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Versions: 00 01 02                                                      
  Internet Draft                                 T. Anderson
  Expiration: March 2002                            Intel
  File: draft-anderson-forces-req-02.txt         E. Bowen
  Working Group: ForCES                             IBM
                                                 R. Dantu
                                                    Netrake Inc.
                                                 A. Doria
                                                    Nortel Networks
                                                 J. Hadi Salim
                                                    Znyx Networks
                                                 H. Khosravi
                                                 M. Minhazuddin
                                                    Avaya Inc.
                                                 M. Wasserman
                                                    Wind River

                                                 September 2001

        Requirements for Separation of IP Control and Forwarding


  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),
   its areas, and its working groups.  Note that other groups may
   also distribute working documents as Internet-Drafts.

   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

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

Anderson                                                      [Page 1]

  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in [RFC-2119].

1. Abstract

   This document defines a set of 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

   Physical Forwarding Element (PFE) û 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 PFE's.

   PFE Partition û 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) û An AE that includes hardware used
   to provide control functionality.  This hardware typically includes
   a general-purpose processor.

   PCE Partition û A logical partition of a PCE consisting of some
   subset of each of the resources available on the PCE.

   Forwarding Element (FE) û A logical entity that implements the
   ForCES protocol.  FE's use the underlying hardware to provide per-
   packet processing and handling as directed by a CE via the ForCES
   protocol.  FE's may use PFE partitions, whole PFE's, or multiple

   Proxy FE û 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

Anderson                                                      [Page 2]

   cannot implement (e.g., due to the lack of a general purpose CPU)
   the ForCES protocol directly.

   Control Element (CE) û A logical entity that implements the ForCES
   protocol and uses it to instruct one or more FE's as to how they
   should process packets.  CE's handle functionality such as the
   execution of control and signaling protocols.  CE's may encompass
   PCE partitions or whole PCE's.  (Whether CE's may encompass multiple
   PCE's or not is an open issue discussed further in Section A.4.)

   Pre-association Phase û The period of time during which a FE does
   not know which CE is to control it and vice versa.

   Post-association Phase û The period of time during which a FE does
   know which CE is to control it and vice versa.

   ForCES Protocol û 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 û The protocol used for post-
   association phase communication between CE's and FE's.  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 FE's are slaves
   and CE's are masters.

   FE Model û A model that describes the logical processing functions
   of a FE.

   FE Manager û 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
   CE's.  A FE manager may use anything from a static configuration to
   a pre-association phase protocol (see below) to determine which CE
   to use.  Being a logical entity, a FE manager might be physically
   combined with any of the other logical entities mentioned in this

   CE Manager û 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
   FE's.  A CE manager may use anything from a static configuration to
   a 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

   Pre-association Phase Protocol û A protocol between FE managers and
   CE managers that helps them determine which CE's or FE's to use.  A

Anderson                                                      [Page 3]

   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 (see Section 11.3).

   ForCES Network Element (NE) û An entity composed of one or more CE's
   and one or more FE's.  To entities outside a NE, the NE represents a
   single point of management.  Similarly, a NE usually hides its
   internal organization from external entities.  However, one
   exception to this rule is that CE's and FE's may be directly managed
   to transition them from the pre-association phase to the post-
   association phase.

   ForCES Protocol Element û 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
   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,

Anderson                                                      [Page 4]

   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 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

   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 FE's to be developed - some general purpose and others more
   specialized.  Some functions that FE's 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 FE's.

   Below is a diagram illustrating an example NE composed of a CE and
   two FE's.

Anderson                                                      [Page 5]

         | NE                           |
         |        -------------         |
         |        |    CE     |         |
         |        -------------         |
         |          /        \          |
         |         /          \         |
         |        /            \        |
         |       /              \       |
         |  -----------     ----------- |
         |  |   FE    |     |    FE   | |
         |  -----------     ----------- |
         |    | | | |         | | | |   |
         |    | | | |         | | | |   |
         |    | | | |         | | | |   |
         |    | | | |         | | | |   |
              | | | |         | | | |
              | | | |         | | | |

5. Architectural Requirements

   The following are the architectural requirements:

     1)CE's and FE's 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.  FE's MAY be
       connected to each other via a different technology than that
       used for CE/FE communication.

     2)FE's 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 FE's 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 FE's 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

     5)The architecture MUST provide a way to prevent unauthorized
       ForCES protocol elements from joining a NE.

Anderson                                                      [Page 6]

     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 FE's
       and PFE's, 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)CE's and FE's MUST determine when a loss of connectivity between
       them has occurred.

     8)FE's MUST redirect packets addressed to their interfaces to
       their CE for further processing.  Furthermore, FE's MUST
       redirect other required packets (e.g., such as those with the
       router alert option set) to their CE as well.  (FE's MAY provide
       any other classification/redirection capabilities that they
       desire as described in Section 6.4 requirement #4.)  Similarly,
       CE's MUST be able to create packets and have its FE's deliver

     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 FE's in the NE are connected.

     11)The ForCES NE architecture and protocols MUST be capable of
       supporting at least hundreds of FE's and tens of thousands of

6. FE Model Requirements

   The variety of FE functionality that the ForCES architecture allows
   poses a potential problem for CE's.  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

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 describe in which order these logical
   functions may be applied.  This ordering is important in many cases.

Anderson                                                      [Page 7]

   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.

6.2. Lower-Level FE Model

   At its lower level, the FE model MUST be capable of expressing the
   data required by each logical function.  As the following examples
   will illustrate, this lower-level data comes in three varieties:
   classification, action, and parameterization.

6.2.1. Classification Data

   Classification data is the data used by a logical function to
   perform pattern matching.  For example, there may be two FE's, 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 Data

   Action data is the data needed by a logical function to manipulate
   the packet as a result 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

6.2.3. Parameterization Data

   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.

6.3. 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

Anderson                                                      [Page 8]

   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.  This minimal set DOES NOT imply
   that all FE's must provide this functionality.  Instead, these
   requirements only specify that the model must be capable of
   expressing the capabilities that FE's may choose to 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,
   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.

   4)Generic Filtering Functions
   The FE model MUST be capable of expressing filtering functions. 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,


   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

Anderson                                                      [Page 9]

   This section specifies the requirements that a ForCES protocol MUST

   1)Configuration of Modeled Elements
   The ForCES protocol MUST allow the CE 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 CE to control all the FE
   capabilities that are discovered through the FE model.

   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.,
   SLA's), the ForCES protocol MUST support a method of securing
   communication between FE's and CE's to ensure that information is
   delivered privately and in an unmodified form.

   3)Event Notification
   The ForCES protocol MUST support the sending of asynchronous events
   (e.g., link up/down, redirected packet, out of memory) from a FE to
   a CE.

8. Security Considerations

   See architecture requirement #5 and protocol requirement #2.

9. References

   [RFC1812]  F. Baker, "Requirements for IP Version 4 Routers",
   RFC1812, June 1995.

   [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-


10. Authors' Addresses

   Todd A. Anderson
   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

Anderson                                                     [Page 10]

   Phone: +41 1 724 83 68
   Email: edbowen@us.ibm.com

   Ram Dantu
   Netrake Corporation
   3000 Technology Drive, #100,
   Plano, Texas, 75074
   214 291 1111

   Avri Doria
   Nortel Networks
   600 Technology Park Drive
   Billerica, MA 01821
   Phone: +1 401 663 5024
   Email: avri@nortelnetworks.com

   Jamal Hadi Salim
   Znyx Networks
   Ottawa, Ontario
   Email: hadi@znyx.com

   Hormuzd Khosravi
   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

11. Appendix A û Open Issues

   This section contains a list of issues on which a requirements
   consensus has not been reached.

11.1. Protocol Issues

Anderson                                                     [Page 11]

   Some issues surrounding the ForCES protocol include the following.
   Should ForCES allow for only reliable delivery of messages or should
   it also allow for unreliable delivery in cases where reliability is
   not needed?  Should the ForCES protocol operate over a variety of
   transports or should a single transport protocol be used?  (It has
   been mandated that in a multihop environment either TCP or SCTP be
   used.  However, whether we should allow alternative transports for
   single hops is an open issue.)

11.2. Modeling Filtering Functions

   How arbitrary should we be in describing where filtering (i.e.,
   generic classification/action) may occur in the FE model?

11.3. Pre-Association Phase Protocol

   We believe it is likely that a pre-association phase protocol will
   be an integral and necessary part of the ForCES architecture but it
   is not known what, if any, requirements should be placed on this
   phase or protocol.  Furthermore, it has not been resolved as to
   whether this protocol should be merged with the post-association
   phase protocol.

11.4. Multiple CE's

   One of the open issues for discussion in the ForCES requirements has
   to do with creating an NE that is composed of more than one CE or
   PCE.  There are several aspects to this discussion.

   - There was acceptance of the possibility of an NE having several
   CE's that provide redundancy.  This option however, would be limited
   to the use of similar CE's, i.e., CE's that provided the same
   functional control capabilities, and would be used only in a
   redundancy mode, disallowing load-sharing applications.  In effect,
   in this model there would be only one functioning CE at a time.

   - There is a fair amount of disagreement over the use of multiple
   CE's for tasks other then redundancy.  Several members of the design
   team have argued for scenarios where the following was possible:
      -- Similar CE's used for load sharing
      -- Dissimilar CE's that provide different capabilities to a set
          of FE's.  For example, one CE could be responsible for IP
          routing while another was responsible for high-touch
          capabilities and a third was responsible for VPN's.

   In the discussions, several issues came up.  Among the issues:

   - If there are multiple CE's, whether similar or dissimilar, would
   there need to be a master CE that maintained a single control
   session with each FE.

Anderson                                                     [Page 12]

   - If there are several similar load sharing CE's, how does the FE
   deal with multiple conflicting commands.
   - If there are several similar load sharing CE's, how is the
   representation of FE state in each of the CE's handled so that all
   CE's have the same state representation.
   - If there are several dissimilar CE's, how are cumulative effects
   handled and how are these effects represented to the CE's.

   There was some concern in the design team that adding multiple CE's
   without a master CE would complicate the ForCES protocol
   unnecessarily.  There was also concern that leaving such a
   capability out would limit the protocol unnecessarily.  The design
   team was not able to reach consensus on this issue.

11.5. FE Model Completeness

   This requirements draft defines a set of logical functions that we
   believe are necessary to allow basic types of FE's to be created.
   Whether this set is sufficient to describe all the functionality of
   any FE is an open issue.  If it is not sufficient, the question of
   what additional logical functions need to be standardized and which
   functions should be left to individual vendors remains an open

11.6. Management

   The current belief is that a NE is the primary management entity and
   that direct management access to individual ForCES protocol elements
   is permitted but only for the purpose of transitioning those
   elements from the pre-association to the post-association phase.
   However, there may be other management concerns that require direct
   access to ForCES elements for other reasons.  Thus, the ultimate
   state of the management model is an open issue.

Anderson                                                     [Page 13]