The Use Cases for Path Computation Element (PCE) as a Central Controller (PCECC).
draft-ietf-teas-pcecc-use-cases-07
TEAS Working Group Z. Li
Internet-Draft D. Dhody
Intended status: Informational Huawei Technologies
Expires: September 9, 2021 Q. Zhao
Etheric Networks
K. Ke
Tencent Holdings Ltd.
B. Khasanov
Yandex LLC
L. Fang
Expedia, Inc.
C. Zhou
HPE
B. Zhang
Telus Communications
A. Rachitskiy
Mobile TeleSystems JLLC
A. Gulida
LLC "Lifetech"
March 8, 2021
The Use Cases for Path Computation Element (PCE) as a Central Controller
(PCECC).
draft-ietf-teas-pcecc-use-cases-07
Abstract
The Path Computation Element (PCE) is a core component of a Software-
Defined Networking (SDN) system. It can compute optimal paths for
traffic across a network and can also update the paths to reflect
changes in the network or traffic demands. PCE was developed to
derive paths for MPLS Label Switched Paths (LSPs), which are supplied
to the head end of the LSP using the Path Computation Element
Communication Protocol (PCEP).
SDN has a 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.
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
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extensions required for stateful PCE usage are covered in separate
documents.
This is a living document to catalog the use cases for PCECC. There
is currently no intention to publish this work as an RFC. [Update:
Chairs are evaluating if the document should be published instead.]
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 9, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Application Scenarios . . . . . . . . . . . . . . . . . . . . 4
3.1. Use Cases of PCECC for Label Management . . . . . . . . . 4
3.2. Using PCECC for SR . . . . . . . . . . . . . . . . . . . 6
3.2.1. PCECC SID Allocation . . . . . . . . . . . . . . . . 7
3.2.2. Use Cases of PCECC for SR Best Effort (BE) Path . . . 8
3.2.3. Use Cases of PCECC for SR Traffic Engineering (TE)
Path . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Use Cases of PCECC for TE LSP . . . . . . . . . . . . . . 9
3.3.1. PCECC Load Balancing (LB) Use Case . . . . . . . . . 11
3.3.2. PCECC and Inter-AS TE . . . . . . . . . . . . . . . . 13
3.4. Use Cases of PCECC for Multicast LSPs . . . . . . . . . . 16
3.4.1. Using PCECC for P2MP/MP2MP LSPs' Setup . . . . . . . 17
3.4.2. Use Cases of PCECC for the Resiliency of P2MP/MP2MP
LSPs . . . . . . . . . . . . . . . . . . . . . . . . 18
3.5. Use Cases of PCECC for LSP in the Network Migration . . . 20
3.6. Use Cases of PCECC for L3VPN and PWE3 . . . . . . . . . . 22
3.7. Using PCECC for Traffic Classification Information . . . 23
3.8. Use Cases of PCECC for SRv6 . . . . . . . . . . . . . . . 23
3.9. Use Cases of PCECC for SFC . . . . . . . . . . . . . . . 25
3.10. Use Cases of PCECC for Native IP . . . . . . . . . . . . 25
3.11. Use Cases of PCECC for Local Protection (RSVP-TE) . . . . 26
3.12. Use Cases of PCECC for BIER . . . . . . . . . . . . . . . 26
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
5. Security Considerations . . . . . . . . . . . . . . . . . . . 27
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.1. Normative References . . . . . . . . . . . . . . . . . . 27
7.2. Informative References . . . . . . . . . . . . . . . . . 27
Appendix A. Using reliable P2MP TE based multicast delivery for
distributed computations (MapReduce-Hadoop) . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
An Architecture for Use of PCE and PCEP [RFC5440] in a Network with
Central Control [RFC8283] describes SDN architecture where the Path
Computation Element (PCE) determines paths for variety of different
usecases, with PCEP as a general southbound communication protocol
with all the nodes along the path..
[I-D.ietf-pce-pcep-extension-for-pce-controller] introduces the
procedures and extensions for PCEP to support the PCECC architecture
[RFC8283].
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This draft describes the various usecases for the PCECC architecture.
This is a living document to catalog the use cases for PCECC. There
is currently no intention to publish this work as an RFC. [Update:
Chairs are evaluating if the document should be published instead.]
2. Terminology
The following terminology is used in this document.
IGP: Interior Gateway Protocol. Either of the two routing
protocols, Open Shortest Path First (OSPF) or Intermediate System
to Intermediate System (IS-IS).
PCC: Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application,
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].
TE: Traffic Engineering.
3. Application Scenarios
In the following sections, several use cases are described,
showcasing scenarios that benefit from the deployment of PCECC.
3.1. Use Cases of 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 taker 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.
[I-D.ietf-pce-pcep-extension-for-pce-controller] describe 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
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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.
[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 (SID) via PCEP. To make such allocation PCE needs to
be aware of the label space from 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 PCEP. The full SRGB/SRLB of a node
could be learned via existing IGP or BGP-LS mechanism too.
[I-D.li-pce-controlled-id-space] defines a PCEP extension to support
advertisement of the MPLS label space to the PCE to control.
There have been various proposals for Global Labels, the PCECC
architecture could be used as 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 Label Management
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o PCC would advertise the PCECC capability to the PCE (central
controller-PCECC)
[I-D.ietf-pce-pcep-extension-for-pce-controller].
o The PCECC could also learn the label range set aside by the PCC
([I-D.li-pce-controlled-id-space]).
o Optionally, the PCECC could determine the shared MPLS global label
range for the network.
o In the case that the shared global label range need to be
negotiated across multiple domains, the central controllers of
these domains would also need to negotiate a common global
label range across domains.
o The PCECC would need to set the shared global label range to
all PCC nodes in the network.
3.2. Using PCECC for SR
Segment Routing (SR) leverages the source routing paradigm. Using
SR, a source node steers a packet through a path without relying on
hop-by-hop signaling protocols such as LDP or RSVP-TE. 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
routing protocol (such as IS-IS or OSPF) or by any other means. PCEP
(and PCECC) could be one such means.
[RFC8664] specify the SR specific PCEP extensions. PCECC may further
use PCEP protocol for SR SID (Segment Identifier) distribution to the
SR nodes (PCC) with some benefits. If the PCECC allocates and
maintains the SID in the network for the nodes and adjacencies; and
further distributes them to the SR nodes directly via the PCEP
session has some advantage over the configurations on each SR node
and flooding via IGP, especially in a SDN environment.
When the PCECC is used for the distribution of the node segment ID
and adjacency segment ID, the node segment ID is allocated from the
SRGB of the node. For the allocation of adjacency segment ID, 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). Also protection can be performed
by the node adjacent to the failed component, commonly referred to as
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local protection techniques or fast-reroute (FRR) techniques. In
case of PCECC, the protection paths can be pre-computed and setup by
the PCE.
The following example illustrate the use case where the node SID and
adjacency SID are allocated by the PCECC.
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
+-----------+
3.2.1. PCECC SID Allocation
Each node (PCC) is allocated a node-SID by the PCECC. The PCECC
needs to update the label map of each node to all the nodes in the
domain. On receiving the label map, each node (PCC) uses the local
routing information to determine the next-hop and download the label
forwarding instructions accordingly. The forwarding behavior and the
end result is same as IGP based Node-SID in SR. 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, PCECC can allocate an Adj-SID.
The PCECC sends PCInitiate message to update the label map of each
Adj to the corresponding nodes in the domain. Each node (PCC)
download the label forwarding instructions accordingly. The
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forwarding behavior and the end result is similar to IGP based "Adj-
SID" in SR.
The various mechanism are described in
[I-D.ietf-pce-pcep-extension-pce-controller-sr].
3.2.2. Use Cases of PCECC for SR Best Effort (BE) Path
In this mode of the solution, the PCECC just need to allocate the
node segment ID and adjacency ID (without calculating the explicit
path for the SR path). The ingress of the forwarding path just need
to encapsulate the destination node segment ID 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 header with
segment list {1008} (Node SID for R8). The path would be the based
on the routing/nexthop calculation on the routers.
3.2.3. Use Cases of PCECC for SR Traffic Engineering (TE) Path
SR-TE paths may not follow an IGP 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 signaling protocol. For the case where strict traffic
engineering path is needed, all the adjacency SID are stacked,
otherwise a combination of node-SID or adj-SID can be used for the
SR-TE paths.
Note that the bandwidth reservations is only guaranteed at controller
and through the enforce of the bandwidth admission control. As for
the RSVP-TE LSP case, the control plane signaling also does the link
bandwidth reservation in each hop of the path.
The SR traffic engineering path examples are explained as bellow:
Note that the node SID for each node is allocated from the SRGB and
adjacency SID for each link are allocated from the SRLB for each
node.
Example 1:
R1 may send a packet P1 to R8 simply by pushing an SR header with
segment list {1008}. Based on the best path, it could be:
R1-R2-R3-R8.
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Example 2:
R1 may send a packet P2 to R8 by pushing an SR header with segment
list {1002, 9001, 1008}. The path should be: R1-R2-link1-R3-R8.
Example 3:
R1 may send a packet P3 to R8 via R4 by pushing an SR header with
segment list {1004, 1008}. The path could be : R1-R2-R4-R3-R8
The local protection examples for SR TE path are explained below:
Example 4: local link protection:
o R1 may send a packet P4 to R8 by pushing an SR header with segment
list {1002, 9001, 1008}. The path should be: R1-R2-link1-R3-R8.
o When node R2 receives the packet from R1 which has the header of
link1-R3-R8, and also find out there is a link failure of link1,
then the R2 can enforce the traffic over the bypass to send out
the packet with header of R3-R8 through link2.
Example 5: local node protection:
o R1 may send a packet P5 to R8 by pushing an SR header with segment
list {1004, 1008}. The path could be : R1-R2-R4-R3-R8.
o When node R2 receives the packet from R1 which has the header of
{1004, 1008}, and also finds out there is a node failure for
node4, then it can enforce the traffic over the bypass and send
out the packet with header of {1005, 1008} to node5 instead of
node4.
3.3. Use Cases of PCECC for TE LSP
In the Section 3.2 the case of SR path via PCECC is discussed.
Although those cases give the simplicity and scalability, but there
are existing functionalities for the traffic engineering path such as
the bandwidth guarantee, monitoring where SR based solution are
complex. Also there are cases where the depth of the label stack is
an issue for existing deployment and certain vendors.
So to address these issues, PCECC architecture also support the TE
LSP functionalities. To achieve this, the existing PCEP can be used
to communicate between the PCECC and nodes along the path. This is
similar to static LSPs, where LSPs can be provisioned as explicit
label instructions at each hop on the end-to-end path. Each router
along the path must be told what label- forwarding instructions to
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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 2: PCECC TE LSP Setup Example
o Based on path computation request / delegation or PCE initiation,
the PCECC receives the PCECC request with constraints and
optimization criteria.
o PCECC would calculate the optimal path according to given
constrains (e.g. bandwidth).
o PCECC would provision each node along the path and assign incoming
and outgoing labels from R1 to R8 with the path: {R1, link1,
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1001}, {1001, R2, link3, 2003], {2003, R4, link10, 4010}, {4010,
R3, link8, 3008}, {3008, R8}.
o For the end to end protection, PCECC program 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}.
o It is also possible to have a bypass path for the local protection
setup 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.
3.3.1. PCECC Load Balancing (LB) Use Case
Very often many service providers use TE tunnels for solving issues
with non-deterministic paths in their networks. One example of such
applications is usage of TEs in the mobile backhaul (MBH). Consider
the following topology -
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 | +--------+ +--------+ +------+ +---+
+---------+ +--------+
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, access ring and aggregation ring
(AGG1...AGGN), connected by Nx10GE interfaces. Aggregation domain
runs its own IGP. There are two Egress routers (AGG N-1,AGG N) that
are connected to the Core domain via L2 interfaces. Core also have
connections to service routers, RSVP-TEs are used for MPLS transport
inside the ring. There could be at least 2 tunnels (one way) from
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each AGG router to egress AGG routers. There are also many L2 access
rings connected to AGG routers.
Service deployment made by means of either L2VPNs (VPLS) or L3VPNs.
Those services use MPLS TE as transport towards egress AGG routers.
TE tunnels could be also used as transport towards service routers in
case of seamless MPLS based architecture in the future.
There is a need to solve the following tasks:
o Perform automatic load-balance amongst TE tunnels according to
current traffic load.
o TE bandwidth (BW) management: Provide guaranteed BW for specific
service: HSI, IPTV, etc., provide time-based BW reservation (BoD)
for other services.
o Simplify development of TE tunnels by automation without any
manual intervention.
o Provide flexibility for Service Router placement (anywhere in the
network by creation of transport LSPs to them).
Since other tasks are already considered by other PCECC use cases, in
this section, the focus is on load balancing (LB) task. LB task
could be solved by means of PCECC in the following way:
o After application or network service or operator can ask SDN
controller (PCECC) for LSP based LB between AGG X and AGG N/AGG
N-1 (egress AGG routers which have connections to core) via North
Bound Interface (NBI). Each of these would have associated
constrains (i.e. Path Setup Type (PST), bandwidth, inclusion or
exclusion specific links or nodes, number of paths, objective
function (OF), need for disjoint LSP paths etc.).
o PCECC could calculate multiple (Say N) LSPs according to given
constrains, 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 constrains.
o Depending on given LSP Path setup type (PST), PCECC would use
download instructions to the PCC. At this stage it is assumed the
PCECC is aware of the label space it controls and in case of SR
the SID allocation and distribution is already done.
o PCECC would send PCInitiate PCEP message [RFC8281] towards ingress
AGG X router(PCC) for each of N LSPs and receives PCRpt PCEP
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message [RFC8231] back from PCCs. If the PST is PCECC-SR, the
PCECC would include the SID stack as per [RFC8664]. If the PST is
PCECC (basic), then the PCECC would assigns labels along the
calculated path; and set up the path by sending central controller
instructions in PCEP message to each node along the path of the
LSP as per [I-D.ietf-pce-pcep-extension-for-pce-controller] and
then send PCUpd message to the ingress AGG X router with
information about new LSP and AGG X(PCC) would respond with PCRpt
with LSP status.
o AGG X as ingress router now have N LSPs towards AGG N and AGG N-1
which are available for installing to router's forwarding and LB
of traffic between them. Traffic distribution between those LSPs
depends on particular realization of hash-function on that router.
o Since PCECC is aware of TEDB (TE state) and LSP-DB, it can manage
and prevent possible over-subscriptions and limit number of
available LB states. Via PCECC mechanism the control can take
quick actions into the network by directly provisioning the
central control instructions.
3.3.2. PCECC and Inter-AS TE
There are various signaling options for establishing Inter-AS TE LSP:
contiguous TE LSP [RFC5151], stitched TE LSP [RFC5150], nested TE LSP
[RFC4206].
Requirements for PCE-based Inter-AS setup [RFC5376] describe the
approach and PCEP functionality that are needed for establishing
Inter-AS TE LSPs.
[RFC5376] also gives Inter- and Intra-AS PCE Reference Model that is
provided below in shorten form for the sake of simplicity.
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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 3: Shorten form of Inter- and Intra-AS PCE Reference Model
[RFC5376]
The PCECC belonging to different domain can co-operate to setup
inter-AS TE LSP. The stateful H-PCE [RFC8751] mechanism could also
be used to first establish a per-domain PCECC LSP. 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 after 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 for handling all path computation request and setup. There is
a potential to use a single PCE for both ASes if the scalability and
performance are enough. The PCE would require interfaces (PCEP and
BGP-LS) to both domains. PCECC redundancy mechanisms are described
in [RFC8283]. Thus routers in AS1 and AS2 (PCCs) can send PCEP
messages towards same PCECC.
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+----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 4: Particular case of Inter-AS PCE
In a case of PCECC Inter-AS TE scenario where service provider
controls both domains (AS1 and AS2), each of them have own IGP and
MPLS transport. There is a need is to setup Inter-AS LSPs for
transporting different services on top of them (Voice, L3VPN etc.).
Inter-AS links with different capacity exist in several regions. The
task is not only to provision those Inter-AS LSPs with given
constrains but also calculate the path and pre-setup the backup
Inter-AS LSPs that will be used if primary LSP fails.
As per the Figure 4, LSP1 from R1 to R3 goes via ASBR1 and ASBR3, and
it is the primary Inter-AS LSP. R1-R3 LSP2 that go via ASBR5 and
ASBR6 is the backup one. In addition there could also be a bypass
LSP setup to protect against ASBR or inter-AS link failure.
After the addition of PCECC functionality to PCE (SDN controller),
PCECC based Inter-AS TE model SHOULD follow as PCECC usecase for TE
LSP as requirements of [RFC5376] with the following details:
o Since PCECC needs to know the topology of both domains AS1 and
AS2, PCECC could use BGP-LS peering with routers (or RRs) in both
domains.
o PCECC needs to PCEP connectivity towards all routers in both
domains (see also section 4 in [RFC5376]) in a similar manner as a
SDN controller.
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o After operator's application or service orchestrator will create
request for tunnel creation of specific service, PCECC should
receive that request via NBI (NBI type is implementation
dependent, could be NETCONF/Yang, REST etc.). Then PCECC would
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, protection. On this step we would have two
paths: R1-ASBR1-ASBR3-R3, R1-ASBR5-ASBR6-R3
o Depending on given LSP PST (PCECC or PCECC-SR), PCECC would use
central control download instructions to the PCC. At this stage
it is assumed the PCECC is aware of the label space it controls
and in case of SR the SID allocation and distribution is already
done.
o PCECC would send PCInitiate PCEP message [RFC8281] towards ingress
router R1 (PCC) in AS1 and receives PCRpt PCEP message [RFC8231]
back from PCC. If the PST is PCECC-SR, the PCECC would include
the SID stack as per [RFC8664]. It may also include binding SID
based on AS boundary. The backup SID stack could also be
installed at ingress but more importantly each node along the SR
path could also do local protection just based on the top segment.
If the PST is PCECC (basic), then the PCECC would assigns labels
along the calculated paths (R1-ASBR1-ASBR3-R3, R1-ASBR5-ASBR6-R3);
and set up the path by sending central controller instructions in
PCEP message to each node along the path of the LSPs as per
[I-D.ietf-pce-pcep-extension-for-pce-controller] and then send
PCUpd message to the ingress R1 router with information about new
LSPs and R1 would respond with PCRpt with LSP(s) status.
o 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.
3.4. Use Cases of PCECC for Multicast LSPs
The current multicast LSPs are setup either using the RSVP-TE P2MP or
mLDP protocols. The setup of these LSPs may require manual
configurations and complex signaling when the protection is
considered. By using the PCECC solution, the multicast LSP can be
computed and setup through 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 signaling, but also it can compute the disjoint
primary path and secondary P2MP path efficiently.
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3.4.1. Using PCECC for P2MP/MP2MP LSPs' Setup
It is assumed the PCECC is aware of the label space it controls for
all nodes and make allocations accordingly.
+----------+
| R1 | Root node of the multicast LSP
+----------+
|6000
+----------+
Transit Node | R2 |
branch +----------+
* | * *
9001* | * *9002
* | * *
+-----------+ | * +-----------+
| R4 | | * | R5 | Transit Nodes
+-----------+ | * +-----------+
* | * * +
9003* | * * +9004
* | * * +
+-----------+ +-----------+
| R3 | | R6 | Leaf Node
+-----------+ +-----------+
9005|
+-----------+
| R8 | Leaf Node
+-----------+
The P2MP examples are explained here, where R1 is root and R8 and R6
are the leaves.
o Based on the P2MP path computation request / delegation or PCE
initiation, the PCECC receives the PCECC request with constraints
and optimization criteria.
o PCECC would calculate the optimal P2MP path according to given
constrains (i.e.bandwidth).
o PCECC would provision each node along the path and assign incoming
and outgoing labels from R1 to {R6, R8} with the path: {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 packet are sent
towards R4 and R5 with 9001 and 9002 labels respectively.
The packet forwarding involves -
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Step1: R1 may send a packet P1 to R2 simply by pushing an label of
6000 to the packet.
Step2: After R2 receives the packet with label 6000, it will
forwarding to R4 by swapping label to 9001 and by swapping label
of 9002 towards R5.
Step3: After R4 receives the packet with label 9001, it will
forwarding to R3 by swapping to 9003. After R5 receives the
packet with label 9002, it will forwarding to R6 by swapping to
9004.
Step4: After R3 receives the packet with label 9003, it will
forwarding to R8 by swapping to 9005 and when R5 receives the
packet with label 9004, it will swap to 9004 and send to R6.
Step5: Packet received at R8 and 9005 is popped; packet receives
at R6 and 9004 is popped.
3.4.2. Use Cases of PCECC for the Resiliency of P2MP/MP2MP LSPs
3.4.2.1. PCECC for the End-to-End Protection of the P2MP/MP2MP LSPs
In this section we describe 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 computation of the primary
multicast trees, PCECC server may also take the computation of a
secondary tree into consideration. A PCE may compute the primary and
backup P2MP (or MP2MP) LSP together or sequentially.
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+----+ +----+
Root node of LSP | R1 |--| R11|
+----+ +----+
/ +
10/ +20
/ +
+----------+ +-----------+
Transit Node | R2 | | R3 |
+----------+ +-----------+
| \ + +
| \ + +
10| 10\ +20 20+
| \ + +
| \ +
| + \ +
+-----------+ +-----------+ Leaf Nodes
| R4 | | R5 | (Downstream LSR)
+-----------+ +-----------+
In the example above, when the PCECC setup the primary multicast tree
from the root node R1 to the leaves, which is R1->R2->{R4, R5}, at
same time, it can setup the backup tree, which is R1->R11->R3->{R4,
R5}. Both the these two primary forwarding tree and secondary
forwarding tree will be downloaded to each routers along the primary
path and the secondary path. The traffic will be forwarded through
the R1->R2->{R4, R5} path normally, and when there is a node in the
primary tree fails (say R2), then the root node R1 will switch the
flow to the backup tree, which is R1->R11->R3->{R4, R5}. By using
the PCECC, the path computation and forwarding path downloading can
all be done without the complex signaling used in the P2MP RSVP-TE or
mLDP.
3.4.2.2. 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 back LSP among PLR, the protected node, and MPs (the downstream
nodes of the protected node). In the cases where the amount of
downstream nodes are huge, this mechanism can avoid unnecessary
packet duplication on PLR and protect the network from traffic
congestion risk.
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+------------+
| 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)
+-----------+ +-----------+
. .
. .
In the example above, when the PCECC setup the primary multicast path
around the PLR node R10 to protect node R20, which is R10->R20->{R40,
R50}, at same time, it can setup the backup path R10->R30->{R40,
R50}. Both the these two primary forwarding path and secondary
bypass forwarding path will be downloaded to each routers 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 for node R20, then the PLR node R10 will
switch the flow to the backup path, which is R10->R30->{R40, R50}.
By using the PCECC, the path computation and forwarding path
downloading can all be done without the complex signaling used in the
P2MP RSVP-TE or mLDP.
3.5. Use Cases of PCECC for LSP in the Network Migration
One of the main advantages for PCECC solution is that it has backward
compatibility naturally since the PCE server itself can function as a
proxy node of MPLS network for all the new nodes which may no longer
support the signaling protocols.
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As it is 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 signal using the existing MPLS protocol such as LDP and
RSVP-TE, and the new nodes setup their portion of the forwarding path
through PCECC directly. With the PCECC function as the proxy of
these new nodes, MPLS signaling can populate through network as
normal.
Example described in this section is based on network configurations
illustrated using the following figure:
+------------------------------------------------------------------+
| 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| |
| +--------+ +--------+ +--------+ +--------+ +--------+ |
| |
+------------------------------------------------------------------+
Example: PCECC Initiated LSP Setup In the Network Migration
In this example, there are five nodes for the TE LSP from head end
(Node1) to the tail end (Node5). Where the Node4 and Node5 are
centrally controlled and other nodes are legacy nodes.
o Node1 sends a path request message for the setup of LSP
destinating to Node5.
o PCECC sends to node1 a reply message for LSP setup with the path:
(Node1, if1),(Node2, if2), (Node3, if3), (Node4, if4), Node5.
o Node1, Node2, Node3 will setup the LSP to Node5 using the local
labels as usual. Node 3 with help of PCECC could proxy the
signaling.
o Then the PCECC will program the out-segment of Node3, the in-
segment/ out-segment of Node4, and the in-segment for Node5.
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3.6. Use Cases of 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 that 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 resources.
In the case of L3VPN, VPN labels can be assigned and distributed
through the PCECC PCEP among the PE router instead of using the BGP
protocols.
Example described in this section is based on network configurations
illustrated using the following figure:
+-------------------------------------------+
| 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 |
+--------+ | +--------+ +--------+ +--------+ | +--------+
| |
+-------------------------------------------+
Example: Using PCECC for L3VPN and PWE3
In the case PWE3, instead of using the LDP signaling 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 routers through the extended
PCEP protocols and PCECC mechanism.
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3.7. Using PCECC for Traffic Classification Information
As described in [RFC8283], traffic classification is an important
part of traffic engineering. It is the process of looking at a
packet to determine how it should be treated as it is forwarded
through the network. It applies in many scenarios including MPLS
traffic engineering (where it determines what traffic is forwarded
onto which LSPs); segment routing (where it is used to select which
set of forwarding instructions to add to a packet); and SFC (where it
indicates along which service function path a packet should be
forwarded). 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 just listed because it determines
how traffic load is balanced and distributed through the network.
Therefore, selecting what traffic classification should be performed
by a router is an important part of the work done by a PCECC.
Instructions can be passed from the controller to the routers using
PCEP. These instructions tell the routers how to map traffic to
paths or connections. Refer [I-D.ietf-pce-pcep-flowspec].
Along with traffic classification, there are few more question that
needs to be considered once the path is setup -
o how to use it
o Whether it is a virtual link
o Whether to advertise it in the IGP as a virtual link
o What bits of this information to signal to the tail end
These are out of scope of this document.
3.8. Use Cases of 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.
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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". Further details are in An illustration is provided in
[RFC8986] where SRv6 SID is represented as LOC:FUNCT.
[I-D.ietf-pce-segment-routing-ipv6] extends [RFC8664] to support SR
for IPv6 data plane. Further a PCECC could be extended to support
SRv6 SID allocation and distribution.
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
+-----------+
In this case, PCECC could assign the SRv6 SID (in form of a IPv6
address) to be used for node and adjacency. Later SRv6 path in form
of list of SRv6 SID could be used at the ingress. Some examples -
o SRv6 SID-List={2001:db8::8} - The best path towards R8
o SRv6 SID-List={2001:db8::5, 2001:db8::8} - The path towards R8 via
R5
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3.9. Use Cases of 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.
PCECC can play the role for setting the traffic classification rules
at the classifier as well as downloading the forwarding instructions
to the SFFs so that they could process the NSH and forward
accordingly.
[Editor's Note - more details to be added]
3.10. Use Cases of PCECC for Native IP
[RFC8735] describes the scenarios, and suggestions for the "Centrally
Control Dynamic Routing (CCDR)" architecture, which integrates the
merit of traditional distributed protocols (IGP/BGP), and the power
of centrally control technologies (PCE/SDN) to provide one feasible
traffic engineering solution in various complex scenarios for the
service provider. [I-D.ietf-teas-pce-native-ip] defines the
framework for CCDR traffic engineering within Native IP network,
using Dual/Multi-BGP session strategy and CCDR architecture. PCEP
protocol can be used to transfer the key parameters between PCE and
the underlying network devices (PCC) using PCECC technique. The
central control instructions from PCECC to identify which prefix
should be advertised on which BGP session.
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3.11. Use Cases of PCECC for Local Protection (RSVP-TE)
[I-D.cbrt-pce-stateful-local-protection] describes the 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 MUST maintain a PCEP session to
the PCE. The Bypass LSPs need to 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.
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.
3.12. Use Cases of 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
the 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 [I-D.ietf-bier-te-arch] 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 Path can be derived from a PCE and used at the ingress as
described in [I-D.chen-pce-bier].
Further, 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 controller can use PCEP to instruct the BIER capable
routers the meaning of the bits as well as other fields needed for
BIER encapsulation.
[Editor's Note - more details to be added]
4. IANA Considerations
This document does not require any action from IANA.
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5. Security Considerations
TBD.
6. Acknowledgments
We would like to thank Adrain Farrel, Aijun Wang, Robert Tao,
Changjiang Yan, Tieying Huang, Sergio Belotti, Dieter Beller, Andrey
Elperin and Evgeniy Brodskiy for their useful comments and
suggestions.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
7.2. Informative References
[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>.
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[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>.
[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>.
[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>.
[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>.
[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>.
[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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[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>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[I-D.ietf-pce-pcep-flowspec]
Dhody, D., Farrel, A., and Z. Li, "PCEP Extension for Flow
Specification", draft-ietf-pce-pcep-flowspec-12 (work in
progress), October 2020.
[I-D.ietf-pce-pcep-extension-for-pce-controller]
Li, Z., Peng, S., Negi, M., Zhao, Q., and C. Zhou, "PCEP
Procedures and Protocol Extensions for Using PCE as a
Central Controller (PCECC) of LSPs", draft-ietf-pce-pcep-
extension-for-pce-controller-10 (work in progress),
January 2021.
[I-D.ietf-pce-pcep-extension-pce-controller-sr]
Li, Z., Peng, S., Negi, M., Zhao, Q., and C. Zhou, "PCEP
Procedures and Protocol Extensions for Using PCE as a
Central Controller (PCECC) for Segment Routing (SR) MPLS
Segment Identifier (SID) Allocation and Distribution.",
draft-ietf-pce-pcep-extension-pce-controller-sr-00 (work
in progress), December 2020.
[I-D.li-pce-controlled-id-space]
Li, C., Chen, M., Wang, A., Cheng, W., and C. Zhou, "PCE
Controlled ID Space", draft-li-pce-controlled-id-space-07
(work in progress), October 2020.
[I-D.ietf-pce-stateful-interdomain]
Dugeon, O., Meuric, J., Lee, Y., and D. Ceccarelli, "PCEP
Extension for Stateful Inter-Domain Tunnels", draft-ietf-
pce-stateful-interdomain-00 (work in progress), January
2021.
[I-D.cbrt-pce-stateful-local-protection]
Barth, C. and R. Torvi, "PCEP Extensions for RSVP-TE
Local-Protection with PCE-Stateful", draft-cbrt-pce-
stateful-local-protection-01 (work in progress), June
2018.
[I-D.ietf-pce-segment-routing-ipv6]
Li, C., Negi, M., Sivabalan, S., Koldychev, M.,
Kaladharan, P., and Y. Zhu, "PCEP Extensions for Segment
Routing leveraging the IPv6 data plane", draft-ietf-pce-
segment-routing-ipv6-08 (work in progress), November 2020.
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[I-D.ietf-teas-pce-native-ip]
Wang, A., Khasanov, B., Zhao, Q., and H. Chen, "Path
Computation Element (PCE) based Traffic Engineering (TE)
in Native IP Networks", draft-ietf-teas-pce-native-ip-16
(work in progress), January 2021.
[I-D.ietf-bier-te-arch]
Eckert, T., Cauchie, G., and M. Menth, "Tree Engineering
for Bit Index Explicit Replication (BIER-TE)", draft-ietf-
bier-te-arch-07 (work in progress), March 2020.
[I-D.chen-pce-bier]
Chen, R., Zhang, Z., Dhanaraj, S., and F. Qin, "PCEP
Extensions for BIER-TE", draft-chen-pce-bier-07 (work in
progress), May 2020.
[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>.
[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>.
7.3. URIs
[1] https://hadoop.apache.org/
Appendix A. 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 [1] 1.0 architecture MapReduce operations
on big data in the Hadoop Distributed File System (HDFS), where
NameNode has the knowledge about resources of the cluster and where
actual data (chunks) for 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.
Proximity level currently has semi-manual allocation and based on
Rack IDs (Assumption is that closer data are better because of access
speed/smaller latency).
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JobTracker node is responsible for computation tasks, scheduling
across DataNodes and also have Rack-awareness. Currently transport
protocols between NameNode/JobTracker and DataNodes are based on IP
unicast. It has simplicity as pros but has numerous drawbacks
related with its flat approach.
It is clear that we should go beyond of one DC for Hadoop cluster
creation and move towards distributed clusters. In that case we need
to handle performance and latency issues. Latency depends on speed
of light in fiber links and also latency introduced by intermediate
devices in between. The last one is closely correlated with network
device architecture and performance. Current performance of NPU
based routers should be enough for creating distribute Hadoop
clusters with predicted latency. Performance of SW based routers
(mainly as VNF) together with additional HW features such as DPDK are
promising but require additional research and testing.
Main question is how can we create simple but effective architecture
for distributed Hadoop cluster?
There is research [MAP-REDUCE] which show how usage of multicast tree
could improve speed of resource or cluster members discovery inside
the cluster as well as increase redundancy in communications between
cluster nodes.
Is traditional IP based multicast enough for that? We doubt it
because it requires additional control plane (IGMP, PIM) and a lot of
signaling, that is not suitable for high performance computations,
that are very sensitive to latency.
P2MP TE tunnels looks much more suitable as potential solution for
creation of multicast based communications between NameNode as root
and DataNodes as leaves inside the cluster. Obviously these P2MP
tunnels should be dynamically created and turned down (no manual
intervention). Here, the PCECC comes to play with main objective to
create optimal topology of each particular request for MapReduce
computation and also create P2MP tunnels with needed parameters such
as bandwidth and delay.
This solution would require to use MPLS label based forwarding inside
the cluster. 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.
The following framework can make this task:
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+--------+
| APP |
+--------+
| NBI (REST API,...)
|
PCEP +----------+ REST API
+---------+ +---| PCECC |----------+
| Client |---|---| | |
+---------+ | +----------+ |
| | | | | |
+-----|---+ |PCEP| |
+--------+ | | | | |
| | | | | |
| REST API | | | | |
| | | | | |
+-------------+ | | | | +----------+
| Job Tracker | | | | | | NameNode |
| | | | | | | |
+-------------+ | | | | +----------+
+------------------+ | +-----------+
| | | |
|---+-----P2MP TE--+-----|-----------| |
+----------+ +----------+ +----------+
| DataNode1| | DataNode2| | DataNodeN|
|TaskTraker| |TaskTraker| .... |TaskTraker|
+----------+ +----------+ +----------+
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 request from application (APP). NameNode
SHOULD query PCECC about available DataNodes, NameNode MAY provide
additional constrains to PCECC such as topological proximity,
redundancy level.
PCECC SHOULD analyze the topology of distributed cluster and perform
constrain based path calculation from client towards most suitable
NameNodes. PCECC SHOULD reply to NameNode the list of most suitable
DataNodes and their resource capabilities. Topology discovery
mechanism for PCECC will be added later to that framework.
Phase 2: PCECC SHOULD create P2MP LSP from client towards those
DataNodes by means of PCEP messages following previously calculated
path.
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Phase 3. NameNode SHOULD send this information to client, PCECC
informs client about optimal P2MP path towards DataNodes via PCEP
message.
Phase 4. Client sends data blocks to those DataNodes for writing via
created P2MP tunnel.
When this task will be finished, P2MP tunnel could be turned down.
Authors' Addresses
Zhenbin (Robin) Li
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: lizhenbin@huawei.com
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Quintin Zhao
Etheric Networks
1009 S CLAREMONT ST
SAN MATEO, CA 94402
USA
Email: qzhao@ethericnetworks.com
King Ke
Tencent Holdings Ltd.
Shenzhen
China
Email: kinghe@tencent.com
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Boris Khasanov
Yandex LLC
Ulitsa Lva Tolstogo 16
Moscow
Russia
Email: bhassanov@yahoo.com
Luyuan Fang
Expedia, Inc.
USA
Email: luyuanf@gmail.com
Chao Zhou
HPE
Email: chaozhou_us@yahoo.com
Boris Zhang
Telus Communications
Email: Boris.zhang@telus.com
Artem Rachitskiy
Mobile TeleSystems JLLC
Nezavisimosti ave., 95
Minsk 220043
Belarus
Email: arachitskiy@mts.by
Anton Gulida
LLC "Lifetech"
Krasnoarmeyskaya str., 24
Minsk 220030
Belarus
Email: anton.gulida@life.com.by
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