Internet Draft T. Anderson
Expiration: May 2002 Intel Labs
File: draft-ietf-forces-requirements-01.txt E. Bowen
Working Group: ForCES IBM
R. Dantu
Netrake Inc.
A. Doria
N/A
J. Hadi Salim
Znyx Networks
H. Khosravi
Intel Labs
M. Minhazuddin
Avaya Inc.
M. Wasserman
Wind River
November 2001
Requirements for Separation of IP Control and Forwarding
draft-ietf-forces-requirements-01.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF),
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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC-2119].
1. Abstract
This document presents an introduction to issues surrounding a
ForCES architecture and defines a set of associated terminology.
Subsequently, this document defines a set of architectural,
modeling, and protocol requirements for mechanisms to logically
separate the control and data forwarding planes of an IP network
device.
2. Definitions
Addressable Entity (AE) - A physical device that is directly
addressable given some interconnect technology. For example, on
Ethernet, an AE is a device to which we can communicate using an
Ethernet MAC address; on IP networks, it is a device to which we can
communicate using an IP address; and on a switch fabric, it is a
device to which we can communicate using a switch fabric port
number.
Physical Forwarding Element (PFE) - An AE that includes hardware
used to provide per-packet processing and handling. This hardware
may consist of (but is not limited to) network processors, ASIC's,
or general-purpose processors. For example, line cards in a
forwarding backplane are PFEs.
PFE Partition - A logical partition of a PFE consisting of some
subset of each of the resources (e.g., ports, memory, forwarding
table entries) available on the PFE. This concept is analogous to
that of the resources assigned to a virtual router [REQ-PART].
Physical Control Element (PCE) - An AE that includes hardware used
to provide control functionality. This hardware typically includes
a general-purpose processor.
PCE Partition - A logical partition of a PCE consisting of some
subset of each of the resources available on the PCE.
Forwarding Element (FE) - A logical entity that implements the
ForCES protocol. FEs use the underlying hardware to provide per-
packet processing and handling as directed by a CE via the ForCES
protocol. FEs may use PFE partitions, whole PFEs, or multiple PFEs.
Proxy FE - A name for a type of FE that cannot directly modify its
underlying hardware but instead manipulates that hardware using some
intermediate form of communication (e.g., a non-ForCES protocol or
DMA). A proxy FE will typically be used in the case where a PFE
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cannot implement (e.g., due to the lack of a general purpose CPU)
the ForCES protocol directly.
Control Element (CE) - A logical entity that implements the ForCES
protocol and uses it to instruct one or more FEs as to how they
should process packets. CEs handle functionality such as the
execution of control and signaling protocols. CEs may encompass PCE
partitions or whole PCEs.
Pre-association Phase - The period of time during which a FE Manager
(see definition below) and a CE Manager (see definition below) are
deciding which FE and CE should be part of the same network element.
Post-association Phase - The period of time during which a FE does
know which CE is to control it and vice versa, including the time
during which the CE and FE are establishing communication with one
another (after they have been associated to the same NE).
ForCES Protocol - While there may be multiple protocols used within
the overall ForCES architecture, the term "ForCES protocol" refers
only to the ForCES post-association phase protocol (see below).
ForCES Post-Association Phase Protocol - The protocol used for post-
association phase communication between CEs and FEs. This protocol
does not apply to CE-to-CE communication, FE-to-FE communication, or
to communication between FE and CE managers. The ForCES protocol is
a master-slave protocol in which FEs are slaves and CEs are masters.
This protocol includes both the management of the communication
channel (e.g., "connection" establishment, heartbeats) and the
control messages themselves.
FE Model - A model that describes the logical processing functions
of a FE.
FE Manager - A logical entity that operates in the pre-association
phase and is responsible for determining to which CE(s) a FE should
communicate. This determination process is called CE discovery and
may involve the FE manager learning the capabilities of available
CEs. A FE manager may use anything from a static configuration to a
pre-association phase protocol (see below) to determine which CE(s)
to use. Being a logical entity, a FE manager might be physically
combined with any of the other logical entities mentioned in this
section.
CE Manager - A logical entity that operates in the pre-association
phase and is responsible for determining to which FE(s) a CE should
communicate. This determination process is called FE discovery and
may involve the CE manager learning the capabilities of available
FEs. A CE manager may use anything from a static configuration to a
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pre-association phase protocol (see below) to determine which FE to
use. Being a logical entity, a CE manager might be physically
combined with any of the other logical entities mentioned in this
section.
Pre-association Phase Protocol - A protocol between FE managers and
CE managers that helps them determine which CEs or FEs are to be
associated to a NE. A pre-association phase protocol may include a
CE and/or FE capability discovery mechanism. It is important to
note that this capability discovery process is wholly separate from
(and does not replace) that used within the ForCES protocol (see
Section 7, requirement #1). However, the two capability discovery
mechanisms may utilize the same FE model (see Section 6). Pre-
association phase protocols are not discussed further in this
document.
ForCES Network Element (NE) - An entity composed of one or more CEs
and one or more FEs. To entities outside a NE, the NE represents a
single point of management. Similarly, a NE usually hides its
internal organization from external entities.
ForCES Protocol Element - A FE or CE.
High Touch Capability - This term will be used to apply to the
capabilities found in some forwarders to take action on the contents
or headers of a packet based on content other than what is found in
the IP header. Examples of these capabilities include NAT-PT,
firewall, and L7 content recognition.
3. Introduction
An IP network element is composed of numerous logically separated
entities that cooperate to provide a given functionality (such as a
routing or IP switching) and yet appear as a normal integrated
network element to external entities. Two primary types of network
element components exist: control-plane components and forwarding-
plane components. In general, forwarding-plane components are ASIC,
network-processor, or general-purpose processor-based devices that
handle all data path operations. Conversely, control-plane
components are typically based on general-purpose processors that
provide control functionality such as the processing of routing or
signaling protocols. A standard set of mechanisms for connecting
these components would provide increased scalability and allow the
control and forwarding planes to evolve independently thus promoting
faster innovation.
For the purpose of illustration, let us consider the architecture of
a router to illustrate the concept and value of separate control and
forwarding planes. The architecture of a router is composed of two
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main parts. These components, while inter-related, perform
functions that are largely independent of each other. At the bottom
is the forwarding path that operates in the data-forwarding plane
and is responsible for per-packet processing and forwarding. Above
the forwarding plane is the network operating system that is
responsible for operations in the control plane. In the case of a
router or switch, the network operating system runs routing,
signaling and control protocols (e.g., RIP, OSPF and RSVP) and
dictates the forwarding behavior by manipulating forwarding tables,
per-flow QoS tables and access control lists. Typically, the
architecture of these devices combines all of this functionality
into a single functional whole with respect to external entities.
4. Architecture
The chief components of a NE architecture are the CE, the FE, and
the interconnect protocol. The CE is mainly responsible for
operations such as signaling and control protocol processing and the
implementation of management protocols. Based on the information
acquired through control processing, the CE(s) dictates the packet-
forwarding behavior of its FE(s) via the interconnect protocol. For
example, the CE might control a FE by manipulating its forwarding
tables, the state of its interfaces, or by adding or removing a NAT
binding.
The FE operates in the forwarding plane and is responsible chiefly
for per-packet processing and handling. By allowing the control and
forwarding planes to evolve independently, we expect different types
of FEs to be developed - some general purpose and others more
specialized. Some functions that FEs could perform include layer 3
forwarding, metering, shaping, firewall, NAT, encapsulation (e.g.,
tunneling), decapsulation, encryption, accounting, etc. Nearly all
combinations of these functions may be present in practical FEs.
Below is a diagram illustrating an example NE composed of a CE and
two FEs.
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--------------------------------
| NE |
| ------------- |
| | CE | |
| ------------- |
| / \ |
| / \ |
| / \ |
| / \ |
| ----------- ----------- |
| | FE | | FE | |
| ----------- ----------- |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
--------------------------------
| | | | | | | |
| | | | | | | |
5. Architectural Requirements
The following are the architectural requirements:
1) CEs and FEs MUST be able to connect by a variety of interconnect
technologies. Examples of interconnect technologies used in current
architectures include Ethernet connections, backplanes, and ATM
(cell) fabrics. FEs MAY be connected to each other via a different
technology than that used for CE/FE communication.
2) FEs MUST support a minimal set of capabilities necessary for
establishing network connectivity (e.g., interface discovery, port
up/down functions). Beyond this minimal set, the ForCES
architecture MUST NOT restrict the types or numbers of capabilities
that FEs may contain.
3) Packets MUST be able to arrive at the NE by one FE and leave the
NE via a different FE.
4) A NE MUST support the appearance of a single functional device.
For example, in a router, the TTL of the packet should be
decremented only once as it traverses the NE regardless of how many
FEs through which it passes. 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.
5) The architecture MUST provide a way to prevent unauthorized
ForCES protocol elements from joining a NE.
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6) A FE MUST be able to asynchronously inform the CE of an
increase/decrease in available resources or capabilities on the FE.
(Since there is not a strict 1-to-1 mapping between FEs and PFEs, it
is possible for the relationship between a FE and its physical
resources to change over time. For example, the number of physical
ports or the amount of memory allocated to a FE may vary over time.
The CE needs to be informed of such changes so that it can control
the FE in an accurate way.)
7) CEs and FEs MUST determine when a loss of connectivity between
them has occurred.
8) FEs MUST redirect packets addressed to their interfaces to their
CE for further processing. Furthermore, FEs MUST redirect other
required packets (e.g., such as those with the router alert option
set) to their CE as well. (FEs MAY provide any other
classification/redirection capabilities that they desire as
described in Section 6.4 requirement #4.) Similarly, CEs MUST be
able to create packets and have its FEs deliver them.
9) All proposed ForCES architectures MUST explain how that
architecture may be applied to support all of a router's functions
as defined in [RFC1812].
10) In a ForCES NE, the CE(s) MUST be able to learn the topology by
which the FEs in the NE are connected.
11) The ForCES NE architecture MUST be capable of supporting (i.e.,
must scale to) at least hundreds of FEs and tens of thousands of
ports.
12) FEs MUST be able to join and leave NEs dynamically.
13) CEs MUST be able to join and leave NEs dynamically.
14) The NE architecture MUST support multiple CEs and FEs.
6. FE Model Requirements
The variety of FE functionality that the ForCES architecture allows
poses a potential problem for CEs. In order for a CE to effectively
control a FE, the CE must understand at a logical level how the FE
processes packets. We therefore REQUIRE that a FE model be created
that can express the logical packet processing capabilities of a FE.
This model will be used in the ForCES protocol to describe FE
capabilities (see Section 7, requirement #1).
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6.1. Higher-Level FE Model
At its higher level, the FE model MUST express what logical
functions can be applied to packets as they pass through a FE.
Furthermore, the model MUST be capable of describing the order in
which these logical functions are applied in a FE. This ordering is
important in many cases. For example, a NAT function may change a
packet's source or destination IP address. Any number of other
logical functions (e.g., layer 3 forwarding, ingress/egress
firewall, shaping, accounting) may make use of the source or
destination IP address when making decisions. The CE needs to know
whether to configure these logical functions with the pre-NAT or
post-NAT IP address. Furthermore, the model MUST be capable of
expressing multiple instances of the same logical function in a FE's
processing path. Using NAT again as an example, one NAT function is
typically performed before the forwarding decision (packets arriving
externally have their public addresses replaced with private
addresses) and one NAT function is performed after the forwarding
decision (for packets exiting the domain, their private addresses
are replaced by public ones).
6.2. Lower-Level FE Model
At its lower level, the FE model MUST be able to express the
capabilities of each logical function. As the following examples
will illustrate, these lower-level capabilities come in five
varieties: classification, action, parameterization, statistic, and
events.
6.2.1. Classification
Classification data is used by a logical function to perform pattern
matching. For example, there may be two FEs, both of which provide
an ingress firewall function. However, the first FE may filter on
any subset of a (source IP, destination IP, IP protocol, source
port, destination port)-tuple whereas the second FE may perform only
a (destination IP, IP protocol)-tuple classification. In either
case, the action applied to matching packets may be the same, e.g.
drop.
6.2.2. Action
Action data is used by a logical function to manipulate the packet
because of a classification. For example, there may be two traffic-
shaping functions, both of which classify only on destination IP
address. However, one of the shaping functions may implement a
leaky bucket that requires two parameters whereas the other function
may implement a token bucket that requires three parameters.
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6.2.3. Parameterization
Parameterization data can be viewed as parameters to the logical
function itself. This data does not affect individual packets but
affects how the function as a whole behaves. For example, there may
be a congestion function that implements two varieties of RED that
require different parameter sets. Parameterization data would be
used to select between the two varieties of RED and to provide the
necessary configuration to each variety.
6.2.4.Statistics
Some logical functions may maintain certain statistics (e.g., number
of packets processed) about their own operation. The FE model needs
to express which statistics a FEÆs logical functions maintain so
that CEs can later query those statistics to answer queries made by
higher level entities.
6.2.5.Event
Some logical functions may be able to generate asynchronous events
that can be sent to the control plane. Two examples of these events
include packet redirection events and port state change events
(e.g., up/down). The FE model must be able to express the events
that a FEÆs logical functions may generate so that CEs can register
to receive those events when they happen to occur.
6.3. Flexibility
Finally, the FE model SHOULD provide a flexible infrastructure in
which new logical functions and new classification, action, and
parameterization data can be easily added. Also, the FE model MUST
be capable of describing the types of statistics gathered by each
logical function.
6.4. Minimal Set of Logical Functions
The rest of this section defines a minimal set of logical functions
that any FE model MUST support. However, this section shall not be
construed as to define a set of functions that all FEs must provide.
On the contrary, FEs are not required to support any of the
following functions. These requirements only specify that the FE
model must be capable of expressing the capabilities that FEs are
likely to initially provide.
1)Port Functions
The FE model MUST be capable of expressing the number of ports on
the device, the static attributes of each port (e.g., port type,
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link speed), and the configurable attributes of each port (e.g., IP
address, administrative status).
2)Forwarding Functions
The FE model MUST be capable of expressing the data that can be used
by the forwarding function to make a forwarding decision.
3)QoS Functions
The FE model MUST allow a FE to express its QoS capabilities in
terms of, e.g., metering, policing, shaping, and queuing functions.
The FE model MUST be capable of expressing the use of these
functions to provide IntServ or DiffServ functionality as described
in [RFC2211], [RFC2212], [RFC2215], and [DS-PIB].
4)Generic Filtering Functions
The FE model MUST be capable of expressing complex sets of filtering
functions. The model MUST be able to express the existence of
multiples of these functions at arbitrary points in a FE's packet
processing path. The FE model MUST be capable of expressing a wide
range of classification abilities from single fields (e.g.,
destination address) to arbitrary n-tuples. Similarly, the FE model
MUST be capable of expressing what actions these filtering functions
can perform on packets that the classifier matches.
5)Vendor-Specific Functions
The FE model SHOULD be extensible so that vendor-specific
functionality can be expressed.
6)High-Touch Functions
The FE model MUST be capable of expressing the encapsulation and
tunneling capabilities of a FE. The FE model MUST support functions
that mark the IPv4 header TOS octet or the IPv6 Traffic Class octet.
The FE model MAY support other high touch functions (e.g., NAT,
ALG).
7)Security Functions
The FE model MUST be capable of expressing the types of encryption
that may be applied to packets in the forwarding path.
7. ForCES Protocol Requirements
This section specifies some of the requirements that a ForCES
protocol MUST meet.
1)Configuration of Modeled Elements
The ForCES protocol MUST allow the CEs to determine the capabilities
of each FE. These capabilities SHALL be expressed using the FE
model whose requirements are defined in Section 6. Furthermore, the
protocol MUST provide a means for the CEs to control all the FE
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capabilities that are discovered through the FE model. (For
example, the protocol must be able to add/remove
classification/action entries, set/delete parameters, query
statistics, and register for and receive events.)
2)Support for Secure Communication
Since FE configuration will contain information critical to the
functioning of a network (such as IP forwarding tables) and may
contain information derived from business relationships (e.g.,
SLAs), the ForCES protocol MUST support a method of securing
communication between FEs and CEs to ensure that information is
delivered privately and in an unmodified form.
3)Scalability
The ForCES protocol MUST be capable of supporting (i.e., must scale
to) at least hundreds of FEs and tens of thousands of ports. For
example, the ForCES protocol field sizes corresponding to FE or port
numbers SHALL be large enough to support the minimum required
numbers. This requirement does not relate to the performance of the
protocol as the number of FEs or ports in the NE grows.
4)Multihop
When the CEs and FEs are separated beyond a single hop, the ForCES
protocol will make use of an existing RFC2914 compliant L4 protocol
with adequate reliability, security and congestion control (e.g.
TCP, SCTP) for transport purposes.
5)Message Priority
The ForCES protocol MUST provide a means to express message
priority.
6)Reliability
The ForCES protocol SHALL assume that it runs on top of an
unreliable, datagram service. For IP networks, an encapsulation of
the ForCES protocol SHALL be defined that uses a [RFC2914]-compliant
transport protocol and provides a datagram service (that could be
unreliable). For non-IP networks, additional encapsulations MAY be
defined so long as they provide a datagram service to the ForCES
protocol. However, since some messages will need to be reliably
delivered to FEs, the ForCES protocol MUST provide internal support
for reliability mechanisms such as message acknowledgements and/or
state change confirmations.
8. Security Considerations
See architecture requirement #5 and protocol requirement #2.
9. References
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[DS-PIB] M. Fine, et. al., "Differentiated Services Quality of
Service Policy Information Base", work in progress, November 2001,
<draft-ietf-diffserv-pib-05.txt>.
[REQ-PART] T. Anderson, C. Wang, J. Buerkle, "Requirements for the
Dynamic Partitioning of Network Elements", work in progress, August
2001, <draft-ietf-gsmp-dyn-part-reqs-00.txt>.
[RFC1812] F. Baker, "Requirements for IP Version 4 Routers",
RFC1812, June 1995.
[RFC2211] J. Wroclawski, "Specification of the Controlled-Load
Network Element Service", RFC2211, September 1997.
[RFC2212] S. Shenker, C. Partridge, R. Guerin, "Specification of
Guaranteed Quality of Service", RFC2212, September 1997.
[RFC2212] S. Shenker, J. Wroclawski, "General Characterization
Parameters for Integrated Service Network Elements", RFC2215,
September 1997.
[RFC2914] S. Floyd, "Congestion Control Principles", RFC2914,
September 2000.
10. Authors' Addresses
Todd A. Anderson
Intel Labs
2111 NE 25th Avenue
Hillsboro, OR 97124 USA
Phone: +1 503 712 1760
Email: todd.a.anderson@intel.com
Ed Bowen
IBM Zurich Research Laboratory
Saumerstrasse 4
CH-8803 Rueschlikon Switzerland
Phone: +41 1 724 83 68
Email: edbowen@us.ibm.com
Ram Dantu
Netrake Corporation
3000 Technology Drive, #100,
Plano, Texas, 75074
rdantu@netrake.com
214 291 1111
Avri Doria
Phone: +1 401 663 5024
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Email: avri@acm.org
Jamal Hadi Salim
Znyx Networks
Ottawa, Ontario
Canada
Email: hadi@znyx.com
Hormuzd Khosravi
Intel Labs
2111 NE 25th Avenue
Hillsboro, OR 97124 USA
Phone: +1 503 264 0334
Email: hormuzd.m.khosravi@intel.com
Muneyb Minhazuddin
Avaya Inc.
123, Epping road,
North Ryde, NSW 2113, Australia
Phone: +61 2 9352 8620
email: muneyb@avaya.com
Margaret Wasserman
Wind River
10 Tara Blvd., Suite 330
Nashua, NH 03062
Phone: +1 603 897 2067
Email: mrw@windriver.com
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