forces A. Crouch
Internet-Draft H. Khosravi
Intended status: Informational Intel
Expires: April 13, 2010 A. Doria
LTU
X. Wang
Huawei
K. Ogawa
NTT Corporation
October 10, 2009
ForCES Applicability Statement
draft-ietf-forces-applicability-07
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Abstract
The ForCES protocol defines a standard framework and mechanism for
the interconnection between Control Elements and Forwarding Elements
in IP routers and similar devices. In this document we describe the
applicability of the ForCES model and protocol. We provide example
deployment scenarios and functionality, as well as document
applications that would be inappropriate for ForCES.
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Table of Contents
1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Applicability to IP Networks . . . . . . . . . . . . . . . . . 4
4.1. Applicable Services . . . . . . . . . . . . . . . . . . . 5
4.1.1. Discovery, Capability Information Exchange . . . . . . 5
4.1.2. Topology Information Exchange . . . . . . . . . . . . 6
4.1.3. Configuration . . . . . . . . . . . . . . . . . . . . 6
4.1.4. Routing Exchange . . . . . . . . . . . . . . . . . . . 6
4.1.5. QoS Exchange . . . . . . . . . . . . . . . . . . . . . 6
4.1.6. Security Exchange . . . . . . . . . . . . . . . . . . 6
4.1.7. Filtering Exchange and Firewalls . . . . . . . . . . . 7
4.1.8. Encapsulation, Tunneling Exchange . . . . . . . . . . 7
4.1.9. NAT and Application-level Gateways . . . . . . . . . . 7
4.1.10. Measurement and Accounting . . . . . . . . . . . . . . 7
4.1.11. Diagnostics . . . . . . . . . . . . . . . . . . . . . 7
4.1.12. CE Redundancy or CE Failover . . . . . . . . . . . . . 7
4.2. CE-FE Link Capability . . . . . . . . . . . . . . . . . . 7
4.3. CE/FE Locality . . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. ForCES Manageability . . . . . . . . . . . . . . . . . . . . . 9
6.1. NE as an atomic element . . . . . . . . . . . . . . . . . 9
6.2. NE as composed of manageable elements . . . . . . . . . . 9
6.3. ForCES Protocol MIB . . . . . . . . . . . . . . . . . . . 10
6.3.1. MIB Management of an FE . . . . . . . . . . . . . . . 10
6.4. The FEM and CEM . . . . . . . . . . . . . . . . . . . . . 11
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Purpose
The purpose of the ForCES Applicability Statement is to capture the
intent of the ForCES protocol [I-D.ietf-forces-protocol] designers as
to how the protocol could be used (in conjunction with the ForCES
model [I-D.ietf-forces-model]).
2. Overview
The ForCES protocol defines a standard framework and mechanism for
the exchange of information between the logically separate
functionality of the control and data forwarding planes of IP routers
and similar devices. It focuses on the communication necessary for
separation of control plane functionality such as routing protocols,
signaling protocols, and admission control from data forwarding plane
per-packet activities such as packet forwarding, queuing, and header
editing.
This document defines the applicability of the ForCES mechanisms. It
describes types of configurations and settings where ForCES is most
appropriately applied. This document also describes scenarios and
configurations where ForCES would not be appropriate for use.
3. Terminology
A set of terminology associated with ForCES is defined in [3, 4].
That terminology is reused here and the reader is directed to [3, 4]
for the following definitions:
o CE: Control Element.
o FE: Forwarding Element.
o ForCES: ForCES protocol.
o TML: Transport Mapping Layer.
4. Applicability to IP Networks
The purpose of this section is to list the areas of ForCES
applicability in IP network devices. Relatively low end routing
systems may be implemented on simple hardware which performs both
control and packet forwarding functionality. ForCES may not make
sense for such devices.
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Higher end routing systems typically distribute work amongst
interface processing elements, and these devices (FEs) therefore need
to communicate with the control element(s) to perform their job.
ForCES provides a standard way to do this communication.
The remainder of this section lists the applicable services which
ForCES may support, applicable FE functionality, applicable CE-FE
link scenarios, and applicable topologies in which ForCES may be
deployed.
4.1. Applicable Services
In this section we describe the applicability of ForCES for the
following control-forwarding plane services:
o Discovery, Capability Information Exchange
o Topology Information Exchange
o Configuration
o Routing Exchange
o QoS Exchange
o Security Exchange
o Filtering Exchange
o Encapsulation/Tunneling Exchange
o NAT and Application-level Gateways
o Measurement and Accounting
o Diagnostics
o CE Redundancy or CE Failover
4.1.1. Discovery, Capability Information Exchange
Discovery is the process by which CEs and FEs learn of each other's
existence. ForCES assumes that CEs and FEs already know sufficient
information to begin communication in a secure manner. The ForCES
protocol is only applicable after CEs and FEs have found each other.
ForCES makes no assumption about whether discovery was performed
using a dynamic protocol or merely static configuration.
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During the discovery phase, CEs and FEs exchange capability
information with each other. For example, the FEs express the number
of interface ports they provide, as well as the static and
configurable attributes of each port.
In addition to initial configuration, the CEs and FEs also exchange
dynamic configuration changes using ForCES. For example, FEs
asynchronously inform the CE of an increase/decrease in available
resources or capabilities on the FE.
4.1.2. Topology Information Exchange
In this context, topology information relates to how the FEs are
interconnected with each other with respect to packet forwarding.
Topology discovery is outside the scope of the ForCES protocol. An
implementation can choose its own method of topology discovery(for
example use a standard topology discovery protocol like LLDP, BFD;or
apply a static topology configuration policy).Once the topology is
established, ForCES protocol may be used to transmit the resulting
information to the CE.
4.1.3. Configuration
ForCES is used to perform FE configuration. For example, CEs set
configurable FE attributes such as IP addresses, etc. for their
interfaces.
4.1.4. Routing Exchange
ForCES may be used to deliver packet forwarding information resulting
from CE routing calculations. For example, CEs may send forwarding
table updates to the FEs, so that they can make forwarding decisions.
FEs may inform the CE in the event of a forwarding table miss.
4.1.5. QoS Exchange
ForCES may be used to exchange QoS capabilities between CEs and FEs.
For example, an FE may express QoS capabilities to the CE. Such
capabilities might include metering, policing, shaping, and queuing
functions. The CE may use ForCES to configure these capabilities.
4.1.6. Security Exchange
ForCES may be used to exchange Security information between CEs and
FEs. For example, the FE may use ForCES to express the types of
encryption that it is capable of using in an IPsec tunnel. The CE
may use ForCES to configure such a tunnel.
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4.1.7. Filtering Exchange and Firewalls
ForCES may be used to exchange filtering information. For example,
FEs may use ForCES to express the filtering functions such as
classification and action that they can perform, and the CE may
configure these capabilities.
4.1.8. Encapsulation, Tunneling Exchange
ForCES may be used to exchange encapsulation capabilities of an FE,
such as tunneling, and the configuration of such capabilities.
4.1.9. NAT and Application-level Gateways
ForCES may be used to exchange configuration information for Network
Address Translators. Whilst ForCES is not specifically designed for
the configuration of application-level gateway functionality, this
may be in scope for some types of application-level gateways.
4.1.10. Measurement and Accounting
ForCES may be used to exchange configuration information regarding
traffic measurement and accounting functionality. In this area,
ForCES may overlap somewhat with functionality provided by
alternative network management mechanisms such as SNMP. In some
cases ForCES may be used to convey information to the CE to be
reported externally using SNMP.
4.1.11. Diagnostics
ForCES may be used for CEs and FEs to exchange diagnostic
information. For example, an FE can send self-test results to the
CE.
4.1.12. CE Redundancy or CE Failover
CE failover and redundancy are out of scope in the initial version of
ForCES protocol. Basic mechanisms for CE redundancy/failover are not
presently implemented. Broad concepts such as implementing CE
Redundancy, CE Failover, and CE-CE communication, while not precluded
by the ForCES architecture, are considered outside the scope of
ForCES protocol. ForCES protocol is designed to handle CE- FE
communication, and is not intended for CE-CE communication.
4.2. CE-FE Link Capability
When using ForCES, the bandwidth of the CE-FE link is a
consideration, and cannot be ignored. For example, sending a full
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routing table is reasonable over a high bandwidth link, but could be
non-trivial over a lower-bandwidth link. ForCES should be
sufficiently future-proof to be applicable in scenarios where routing
tables grow to several orders of magnitude greater than their current
size. However, we also note that not all IP routers need full
routing tables.
4.3. CE/FE Locality
ForCES is intended for environments where one of the following
applies:
o The control interconnect is some form of local bus, switch, or LAN,
where reliability is high, closely controlled, and not susceptible to
external disruption that does not also affect the CEs and/or FEs.
o The control interconnect shares fate with the FE's forwarding
function. Typically this is because the control connection is also
the FE's primary packet forwarding connection, and so if that link
goes down, the FE cannot forward packets anyway.
The key guideline is that the reliability of the device should not be
significantly reduced by the separation of control and forwarding
functionality.
Taking this into account, ForCES is applicable in the following CE/FE
localities:
o single box NE: chassis with multiple CEs and FEs setup. ForCES is
applicable in localities consisting of control and forwarding
elements which are components in the same physical box.
Example: a network element with a single control blade, and one or
more forwarding blades, all present in the same chassis and sharing
an interconnect such as Ethernet or PCI. In this locality, the
majority of the data traffic being forwarded typically does not
traverse the same links as the ForCES control traffic.
o multiple boxes: separated CE and FE where physical locality could
be same rack, room, building, or long distance which could span
across continents and oceans. ForCES is applicable in localities
consisting of control and forwarding elements which are separated by
a single hop or multiple hops in the network.
5. Security Considerations
The ForCES architecture allows for a variety of security levels[6].
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When operating under a secured physical environment, or for other
operational concerns (in some cases performance issues) the operator
may turn off all the security functions between CE and FE. When the
operator makes a decision to secure the path between the FE and CE
then the operator chooses from one of the options provided by the
TML. Security choices provided by the TML take effect during the
pre-association phase of the ForCES protocol. An operator may choose
to use all, some or none of the security services provided by the TML
in a CE-FE connection. A ForCES NE is required to provide CE/FE node
authentication services, and may provide message integrity and
confidentially services. The NE may provide these services by
employing IPSEC or TLS depending on the choice of TML used in the
deployment of the NE.
6. ForCES Manageability
From the management perspective, an NE can be viewed in at least two
ways. From one perspective, it is a single network element,
specifically a router that needs to be managed in essentially the
same way any router is managed. From another perspective element
management can view the individual entities and interfaces that make
up a ForCES NE.
6.1. NE as an atomic element
From the ForCES requirements RFC 3654, Section 4, point 4:
A NE must support the appearance of a single functional device.
As a single functional device a ForCES NE runs protocols and each of
the protocols has it own existing manageability aspects that are
documented elsewhere. As a router it would also have a configuration
interface. When viewed in this manner, the NE is controlled as a
single routing entity and no new management beyond what is already
available for routers and routing protocols would be required for a
ForCES NE.
6.2. NE as composed of manageable elements
When viewed as a decomposed set of elements from the management
perspective, the ForCES NE is divided into a set of one of more
Control Elements, Forwarding Elements and the interfaces between
them. The interface functionality between the CE and the FE is
provided by the ForCES protocol. As with all IETF protocols a MIB is
provided for the purposes of managing the protocol.
Additionally the architecture makes provision for configuration
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control of the individual CEs and FEs. This is handled by elements
named FE manager (FEM) and the CE manager (CEM). Specifically from
the ForCES requirements RFC [RFC 3654], Section 4, point 4:
However, external entities (e.g., FE managers and CE managers) may
have direct access to individual ForCES protocol elements for
providing information to transition them from the pre-association to
post-association phase.
6.3. ForCES Protocol MIB
The ForCES MIB [I-D.ietf-forces-mib] is a primarily read-only MIB
that captures information related to the ForCES protocol. This
includes state information about the associations between CE(s) and
FE(s) in the NE.
The ForCES MIB does not include information that is specified in
other MIBs, such as packet counters for interfaces, etc.
More specifically, the information in the ForCES MIB relative to
associations includes:
- identifiers of the elements in the association
- state of the association
- configuration parameters of the association
- statistics of the association
6.3.1. MIB Management of an FE
While it is possible to manage a FE from a element manager, several
requirements relating to this have been included in the ForCES
Requirements.
From the ForCES Requirements [RFC 3654], Section 4, point 14:
1. The ability for a management tool (e.g., SNMP) to be used to read
(but not change) the state of FE should not be precluded.
2. It must not be possible for management tools (e.g., SNMP, etc) to
change the state of a FE in a manner that affects overall NE behavior
without the CE being notified.
The ForCES Requirements [RFC 3654], Section 5.7, goes further in
discussing the manner in which FEs should handle management requests
that are specifically directed to the FE:
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RFC 1812 [2] also dictates that "Routers must be manageable by SNMP".
In general, for the post-association phase, most external management
tasks (including SNMP) should be done through interaction with the CE
in order to support the appearance of a single functional device.
Therefore, it is recommended that an SNMP agent be implemented by CEs
and that the SNMP messages received by FEs be redirected to their
CEs. AgentX framework defined in RFC 2741 ([6]) may be applied here
such that CEs act in the role of master agent to process SNMP
protocol messages while FEs act in the role of subagent to provide
access to the MIB objects residing on FEs. AgentX protocol messages
between the master agent (CE) and the subagent (FE) are encapsulated
and transported via ForCES, just like data packets from any other
application layer protocols.
6.4. The FEM and CEM
Though out of scope for the initial ForCES specification effort, the
ForCES architecture include two entities, the CE Manager (CEM) and
the FE Manager (FEM). From the ForCES Protocols Specification
[I-D.ietf-forces-protocol].
CE Manager (CEM) - A logical entity responsible for generic CE
management tasks. It is particularly used during the pre-association
phase to determine with which FE(s) a CE should communicate.
FE Manager (FEM) - A logical entity responsible for generic FE
management tasks. It is used during pre-association phase to
determine with which CE(s) an FE should communicate.
7. Contributors
The following are the contributors who were instrumental in the
creation of earlier releases of this document or who gave good
suggestions to this document.
Mark Handley,ICIR.
8. IANA Considerations
This document has no IANA actions.
[RFC Editor: please remove this section prior to publication.]
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9. Acknowledgments
Many of the colleagues in our companies and participants in the
ForCES mailing list have provided invaluable input into this work.
Particular thanks to Jamal Hadi Salim.
10. References
10.1. Normative References
[I-D.ietf-forces-mib]
HAAS, R., "ForCES MIB", draft-ietf-forces-mib-10 (work in
progress), September 2008.
[I-D.ietf-forces-model]
Halpern, J. and J. Salim, "ForCES Forwarding Element
Model", draft-ietf-forces-model-16 (work in progress),
October 2008.
[I-D.ietf-forces-protocol]
Dong, L., Doria, A., Gopal, R., HAAS, R., Salim, J.,
Khosravi, H., and W. Wang, "ForCES Protocol
Specification", draft-ietf-forces-protocol-22 (work in
progress), March 2009.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[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.
10.2. Informative References
[RFC3015] Cuervo, F., Greene, N., Rayhan, A., Huitema, C., Rosen,
B., and J. Segers, "Megaco Protocol Version 1.0",
RFC 3015, November 2000.
[RFC3292] Doria, A., Hellstrand, F., Sundell, K., and T. Worster,
"General Switch Management Protocol (GSMP) V3", RFC 3292,
June 2002.
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Authors' Addresses
Alan Crouch
Intel
2111 NE 25th Avenue
Hillsboro, OR 97124 USA
USA
Phone: +1 503 264 2196
Email: alan.crouch@intel.com
Hormuzd Khosravi
Intel
2111 NE 25th Avenue
Hillsboro, OR 97124 USA
USA
Phone: 1-503-264-0334
Email: hormuzd.m.khosravi@intel.com
Avri Doria
LTU
Lulea University of Technology
Sweden
Phone: +46 73 277 1788
Email: avri@acm.org
Xin-ping Wang
Huawei
Beijing
China
Phone: +86 10 82836067
Email: carly.wang@huawei.com
Kentaro Ogawa
NTT Corporation
3-9-11 Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: ogawa.kentaro@lab.ntt.co.jp
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