Internet DRAFT - draft-chen-lsr-ctr-availability
draft-chen-lsr-ctr-availability
Network Working Group H. Chen
Internet-Draft Futurewei
Intended status: Standards Track M. Toy
Expires: 10 April 2024 Verizon
A. Wang
China Telecom
L. Liu
Fujitsu
X. Liu
IBM Corporation
8 October 2023
IGP for Network High Availability
draft-chen-lsr-ctr-availability-07
Abstract
This document describes protocol extensions to OSPF and IS-IS 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-
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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 10 April 2024.
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Copyright Notice
Copyright (c) 2023 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IGP for Controller Cluster Reliability . . . . . . . . . . . 3
3.1. Overview of Mechanism . . . . . . . . . . . . . . . . . . 4
3.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Extensions to IGP . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Extensions to OSPF . . . . . . . . . . . . . . . . . . . 6
4.2. Extensions to IS-IS . . . . . . . . . . . . . . . . . . . 8
5. Recovery Procedure . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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 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.
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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 to control the
network at the same time, which may cause some issues.
This document proposes some procedures and extensions to OSPF and IS-
IS 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.
IGP: Interior Gateway Protocol
OSPF: Open Shortest Path First
IS-IS: Intermediate System to Intermediate System
LSA: Link State Advertisement in OSPF
LSP: Link State Protocol PDU in IS-IS
PDU: Protocol Data Unit
LS: Link Sate, which is LSA in OSPF or LSP in IS-IS
NE: Network Element
CE: Customer Edge
PE: Provider Edge
3. IGP for Controller Cluster Reliability
This section briefs the mechanism of controller cluster reliability
or availability using IGP, and illustrates some details through a
simple example.
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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 may comprise an IGP as an information proxy, called
IGP information proxy or IGP for short. The IGP has an IGP adjacency
relation with each of a given number of NEs (such as one NE) in the
network. When one adjacency is broken, a new adjacency is created
and maintained if possible. The given number of adjacency relations
is retained.
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 IGP adjacencies. The
extensions to IGP below is used.
When the cluster is split into a few separated groups, 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 advertises the
information about the controllers in the group.
The information advertised by the (intent) primary controller
includes its current (intent) position, its old position, its
priority to become a primary controller, the number of controllers,
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
includes an IGP as an information proxy.
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+---------------------------------------------------+
| Controller Cluster |
| |
| +------------+ +------------+ |
| |Controller A| Synchronize |Controller B| |
| |(Primary) +---------------+(Secondary) | |
| | [IGP]| | [IGP]| |
| ++-----------+ +-----------++ |
| | ^ | |
| | |_______________ | |
| | | | |
| | v | |
+-----|------------Control Channels-----------|-----+
| / \ |
|IGP Adj / \____ |
\ / \ \____ |IGP Adj
\____ /\ .---. .---+ \ |
\ | \( ' |'.---. | |
\ |---\ Network | '+. |
NE1 (o \ | | ) /
( | | o) NE4
( | | )
( o NE2 o NE3.-'
' )
'---._.-. )
'---'
Figure 1: Controller Cluster of 2 Controllers
The IGP in a controller has one IGP adjacency relation with one NE in
the network. In Figure 1, the IGP in controller A has IGP adjacency
with NE1, the IGP in B has IGP adjacency with NE4.
In normal operations, the IGP of the primary controller originates
link state (LS) containing the information about the controllers
connected to it. The LS originated by Controller A (Primary) in
Figure 1 having the following contents:
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:
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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.
For the Primary Controller (e.g., A), if it is alive, it continues to
be the primary controller.
With the extensions to IGP, the secondary controller can determine
the status of the primary controller through using IGP and obtaining
the information about the primary controller. 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 its link state database (LSDB) in the IGP
to see whether the IGP for the primary controller is connected to
some network elements and advertises the LS. If so, the primary
controller is alive; otherwise, it is dead.
4. Extensions to IGP
This section describes extensions to OSPF and IS-IS.
4.1. Extensions to OSPF
A new TLV, called OSPF Controllers TLV, is defined. When OSPF acts
as a proxy of a controller in a cluster, it may advertise the
information about the controllers such as the number of controllers
connected to it (including itself) in its router information LSA,
which contains a Controllers TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |C| Position | OldPosition | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | NoControllers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Controller 1 ID |
: : |
| Controller n ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: OSPF Controllers TLV
Type: TBD1 is to be assigned by IANA.
Length: 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.
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When the information about the controllers is changed, OSPF of a
primary controller originates an OSPF Router Information Opaque LSA,
which includes a OSPF Controllers TLV.
4.2. Extensions to IS-IS
Similar to OSPF, a new TLV, called IS-IS Controllers TLV, is defined.
When IS-IS acts as a proxy of a controller in a cluster, it may
advertise the information about the cluster such as the number of
controllers connected to it (including itself) in its LSP, which
contains an IS-IS Controllers TLV of 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 | NoControllers | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Controller 1 ID |
: : |
| Controller n ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: IS-IS Controllers TLV
Type (8 bits): TBD2 is to be assigned by IANA.
Length (8 bits): It indicates the length of the value portion in
octets.
All other fields: The meaning of each of the other fields is the
same as the one of the corresponding field in the OSPF Controllers
TLV defined above.
When the information about the controllers is changed, the IS-IS of a
primary controller originates an LSP, which includes an IS-IS
Controllers TLV.
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.
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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.
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 the
group through its IGP. 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 priority
controller wins in one policy. In another policy, the group with the
highest old position controller (e.g., the old primary 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 Controllers TLV 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 Controllers TLV
containing:
C = 0, Position = 1, Old Position = 1, Intent Primary Controller's
priority, NoControllers = m (m is the number of controllers in the
group that the primary controller is connected 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 Controllers TLV containing:
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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
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
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9.1. Normative References
[ISO10589] ISO, "Intermediate System to Intermediate System Intra-
Domain Routing Exchange Protocol for use in Conjunction
with the Protocol for Providing the Connectionless-mode
Network Service (ISO 8473)", ISO/IEC 10589:2002, November
2002.
[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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3",
RFC 5329, DOI 10.17487/RFC5329, September 2008,
<https://www.rfc-editor.org/info/rfc5329>.
9.2. Informative References
[RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
2007, <https://www.rfc-editor.org/info/rfc4970>.
Authors' Addresses
Huaimo Chen
Futurewei
Boston, MA,
United States of America
Email: Huaimo.chen@futurewei.com
Mehmet Toy
Verizon
United States of America
Email: mehmet.toy@verizon.com
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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
IBM Corporation
United States of America
Email: xufeng.liu.ietf@gmail.com
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