Network Working Group K. Ogawa
Internet-Draft NTT Corporation
Intended status: Standards Track W. M. Wang
Expires: April 20, 2011 Zhejiang Gongshang University
E. Haleplidis
University of Patras
J. Hadi Salim
Mojatatu Networks
Oct 17, 2010
ForCES Intra-NE High Availability
draft-ietf-forces-ceha-00
Abstract
This document discusses CE High Availability within a ForCES NE.
Status of this Memo
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described in the Simplified BSD License.
Table of Contents
1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Document Scope . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Quantifying Problem Scope . . . . . . . . . . . . . . . . 5
3. RFC5810 CE HA Framework . . . . . . . . . . . . . . . . . . . 6
3.1. Current CE High Availability Support . . . . . . . . . . . 6
3.1.1. Cold Standby Interaction with ForCES Protocol . . . . 7
3.1.2. Responsibilities for HA . . . . . . . . . . . . . . . 9
4. CE HA Hot Standby . . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Definitions
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.
The following definitions are taken from [RFC3654]and [RFC3746]:
Logical Functional Block (LFB) -- A template that represents a fine-
grained, logically separate aspects of FE processing.
ForCES Protocol -- The protocol used at the Fp reference point in the
ForCES Framework in [RFC3746].
ForCES Protocol Layer (ForCES PL) -- A layer in the ForCES
architecture that embodies the ForCES protocol and the state transfer
mechanisms as defined in [RFC5810].
ForCES Protocol Transport Mapping Layer (ForCES TML) -- A layer in
ForCES protocol architecture that specifically addresses the protocol
message transportation issues, such as how the protocol messages are
mapped to different transport media (like SCTP, IP, TCP, UDP, ATM,
Ethernet, etc), and how to achieve and implement reliability,
security, etc.
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2. Introduction
Figure 1 illustrates a ForCES NE controlled by a set of redundant CEs
with CE1 being active and CE2 and CEn-1 being a backup.
-----------------------------------------
| ForCES Network Element |
| +-----------+ |
| | CEn-1 | |
| | (Backup) | |
-------------- Fc | +------------+ +------------+ | |
| CE Manager |--------+-| CE1 |------| CE2 |-+ |
-------------- | | (Active) | Fr | (Backup) | |
| | +-------+--+-+ +---+---+----+ |
| Fl | | | Fp / | |
| | | +---------+ / | |
| | Fp| |/ |Fp |
| | | | | |
| | | Fp /+--+ | |
| | | +-------+ | | |
| | | | | | |
-------------- Ff | --------+--+-- ----+---+----+ |
| FE Manager |--------+-| FE1 | Fi | FE2 | |
-------------- | | |------| | |
| -------------- -------------- |
| | | | | | | | | |
----+--+--+--+----------+--+--+--+-------
| | | | | | | |
| | | | | | | |
Fi/f Fi/f
Fp: CE-FE interface
Fi: FE-FE interface
Fr: CE-CE interface
Fc: Interface between the CE Manager and a CE
Ff: Interface between the FE Manager and an FE
Fl: Interface between the CE Manager and the FE Manager
Fi/f: FE external interface
Figure 1: ForCES Architecture
The ForCES architecture allows FEs to be aware of multiple CEs but
enforces that only one CE be the master controller. This is known in
the industry as 1+N redundancy [refxxxx]. The master CE controls the
FEs via the ForCES protocol operating in the Fp interface. If the
master CE becomes faulty, a backup CE takes over and NE operation
continues. By definition, the current documented setup is known as
cold-standby [refxxxx]. The CE set is static and is passed to the FE
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by the FE Manager (FEM) via the Ff interface and to each CE by the CE
Manager (CEM) in the Fc interface during the pre-association phase.
From an FE perspective, the knobs of control for a CE set are defined
by the FEPO LFB in [RFC5810], Appendix B. Section 3.1 of this
document details these knobs further.
2.1. Document Scope
By current definition, the Fr interface is out of scope for the
ForCES architecture. However, it is expected that organizations
implementing a set of CEs will need to have the CEs communicate to
each other via the Fr interface in order to achieve the
synchronization necessary for controlling the FEs.
The problem scope addressed by this document falls into 2 areas:
1. To describe with more clarity (than [RFC5810]) how current cold-
standby approach operates within the NE cluster.
2. To describe how to evolve the cold-standby setup to a hot-standby
redundancy setup so as to improve the failover time and NE
availability.
2.2. Quantifying Problem Scope
The NE recovery and availability is dependent on several time-
sensitive metrics:
1. How fast the CE plane failure is detected the FE.
2. How fast a backup CE becomes operational.
3. How fast the FEs associate with the new master CE.
4. How fast the FEs recover their state and become operational.
The design goals of the current [RFC5810] choices to meet the above
goals are driven by desire for simplicity.
To quantify the above criteria with the current prescribed ForCES CE
setup in [RFC5810]:
1. How fast the CE side detects a CE failure is left undefined. To
illustrate an extreme scenario, we could have a human operator
acting as the monitoring entity to detect faulty CEs. How fast
such detection happens could be in the range of seconds to days.
A more active monitor on the Fr interface could improve this
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detection.
2. How fast the backup CE becomes operational is also currently out
of scope. In the current setup, a backup CE need not be
operational at all (for example, to save power) and therefore it
is feasible for a monitoring entity to boot up a backup CE after
it detects the failure of the master CE. In this document
Section 4 we suggest that at least one backup CE be online so as
to improve this metric.
3. How fast an FE associates with new master CE is also currently
undefined. The cost of an FE connecting and associating adds to
the recovery overhead. As mentioned above we suggest having at
least one backup CE online. In Section 4 we propose to zero out
the connection and association cost on failover by having each FE
associate with all online backup CEs after associating to the
active CE. Note that if an FE pre-associates with backup CEs,
then the system will be technically operating in hot-standby
mode.
4. And last: How fast an FE recovers its state depends on how much
NE state exists. By ForCES current definition, the new master CE
assumes zero state on the FE and starts from scratch to update
the FE. So the larger the state, the longer the recovery.
3. RFC5810 CE HA Framework
To achieve CE High Availabilty, FEs and CEs MUST inter-operate per
[RFC5810] definition which is repeated for contextual reasons in
Section 3.1. It should be noted that in this default setup, which
MUST be implemented by CEs and FEs needing HA, the Fr plane is out of
scope (and if available is proprietary to an implementation).
3.1. Current CE High Availability Support
As mentioned earlier, although there can be multiple redundant CEs,
only one CE actively controls FEs in a ForCES NE. In practice there
may be only one backup CE. At any moment in time only one master CE
can control the FEs. In addition, the FE connects and associates to
only the master CE. The FE and the CE PL are aware of the primary
and one or more secondary CEs. This information (primary, secondary
CEs) is configured on the FE and the CE PLs during pre-association by
the FEM and the CEM respectively.
Figure 2 below illustrates the Forces message sequences that the FE
uses to recover the connection in current defined cold-standby
scheme.
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FE CE Primary CE Secondary
| | |
| Asso Estb,Caps exchg | |
1 |<--------------------->| |
| | |
| state update | |
2 |<--------------------->| |
| | |
| | |
| FAILURE |
| |
| Asso Estb,Caps exchange |
3 |<------------------------------------------>|
| |
| Event Report (pri CE down) |
4 |------------------------------------------->|
| |
| state update from scratch |
5 |<------------------------------------------>|
Figure 2: CE Failover for Cold Standby
3.1.1. Cold Standby Interaction with ForCES Protocol
High Availability parameterization in an FE is driven by configuring
the FE Protocol Object (FEPO) LFB.
The FEPO CEID component identifies the current master CE and the
component table BackupCEs identifies the backup CEs. The FEPO FE
Heartbeat Interval, CE Heartbeat Dead Interval, and CE Heartbeat
policy help in detecting connectivity problems between an FE and CE.
The CE Failover policy defines how the FE should react on a detected
failure.
Figure 3 illustrates the defined state machine that facilitates
connection recovery.
The FE connects to the CE specified on FEPO CEID component. If it
fails to connect to the defined CE, it moves it to the bottom of
table BackupCEs and sets its CEID component to be the first CE
retrieved from table BackupCEs. The FE then attempts to associate
with the CE designated as the new primary CE. The FE continues
through this procedure until it successfully connects to one of the
CEs.
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(CE issues Teardown || +-----------------+
Lost association) && | Pre-Association |
CE failover policy = 0 | (Association |
+------------>-->-->| in +<----+
| | progress) | |
| CE Issues +--------+--------+ |
| Association | | CEFTI
| Response V | timer
| ___________________+ | expires
| | |
| V ^
+-+-----------+ +-------+-----+
| | | Not |
| | (CE issues Teardown || | Associated |
| | Lost association) && | |
| Associated | CE Failover Policy = 1 | (May |
| | | Continue |
| |---------->------->------>| Forwarding)|
| | | |
+-------------+ +-------------+
^ V
| |
| CE Issues |
| Association |
| Setup |
+_________________________________________+
Figure 3: FE State Machine considering HA
When communication fails between the FE and CE (which can be caused
by either the CE or link failure but not FE related), either the TML
on the FE will trigger the FE PL regarding this failure or it will be
detected using the HB messages between FEs and CEs. The
communication failure, regardless of how it is detected, MUST be
considered as a loss of association between the CE and corresponding
FE.
If the FE's FEPO CE Failover Policy is configured to mode 0 (the
default), it will immediately transition to the pre-association
phase. This means that if association is again established, all FE
state will need to be re-established.
If the FE's FEPO CE Failover Policy is configured to mode 1, it
indicates that the FE is capable of HA restart recovery. In such a
case, the FE transitions to the not associated state and the CEFTI
timer[RFC 5810] is started. The FE MAY continue to forward packets
during this state. It MAY also recycle through any configured backup
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CEs in a round-robin fashion. It first adds its primary CE to the
bottom of table BackupCEs and sets its CEID component to be the first
secondary retrieved from table BackupCEs. The FE then attempts to
associate with the CE designated as the new primary CE. If it fails
to re-associate with any CE and the CEFTI expires, the FE then
transitions to the pre-association state.
If the FE, while in the not associated state, manages to reconnect to
a new primary CE before CEFTI expires it transitions to the
Associated state. Once re-associated, the FE tries to recover any
state that may have been lost during the not associated state. How
the FE achieves to re-synchronize its state is out of scope for the
current ForCES architecture.
An explicit message (a Config message setting Primary CE component in
ForCES Protocol object) from the primary CE, can also be used to
change the Primary CE for an FE during normal protocol operation. In
this case, the FE transitions to the Not Associated State and
attempts to Associate with the new CE.
3.1.2. Responsibilities for HA
XXX: we may remove this section (not much value to overall
discussion)
TML Level:
1. The TML controls logical connection availability and failover.
2. The TML also controls peer HA management.
At this level, control of all lower layers, for example transport
level (such as IP addresses, MAC addresses etc) and associated links
going down are the role of the TML.
PL Level:
All other functionality, including configuring the HA behavior during
setup, the CE IDs used to identify primary and secondary CEs,
protocol messages used to report CE failure (Event Report), Heartbeat
messages used to detect association failure, messages to change the
primary CE (Config), and other HA related operations described
before, are the PL responsibility.
To put the two together, if a path to a primary CE is down, the TML
would take care of failing over to a backup path, if one is
available. If the CE is totally unreachable then the PL would be
informed and it would take the appropriate actions described before.
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4. CE HA Hot Standby
In this section we make some small extensions to the existing scheme
to enable it to achieve hot standby HA. With these suggested changes
we achieve some of the goals defined in Section 2.2, namely:
o How fast a backup CE becomes operational.
o How fast the FEs associate with the new master CE.
As described in Section 3.1, the FEM configures the FE to make it
aware of all the CEs in the NE. The FEM also configures the FE to
make it aware of which CE is the master and which are backup(s). The
FE's FEPO LFB CEID component identifies the current master CE and
table BackupCEs identifies the backup CEs. The FE only connects to
the master CE and then proceeds to associate with it. The master
thereafter controls the FE and receives events from it. This
continues until there is communication failure between the FE and CE
at which point the FE attempts to connect to a CE from the BackupCEs
table until it succeeds to connect and associate with one listed CE.
It is recommended that at least one backup CE should be online.
Doing so will improve how fast the backup CE will take to be
operational (as opposed to bringing up a backup CE when we detect a
master CE fault). If we assume that a CE implementation does state
synchronization between CEs, then the cost of making the backup CE
operational and ready to serve FEs; in such a case an associating FE
could immediately become operational.
If we assume the presence of at least one backup CE online, we can
improve how fast the FEs associate with a new master CE by making two
changes:
The first change that needs to be made is to have the FE, soon after
successfully connecting and associating with the master CE, to
proceed and connect as well as associate with the rest of the CEs
listed in the BackupCEs table.
By virtue of having multiple CE connections, the FE switchover to a
new master CE will be relatively much faster. The overall effect is
improving the NE recovery time in case of communication failure or
faults of the master CE.
XXX: below paragraph needs more text discussion ..
The FE MUST respond to messages issued by only the master CE. This
simplifies the synchronization and avoids the concept of locking FE
state. The FE MUST drop any messages from backup CEs (XXX: Should we
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log and increment some stat?).
XXX: below paragraph needs text discussion ..
Again for the sake of simplicity, asynchronous events and heartbeats
are sent to all associated-to CEs. Packet redirects continue to be
sent only to the master CE.
XXXX: We need to have an extra state for each CE (master, connected,
associated, stats etc) on the FEPO - so probably another change to
current FEPO components.
5. IANA Considerations
TBA
6. Security Considerations
TBA
7. References
7.1. Normative References
[RFC5810] Doria, A., Hadi Salim, J., Haas, R., Khosravi, H., Wang,
W., Dong, L., Gopal, R., and J. Halpern, "Forwarding and
Control Element Separation (ForCES) Protocol
Specification", RFC 5810, March 2010.
7.2. Informative References
[RFC3654] Khosravi, H. and T. Anderson, "Requirements for Separation
of IP Control and Forwarding", RFC 3654, November 2003.
[RFC3746] Yang, L., Dantu, R., Anderson, T., and R. Gopal,
"Forwarding and Control Element Separation (ForCES)
Framework", RFC 3746, April 2004.
[RFC5812] Halpern, J. and J. Hadi Salim, "Forwarding and Control
Element Separation (ForCES) Forwarding Element Model",
RFC 5812, March 2010.
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Authors' Addresses
Kentaro Ogawa
NTT Corporation
3-9-11 Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: ogawa.kentaro@lab.ntt.co.jp
Weiming Wang
Zhejiang Gongshang University
149 Jiaogong Road
Hangzhou 310035
P.R.China
Phone: +86-571-88057712
Email: wmwang@mail.zjgsu.edu.cn
Evangelos Haleplidis
University of Patras
Patras
Greece
Email: ehalep@ece.upatras.gr
Jamal Hadi Salim
Mojatatu Networks
Ottawa, Ontario
Canada
Email: hadi@mojatatu.com
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