PCE for Network High Availability
draft-chen-pce-ctr-availability-04
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Huaimo Chen , Aijun Wang , Lei Liu , Xufeng Liu | ||
| Last updated | 2022-03-20 | ||
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draft-chen-pce-ctr-availability-04
Network Working Group H. Chen
Internet-Draft Futurewei
Intended status: Standards Track A. Wang
Expires: 21 September 2022 China Telecom
L. Liu
Fujitsu
X. Liu
Volta Networks
20 March 2022
PCE for Network High Availability
draft-chen-pce-ctr-availability-04
Abstract
This document describes extensions to Path Computation Element (PCE)
communication Protocol (PCEP) for improving the reliability or
availability of a network controlled by a controller cluster.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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 21 September 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 3
3. PCE for Controller Cluster Reliability . . . . . . . . . . . 3
3.1. Overview of Mechanism . . . . . . . . . . . . . . . . . . 3
3.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Extensions to PCEP . . . . . . . . . . . . . . . . . . . . . 6
4.1. Capability . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Controllers Object . . . . . . . . . . . . . . . . . . . 7
5. Recovery Procedure . . . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
More and more networks are controlled by central controllers or
controller clusters. A controller cluster is a single controller
externally. It normally consists of two or more controllers
internally working together as a single controller externally to
control a network, i.e., every network element (NE) in the network.
The reliability or availability of a network is heavily dependent on
its controller cluster. The issues or failures in the controller
cluster may impact the reliability or availability of the network
greatly.
For a controller cluster comprising two or more controllers (i.e.,
primary controller, secondary controller, and so on), the failures in
the cluster may split the cluster into a few of separated controller
groups. These groups do not know each other and may be out of
synchronization. Two or more groups may be elected as primary groups
to control the network at the same time, which may cause some issues.
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This document proposes some procedures and extensions to PCEP for the
separated controllers or controller groups to know each other thus
elect one new primary controller or controller group correctly when
the cluster is split because of failures in the cluster.
2. Terminologies
The following terminologies are used in this document.
PCE: Path Computation Element
PCEP: PCE communication Protocol
PCC: Path Computation Client
NE: Network Element
CE: Customer Edge
PE: Provider Edge
3. PCE for Controller Cluster Reliability
This section briefs the mechanism of controller cluster reliability
or availability using PCEP, and illustrates some details through a
simple example.
3.1. Overview of Mechanism
When a cluster of controllers is split into a few of separated groups
because of failures in the cluster, the live controllers are still
actually connected to the network (i.e., network elements). Through
some of these connections, each group can get the information about
the other groups. A new primary controller or controller group is
correctly elected to control the network based on the information.
Each controller has a PCEP session with each of a give number of the
same NEs in the network and the session is established and maintained
over an IP path between the controller and the NE. The session is a
session of PCEP with extensions.
In one example or configuration, the given number of NEs is one NE
with the highest node ID. Suppose that node PE2 as NE has the
highest ID. The session between the primary controller (e.g., A) and
the NE (e.g., PE2) is the session of PCEP with extensions. Each of
the non-primary controllers (e.g., B, C, ...) creates and maintains a
PCEP session with this NE (e.g., PE2).
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In normal operations, the cluster has all its controllers connected.
They are the primary controller controlling the network, the
secondary controller, and so on. They have current position 1, 2,
and so on respectively. The primary controller advertises the
information about the controllers via its PCEP sessions to the given
number of the same NEs.
For example, it sends the information in a PCEP message to the NE
(e.g., PE2), which transfers the information to each of the other
controllers via the PCEP sessions to the other controllers.
When the cluster is split into a few separated groups of controllers,
each group elects an intent primary controller, secondary controller
and so on from the group, which have intent position 1, 2, and so on
respectively. The intent primary controller in each group advertises
the information about the controllers in its group.
The information advertised by the (intent) primary controller
includes its current (intent) position, its old position, its
priority to become a primary controller, number of controllers in its
group or cluster, and the IDs of the controllers which are ordered
according to their (intent) positions. In addition, a flag C
indicating that whether it is Controlling the network (i.e., it is
the primary controller or intent primary controller) is included.
3.2. Example
Figure 1 shows a controller cluster comprising two controllers: the
primary controller and the secondary controller. Each controller has
a PCEP session with the same NE, which is NE4.
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+---------------------------------------------------+
| Controller Cluster |
| |
| +------------+ +------------+ |
| |Controller A| Synchronize |Controller B| |
| |(Primary) +---------------+(Secondary) | |
| +------------+ +-----------++ |
| ^ | |
| |_______________ | |
| | | |
| v | |
+-----------------Channels to Network---------|-----+
/ \ |
PCEP session----> / \____ |
between / \ \____ | <--PCEP session
A and NEi /\ .---. .---+ \ | between
(i=1,2,..) | \( ' |'.---. | | B and NE4
|---\ Network | '+. |
(o NE1\ | | ) /
( | | o) /
( | | ) NE4
( o NE2 o NE3.-'
' )
'---._.-. )
'---'
Figure 1: Controller Cluster of 2 Controllers
The primary PCE controller (i.e., A) has a PCEP session with each NE
in the network, including NE4. The secondary controller (i.e., B)
has a PCEP session with the same NE4 in the network and the session
is established and maintained over an IP path between B and NE4.
In normal operations, controller A (Primary) sends NE4 a PCEP message
containing the information about the controllers connected to it.
NE4 transfers the information to controller B (Secondary). The
information includes:
C = 1, A's current Position = 1, A's OldPosition = 1, A's Priority,
NoControllers = 2, A's ID, B's ID
When failures happen in the cluster, the live controllers act as
follows:
For the primary controller (e.g., A), if it is alive, it continues to
be the primary controller.
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For the secondary controller (e.g., B) alive, if the primary
controller is dead, it promotes itself as the new primary controller;
if the primary controller is alive but separated from the secondary
controller, the secondary controller will not promote itself to be a
new primary controller.
With the extensions to PCEP, the secondary controller can determine
the status of the primary controller based on the information about
the primary controller received. The conditions that the primary
controller is alive but separated from the secondary controller
(i.e., condition a: the connection between the primary controller and
the secondary controller in the cluster failed, but condition b: the
two controllers are alive) can be determined by the secondary
controller as follows:
For condition a, when the heartbeat from the primary stops, the
secondary knows that the connection between the primary and secondary
controller failed.
For condition b, it checks whether the information about the primary
controller is updated within a given time. If so, the primary
controller is alive; otherwise, it is dead.
4. Extensions to PCEP
This section describes extensions to PCEP.
4.1. Capability
During a PCEP session establishment, PCEP Speakers (PCE or PCC)
advertise their support for PCEP extensions for network reliability,
especially the High Availability of Controller cluster (HAC). A new
Controller HA Support Capability TLV is defined for HAC below. A
PCEP speaker indicates its support for HAC by including the TLV in
the OPEN object in its OPEN message if it supports for HAC.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD1) | Length (4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |C|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Controller HA Support Capability TLV
Type (16 bits): TBD1 is to be assigned by IANA.
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Length (16 bits): It indicates the length of the Capability value
portion in octets, which is 4.
Flag (32 bits): One flag bit, C-bit, is defined. When it is set to
one, it indicates that the PCEP speaker supports the high
availability of controller cluster as a Controller. When it is
set to zero, it indicates that the PCEP speaker supports the high
availability of controller cluster as a network element (NE).
When two PCEP speakers establish a PCEP session between them, each of
the speakers indicates its support for HAC by including a Controller
HA Support Capability TLV in the OPEN object in its OPEN message if
it supports for HAC.
For a PCEP speaker supporting for HAC, if it receives the Controller
HA Support Capability TLV in the OPEN message from the other PCEP
speaker over the PCEP session, it records that the other PCEP speaker
(i.e., the other/remote end of the session) supports for HAC;
otherwise, it records that the other speaker does not. Thus for all
its PCEP sessions, it knows whether each session's remote end PCEP
speaker supports for HAC. If the C-bit in the TLV is set to one, the
PCEP speaker is a controller; otherwise, it is a NE.
A PCE as a controller supporting for HAC acts on the information
about the controllers in its cluster or group as follows:
It sends the information in a PCEP message to each of a given set of
NEs that runs PCEP with HAC support whenever the information changes.
The given set of NEs may be the one NE with the highest ID.
It adjusts the positions of the controllers accordingly whenever
there is a change in the information about the controllers received
from the NE supporting for HAC.
An NE running PCEP with HAC support receives the information about
the controllers from the PCE as a controller supporting for HAC, and
sends the information to every PCE as a controller supporting for HAC
and having a PCEP session with the NE except for the one from which
the information is received.
4.2. Controllers Object
A new object, called Controllers Object, is defined to contain the
information about controllers. A controller in a cluster may
advertise the information in a PCEP Report message containing a
Controllers Object of the following format.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Object-Class | OT |Res|P|I| Object Length (bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ TLVs +
| (including Controllers TLV) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Controllers Object
Object-Class (8 bits): It is to be assigned by IANA. It identifies
the PCEP object class.
OT (4 bits): It is to be assigned by IANA. It identifies the PCEP
object type.
Res flags (2 bits): Reserved field. This field MUST be set to zero
on transmission and MUST be ignored.
P flag and I flag: Refer to RFC 5440, page 25.
Object Length (16 bits): It specifies the total object length
including the header, in bytes.
TLVs: This field includes one TLV, called Controllers TLV to be
defined below.
Under the Controllers Object, a new TLV, called Controllers TLV, is
defined to contain the information about controllers. It has the
following format.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |C| Position | OldPosition | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | NoControllers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Connected Controller 1 ID |
: : |
| Connected Controller n ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 4: Controllers TLV
Type (16 bits): TBD2 is to be assigned by IANA.
Length (16 bits): It indicates the length of the value portion in
octets.
Flag (8 bits): One flag bit, C-bit, is defined. When set, it
indicates that the position is the position of the current active
primary controller. In this case, C = 1 and Position = 1, which
indicate that the controller is the current active primary
controller controlling the network.
Position (8 bits): It indicates the current/intent position of the
controller in the controller cluster or group. 1: primary (first)
controller, 2: secondary controller, 3: third controller, and so
on (i.e., Controller Position of value n: n-th controller in the
cluster or group).
OldPosition (8 bits): ): It indicates the old position of the
controller in the controller cluster before it is split.
Priority (8 bits): It indicates the priority of the controller to be
elected as a primary controller.
Reserved (24 bits): Reserved field, must set to zero for
transmission and ignored for reception.
NoControllers (8 bits): It indicates the number of controllers
connected to the controller advertising the TLV.
Controller i ID (32 bits): It represents the identifier (ID) of
controller i at position i (i = 1, ..., n) in the cluster or
group.
5. Recovery Procedure
This section describes the recovery procedure for a controller
cluster of n (n > 2) controllers, which are the primary controller A,
the secondary controller B, ..., the n-th controller N.
When failures happen in the cluster, it may be split into a few
separated groups of controllers. In one policy, the group with the
maximum number of controllers is responsible for controlling the
network as the primary group of the cluster, in which the new primary
controller, secondary controller, and so on are elected.
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For each separated group of controllers, the intent primary
controller, secondary controller, and so on are elected. The intent
primary controller of the group advertises the information about its
group. The information includes its intent position, its old
position, its priority to become a primary controller, the number of
controllers in the group, and identifiers of the controllers in the
group. The identifiers of the controllers are ordered according to
their positions. The identifier of the intent primary controller,
which has position 1, is the first one; The identifier of the intent
secondary controller, which has position 2, is the second one; and so
on. Thus every separated group has the information about the other
groups and can determine which group has the maximum number of
controllers.
In the case of tie (i.e., two or more groups have the same maximum
number of controllers), the group with the highest old position
controller (e.g., the old primary controller) wins in one policy. In
another policy, the group with the highest priority controller wins.
Some details of the recovery procedures in the current and intent
primary controller in a controller cluster or group are as follows.
In normal operations, it advertises the information about controllers
containing:
C = 1, Position = 1, Old Position = 1, Primary Controller's priority,
NoControllers = n, Primary Controller's ID, secondary controller's
ID, ..., and n-th Controller's ID.
When failures cause the cluster split, it advertises the information
about controllers containing:
C = 0, Position = 1, Old Position = 1, Intent Primary Controller's
priority, NoControllers = m (m is the number of controllers in the
group to which the intent primary controller belongs after the
failures), Intent Primary Controller's ID, IDs of the other
controllers connected.
Then after a given time, it checks if the group is elected as the
primary group. If so, it advertises the information about
controllers containing:
C = 1, Position = 1, Old Position = 1, its Priority, NoControllers =
m, the IDs of the controllers in the group.
One example is that failures split the cluster into two separated
groups: group 1 comprising A and C, group 2 consisting of B and N.
Each group elects its intent primary controller, secondary
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controller, and so on. Suppose that controller A and C are elected
as the intent primary and secondary controller respectively in group
1; controller B and N are elected as the intent primary and secondary
controller respectively in group 2.
Each of the intent primary controllers A and B advertises the
information about the controllers in its group. The information
advertised by A includes:
C = 0, Position = 1, OldPosition = 1, A's Priority, NoControllers =
2, A's ID, C's ID.
The information advertised by B includes:
C = 0, Position = 1, OldPosition = 2, B's Priority, NoControllers =
2, B's ID, N's ID.
Group 1 and 2 have the same number of controllers, which is 2. But
OldPosition in group 1 is higher than that in group 2. Group 1 is
elected as the primary group, and the intent primary controller A in
the primary group is determined as the current primary controller.
After the determination, the information about the controllers in
group 1 (i.e., the primary group) is changed. The updated
information advertised by A includes:
C = 1, Position = 1, OldPosition = 1, A's Priority, NoControllers =
2, A's ID, C's ID.
6. IANA Considerations
TBD
7. Security Considerations
TBD
8. Acknowledgements
TBD
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
9.2. Informative References
[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>.
[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>.
Authors' Addresses
Huaimo Chen
Futurewei
Boston, MA,
United States of America
Email: Huaimo.chen@futurewei.com
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing
102209
China
Email: wangaj3@chinatelecom.cn
Lei Liu
Fujitsu
United States of America
Email: liulei.kddi@gmail.com
Xufeng Liu
Volta Networks
McLean, VA
United States of America
Email: xufeng.liu.ietf@gmail.com
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