanisms are described in
[I-D.ietf-pce-pcep-extension-pce-controller-sr].
3.2.2. PCECC for SR-MPLS Best Effort (BE) Path
In this use case, the PCECC needs to allocate the Node-SID (without
calculating the explicit path for the SR path). The ingress router
of the forwarding path needs to encapsulate the destination Node-SID
on top of the packet. All the intermediate nodes will forward the
packet based on the destination Node-SID. It is similar to the LDP
LSP.
R1 may send a packet to R8 simply by pushing an SR label with segment
{1008} (Node-SID for R8). The path will be based on the routing/
nexthop calculation on the routers.
3.2.3. PCECC for SR-MPLS TE Path
SR-TE paths may not follow an IGP shortest path tree (SPT). Such
paths may be chosen by a PCECC and provisioned on the ingress node of
the SR-TE path. The SR header consists of a list of SIDs (or MPLS
labels). The header has all necessary information so that the
packets can be guided from the ingress node to the egress node of the
path. Hence, there is no need for any signalling protocol. For the
case where a strict traffic engineering path is needed, all the Adj-
SID are stacked, otherwise, a combination of node-SID or adj-SID can
be used for the SR-TE paths.
As shown in Figure 3, R1 may send a packet to R8 by pushing an SR
header with segment list {1002, 9001, 1008}. Where 1002 and 1008 are
the Node-SID of R2 and R8 respectively. 9001 is the Adj-SID for
link1. The path should be: R1-R2-link1-R3-R8.
To achieve this, the PCECC first allocates and distributes SIDs as
described in Section 3.2.1. [RFC8664] describes the mechanism for a
PCE to compute, update, or initiate SR-MPLS TE paths.
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192.0.2.1/32
+----------+
| R1 (1001)|
+----------+
| |
90011 | |90012
link1 | |link2
+----------+
| R2 (1002)| 192.0.2.2/32
+----------+
link3 * | * * link4
90023 * | * * 90024
*link5| * *
192.0.2.4/32 *90025 | *link6 * 192.0.2.5/32
+-----------+ | *90026+-----------+
| R4 (1004) | | * | R5 (1005) |
+-----------+ | * +-----------+
* | * +
link10 * | * link7 +
* | * +
+-----------+ +-----------+
192.0.2.3/32 | R3 (1003) | |R6 (1006) |192.0.2.6/32
+-----------+ +-----------+
| |
|link8 |
| |----------|link9
+-----------+
| R8 (1008) | 192.0.2.8/32
+-----------+
Figure 3: PCECC TE LSP Setup Example
Refer to Figure 3 for an example of TE topology, where, 100x - are
Node-SIDs and 900xx - are Adj-SIDs.
* The SID allocation and distribution are done by the PCECC with all
Node-SIDs (100x) and all Adj-SIDs (900xx).
* Based on path computation request/delegation or PCE initiation,
the PCECC receives a request with constraints and optimization
criteria from a PCC.
* PCECC will calculate the optimal path according to the given
constraints (e.g. bandwidth).
* PCECC will provision SR-MPLS TE LSP (path R1-link1-R2-link6-R3-R8)
at the ingress node: {90011,1002,90026,1003,1008}
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* For the end-to-end protection, PCECC can provision the secondary
path (R1-link2-R2-link4-R5-R8): {90012,1002,90024,1005,1008}.
3.2.3.1. PCECC for SR Policy
[RFC8402] defines Segment Routing architecture, which uses an SR
Policy to steer packets from a node through an ordered list of
segments. The SR Policy could be configured on the headend or
instantiated by an SR controller. The SR architecture does not
restrict how the controller programs the network. In this case, the
focus is on PCEP as the protocol for SR Policy delivery from PCE to
PCC.
An SR Policy architecture is described in [RFC9256]. An SR Policy is
a framework that enables the instantiation of an ordered list of
segments on a node for implementing a source routing policy for the
steering of traffic for a specific purpose (e.g. for a specific SLA)
from that node.
An SR Policy is identified through the tuple <headend, color,
endpoint>.
Figure 3 is used as an example of PCECC application for SR Policy
instantiation for SR-MPLS, where, 100x - are Node-SIDs and 900xx -
are Adj-SIDs.
Let's assume that R1 needs to have two disjoint SR Policies towards
R8 based on different bandwidths, the possible paths are:
POL1: {Headend R1, color 100, Endpoint R8; Candidate Path1:
Segment List 1: {90011,1002,90023,1004,1003,1008}}
POL2: {Headend R1, color 200, Endpoint R8; Candidate Path1:
Segment List 1: {90012,1002,90024,1005,1006,1008}}
Each SR Policy (including candidate path and segment list) will be
signalled to a headend (R1) via PCEP
[I-D.ietf-pce-segment-routing-policy-cp] with the addition of an
ASSOCIATION object. Binding SID (BSID) [RFC8402] can be used for
traffic steering of labelled traffic into SR Policy, BSID can be
provisioned from PCECC also via PCEP
[I-D.ietf-pce-binding-label-sid]. For non-labelled traffic steering
into the SR Policy POL1 or POL2, a per-destination traffic steering
will be used by means of the BGP Color extended community [RFC9012]
The procedure:
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PCECC allocates Node-SIDs and Adj-SIDs using the mechanism
described in Section 3.2.1 for all nodes and links.
PCECC will calculate disjoint paths for POL1 and POL2 and create
Segment Lists for them:{90011,1002,90023,1004,1003,1008};{90012,10
02,90024,1005,1006,1008}.
PCECC will form both SR Policies POL1 and POL2.
PCECC will send both POL1 and POl2 to R1 via PCEP.
PCECC optionally can allocate BSIDs for the SR Policies.
The traffic from R1 to R8 which fits to color 100 will be steered
to POL1 and follows the path: R1-link1-R2-link3-R4-R3-R8. The
traffic from R1 to R8 which fits color 200 will be steered to POL2
and follows the path: R1-link2-R2-link4-R5-R6-R8. Due to the
possibility of having many Segment Lists in the same Candidate
Path of each POL1/POL2, PCECC could provision more paths towards
R8 and traffic will be balanced either as ECMP or as w/ECMP. This
is the advantage of SR Policy architecture.
Note that an SR Policy can be associated with multiple candidate
paths. A candidate path is selected when it is valid and it is
determined to be the best path of the SR Policy as described in
[RFC9256].
3.2.4. PCECC for SRv6
As per [RFC8402], with Segment Routing (SR), a node steers a packet
through an ordered list of instructions, called segments. Segment
Routing can be applied to the IPv6 architecture with the Segment
Routing Header (SRH) [RFC8754]. A segment is encoded as an IPv6
address. An ordered list of segments is encoded as an ordered list
of IPv6 addresses in the routing header. The active segment is
indicated by the Destination Address of the packet. Upon completion
of a segment, a pointer in the new routing header is incremented and
indicates the next segment.
As per [RFC8754], an SRv6 Segment is a 128-bit value. "SRv6 SID" or
simply "SID" are often used as a shorter reference for "SRv6
Segment". [RFC8986] defines the SRv6 SID as consisting of
LOC:FUNCT:ARG.
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[I-D.ietf-pce-segment-routing-ipv6] extends [RFC8664] to support SR
for the IPv6 data plane. Further, a PCECC could be extended to
support SRv6 SID allocation and distribution. An example of how PCEP
extensions could be extended for SRv6 for PCECC is described in
[I-D.dhody-pce-pcep-extension-pce-controller-srv6].
2001:db8::1
+----------+
| R1 |
+----------+
|
+----------+
| R2 | 2001:db8::2
+----------+
* | * *
* | * *
*link1| * *
2001:db8::4 * | *link2 * 2001:db8::5
+-----------+ | * +-----------+
| R4 | | * | R5 |
+-----------+ | * +-----------+
* | * * +
* | * * +
* | * * +
+-----------+ +-----------+
2001:db8::3 | R3 | |R6 |2001:db8::6
+-----------+ +-----------+
|
+-----------+
| R8 | 2001:db8::8
+-----------+
Figure 4: PCECC for SRv6
In this case, as shown in Figure 4, PCECC could assign the SRv6 SID
(in the form of an IPv6 address) to be used for node and adjacency.
Later, the SRv6 path in the form of a list of SRv6 SIDs could be used
at the ingress. Some examples -
* SRv6 SID-List={2001:db8::8} - The best path towards R8
* SRv6 SID-List={2001:db8::5, 2001:db8::8} - The path towards R8 via
R5
The rest of the procedures and mechanisms remain the same as SR-MPLS.
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3.3. PCECC for Static TE LSP
As described in Section 3.1.2 of [RFC8283], PCECC architecture
supports the provisioning of static TE LSP. To achieve this, the
existing PCEP can be used to communicate between the PCECC and nodes
along the path to provision 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.
192.0.2.1/32
+----------+
| R1 |
+----------+
| |
|link1 |
| |link2
+----------+
| R2 | 192.0.2.2/32
+----------+
link3 * | * * link4
* | * *
*link5| * *
192.0.2.4/32 * | *link6 * 192.0.2.5/32
+-----------+ | * +-----------+
| R4 | | * | R5 |
+-----------+ | * +-----------+
* | * * +
link10 * | * *link7 +
* | * * +
+-----------+ +-----------+
192.0.2.3/32 | R3 | |R6 |192.0.2.6/32
+-----------+ +-----------+
| |
|link8 |
| |link9
+-----------+
| R8 | 192.0.2.8/32
+-----------+
Figure 5: PCECC TE LSP Setup Example
Refer to Figure 5 for an example TE topology.
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* Based on path computation request/delegation or PCE initiation,
the PCECC receives a request with constraints and optimization
criteria.
* PCECC will calculate the optimal path according to the given
constraints (e.g. bandwidth).
* PCECC will provision each node along the path and assign incoming
and outgoing labels from R1 to R8 with the path as
"R1-link1-R2-link3-R4-link10-R3-link8-R8":
- R1: Outgoing label 1001 on link 1
- R2: Incoming label 1001 on link 1
- R2: Outgoing label 2003 on link 3
- R4: Incoming label 2003 on link 3
- R4: Outgoing label 4010 on link 10
- R3: Incoming label 4010 on link 10
- R3: Outgoing label 3008 on link 8
- R8: Incoming label 3008 on link 8
* This can also be represented as {R1, link1, 1001}, {1001, R2,
link3, 2003], {2003, R4, link10, 4010}, {4010, R3, link8, 3008},
{3008, R8}.
* For the end-to-end protection, PCECC programs each node along the
path from R1 to R8 with the secondary path: {R1, link2, 1002},
{1002, R2, link4, 2004], {2004, R5, link7, 5007}, {5007, R3,
link9, 3009}, {3009, R8}.
* It is also possible to have a bypass path for the local protection
set up by the PCECC. For example, the primary path as above, then
to protect the node R4 locally, PCECC can program the bypass path
like this: {R2, link5, 2005}, {2005, R3}. By doing this, the node
R4 is locally protected at R2.
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3.4. PCECC for Load Balancing (LB)
Very often many service providers use TE tunnels for solving issues
with non-deterministic paths in their networks. One example of such
applications is the usage of TEs in the mobile backhaul (MBH).
Consider the topology as shown in Figure 6 (AGG1...AGGN are
Aggregation Routers, Core 1...Core N are Core routers) -
TE1 -------------->
+---------+ +--------+ +--------+ +--------+ +------+ +---+
| Access |----| Access |----| AGG 1 |----| AGG N-1|----|Core 1|--|SR1|
| SubNode1| | Node 1 | +--------+ +--------+ +------+ +---+
+---------+ +--------+ | | | ^ |
| Access | Access | AGG Ring 1 | | |
| SubRing 1 | Ring 1 | | | | |
+---------+ +--------+ +--------+ | | |
| Access | | Access | | AGG 2 | | | |
| SubNode2| | Node 2 | +--------+ | | |
+---------+ +--------+ | | | | |
| | | | | | |
| | | +----TE2----|-+ |
+---------+ +--------+ +--------+ +--------+ +------+ +---+
| Access | | Access |----| AGG 3 |----| AGG N |----|Core N|--|SRn|
| SubNodeN|----| Node N | +--------+ +--------+ +------+ +---+
+---------+ +--------+
Figure 6: PCECC Load Balancing (LB) Use Case
This MBH architecture uses L2 access rings and sub-rings. L3 starts
at the aggregation layer. For the sake of simplicity, the figure
shows only one access sub-ring. The access ring and aggregation ring
are connected by Nx10GE interfaces. The aggregation domain runs its
own IGP. There are two Egress routers (AGG N-1, AGG N) that are
connected to the Core domain (Core 1...Core N) via L2 interfaces.
Core also has connections to service routers, RSVP-TE or SR-TE is
used for MPLS transport inside the ring. There could be at least 2
tunnels (one way) from each AGG router to egress AGG routers. There
are also many L2 access rings connected to AGG routers.
Service deployment is made by means of Layer 2 Virtual Private
Networks (L2VPNs) (Virtual Private LAN Services (VPLS)), Layer 3
Virtual Private Networks (L3VPNs) or Ethernet VPNs (EVPNs). Those
services use MPLS TE (or SR-TE) as transport towards egress AGG
routers. TE tunnels could be used as transport towards service
routers in case of seamless MPLS ([I-D.ietf-mpls-seamless-mpls])
based architecture.
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Load balancing between TE tunnels involves distributing network
traffic across multiple TE tunnels to optimize the use of available
network resources, enhance performance, and ensure reliability. Some
common techniques include Equal-Cost Multi-Path (ECMP) and Unequal-
Cost Multi-Path (UCMP) based on the bandwidth of the TE tunnels.
There is a need to solve the following tasks:
* Perform automatic load-balance amongst TE tunnels according to
current traffic load.
* TE bandwidth (BW) management: Provide guaranteed BW for specific
services: High-Speed Data Service (HSI)), IPTV, etc., and provide
time-based BW reservation (BW on demand (BoD)) for other services.
* Simplify the development of TE tunnels by automation without any
manual intervention.
* Provide flexibility for Service Router placement (anywhere in the
network by the creation of transport LSPs to them).
In this section, the focus is on load balancing (LB) tasks. LB task
could be solved by means of PCECC in the following way:
* Application or network service or operator can ask the SDN
controller (PCECC) for LSP-based load balancing between AGG X and
AGG N/AGG N-1 (egress AGG routers that have connections to the
core). Each of these will have associated constraints (i.e.
bandwidth, inclusion or exclusion specific links or nodes, number
of paths, objective function (OF), need for disjoint LSP paths
etc.);
* PCECC could calculate multiple (say N) LSPs according to given
constraints, the calculation is based on results of Objective
Function (OF) [RFC5541], constraints, endpoints, same or different
bandwidth (BW), different links (in case of disjoint paths) and
other constraints.
* Depending on the given LSP Path setup type (PST), PCECC will
download instructions to the PCC. At this stage, it is assumed
the PCECC is aware of the label space it controls and SID
allocation and distribution is already done in the case of SR.
* PCECC will send PCInitiate message [RFC8281] towards ingress AGG X
router(PCC) for each of N LSPs and receive PCRpt message [RFC8231]
back from PCCs. If PST is PCECC-SR, the PCECC will include a SID
stack as per [RFC8664]. If PST is PCECC (basic), then the PCECC
will assign labels along the calculated path and set up the path
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by sending central controller instructions in a PCEP message to
each node along the path of the LSP as per [RFC9050] and then send
PCUpd message to the ingress AGG X router with information about
new LSP. AGG X(PCC) will respond with PCRpt with LSP status.
* AGG X as an ingress router now has N LSPs towards AGG N and AGG
N-1 which are available for installation to the router's
forwarding table and load-balance traffic between them. Traffic
distribution between those LSPs depends on the particular
realization of the hash-function on that router.
* Since PCECC is aware of TEDB (TE state) and LSP-DB, it can manage
and prevent possible over-subscriptions and limit the number of
available load-balance states. Via PCECC mechanism the control
can take quick actions into the network by directly provisioning
the central control instructions.
3.5. PCECC and Inter-AS TE
There are various signalling options for establishing Inter-AS TE
LSP: contiguous TE LSP [RFC5151], stitched TE LSP [RFC5150], and
nested TE LSP [RFC4206].
Requirements for PCE-based Inter-AS setup [RFC5376] describe the
approach and PCEP functionality that is needed for establishing
Inter-AS TE LSPs.
[RFC5376] also gives Inter- and Intra-AS PCE Reference Model (as
shown in Figure 7) that is provided below in shortened form for the
sake of simplicity.
Inter-AS Inter-AS
PCC <-->PCE1<--------->PCE2
:: :: ::
:: :: ::
R1----ASBR1====ASBR3---R3---ASBR5
| AS1 | | PCC |
| | | AS2 |
R2----ASBR2====ASBR4---R4---ASBR6
:: ::
:: ::
Intra-AS Intra-AS
PCE3 PCE4
Figure 7: Shortened form of Inter- and Intra-AS PCE Reference Model
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The PCECC belonging to the different domains can cooperate to set up
inter-AS TE LSP. The stateful H-PCE [RFC8751] mechanism could also
be used to establish a per-domain PCECC LSP first. These could be
stitched together to form inter-AS TE LSP as described in
[I-D.ietf-pce-stateful-interdomain].
For the sake of simplicity, here the focus is on a simplified Inter-
AS case when both AS1 and AS2 belong to the same service provider
administration. In that case, Inter and Intra-AS PCEs could be
combined in one single PCE if such combined PCE performance is enough
to handle the load. The PCE will require interfaces (PCEP and BGP-
LS) to both domains. PCECC redundancy mechanisms are described in
[RFC8283]. Thus routers (PCCs) in AS1 and AS2 can send PCEP messages
towards the same PCECC. In Figure 8, PCECC maintains a BGP-LS
session with route reflectors (RRs) in each AS. This allows the RRs
to redistribute routes to other BGP routers (clients) without
requiring a full mesh. The RRs act as BGP-LS Propagator and PCECC
act as a BGP-LS Consumer [RFC9552].
+----BGP-LS------+ +------BGP-LS-----+
| | | |
+-PCEP-|----++-+-------PCECC-----PCEP--++-+-|-------+
+-:------|----::-:-+ +--::-:-|-------:---+
| : | :: : | | :: : | : |
| : RR1 :: : | | :: : RR2 : |
| v v: : | LSP1 | :: v v |
| R1---------ASBR1=======================ASBR3--------R3 |
| | v : | | :v | |
| +----------ASBR2=======================ASBR4---------+ |
| | Region 1 : | | : Region 1 | |
|----------------:-| |--:-------------|--|
| | v | LSP2 | v | |
| +----------ASBR5=======================ASBR6---------+ |
| Region 2 | | Region 2 |
+------------------+ <--------------> +-------------------+
MPLS Domain 1 Inter-AS MPLS Domain 2
<=======AS1=======> <========AS2=======>
Figure 8: Particular case of Inter-AS PCE
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In the case of the PCECC Inter-AS TE scenario (as shown in Figure 8)
where the service provider controls both domains (AS1 and AS2), each
of them has its own IGP and MPLS transport. There is a need to set
up Inter-AS LSPs for transporting different services on top of them
(Voice, L3VPN etc.). Inter-AS links with different capacities exist
in several regions. The task is not only to provision those Inter-AS
LSPs with given constraints but also to calculate the path and pre-
setup the backup Inter-AS LSPs that will be used if the primary LSP
fails.
As per Figure 8, LSP1 from R1 to R3 goes via ASBR1 and ASBR3, and it
is the primary Inter-AS LSP. R1-R3 LSP2 that goes via ASBR5 and
ASBR6 are the backup ones. In addition, there could also be a bypass
LSP setup to protect against ASBR or inter-AS link failures.
After the addition of PCECC functionality to PCE (SDN controller),
the PCECC-based Inter-AS TE model should follow the PCECC use case
for TE LSP including requirements of [RFC5376] with the following
details:
* Since PCECC needs to know the topology of both domains AS1 and
AS2, PCECC can utilize the BGP-LS peering with BGP routers (or
RRs) in both domains.
* PCECC needs to establish PCEP connectivity with all routers in
both domains (see also section 4 in [RFC5376]).
* After the operator's application or service orchestrator creates a
request for tunnel creation of a specific service, PCECC will
receive that request via NBI (NBI type is implementation
dependent, it could be NETCONF/Yang, REST etc.). Then PCECC will
calculate the optimal path based on Objective Function (OF) and
given constraints (i.e. path setup type, bandwidth etc.),
including those from [RFC5376]: priority, AS sequence, preferred
ASBR, disjoint paths, and protection type. In this step, we will
have two paths: R1-ASBR1-ASBR3-R3, R1-ASBR5-ASBR6-R3
* PCECC will use central control download instructions to the PCC
based on the PST. At this stage, it is assumed the PCECC is aware
of the label space it controls and in the case of SR the SID
allocation and distribution is already done.
* PCECC will send PCInitiate message [RFC8281] towards the ingress
router R1 (PCC) in AS1 and receive the PCRpt message [RFC8231]
back from it.
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- If the PST is SR-MPLS, the PCECC will include the SID stack as
per [RFC8664]. Optionally, a binding SID or BGP Peering-SID
[RFC9087] can also be included on the AS boundary. The backup
SID stack can be installed at ingress R1 but more importantly,
each node along the SR path could also do the local protection
just based on the top segment.
- If the PST is PCECC, the PCECC will assign labels along the
calculated paths (R1-ASBR1-ASBR3-R3, R1-ASBR5-ASBR6-R3) and
sets up the path by sending central controller instructions in
PCEP message to each node along the path of the LSPs as per
[RFC9050]. After these steps, the PCECC will send a PCUpd
message to the ingress R1 router with information about new
LSPs and R1 will respond by PCRpt with LSP(s) status.
* After that step, R1 now have primary and backup TEs (LSP1 and
LSP2) towards R3. It is up to router implementation how to make
switchover to backup LSP2 if LSP1 fails.
3.6. PCECC for Multicast LSPs
The multicast LSPs can be set up via the RSVP-TE P2MP or Multipoint
LDP (mLDP) protocols. The setup of these LSPs may require manual
configurations and complex signalling when the protection is
considered. By using the PCECC solution, the multicast LSP can be
computed and set up through a centralized controller which has the
full picture of the topology and bandwidth usage for each link. It
not only reduces the complex configurations comparing the distributed
RSVP-TE P2MP or mLDP signalling, but also it can compute the disjoint
primary path and secondary P2MP path efficiently.
3.6.1. PCECC for P2MP/MP2MP LSPs' Setup
It is assumed the PCECC is aware of the label space it controls for
all nodes and makes allocations accordingly.
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+----------+
| R1 | Root node of the multicast LSP
+----------+
|9000 (L0)
+----------+
Transit Node | R2 |
branch +----------+
* | * *
9001* | * *9002
L1 * | * *L2
+-----------+ | * +-----------+
| R4 | | * | R5 | Transit Nodes
+-----------+ | * +-----------+
* | * * +
9003* | * * +9004
L3 * | * * +L4
+-----------+ +-----------+
| R3 | | R6 | Leaf Node
+-----------+ +-----------+
9005| L5
+-----------+
| R8 | Leaf Node
+-----------+
Figure 9: Using PCECC for P2MP/MP2MP LSPs' Setup
The P2MP examples (based on Figure 9) are explained here, where R1 is
the root and the router R8 and R6 are the leaves.
* Based on the P2MP path computation request/delegation or PCE
initiation, the PCECC receives the request with constraints and
optimization criteria.
* PCECC will calculate the optimal P2MP path according to given
constraints (i.e.bandwidth).
* PCECC will provision each node along the path and assign incoming
and outgoing labels from R1 to {R6, R8} with the path as
"R1-L0-R2-L2-R5-L4-R6" and "R1-L0-R2-L1-R4-L3-R3-L5-R8":
- R1: Outgoing label 9000 on link L0
- R2: Incoming label 9000 on link L0
- R2: Outgoing label 9001 on link L1 (*)
- R2: Outgoing label 9002 on link L2 (*)
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- R5: Incoming label 9002 on link L2
- R5: Outgoing label 9004 on link L4
- R6: Incoming label 9004 on link L4
- R4: Incoming label 9001 on link L1
- R4: Outgoing label 9003 on link L3
- R3: Incoming label 9003 on link L3
- R3: Outgoing label 9005 on link L5
- R8: Incoming label 9005 on link L5
* This can also be represented as : {R1, 6000}, {6000, R2,
{9001,9002}}, {9001, R4, 9003}, {9002, R5, 9004} {9003, R3, 9005},
{9004, R6}, {9005, R8}. The main difference (*) is in the branch
node instruction at R2 where two copies of a packet are sent
towards R4 and R5 with 9001 and 9002 labels respectively.
The packet forwarding involves -
Step 1: R1 sends a packet to R2 simply by pushing the label of
9000 to the packet.
Step 2: When R2 receives the packet with label 9000, it will
forward it to R4 by swapping label 9000 to 9001 and at the same
time, it will replicate the packet and swap the label 9000 to 9002
and forward it to R5.
Step 3: When R4 receives the packet with label 9001, it will
forward it to R3 by swapping 9001 to 9003. When R5 receives the
packet with the label 9002, it will forward it to R6 by swapping
9002 to 9004.
Step 4: When R3 receives the packet with label 9003, it will
forward it to R8 by swapping it to 9005 and when R5 receives the
packet with label 9002, it will be swapped to 9004 and sent to R6.
Step 5: When R8 receives the packet with label 9005, it will pop
the label; when R6 receives the packet with label 9004, it will
pop the label.
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3.6.2. PCECC for the End-to-End Protection of P2MP/MP2MP LSPs
In this section, the end-to-end managed path protection service as
well as the local protection with the operation management in the
PCECC network for the P2MP/MP2MP LSP.
An end-to-end protection principle can be applied for computing
backup P2MP or MP2MP LSPs. During the computation of the primary
multicast trees, PCECC could also take the computation of a secondary
tree into consideration. A PCECC could compute the primary and
backup P2MP (or MP2MP) LSPs together or sequentially.
+----+ +----+
Root node of LSP | R1 |--| R11|
+----+ +----+
/ +
10/ +20
/ +
+----------+ +-----------+
Transit Node | R2 | | R3 |
+----------+ +-----------+
| \ + +
| \ + +
10| 10\ +20 20+
| \ + +
| \ +
| + \ +
+-----------+ +-----------+ Leaf Nodes
| R4 | | R5 | (Downstream LSR)
+-----------+ +-----------+
Figure 10: PCECC for the End-to-End Protection of the P2MP/MP2MP LSPs
In Figure 10, when the PCECC setups the primary multicast tree from
the root node R1 to the leaves, which is R1->R2->{R4, R5}, at the
same time, it can setup the backup tree, which is R1->R11->R3->{R4,
R5}. Both of them (primary forwarding tree and secondary forwarding
tree) will be downloaded to each router along the primary path and
the secondary path. The traffic will be forwarded through the
R1->R2->{R4, R5} path normally, but when a node in the primary tree
fails (say R2) the root node R1 will switch the flow to the backup
tree, which is R1->R11->R3->{R4, R5}. By using the PCECC a path
computation, label downloading and finally forwarding can be done
without complex signalling used in the P2MP RSVP-TE or mLDP.
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3.6.3. PCECC for the Local Protection of the P2MP/MP2MP LSPs
In this section, we describe the local protection service in the
PCECC network for the P2MP/MP2MP LSP.
While the PCECC sets up the primary multicast tree, it can also build
the backup LSP between the Point of Local Repair (PLR), the protected
node and Merge Points (MPs) (the downstream nodes of the protected
node). In the cases where the amount of downstream nodes is huge,
this mechanism can avoid unnecessary packet duplication on PLR and
protect the network from traffic congestion risk.
+------------+
| R1 | Root Node
+------------+
.
.
.
+------------+ Point of Local Repair/
| R10 | Switchover Point
+------------+ (Upstream LSR)
/ +
10/ +20
/ +
+----------+ +-----------+
Protected Node | R20 | | R30 |
+----------+ +-----------+
| \ + +
| \ + +
10| 10\ +20 20+
| \ + +
| \ +
| + \ +
+-----------+ +-----------+ Merge Point
| R40 | | R50 | (Downstream LSR)
+-----------+ +-----------+
. .
. .
Figure 11: PCECC for the Local Protection of the P2MP/MP2MP LSPs
In Figure 11, when the PCECC setups the primary multicast path around
the PLR node R10 to protect node R20, which is R10->R20->{R40, R50},
at the same time, it can set up the backup path R10->R30->{R40, R50}.
Both the primary forwarding path and secondary bypass forwarding path
will be downloaded to each router along the primary path and the
secondary bypass path. The traffic will be forwarded through the
R10->R20->{R40, R50} path normally and when there is a node failure
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for node R20, the PLR node R10 will switch the flow to the backup
path, which is R10->R30->{R40, R50}. By using the PCECC, path
computation, label downloading and finally forwarding can be done
without complex signalling used in the P2MP RSVP-TE or mLDP.
3.7. PCECC for Traffic Classification
As described in [RFC8283], traffic classification is an important
part of traffic engineering. It is the process of looking into a
packet to determine how it should be treated while it is forwarded
through the network. It applies in many scenarios including the
following:
MPLS traffic engineering (where it determines what traffic is
forwarded into which LSPs),
Segment Routing (where it is used to select which set of
forwarding instructions (SIDs) to add to a packet),
SFC (where it indicates how a packet should be forwarded across
which service function path ).
In conjunction with traffic engineering, traffic classification is an
important enabler for load balancing. Traffic classification is
closely linked to the computational elements of planning for the
network functions because it determines how traffic is balanced and
distributed through the network. Therefore, selecting what traffic
classification mechanism should be performed by a router is an
important part of the work done by a PCECC.
The description of traffic flows by the combination of multiple Flow
Specification components and their dissemination as traffic flow
specifications (Flow Specifications) is described for BGP in
[RFC8955]. When a PCECC is used to initiate tunnels (such as TE-LSPs
or SR paths) using PCEP, it is important that the head end of the
tunnels understands what traffic to place on each tunnel. [RFC9168]
specifies a set of extensions to PCEP to support the dissemination of
Flow Specification components where the instructions are passed from
the PCECC to the routers using PCEP.
Along with traffic classification, there are a few more questions
that need to be considered after path setup:
* how to use it
* Whether it is a virtual link
* Whether to advertise it in the IGP as a virtual link
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* What bits of this information to signal to the tail end
These are out of the scope of this document.
3.8. PCECC for SFC
Service Function Chaining (SFC) is described in [RFC7665]. It is the
process of directing traffic in a network such that it passes through
specific hardware devices or virtual machines (known as service
function nodes) that can perform particular desired functions on the
traffic. The set of functions to be performed and the order in which
they are to be performed is known as a service function chain. The
chain is enhanced with the locations at which the service functions
are to be performed to derive a Service Function Path (SFP). Each
packet is marked as belonging to a specific SFP, and that marking
lets each successive service function node know which functions to
perform and to which service function node to send the packet next.
To operate an SFC network, the service function nodes must be
configured to understand the packet markings, and the edge nodes must
be told how to mark packets entering the network. Additionally, it
may be necessary to establish tunnels between service function nodes
to carry the traffic. Planning an SFC network requires load
balancing between service function nodes and traffic engineering
across the network that connects them. As per [RFC8283], these are
operations that can be performed by a PCE-based controller, and that
controller can use PCEP to program the network and install the
service function chains and any required tunnels.
A possible mechanism could add support for SFC-based central control
instructions. PCECC will be able to instruct each SFF along the SFP.
* Service Path Identifier (SPI): Uniquely identifies an SFP.
* Service Index (SI): Provides location within the SFP.
* SFC Proxy handling
PCECC can play the role of setting the traffic classification rules
(as per Section 3.7) at the classifier to impose the Network Service
Header (NSH) [RFC8300] as well as downloading the forwarding
instructions to each SFF along the way so that they could process the
NSH and forward accordingly. Including instructions for the service
classifier that handles the context header, metadata etc. This
metadata/context is shared amongst SFs and classifiers, between SFs,
and between external systems (such as PCECC) and SFs. As described
in [RFC7665], the SFC encapsulation enables the sharing of metadata/
context information along the SFP.
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It is also possible to support SFC with SR in conjunction with or
without NSH such as [RFC9491] and
[I-D.ietf-spring-sr-service-programming]. PCECC technique can also
be used for service function-related segments and SR service
policies.
3.9. PCECC for Native IP
[RFC8735] describes the scenarios and simulation results for the
"Centrally Control Dynamic Routing (CCDR)" solution, which integrates
the advantage of using distributed protocols (IGP/BGP) and the power
of a centralized control technology (PCE/SDN), providing traffic
engineering for native IP networks. [RFC8821] defines the framework
for CCDR traffic engineering within a Native IP network, using
multiple BGP sessions and a PCE as the centralized controller. It
requires the PCECC to send the instructions to the PCCs, to build
multiple BGP sessions, distribute different prefixes on the
established BGP sessions and assign the different paths to the BGP
next hops. PCEP protocol is used to transfer the key parameters
between PCE and the underlying network devices (PCC) using the PCECC
technique. The central control instructions from PCECC to PCC will
identify which prefix should be advertised on which BGP session.
There are PCEP extensions defined in
[I-D.ietf-pce-pcep-extension-native-ip] for it.
+------+
+----------+ PCECC+-------+
| +------+ |
| |
PCEP | BGP Session 1(lo11/lo21)| PCEP
+-------------------------+
| |
| BGP Session 2(lo12/lo22)|
+-------------------------+
PF12 | | PF22
PF11 | | PF21
+---+ +-----+-----+ +-----+-----+ +---+
|SW1+---------+(lo11/lo12)+-------------+(lo21/lo22)+-----------+SW2|
+---+ | R1 +-------------+ R2 | +---+
+-----------+ +-----------+
Figure 12: PCECC for Native IP
In the case, as shown in Figure 12, PCECC will instruct both R1 and
R2 via PCEP how to form BGP sessions with each other and which IP
prefixes need to be advertised via which BGP session.
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3.10. PCECC for BIER
Bit Index Explicit Replication (BIER) [RFC8279] defines an
architecture where all intended multicast receivers are encoded as a
bitmask in the multicast packet header within different
encapsulations. A router that receives such a packet will forward
that packet based on the bit position in the packet header towards
the receiver(s) following a precomputed tree for each of the bits in
the packet. Each receiver is represented by a unique bit in the
bitmask.
BIER-TE [RFC9262] shares architecture and packet formats with BIER.
BIER-TE forwards and replicates packets based on a BitString in the
packet header, but every BitPosition of the BitString of a BIER-TE
packet indicates one or more adjacencies. BIER-TE paths can be
derived from a PCE and used at the ingress ( a possible mechanism is
described in [I-D.chen-pce-bier]).
PCECC mechanism could be used for the allocation of bits for the BIER
router for BIER as well as for the adjacencies for BIER-TE. PCECC-
based controllers can use PCEP to instruct the BIER-capable routers
on the meaning of the bits as well as other fields needed for BIER
encapsulation. The PCECC could be used to program the BIER router
with various parameters used in the BIER encapsulation such as BIER
subdomain-ID, BFR-ID, BIER Encapsulation etc. for both node and
adjacency.
A possible way for the PCECC usage and PCEP extension is described in
[I-D.chen-pce-pcep-extension-pce-controller-bier].
4. IANA Considerations
This document does not require any action from IANA.
5. Security Considerations
[RFC8283] describes how the security considerations for a PCE-based
controller are a little different from those for any other PCE
system. PCECC operations rely heavily on the use and security of
PCEP, so due consideration should be given to the security features
discussed in [RFC5440] and the additional mechanisms described in
[RFC8253]. It further lists the vulnerability of a central
controller architecture, such as a central point of failure, denial
of service, and a focus on interception and modification of messages
sent to individual Network Elements (NEs).
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As per [RFC9050], the use of Transport Layer Security (TLS) in PCEP
is recommended, as it provides support for peer authentication,
message encryption, and integrity. It further provides mechanisms
for associating peer identities with different levels of access and/
or authoritativeness via an attribute in X.509 certificates or a
local policy with a specific accept-list of X.509 certificates. This
can be used to check the authority for the PCECC operations.
It is expected that each new document that is produced for a specific
use case will also include considerations of the security impacts of
the use of a PCE-based central controller on the network type and
services being managed.
6. Acknowledgments
Thanks to Adrian Farrel, Aijun Wang, Robert Tao, Changjiang Yan,
Tieying Huang, Sergio Belotti, Dieter Beller, Andrey Elperin and
Evgeniy Brodskiy for their useful comments and suggestions.
Thanks to Mach Chen and Carlos Pignataro for the RTGDIR review.
Thanks to Derrell Piper for the SECDIR review. Thanks to Sue Hares
for GENART review.
Thanks to Vishnu Pavan Beeram for being the document shepherd and Jim
Guichard for being the responsible AD.
Thanks to Roman Danyliw for the IESG review comments.
7. References
7.1. Normative References
[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>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
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[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>.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
7.2. Informative References
[I-D.cbrt-pce-stateful-local-protection]
Barth, C. and R. Torvi, "PCEP Extensions for RSVP-TE
Local-Protection with PCE-Stateful", Work in Progress,
Internet-Draft, draft-cbrt-pce-stateful-local-protection-
01, 29 June 2018, <https://datatracker.ietf.org/doc/html/
draft-cbrt-pce-stateful-local-protection-01>.
[I-D.chen-pce-bier]
Chen, R., Zhang, Z., Chen, H., Dhanaraj, S., Qin, F., and
A. Wang, "PCEP Extensions for Tree Engineering for Bit
Index Explicit Replication (BIER-TE)", Work in Progress,
Internet-Draft, draft-chen-pce-bier-13, 1 October 2023,
<https://datatracker.ietf.org/doc/html/draft-chen-pce-
bier-13>.
[I-D.chen-pce-pcep-extension-pce-controller-bier]
Chen, R., Xu, B., Chen, H., and A. Wang, "PCEP Procedures
and Protocol Extensions for Using PCE as a Central
Controller (PCECC) of BIER", Work in Progress, Internet-
Draft, draft-chen-pce-pcep-extension-pce-controller-bier-
05, 19 October 2023,
<https://datatracker.ietf.org/doc/html/draft-chen-pce-
pcep-extension-pce-controller-bier-05>.
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[I-D.dhody-pce-pcep-extension-pce-controller-srv6]
Li, Z., Peng, S., Geng, X., and M. S. Negi, "PCE
Communication Protocol (PCEP) Extensions for Using the PCE
as a Central Controller (PCECC) for Segment Routing over
IPv6 (SRv6) Segment Identifier (SID) Allocation and
Distribution.", Work in Progress, Internet-Draft, draft-
dhody-pce-pcep-extension-pce-controller-srv6-10, 15
January 2023, <https://datatracker.ietf.org/doc/html/
draft-dhody-pce-pcep-extension-pce-controller-srv6-10>.
[I-D.ietf-mpls-seamless-mpls]
Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
M., and D. Steinberg, "Seamless MPLS Architecture", Work
in Progress, Internet-Draft, draft-ietf-mpls-seamless-
mpls-07, 28 June 2014,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
seamless-mpls-07>.
[I-D.ietf-pce-binding-label-sid]
Sivabalan, S., Filsfils, C., Tantsura, J., Previdi, S.,
and C. Li, "Carrying Binding Label/Segment Identifier
(SID) in PCE-based Networks.", Work in Progress, Internet-
Draft, draft-ietf-pce-binding-label-sid-16, 27 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
binding-label-sid-16>.
[I-D.ietf-pce-pcep-extension-native-ip]
Wang, A., Khasanov, B., Fang, S., Tan, R., and C. Zhu,
"Path Computation Element Communication Protocol (PCEP)
Extensions for Native IP Networks", Work in Progress,
Internet-Draft, draft-ietf-pce-pcep-extension-native-ip-
30, 1 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
pcep-extension-native-ip-30>.
[I-D.ietf-pce-pcep-extension-pce-controller-sr]
Li, Z., Peng, S., Negi, M. S., Zhao, Q., and C. Zhou, "PCE
Communication Protocol (PCEP) Extensions for Using PCE as
a Central Controller (PCECC) for Segment Routing (SR) MPLS
Segment Identifier (SID) Allocation and Distribution.",
Work in Progress, Internet-Draft, draft-ietf-pce-pcep-
extension-pce-controller-sr-08, 1 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
pcep-extension-pce-controller-sr-08>.
[I-D.ietf-pce-segment-routing-ipv6]
Li, C., Kaladharan, P., Sivabalan, S., Koldychev, M., and
Y. Zhu, "Path Computation Element Communication Protocol
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(PCEP) Extensions for IPv6 Segment Routing", Work in
Progress, Internet-Draft, draft-ietf-pce-segment-routing-
ipv6-25, 4 April 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
segment-routing-ipv6-25>.
[I-D.ietf-pce-segment-routing-policy-cp]
Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
Bidgoli, "Path Computation Element Communication Protocol
(PCEP) Extensions for Segment Routing (SR) Policy
Candidate Paths", Work in Progress, Internet-Draft, draft-
ietf-pce-segment-routing-policy-cp-16, 28 May 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
segment-routing-policy-cp-16>.
[I-D.ietf-pce-stateful-interdomain]
Dugeon, O., Meuric, J., Lee, Y., and D. Ceccarelli, "PCEP
Extension for Stateful Inter-Domain Tunnels", Work in
Progress, Internet-Draft, draft-ietf-pce-stateful-
interdomain-04, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
stateful-interdomain-04>.
[I-D.ietf-spring-sr-service-programming]
Clad, F., Xu, X., Filsfils, C., Bernier, D., Li, C.,
Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and
S. Salsano, "Service Programming with Segment Routing",
Work in Progress, Internet-Draft, draft-ietf-spring-sr-
service-programming-09, 20 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
sr-service-programming-09>.
[I-D.li-pce-controlled-id-space]
Li, C., Shi, H., Wang, A., Cheng, W., and C. Zhou, "Path
Computation Element Communication Protocol (PCEP)
extension to advertise the PCE Controlled Identifier
Space", Work in Progress, Internet-Draft, draft-li-pce-
controlled-id-space-16, 25 January 2024,
<https://datatracker.ietf.org/doc/html/draft-li-pce-
controlled-id-space-16>.
[MAP-REDUCE]
Lee, K., Choi, T., Ganguly, A., Wolinsky, D., Boykin, P.,
and R. Figueiredo, "Parallel Processing Framework on a P2P
System Using Map and Reduce Primitives", , May 2011,
<http://leeky.me/publications/mapreduce_p2p.pdf>.
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[MPLS-DC] Afanasiev, D. and D. Ginsburg, "MPLS in DC and inter-DC
networks: the unified forwarding mechanism for network
programmability at scale", , March 2014,
<https://www.slideshare.net/DmitryAfanasiev1/yandex-
nag201320131031>.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[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>.
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
<https://www.rfc-editor.org/info/rfc3985>.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206,
DOI 10.17487/RFC4206, October 2005,
<https://www.rfc-editor.org/info/rfc4206>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<https://www.rfc-editor.org/info/rfc4456>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
October 2007, <https://www.rfc-editor.org/info/rfc5036>.
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[RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, DOI 10.17487/RFC5150, February 2008,
<https://www.rfc-editor.org/info/rfc5150>.
[RFC5151] Farrel, A., Ed., Ayyangar, A., and JP. Vasseur, "Inter-
Domain MPLS and GMPLS Traffic Engineering -- Resource
Reservation Protocol-Traffic Engineering (RSVP-TE)
Extensions", RFC 5151, DOI 10.17487/RFC5151, February
2008, <https://www.rfc-editor.org/info/rfc5151>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC5376] Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS
Requirements for the Path Computation Element
Communication Protocol (PCECP)", RFC 5376,
DOI 10.17487/RFC5376, November 2008,
<https://www.rfc-editor.org/info/rfc5376>.
[RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
Objective Functions in the Path Computation Element
Communication Protocol (PCEP)", RFC 5541,
DOI 10.17487/RFC5541, June 2009,
<https://www.rfc-editor.org/info/rfc5541>.
[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>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[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>.
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[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
[RFC8355] Filsfils, C., Ed., Previdi, S., Ed., Decraene, B., and R.
Shakir, "Resiliency Use Cases in Source Packet Routing in
Networking (SPRING) Networks", RFC 8355,
DOI 10.17487/RFC8355, March 2018,
<https://www.rfc-editor.org/info/rfc8355>.
[RFC8408] Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
Hardwick, "Conveying Path Setup Type in PCE Communication
Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408,
July 2018, <https://www.rfc-editor.org/info/rfc8408>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[RFC8735] Wang, A., Huang, X., Kou, C., Li, Z., and P. Mi,
"Scenarios and Simulation Results of PCE in a Native IP
Network", RFC 8735, DOI 10.17487/RFC8735, February 2020,
<https://www.rfc-editor.org/info/rfc8735>.
[RFC8751] Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., and D. King,
"Hierarchical Stateful Path Computation Element (PCE)",
RFC 8751, DOI 10.17487/RFC8751, March 2020,
<https://www.rfc-editor.org/info/rfc8751>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8821] Wang, A., Khasanov, B., Zhao, Q., and H. Chen, "PCE-Based
Traffic Engineering (TE) in Native IP Networks", RFC 8821,
DOI 10.17487/RFC8821, April 2021,
<https://www.rfc-editor.org/info/rfc8821>.
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[RFC8955] Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
Bacher, "Dissemination of Flow Specification Rules",
RFC 8955, DOI 10.17487/RFC8955, December 2020,
<https://www.rfc-editor.org/info/rfc8955>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
[RFC9050] Li, Z., Peng, S., Negi, M., Zhao, Q., and C. Zhou, "Path
Computation Element Communication Protocol (PCEP)
Procedures and Extensions for Using the PCE as a Central
Controller (PCECC) of LSPs", RFC 9050,
DOI 10.17487/RFC9050, July 2021,
<https://www.rfc-editor.org/info/rfc9050>.
[RFC9087] Filsfils, C., Ed., Previdi, S., Dawra, G., Ed., Aries, E.,
and D. Afanasiev, "Segment Routing Centralized BGP Egress
Peer Engineering", RFC 9087, DOI 10.17487/RFC9087, August
2021, <https://www.rfc-editor.org/info/rfc9087>.
[RFC9168] Dhody, D., Farrel, A., and Z. Li, "Path Computation
Element Communication Protocol (PCEP) Extension for Flow
Specification", RFC 9168, DOI 10.17487/RFC9168, January
2022, <https://www.rfc-editor.org/info/rfc9168>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
[RFC9262] Eckert, T., Ed., Menth, M., and G. Cauchie, "Tree
Engineering for Bit Index Explicit Replication (BIER-TE)",
RFC 9262, DOI 10.17487/RFC9262, October 2022,
<https://www.rfc-editor.org/info/rfc9262>.
[RFC9491] Guichard, J., Ed. and J. Tantsura, Ed., "Integration of
the Network Service Header (NSH) and Segment Routing for
Service Function Chaining (SFC)", RFC 9491,
DOI 10.17487/RFC9491, November 2023,
<https://www.rfc-editor.org/info/rfc9491>.
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[RFC9522] Farrel, A., Ed., "Overview and Principles of Internet
Traffic Engineering", RFC 9522, DOI 10.17487/RFC9522,
January 2024, <https://www.rfc-editor.org/info/rfc9522>.
[RFC9552] Talaulikar, K., Ed., "Distribution of Link-State and
Traffic Engineering Information Using BGP", RFC 9552,
DOI 10.17487/RFC9552, December 2023,
<https://www.rfc-editor.org/info/rfc9552>.
Appendix A. Other Use Cases of PCECC
This section lists some more use cases of PCECC that were proposed by
operators and discussed within the working group, but are not in
active development at the time of publication. They are listed here
for future consideration.
A.1. PCECC for Network Migration
One of the main advantages of the PCECC solution is its backward
compatibility. The PCE server can function as a proxy node of the
MPLS network for all the new nodes that no longer support the
signalling protocols.
As illustrated in the following example, the current network could
migrate to a total PCECC-controlled network gradually by replacing
the legacy nodes. During the migration, the legacy nodes still need
to use the existing MPLS protocols signalling such as LDP and RSVP-
TE, and the new nodes will set up their portion of the forwarding
path through PCECC directly. With the PCECC function as the proxy of
these new nodes, MPLS signalling can populate through the network for
both: old and new nodes.
The example described in this section is based on network
configurations illustrated using Figure 13:
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+------------------------------------------------------------------+
| PCE DOMAIN |
| +-----------------------------------------------------+ |
| | PCECC | |
| +-----------------------------------------------------+ |
| ^ ^ ^ ^ |
| | PCEP | | PCEP | |
| V V V V |
| +--------+ +--------+ +--------+ +--------+ +--------+ |
| | NODE 1 | | NODE 2 | | NODE 3 | | NODE 4 | | NODE 5 | |
| | |...| |...| |...| |...| | |
| | Legacy |if1| Legacy |if2|Legacy |if3| PCECC |if4| PCECC | |
| | Node | | Node | |Enabled | |Enabled | | Enabled| |
| +--------+ +--------+ +--------+ +--------+ +--------+ |
| |
+------------------------------------------------------------------+
Figure 13: PCECC Initiated LSP Setup In the Network Migration
In this example, there are five nodes for the TE LSP from the head
end (Node1) to the tail end (Node5). Where Node4 and Node5 are
centrally controlled and other nodes are legacy nodes.
* Node1 sends a path request message for the setup of LSP with the
destination as Node5.
* PCECC sends to Node1 a reply message for LSP setup with the path:
(Node1, if1),(Node2, if2), (Node3, if3), (Node4, if4), Node5.
* Node1, Node2, and Node3 will set up the LSP to Node5 using the
local labels as usual. Node 3 with the help of PCECC could proxy
the signalling.
* Then the PCECC will program the out-segment of Node3, the in-
segment/ out-segment of Node4, and the in-segment for Node5.
A.2. PCECC for L3VPN and PWE3
As described in [RFC8283], various network services may be offered
over a network. These include protection services (including Virtual
Private Network (VPN) services (such as Layer 3 VPNs [RFC4364] or
Ethernet VPNs [RFC7432]); or Pseudowires [RFC3985]. Delivering
services over a network in an optimal way requires coordination in
the way where network resources are allocated to support the
services. A PCE-based central controller can consider the whole
network and all components of a service at once when planning how to
deliver the service. It can then use PCEP to manage the network
resources and to install the necessary associations between those
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resources.
In the case of L3VPN, VPN labels could also be assigned and
distributed through PCEP among the PE router instead of using the BGP
protocols.
The example described in this section is based on network
configurations illustrated using Figure 14:
+-------------------------------------------+
| PCE DOMAIN |
| +-----------------------------------+ |
| | PCECC | |
| +-----------------------------------+ |
| ^ ^ ^ |
|PWE3/L3VPN | PCEP PCEP|LSP PWE3/L3VPN|PCEP |
| V V V |
+--------+ | +--------+ +--------+ +--------+ | +--------+
| CE | | | PE1 | | NODE x | | PE2 | | | CE |
| |...... | |...| |...| |.....| |
| Legacy | |if1 | PCECC |if2|PCCEC |if3| PCECC |if4 | Legacy |
| Node | | | Enabled| |Enabled | |Enabled | | | Node |
+--------+ | +--------+ +--------+ +--------+ | +--------+
| |
+-------------------------------------------+
Figure 14: PCECC for L3VPN and PWE3
In the case of PWE3, instead of using the LDP signalling protocols,
the label and port pairs assigned to each pseudowire can be assigned
through PCECC among the PE routers and the corresponding forwarding
entries will be distributed into each PE router through the extended
PCEP and PCECC mechanism.
A.3. PCECC for Local Protection (RSVP-TE)
[I-D.cbrt-pce-stateful-local-protection] claim that there is a need
for the PCE to maintain and associate the local protection paths for
the RSVP-TE LSP. Local protection requires the setup of a bypass at
the PLR. This bypass can be PCC-initiated and delegated, or PCE-
initiated. In either case, the PLR needs to maintain a PCEP session
with the PCE. The Bypass LSPs need to be mapped to the primary LSP.
This could be done locally at the PLR based on a local policy but
there is a need for a PCE to do the mapping as well to exert greater
control.
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This mapping can be done via PCECC procedures where the PCE could
instruct the PLR to the mapping and identify the primary LSP for
which bypass should be used.
A.4. Using reliable P2MP TE based multicast delivery for distributed
computations (MapReduce-Hadoop)
MapReduce model of distributed computations in computing clusters is
widely deployed. In Hadoop (https://hadoop.apache.org/) 1.0
architecture MapReduce operations on big data in the Hadoop
Distributed File System (HDFS), where NameNode knows about resources
of the cluster and where actual data (chunks) for a particular task
are located (which DataNode). Each chunk of data (64MB or more)
should have 3 saved copies in different DataNodes based on their
proximity.
The proximity level currently has a semi-manual allocation and is
based on Rack IDs (The assumption is that closer data are better
because of access speed/smaller latency).
JobTracker node is responsible for computation tasks, and scheduling
across DataNodes and also has Rack-awareness. Currently, transport
protocols between NameNode/JobTracker and DataNodes are based on IP
unicast. It has simplicity as an advantage but has numerous
drawbacks related to its flat approach.
There is a need to go beyond one data centre (DC) for Hadoop cluster
creation and move towards distributed clusters. In that case, one
needs to handle performance and latency issues. Latency depends on
the speed of light in the fibre links and on the latency introduced
by intermediate devices in between. The latter is closely correlated
with network device architecture and performance. The current
performance of NPU-based routers should be enough for creating
distributed Hadoop clusters with predicted latency. The performance
of software-based routers (mainly virtual network functions (VNF))
with additional hardware features such as the Data Plane Development
Kit (DPDK) is promising but requires additional research and testing.
The main question is how to create a simple but effective
architecture for a distributed Hadoop cluster.
There is research [MAP-REDUCE] that show how usage of the multicast
tree could improve the speed of resource or cluster members'
discovery inside the cluster as well as increased redundancy in
communications between cluster nodes.
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The traditional IP-based multicast may not be appropriate because it
requires an additional control plane (IGMP, PIM) and a lot of
signalling, that is not suitable for high-performance computations,
that are very sensitive to latency.
P2MP TE tunnels are more suitable as a potential solution for the
creation of multicast-based communications between NameNode as root
and DataNodes as leaves inside the cluster. These P2MP tunnels could
be dynamically created and turned down (with no manual intervention).
Here, the PCECC comes into play with the main objective of creating
an optimal topology for each particular request for MapReduce
computation and creating P2MP tunnels with needed parameters such as
bandwidth and delay.
This solution will require the use of MPLS label-based forwarding
inside the cluster. The usage of label-based forwarding inside DC
was proposed by Yandex [MPLS-DC]. Technically it is already possible
because MPLS on switches is already supported by some vendors, MPLS
also exists on Linux and OVS.
A possible framework for this task is shown in Figure 15:
+--------+
| APP |
+--------+
| NBI (REST API,...)
|
PCEP +----------+ REST API
+---------+ +---| PCECC |----------+
| Client |---|---| | |
+---------+ | +----------+ |
| | | | | |
+-----|---+ |PCEP| |
+--------+ | | | | |
| | | | | |
| REST API | | | | |
| | | | | |
+-------------+ | | | | +----------+
| Job Tracker | | | | | | NameNode |
| | | | | | | |
+-------------+ | | | | +----------+
+------------------+ | +-----------+
| | | |
|---+-----P2MP TE--+-----|-----------| |
+----------+ +----------+ +----------+
| DataNode1| | DataNode2| | DataNodeN|
|TaskTraker| |TaskTraker| .... |TaskTraker|
+----------+ +----------+ +----------+
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Figure 15: Using reliable P2MP TE based multicast delivery for
distributed computations (MapReduce-Hadoop)
Communication between JobTracker, NameNode and PCECC can be done via
REST API directly or via cluster manager such as Mesos.
Phase 1: Distributed cluster resources discovery During this phase,
JobTracker and NameNode should identify and find available DataNodes
according to computing requests from the application (APP). NameNode
should query PCECC about available DataNodes, NameNode may provide
additional constraints to PCECC such as topological proximity, and
redundancy level.
PCECC should analyze the topology of the distributed cluster and
perform constraint-based path calculation from the client towards the
most suitable NameNodes. PCECC should reply to NameNode with the
list of the most suitable DataNodes and their resource capabilities.
The topology discovery mechanism for PCECC will be added later to
that framework.
Phase 2: PCECC should create P2MP LSP from the client towards those
DataNodes by means of PCEP messages following the previously
calculated path.
Phase 3. NameNode should send this information to the client, and
PCECC should inform the client about the optimal P2MP path towards
DataNodes via PCEP message.
Phase 4. The Client sends data blocks to those DataNodes for writing
via the created P2MP tunnel.
When this task is finished, the P2MP tunnel could be turned down.
Appendix B. Contributor Addresses
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Luyuan Fang
United States of America
Email: luyuanf@gmail.com
Chao Zhou
HPE
Email: chaozhou_us@yahoo.com
Boris Zhang
Amazon
Email: zhangyud@amazon.com
Artsiom Rachytski
Belarus
Email: arachyts@gmail.com
Anton Gulida
EPAM Systems, Inc.
Belarus
Email: Anton_Hulida@epam.com
Authors' Addresses
Zhenbin (Robin) Li
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: lizhenbin@huawei.com
Dhruv Dhody
Huawei Technologies
India
Email: dhruv.ietf@gmail.com
Quintin Zhao
Etheric Networks
1009 S CLAREMONT ST
SAN MATEO, CA 94402
United States of America
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Email: qzhao@ethericnetworks.com
King He
Tencent Holdings Ltd.
Shenzhen
China
Email: kinghe@tencent.com
Boris Khasanov
Yandex LLC
Ulitsa Lva Tolstogo 16
Moscow
Email: bhassanov@yahoo.com
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