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rfc:rfc3746

Network Working Group L. Yang Request for Comments: 3746 Intel Corp. Category: Informational R. Dantu

                                                  Univ. of North Texas
                                                           T. Anderson
                                                           Intel Corp.
                                                              R. Gopal
                                                                 Nokia
                                                            April 2004
   Forwarding and Control Element Separation (ForCES) Framework

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

 This document defines the architectural framework for the ForCES
 (Forwarding and Control Element Separation) network elements, and
 identifies the associated entities and their interactions.

Table of Contents

 1.  Definitions. . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1. Conventions used in this document . . . . . . . . . . . .  2
     1.2. Terminologies . . . . . . . . . . . . . . . . . . . . . .  3
 2.  Introduction to Forwarding and Control Element Separation
     (ForCES) . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
 3.  Architecture . . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.1. Control Elements and Fr Reference Point . . . . . . . . . 10
     3.2. Forwarding Elements and Fi reference point. . . . . . . . 11
     3.3. CE Managers . . . . . . . . . . . . . . . . . . . . . . . 14
     3.4. FE Managers . . . . . . . . . . . . . . . . . . . . . . . 14
 4.  Operational Phases . . . . . . . . . . . . . . . . . . . . . . 15
     4.1. Pre-association Phase . . . . . . . . . . . . . . . . . . 15
          4.1.1. Fl Reference Point . . . . . . . . . . . . . . . . 15
          4.1.2. Ff Reference Point . . . . . . . . . . . . . . . . 16
          4.1.3. Fc Reference Point . . . . . . . . . . . . . . . . 17
     4.2. Post-association Phase and Fp reference point . . . . . . 17
          4.2.1. Proximity and Interconnect between CEs and FEs . . 18

Yang, et al. Informational [Page 1] RFC 3746 ForCES Framework April 2004

          4.2.2. Association Establishment. . . . . . . . . . . . . 18
          4.2.3. Steady-state Communication . . . . . . . . . . . . 19
          4.2.4. Data Packets across Fp reference point . . . . . . 21
          4.2.5. Proxy FE . . . . . . . . . . . . . . . . . . . . . 22
     4.3. Association Re-establishment. . . . . . . . . . . . . . . 22
          4.3.1. CE graceful restart. . . . . . . . . . . . . . . . 23
          4.3.2. FE restart . . . . . . . . . . . . . . . . . . . . 24
 5.  Applicability to RFC 1812. . . . . . . . . . . . . . . . . . . 25
     5.1. General Router Requirements . . . . . . . . . . . . . . . 25
     5.2. Link Layer. . . . . . . . . . . . . . . . . . . . . . . . 26
     5.3. Internet Layer Protocols. . . . . . . . . . . . . . . . . 27
     5.4. Internet Layer Forwarding . . . . . . . . . . . . . . . . 27
     5.5. Transport Layer . . . . . . . . . . . . . . . . . . . . . 28
     5.6. Application Layer -- Routing Protocols. . . . . . . . . . 29
     5.7. Application Layer -- Network Management Protocol. . . . . 29
 6.  Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
 7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30
 8.  Security Considerations. . . . . . . . . . . . . . . . . . . . 30
     8.1. Analysis of Potential Threats Introduced by ForCES. . . . 31
          8.1.1. "Join" or "Remove" Message Flooding on CEs . . . . 31
          8.1.2. Impersonation Attack . . . . . . . . . . . . . . . 31
          8.1.3. Replay Attack. . . . . . . . . . . . . . . . . . . 31
          8.1.4. Attack during Fail Over. . . . . . . . . . . . . . 32
          8.1.5. Data Integrity . . . . . . . . . . . . . . . . . . 32
          8.1.6. Data Confidentiality . . . . . . . . . . . . . . . 32
          8.1.7. Sharing security parameters. . . . . . . . . . . . 33
          8.1.8. Denial of Service Attack via External Interface. . 33
     8.2. Security Recommendations for ForCES . . . . . . . . . . . 33
          8.2.1. Using TLS with ForCES. . . . . . . . . . . . . . . 34
          8.2.2. Using IPsec with ForCES. . . . . . . . . . . . . . 35
 9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     9.1. Normative References. . . . . . . . . . . . . . . . . . . 37
     9.2. Informative References. . . . . . . . . . . . . . . . . . 37
 10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 39
 11. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 40

1. Definitions

1.1. Conventions used in this document

 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 BCP 14, RFC 2119 [1].

Yang, et al. Informational [Page 2] RFC 3746 ForCES Framework April 2004

1.2. Terminologies

 A set of terminology associated with the ForCES requirements is
 defined in [4] and we only include the definitions that are most
 relevant to this document here.
 Addressable Entity (AE) - An entity that is directly addressable
 given some interconnect technology.  For example, on IP networks, it
 is a device to which we can communicate using an IP address; 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, ASICs
 (Application-Specific Integrated Circuits), or general purpose
 processors, installed on line cards, daughter boards, mezzanine
 cards, or in stand-alone boxes.
 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 switching element as
 described in [9].
 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 happen to be a single blade (or PFE), a partition of a PFE,
 or multiple PFEs.
 Control Element (CE) - A logical entity that implements the ForCES
 Protocol and uses it to instruct one or more FEs on how to process
 packets.  CEs handle functionality such as the execution of control
 and signaling protocols.  CEs may consist of PCE partitions or whole
 PCEs.
 ForCES Network Element (NE) - An entity composed of one or more CEs
 and one or more FEs.  An NE usually hides its internal organization
 from external entities and represents a single point of management to
 entities outside the NE.

Yang, et al. Informational [Page 3] RFC 3746 ForCES Framework April 2004

 Pre-association Phase - The period of time during which an FE Manager
 (see below) and a CE Manager (see below) are determining whether an
 FE and a CE should be part of the same network element.  It is
 possible for some elements of the NE to be in pre-association phase
 while other elements are in the post-association phase.
 Post-association Phase - The period of time during which an FE knows
 which CE is to control it and vice versa, including the time during
 which the CE and FE are establishing communication with one another.
 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.  This protocol could be a single protocol or
 could consist of multiple protocols working together, and may be
 unicast or multicast based.  A separate protocol document will
 specify this information.
 FE Manager - A logical entity that operates in the pre-association
 phase and is responsible for determining to which CE(s) an FE should
 communicate.  This process is called CE discovery and may involve the
 FE manager learning the capabilities of available CEs.  An FE manager
 may use anything from a static configuration to a pre-association
 phase protocol (see below) to determine which CE(s) to use; however,
 this is currently out of scope.  Being a logical entity, an 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 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 pre-association
 phase protocol (see below) to determine which FE to use; however,
 this is currently out of scope.  Being a logical entity, a CE manager
 might be physically combined with any of the other logical entities
 mentioned in this section.

Yang, et al. Informational [Page 4] RFC 3746 ForCES Framework April 2004

 Pre-association Phase Protocol - A protocol between FE managers and
 CE managers that is used to determine which CEs or FEs to use.  A
 pre-association phase protocol may include a CE and/or FE capability
 discovery mechanism.  Note that this capability discovery process is
 wholly separate from (and does not replace) that used within the
 ForCES Protocol.  However, the two capability discovery mechanisms
 may utilize the same FE model.
 FE Model - A model that describes the logical processing functions of
 an FE.
 ForCES Protocol Element - An FE or CE.
 Intra-FE topology - Representation of how a single FE is realized by
 combining possibly multiple logical functional blocks along multiple
 data paths.  This is defined by the FE model.
 FE Topology - Representation of how the multiple FEs in a single NE
 are interconnected.  Sometimes it is called inter-FE topology, to be
 distinguished from intra-FE topology used by the FE model.
 Inter-FE topology - See FE Topology.

2. Introduction to Forwarding and Control Element Separation (ForCES)

 An IP network element (NE) appears to external entities as a
 monolithic piece of network equipment, e.g., a router, NAT, firewall,
 or load balancer.  Internally, however, an IP network element (NE)
 (such as a router) is composed of numerous logically separated
 entities that cooperate to provide a given functionality (such as
 routing).  Two types of network element components exist: control
 element (CE) in control plane and forwarding element (FE) in
 forwarding plane (or data plane).  Forwarding elements are typically
 ASIC, network-processor, or general-purpose processor-based devices
 that handle data path operations for each packet.  Control elements
 are typically based on general-purpose processors that provide
 control functionality, like routing and signaling protocols.
 ForCES aims to define a framework and associated protocol(s) to
 standardize information exchange between the control and forwarding
 plane.  Having standard mechanisms allows CEs and FEs to become
 physically separated standard components.  This physical separation
 accrues several benefits to the ForCES architecture.  Separate
 components would allow component vendors to specialize in one
 component without having to become experts in all components.
 Standard protocol also allows the CEs and FEs from different
 component vendors to interoperate with each other and hence it
 becomes possible for system vendors to integrate together the CEs and

Yang, et al. Informational [Page 5] RFC 3746 ForCES Framework April 2004

 FEs from different component suppliers.  This interoperability
 translates into increased design choices and flexibility for the
 system vendors.  Overall, ForCES will enable rapid innovation in both
 the control and forwarding planes while maintaining interoperability.
 Scalability is also easily provided by this architecture in that
 additional forwarding or control capacity can be added to existing
 network elements without the need for forklift upgrades.
  1. ———————— ————————-

| Control Blade A | | Control Blade B |

    |       (CE)            |       |          (CE)         |
    -------------------------       -------------------------
            ^   |                           ^    |
            |   |                           |    |
            |   V                           |    V
    ---------------------------------------------------------
    |               Switch Fabric Backplane                 |
    ---------------------------------------------------------
           ^  |            ^  |                   ^  |
           |  |            |  |     . . .         |  |
           |  V            |  V                   |  V
       ------------    ------------           ------------
       |Router    |    |Router    |           |Router    |
       |Blade #1  |    |Blade #2  |           |Blade #N  |
       |   (FE)   |    |   (FE)   |           |   (FE)   |
       ------------    ------------           ------------
           ^  |            ^  |                   ^  |
           |  |            |  |     . . .         |  |
           |  V            |  V                   |  V
    Figure 1. A router configuration example with separate blades.
 One example of such physical separation is at the blade level. Figure
 1 shows such an example configuration of a router, with two control
 blades and multiple forwarding blades, all interconnected into a
 switch fabric backplane.  In such a chassis configuration, the
 control blades are the CEs while the router blades are the FEs, and
 the switch fabric backplane provides the physical interconnect for
 all the blades.  Control blade A may be the primary CE while control
 blade B may be the backup CE providing redundancy.  It is also
 possible to have a redundant switch fabric for high availability
 support.  Routers today with this kind of configuration use
 proprietary interfaces for messaging between CEs and FEs.  The goal
 of ForCES is to replace such proprietary interfaces with a standard
 protocol.  With a standard protocol like ForCES implemented on all
 blades, it becomes possible for control blades from vendor X and
 forwarding blades from vendor Y to work seamlessly together in one
 chassis.

Yang, et al. Informational [Page 6] RFC 3746 ForCES Framework April 2004

  1. —— ——-

| CE1 | | CE2 |

  1. —— ——-

^ ^

           |               |
           V               V
    ============================================ Ethernet
        ^       ^       . . .   ^
        |       |               |
        V       V               V
     -------  -------         --------
     | FE#1|  | FE#2|         | FE#n |
     -------  -------         --------
       ^  |     ^  |            ^  |
       |  |     |  |            |  |
       |  V     |  V            |  V
    Figure 2. A router configuration example with separate boxes.
 Another level of physical separation between the CEs and FEs can be
 at the box level.  In such a configuration, all the CEs and FEs are
 physically separated boxes, interconnected with some kind of high
 speed LAN connection (like Gigabit Ethernet).  These separated CEs
 and FEs are only one hop away from each other within a local area
 network.  The CEs and FEs communicate to each other by running
 ForCES, and the collection of these CEs and FEs together become one
 routing unit to the external world.  Figure 2 shows such an example.
 In both examples shown here, the same physical interconnect is used
 for both CE-to-FE and FE-to-FE communication.  However, that does not
 have to be the case.  One reason to use different interconnects is
 that the CE-to-FE interconnect does not have to be as fast as the
 FE-to-FE interconnect, so the more faster and more expensive
 connections can be saved for FE-to-FE.  The separate interconnects
 may also provide reliability and redundancy benefits for the NE.
 Some examples of control functions that can be implemented in the CE
 include routing protocols like RIP, OSPF, and BGP, control and
 signaling protocols like RSVP (Resource Reservation Protocol), LDP
 (Label Distribution Protocol) for MPLS, etc.  Examples of forwarding
 functions in the FE include LPM (longest prefix match) forwarder,
 classifiers, traffic shaper, meter, NAT (Network Address
 Translators), etc.  Figure 3 provides example functions in both CE
 and FE.  Any given NE may contain one or many of these CE and FE
 functions in it.  The diagram also shows that the ForCES Protocol is
 used to transport both the control messages for ForCES itself and the

Yang, et al. Informational [Page 7] RFC 3746 ForCES Framework April 2004

 data packets that are originated/destined from/to the control
 functions in the CE (e.g., routing packets).  Section 4.2.4 provides
 more detail on this.
  1. ————————————————

| | | | | | |

    |OSPF   |RIP    |BGP    |RSVP   |LDP    |. . .  |
    |       |       |       |       |       |       |
    -------------------------------------------------
    |               ForCES Interface                |
    -------------------------------------------------
                            ^   ^
                    ForCES  |   |data
                    control |   |packets
                    messages|   |(e.g., routing packets)
                            v   v
    -------------------------------------------------
    |               ForCES Interface                |
    -------------------------------------------------
    |       |       |       |       |       |       |
    |LPM Fwd|Meter  |Shaper |NAT    |Classi-|. . .  |
    |       |       |       |       |fier   |       |
    -------------------------------------------------
    |               FE resources                    |
    -------------------------------------------------
         Figure 3. Examples of CE and FE functions.
 A set of requirements for control and forwarding separation is
 identified in [4].  This document describes a ForCES architecture
 that satisfies the architectural requirements of [4] and defines a
 framework for ForCES network elements and the associated entities to
 facilitate protocol definition.  Whenever necessary, this document
 uses many examples to illustrate the issues and/or possible solutions
 in ForCES.  These examples are intended to be just examples, and
 should not be taken as the only or definite ways of doing certain
 things.  It is expected that a separate document will be produced by
 the ForCES working group to specify the ForCES Protocol.

3. Architecture

 This section defines the ForCES architectural framework and the
 associated logical components.  This ForCES framework defines
 components of ForCES NEs, including several ancillary components.
 These components may be connected in different kinds of topologies
 for flexible packet processing.

Yang, et al. Informational [Page 8] RFC 3746 ForCES Framework April 2004

  1. ————————————–

| ForCES Network Element |

  1. ————- Fc | ————– ————– |

| CE Manager |———+-| CE 1 |——| CE 2 | |

  1. ————- | | | Fr | | |

| | ————– ————– |

       | Fl             |         |  |    Fp       /          |
       |                |       Fp|  |----------| /           |
       |                |         |             |/            |
       |                |         |             |             |
       |                |         |     Fp     /|----|        |
       |                |         |  /--------/      |        |
 --------------     Ff  | --------------      --------------  |
 | FE Manager |---------+-|     FE 1   |  Fi  |     FE 2   |  |
 --------------         | |            |------|            |  |
                        | --------------      --------------  |
                        |   |  |  |  |          |  |  |  |    |
                        ----+--+--+--+----------+--+--+--+-----
                            |  |  |  |          |  |  |  |
                            |  |  |  |          |  |  |  |
                              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 4. ForCES Architectural Diagram
 The diagram in Figure 4 shows the logical components of the ForCES
 architecture and their relationships.  There are two kinds of
 components inside a ForCES network element: control element (CE) and
 forwarding element (FE).  The framework allows multiple instances of
 CE and FE inside one NE.  Each FE contains one or more physical media
 interfaces for receiving and transmitting packets from/to the
 external world.  The aggregation of these FE interfaces becomes the
 NE's external interfaces.  In addition to the external interfaces,
 there must also exist some kind of interconnect within the NE so that
 the CE and FE can communicate with each other, and one FE can forward
 packets to another FE.  The diagram also shows two entities outside
 of the ForCES NE: CE Manager and FE Manager.  These two ancillary
 entities provide configuration to the corresponding CE or FE in the
 pre-association phase (see Section 4.1).

Yang, et al. Informational [Page 9] RFC 3746 ForCES Framework April 2004

 For convenience, the logical interactions between these components
 are labeled by reference points Fp, Fc, Ff, Fr, Fl, and Fi, as shown
 in Figure 4.  The FE external interfaces are labeled as Fi/f.  More
 detail is provided in Section 3 and 4 for each of these reference
 points.  All these reference points are important in understanding
 the ForCES architecture, however, the ForCES Protocol is only defined
 over one reference point -- Fp.
 The interface between two ForCES NEs is identical to the interface
 between two conventional routers and these two NEs exchange the
 protocol packets through the external interfaces at Fi/f.  ForCES NEs
 connect to existing routers transparently.

3.1. Control Elements and Fr Reference Point

 It is not necessary to define any protocols across the Fr reference
 point to enable control and forwarding separation for simple
 configurations like single CE and multiple FEs.  However, this
 architecture permits multiple CEs to be present in a network element.
 In cases where an implementation uses multiple CEs, the invariant
 that the CEs and FEs together appear as a single NE must be
 maintained.
 Multiple CEs may be used for redundancy, load sharing, distributed
 control, or other purposes.  Redundancy is the case where one or more
 CEs are prepared to take over should an active CE fail.  Load sharing
 is the case where two or more CEs are concurrently active and any
 request that can be serviced by one of the CEs can also be serviced
 by any of the other CEs.  For both redundancy and load sharing, the
 CEs involved are equivalently capable.  The only difference between
 these two cases is in terms of how many active CEs there are
 simultaneously.  Distributed control is the case where two or more
 CEs are concurrently active but certain requests can only be serviced
 by certain CEs.
 When multiple CEs are employed in a ForCES NE, their internal
 organization is considered an implementation issue that is beyond the
 scope of ForCES.  CEs are wholly responsible for coordinating amongst
 themselves via the Fr reference point to provide consistency and
 synchronization.  However, ForCES does not define the implementation
 or protocols used between CEs, nor does it define how to distribute
 functionality among CEs.  Nevertheless, ForCES will support
 mechanisms for CE redundancy or fail over, and it is expected that
 vendors will provide redundancy or fail over solutions within this
 framework.

Yang, et al. Informational [Page 10] RFC 3746 ForCES Framework April 2004

3.2. Forwarding Elements and Fi reference point

 An FE is a logical entity that implements the ForCES Protocol and
 uses the underlying hardware to provide per-packet processing and
 handling as directed by a CE.  It is possible to partition one
 physical FE into multiple logical FEs.  It is also possible for one
 FE to use multiple physical FEs.  The mapping between physical FE(s)
 and logical FE(s) is beyond the scope of ForCES.  For example, a
 logical partition of a physical FE can be created by assigning some
 portion of each of the resources (e.g., ports, memory, forwarding
 table entries) available on the ForCES physical FE to each of the
 logical FEs.  Such a concept of FE virtualization is analogous to a
 virtual switching element as described in [9].  If FE virtualization
 occurs only in the pre-association phase, it has no impact on ForCES.
 However, if FE virtualization results in a resource change taken from
 an existing FE (already participating in ForCES post-association
 phase), the ForCES Protocol needs to be able to inform the CE of such
 a change via asynchronous messages (see [4], Section 5, requirement
 #6).
 FEs perform all packet processing functions as directed by CEs.  FEs
 have no initiative of their own.  Instead, FEs are slaves and only do
 as they are told.  FEs may communicate with one or more CEs
 concurrently across reference point Fp.  FEs have no notion of CE
 redundancy, load sharing, or distributed control.  Instead, FEs
 accept commands from any CE authorized to control them, and it is up
 to the CEs to coordinate among themselves to achieve redundancy, load
 sharing, or distributed control.  The idea is to keep FEs as simple
 and dumb as possible so that FEs can focus their resources on the
 packet processing functions.  Unless otherwise configured or
 determined by a ForCEs Protocol exchange, each FE will process
 authorized incoming commands directed at it as it receives them on a
 first come first serve basis.
 For example, in Figure 5, FE1 and FE2 can be configured to accept
 commands from both the primary CE (CE1) and the backup CE (CE2).
 Upon detection of CE1 failure, perhaps across the Fr or Fp reference
 point, CE2 is configured to take over activities of CE1.  This is
 beyond the scope of ForCES and is not discussed further.
 Distributed control can be achieved in a similar fashion, without
 much intelligence on the part of FEs.  For example, FEs can be
 configured to detect RSVP and BGP protocol packets, and forward RSVP
 packets to one CE and BGP packets to another CE.  Hence, FEs may need
 to do packet filtering for forwarding packets to specific CEs.

Yang, et al. Informational [Page 11] RFC 3746 ForCES Framework April 2004

  1. —— Fr ——-

| CE1 | ——| CE2 |

  1. —— ——-

| \ / |

      |    \    /    |
      |     \  /     |
      |      \/Fp    |
      |      /\      |
      |     /  \     |
      |    /    \    |
    -------  Fi   -------
    | FE1 |<----->| FE2 |
    -------       -------
    Figure 5. CE redundancy example.
 This architecture permits multiple FEs to be present in an NE.  [4]
 dictates that the ForCES Protocol must be able to scale to at least
 hundreds of FEs (see [4] Section 5, requirement #11).  Each of these
 FEs may potentially have a different set of packet processing
 functions, with different media interfaces.  FEs are responsible for
 basic maintenance of layer-2 connectivity with other FEs and with
 external entities.  Many layer-2 media include sophisticated control
 protocols.  The FORCES Protocol (over the Fp reference point) will be
 able to carry messages for such protocols so that, in keeping with
 the dumb FE model, the CE can provide appropriate intelligence and
 control over these media.
 When multiple FEs are present, ForCES requires that packets must be
 able to arrive at the NE by one FE and leave the NE via a different
 FE (See [4], Section 5, Requirement #3).  Packets that enter the NE
 via one FE and leave the NE via a different FE are transferred
 between FEs across the Fi reference point.  The Fi reference point
 could be used by FEs to discover their (inter-FE) topology, perhaps
 during the pre-association phase.  The Fi reference point is a
 separate protocol from the Fp reference point and is not currently
 defined by the ForCES Protocol.
 FEs could be connected in different kinds of topologies and packet
 processing may spread across several FEs in the topology.  Hence,
 logical packet flow may be different from physical FE topology.
 Figure 6 provides some topology examples.  When it is necessary to
 forward packets between FEs, the CE needs to understand the FE
 topology.  The FE topology may be queried from the FEs by the CEs via
 the ForCES Protocol, but the FEs are not required to provide that
 information to the CEs.  So, the FE topology information may also be
 gathered by other means outside of the ForCES Protocol (like inter-FE
 topology discovery protocol).

Yang, et al. Informational [Page 12] RFC 3746 ForCES Framework April 2004

  1. —————-

| CE |

  1. —————-

^ ^ ^

          /       |       \
         /        v        \
        /      -------      \
       /    +->| FE3 |<-+    \
      /     |  |     |  |     \
     v      |  -------  |      v
   -------  |           |  -------
   | FE1 |<-+           +->| FE2 |
   |     |<--------------->|     |
   -------                 -------
      ^  |                   ^  |
      |  |                   |  |
      |  v                   |  v
  (a) Full mesh among FE1, FE2, and FE3
  1. ———-

| CE |

  1. ———-

^ ^ ^ ^

            /  |       |  \
     /------   |       |   ------\
     v         v       v          v
 -------   -------   -------   -------
 | FE1 |<->| FE2 |<->| FE3 |<->| FE4 |
 -------   -------   -------   -------
   ^  |     ^  |       ^  |     ^  |
   |  |     |  |       |  |     |  |
   |  v     |  v       |  v     |  v
 (b) Multiple FEs in a daisy chain

Yang, et al. Informational [Page 13] RFC 3746 ForCES Framework April 2004

                 ^ |
                 | v
              -----------
              |   FE1   |<-----------------------|
              -----------                        |
                ^    ^                           |
               /      \                          |
        | ^   /        \   ^ |                   V
        v |  v          v  | v                ----------
      ---------        ---------              |        |
      | FE2   |        |  FE3  |<------------>|   CE   |
      ---------        ---------              |        |
          ^  ^          ^                     ----------
          |   \        /                        ^  ^
          |    \      /                         |  |
          |    v     v                          |  |
          |   -----------                       |  |
          |   |   FE4   |<----------------------|  |
          |   -----------                          |
          |      |  ^                              |
          |      v  |                              |
          |                                        |
          |----------------------------------------|
      (c) Multiple FEs connected by a ring
      Figure 6. Some examples of FE topology

3.3. CE Managers

 CE managers are responsible for determining which FEs a CE should
 control.  It is legitimate for CE managers to be hard-coded with the
 knowledge of with which FEs its CEs should communicate with.  A CE
 manager may also be physically embedded into a CE and be implemented
 as a simple keypad or other direct configuration mechanism on the CE.
 Finally, CE managers may be physically and logically separate
 entities that configure the CE with FE information via such
 mechanisms as COPS-PR [7] or SNMP [5].

3.4. FE Managers

 FE managers are responsible for determining with which CE any
 particular FE should initially communicate.  Like CE managers, no
 restrictions are placed on how an FE manager decides with which CE
 its FEs should communicate, nor are restrictions placed on how FE
 managers are implemented.  Each FE should have one and only one FE

Yang, et al. Informational [Page 14] RFC 3746 ForCES Framework April 2004

 manager, while different FEs may have the same or different FE
 manager(s).  Each manager can choose to exist and operate
 independently of other manager.

4. Operational Phases

 Both FEs and CEs require some configuration to be in place before
 they can start information exchange and function as a coherent
 network element.  Two operational phases are identified in this
 framework: pre-association and post-association.

4.1. Pre-association Phase

 The Pre-association phase is the period of time during which an FE
 Manager and a CE Manager are determining whether an FE and a CE
 should be part of the same network element.  The protocols used
 during this phase may include all or some of the message exchange
 over Fl, Ff, and Fc reference points.  However, all these may be
 optional and none of this is within the scope of the ForCES Protocol.

4.1.1. Fl Reference Point

 CE managers and FE managers may communicate across the Fl reference
 point in the pre-association phase in order to determine whether an
 individual CE and FE, or a set of CEs and FEs should be associated.
 Communication across the Fl reference point is optional in this
 architecture.  No requirements are placed on this reference point.
 CE managers and FE managers may be operated by different entities.
 The operator of the CE manager may not want to divulge, except to
 specified FE managers, any characteristics of the CEs it manages.
 Similarly, the operator of the FE manager may not want to divulge FE
 characteristics, except to authorized entities.  As such, CE managers
 and FE managers may need to authenticate one another.  Subsequent
 communication between CE managers and FE managers may require other
 security functions such as privacy, non-repudiation, freshness, and
 integrity.

Yang, et al. Informational [Page 15] RFC 3746 ForCES Framework April 2004

 FE Manager      FE               CE Manager     CE
  |              |                 |             |
  |              |                 |             |
  |(security exchange)             |             |
 1|<------------------------------>|             |
  |              |                 |             |
  |(a list of CEs and their attributes)          |
 2|<-------------------------------|             |
  |              |                 |             |
  |(a list of FEs and their attributes)          |
 3|------------------------------->|             |
  |              |                 |             |
  |              |                 |             |
  |<----------------Fl------------>|             |
 Figure 7. An example of a message exchange over the Fl reference
           point
 Once the necessary security functions have been performed, the CE and
 FE managers communicate to determine which CEs and FEs should
 communicate with each other.  At the very minimum, the CE and FE
 managers need to learn of the existence of available FEs and CEs
 respectively.  This discovery process may entail one or both managers
 learning the capabilities of the discovered ForCES protocol elements.
 Figure 7 shows an example of a possible message exchange between the
 CE manager and FE manager over the Fl reference point.

4.1.2. Ff Reference Point

 The Ff reference point is used to inform forwarding elements of the
 association decisions made by the FE manager in the pre-association
 phase.  Only authorized entities may instruct an FE with respect to
 which CE should control it.  Therefore, privacy, integrity,
 freshness, and authentication are necessary between the FE manager
 and FEs when the FE manager is remote to the FE.  Once the
 appropriate security has been established, the FE manager instructs
 the FEs across this reference point to join a new NE or to disconnect
 from an existing NE.  The FE Manager could also assign unique FE
 identifiers to the FEs using this reference point.  The FE
 identifiers are useful in the post association phase to express FE
 topology.  Figure 8 shows example of a message exchange over the Ff
 reference point.

Yang, et al. Informational [Page 16] RFC 3746 ForCES Framework April 2004

 FE Manager      FE               CE Manager     CE
  |              |                |             |
  |              |                |             |
  |(security exchange)            |(security exchange)
 1|<------------>|authentication 1|<----------->|authentication
  |              |                |             |
  |(FE ID, attributes)            |(CE ID, attributes)
 2|<-------------|request        2|<------------|request
  |              |                |             |
 3|------------->|response       3|------------>|response
  |(corresponding CE ID)          |(corresponding FE ID)
  |              |                |             |
  |              |                |             |
  |<-----Ff----->|                |<-----Fc---->|
       Figure 8. Examples of a message exchange
                 over the Ff and Fc reference points
 Note that the FE manager function may be co-located with the FE (such
 as by manual keypad entry of the CE IP address), in which case this
 reference point is reduced to a built-in function.

4.1.3. Fc Reference Point

 The Fc reference point is used to inform control elements of the
 association decisions made by CE managers in the pre-association
 phase.  When the CE manager is remote, only authorized entities may
 instruct a CE to control certain FEs.  Privacy, integrity, freshness,
 and authentication are also required across this reference point in
 such a configuration.  Once appropriate security has been
 established, the CE manager instructs the CEs as to which FEs they
 should control and how they should control them.  Figure 8 shows
 example of a message exchange over the Fc reference point.
 As with the FE manager and FEs, configurations are possible where the
 CE manager and CE are co-located and no protocol is used for this
 function.

4.2. Post-association Phase and Fp reference point

 The Post-association phase is the period of time during which an FE
 and CE have been configured with information necessary to contact
 each other and includes both association establishment and steady-
 state communication.  The communication between CE and FE is
 performed across the Fp ("p" meaning protocol) reference point.
 ForCES Protocol is exclusively used for all communication across the
 Fp reference point.

Yang, et al. Informational [Page 17] RFC 3746 ForCES Framework April 2004

4.2.1. Proximity and Interconnect between CEs and FEs

 The ForCES Working Group has made a conscious decision that the first
 version of ForCES will be focused on "very close" CE/FE localities in
 IP networks.  Very Close localities consist of control and forwarding
 elements that are either components in the same physical box, or
 separated at most by one local network hop ([8]).  CEs and FEs can be
 connected by a variety of interconnect technologies, including
 Ethernet connections, backplanes, ATM (cell) fabrics, etc.  ForCES
 should be able to support each of these interconnects (see [4]
 Section 5, requirement #1).  When the CEs and FEs are separated
 beyond a single L3 routing hop, the ForCES Protocol will make use of
 an existing RFC 2914 [3] compliant L4 protocol with adequate
 reliability, security, and congestion control (e.g., TCP, SCTP) for
 transport purposes.

4.2.2. Association Establishment

              FE                      CE
              |                       |
              |(Security exchange.)   |
             1|<--------------------->|
              |                       |
              |(Let me join the NE please.)
             2|---------------------->|
              |                       |
              |(What kind of FE are you? -- capability query)
             3|<----------------------|
              |                       |
              |(Here is my FE functions/state: use model to
 describe)
             4|---------------------->|
              |                       |
              |(Initial config for FE -- optional)
             5|<----------------------|
              |                       |
              |(I am ready to go. Shall I?)
             6|---------------------->|
              |                       |
              |(Go ahead!)            |
             7|<----------------------|
              |                       |
 Figure 9. Example of a message exchange between CE and FE
           over Fp to establish an NE association

Yang, et al. Informational [Page 18] RFC 3746 ForCES Framework April 2004

 As an example, figure 9 shows some of the message exchange that may
 happen before the association between the CE and FE is fully
 established.  Either the CE or FE can initiate the connection.
 Security handshake is necessary to authenticate the two communication
 endpoints to each other before any further message exchange can
 happen.  The security handshake should include mutual authentication
 and authorization between the CE and FE, but the exact details depend
 on the security solution chosen by the ForCES Protocol.
 Authorization can be as simple as checking against the list of
 authorized end points provided by the FE or CE manager during the
 pre-association phase.  Both authentication and authorization must be
 successful before the association can be established.  If either
 authentication or authorization fails, the end point must not be
 allowed to join the NE.  After the successful security handshake,
 message authentication and confidentiality are still necessary for
 the on-going information exchange between the CE and FE, unless some
 form of physical security exists.  Whenever a packet fails
 authentication, it must be dropped and a notification may be sent to
 alert the sender of the potential attack.  Section 8 provides more
 details on the security considerations for ForCES.
 After the successful security handshake, the FE needs to inform the
 CE of its own capability and optionally its topology in relation to
 other FEs.  The capability of the FE shall be represented by the FE
 model, as required in [4] (Section 6, requirement #1).  The model
 would allow an FE to describe what kind of packet processing
 functions it contains, in what order the processing happens, what
 kinds of configurable parameters it allows, what statistics it
 collects, and what events it might throw, etc.  Once such information
 is available to the CE, the CE may choose to send some initial or
 default configuration to the FE so that the FE can start receiving
 and processing packets correctly.  Such initialization may not be
 necessary if the FE already obtains the information from its own
 bootstrap process.  Once the necessary initial information is
 exchanged, the process of association is completed.  Packet
 processing and forwarding at the FE cannot begin until association is
 established.  After the association is established, the CE and FE
 enter steady-state communication.

4.2.3. Steady-state Communication

 Once an association is established between the CE and FE, the ForCES
 Protocol is used by the CE and FE over the Fp reference point to
 exchange information to facilitate packet processing.

Yang, et al. Informational [Page 19] RFC 3746 ForCES Framework April 2004

         FE                      CE
         |                       |
         |(Add these new routes.)|
        1|<----------------------|
         |                       |
         |(Successful.)          |
        2|---------------------->|
         |                       |
         |                       |
         |(Query some stats.)    |
        1|<----------------------|
         |                       |
         |(Reply with stats collected.)
        2|---------------------->|
         |                       |
         |                       |
         |(My port is down, with port #.)
        1|---------------------->|
         |                       |
         |(Here is a new forwarding table)
        2|<----------------------|
         |                       |
 Figure 10. Examples of a message exchange between CE and FE
            over Fp during steady-state communication
 Based on the information acquired through CEs' control processing,
 CEs will frequently need to manipulate the packet-forwarding
 behaviors of their FE(s) by sending instructions to FEs.  For
 example, Figure 10 shows message exchange examples in which the CE
 sends new routes to the FE so that the FE can add them to its
 forwarding table.  The CE may query the FE for statistics collected
 by the FE and the FE may notify the CE of important events such as
 port failure.

Yang, et al. Informational [Page 20] RFC 3746 ForCES Framework April 2004

4.2.4. Data Packets across Fp reference point

  1. ——————– ———————-

| | | |

 |    +--------+     |           |     +--------+     |
 |    |CE(BGP) |     |           |     |CE(BGP) |     |
 |    +--------+     |           |     +--------+     |
 |        |          |           |          ^         |
 |        |Fp        |           |          |Fp       |
 |        v          |           |          |         |
 |    +--------+     |           |     +--------+     |
 |    |  FE    |     |           |     |   FE   |     |
 |    +--------+     |           |     +--------+     |
 |        |          |           |          ^         |
 | Router |          |           | Router   |         |
 | A      |          |           | B        |         |
 ---------+-----------           -----------+----------
          v                                 ^
          |                                 |
          |                                 |
          ------------------->---------------
 Figure 11. Example to show data packet flow between two NEs.
 Control plane protocol packets (such as RIP, OSPF messages) addressed
 to any of NE's interfaces are typically redirected by the receiving
 FE to its CE, and CE may originate packets and have its FE deliver
 them to other NEs.  Therefore, the ForCES Protocol over Fp not only
 transports the ForCES Protocol messages between CEs and FEs, but also
 encapsulates the data packets from control plane protocols.
 Moreover, one FE may be controlled by multiple CEs for distributed
 control.  In this configuration, the control protocols supported by
 the FORCES NEs may spread across multiple CEs.  For example, one CE
 may support routing protocols like OSPF and BGP, while a signaling
 and admission control protocol like RSVP is supported in another CE.
 FEs are configured to recognize and filter these protocol packets and
 forward them to the corresponding CE.
 Figure 11 shows one example of how the BGP packets originated by
 router A are passed to router B.  In this example, the ForCES
 Protocol is used to transport the packets from the CE to the FE
 inside router A, and then from the FE to the CE inside router B.  In
 light of the fact that the ForCES Protocol is responsible for
 transporting both the control messages and the data packets between
 the CE and FE over the Fp reference point, it is possible to use
 either a single protocol or multiple protocols.

Yang, et al. Informational [Page 21] RFC 3746 ForCES Framework April 2004

4.2.5. Proxy FE

 In the case where a physical FE cannot implement (e.g., due to the
 lack of a general purpose CPU) the ForCES Protocol directly, a proxy
 FE can be used to terminate the Fp reference point instead of the
 physical FE.  This allows the CE to communicate to the physical FE
 via the proxy by using ForCES, while the proxy manipulates the
 physical FE using some intermediary form of communication (e.g., a
 non-ForCES protocol or DMA).  In such an implementation, the
 combination of the proxy and the physical FE becomes one logical FE
 entity.  It is also possible for one proxy to act on behalf of
 multiple physical FEs.
 One needs to be aware of the security implication introduced by the
 proxy FE.  Since the physical FE is not capable of implementing
 ForCES itself, the security mechanism of ForCES can only secure the
 communication channel between the CE and the proxy FE, but not all
 the way to the physical FE.  It is recommended that other security
 mechanisms (including physical security property) be employed to
 ensure the security between the CE and the physical FE.

4.3. Association Re-establishment

 FEs and CEs may join and leave NEs dynamically (see [4] Section 5,
 requirements #12).  When an FE or CE leaves the NE, the association
 with the NE is broken.  If the leaving party rejoins an NE later, to
 re-establish the association, it may need to re-enter the pre-
 association phase.  Loss of association can also happen unexpectedly
 due to a loss of connection between the CE and the FE.  Therefore,
 the framework allows the bi-directional transition between these two
 phases, but the ForCES Protocol is only applicable for the post-
 association phase.  However, the protocol should provide mechanisms
 to support association re-establishment.  This includes the ability
 for CEs and FEs to determine when there is a loss of association
 between them, and to restore association and efficient state
 (re)synchronization mechanisms (see [4] Section 5, requirement #7).
 Note that security association and state must also be re-established
 to guarantee the same level of security (including both
 authentication and authorization) exists before and after the
 association re-establishment.
 When an FE leaves or joins an existing NE that is already in
 operation, the CE needs to be aware of the impact on FE topology and
 deal with the change accordingly.

Yang, et al. Informational [Page 22] RFC 3746 ForCES Framework April 2004

4.3.1. CE graceful restart

 The failure and restart of the CE in a router can potentially cause
 much stress and disruption on the control plane throughout a network
 because in restarting a CE for any reason, the router loses routing
 adjacencies or sessions with its routing neighbors.  Neighbors who
 detect the lost adjacency normally re-compute new routes and then
 send routing updates to their own neighbors to communicate the lost
 adjacency.  Their neighbors do the same thing to propagate throughout
 the network.  In the meantime, the restarting router cannot receive
 traffic from other routers because the neighbors have stopped using
 the router's previously advertised routes.  When the restarting
 router restores adjacencies, neighbors must once again re-compute new
 routes and send out additional routing updates.  The restarting
 router is unable to forward packets until it has re-established
 routing adjacencies with neighbors, received route updates through
 these adjacencies, and computed new routes.  Until convergence takes
 place throughout the network, packets may be lost in transient black
 holes or forwarding loops.
 A high availability mechanism known as the "graceful restart" has
 been used by the IP routing protocols (OSPF [11], BGP [12], IS-IS
 [13]) and MPLS label distribution protocol (LDP [10]) to help
 minimize the negative effects on routing throughout an entire network
 caused by a restarting router.  Route flap on neighboring routers is
 avoided, and a restarting router can continue to forward packets that
 would otherwise be dropped.
 While the details differ from protocol to protocol, the general idea
 behind the graceful restart mechanism remains the same.  With the
 graceful restart, a restarting router can inform its neighbors when
 it restarts.  The neighbors may detect the lost adjacency but do not
 recompute new routes or send routing updates to their neighbors.  The
 neighbors also hold on to the routes received from the restarting
 router before restart and assume they are still valid for a limited
 time.  By doing so, the restarting router's FEs can also continue to
 receive and forward traffic from other neighbors for a limited time
 by using the routes they already have.  The restarting router then
 re-establishes routing adjacencies, downloads updated routes from all
 its neighbors, recomputes new routes, and uses them to replace the
 older routes it was using.  It then sends these updated routes to its
 neighbors and signals the completion of the graceful restart process.
 Non-stop forwarding is a requirement for graceful restart.  It is
 necessary so a router can continue to forward packets while it is
 downloading routing information and recomputing new routes.  This
 ensures that packets will not be dropped.  As one can see, one of the
 benefits afforded by the separation of CE and FE is exactly the

Yang, et al. Informational [Page 23] RFC 3746 ForCES Framework April 2004

 ability of non-stop forwarding in the face of the CE failure and
 restart.  The support of dynamic changes to CE/FE association in
 ForCES also makes it compatible with high availability mechanisms,
 such as graceful restart.
 ForCES should be able to support a CE graceful restart easily.  When
 the association is established the first time, the CE must inform the
 FEs what to do in the case of a CE failure.  If graceful restart is
 not supported, the FEs may be told to stop packet processing all
 together if its CE fails.  If graceful restart is supported, the FEs
 should be told to cache and hold on to its FE state, including the
 forwarding tables across the restarts.  A timer must be included so
 that the timeout causes such a cached state to eventually expire.
 Those timers should be settable by the CE.

4.3.2. FE restart

 In the same example in Figure 5, assuming CE1 is the working CE for
 the moment, what would happen if one of the FEs, say FE1, leaves the
 NE temporarily?  FE1 may voluntarily decide to leave the association.
 Alternatively, FE1 may stop functioning simply due to unexpected
 failure.  In the former case, CE1 receives a "leave-association
 request" from FE1.  In the latter, CE1 detects the failure of FE1 by
 some other means.  In both cases, CE1 must inform the routing
 protocols of such an event, most likely prompting a reachability and
 SPF (Shortest Path First) recalculation and associated downloading of
 new FIBs from CE1 to the other remaining FEs (only FE2 in this
 example).  Such recalculation and FIB updates will also be propagated
 from CE1 to the NE's neighbors that are affected by the connectivity
 of FE1.
 When FE1 decides to rejoin again, or when it restarts again after the
 failure, FE1 needs to re-discover its master (CE).  This can be
 achieved by several means.  It may re-enter the pre-association phase
 and get that information from its FE manager.  It may retrieve the
 previous CE information from its cache, if it can validate the
 information freshness.  Once it discovers its CE, it starts message
 exchange with the CE to re-establish the association, as outlined in
 Figure 9, with the possible exception that it might be able to bypass
 the transport of the complete initial configuration.  Suppose that
 FE1 still has its routing table and other state information from the
 last association.  Instead of re-sending all the information, it may
 be able to use a more efficient mechanism to re-sync the state with
 its CE, if such a mechanism is supported by the ForCES Protocol.  For
 example, CRC-32 of the state might give a quick indication of whether
 or not the state is in-sync with its CE.  By comparing its state with
 the CE first, it sends an information update

Yang, et al. Informational [Page 24] RFC 3746 ForCES Framework April 2004

 only if it is needed.  The ForCES Protocol may choose to implement
 similar optimization  mechanisms, but it may also choose not to, as
 this is not a requirement.

5. Applicability to RFC 1812

 [4] Section 5, requirement #9 dictates "Any proposed ForCES
 architecture must explain how that architecture supports all of the
 router functions as defined in RFC 1812."  RFC 1812 [2] discusses
 many important requirements for IPv4 routers from the link layer to
 the application layer.  This section addresses the relevant
 requirements in RFC 1812 for implementing IPv4 routers based on
 ForCES architecture and explains how ForCES satisfies these
 requirements by providing guidelines on how to separate the
 functionalities required into the forwarding plane and control plane.
 In general, the forwarding plane carries out the bulk of the per-
 packet processing that is required at line speed, while the control
 plane carries most of the computationally complex operations that are
 typical of the control and signaling protocols.  However, it is
 impossible to draw a rigid line to divide the processing into CEs and
 FEs cleanly and the ForCES architecture should not limit the
 innovative approaches in control and forwarding plane separation.  As
 more and more processing power is available in the FEs, some of the
 control functions that traditionally are performed by CEs may now be
 moved to FEs for better performance and scalability.  Such offloaded
 functions may include part of ICMP or TCP processing, or part of
 routing protocols.  Once off-loaded onto the forwarding plane, such
 CE functions, even though logically belonging to the control plane,
 now become part of the FE functions.  Just like the other logical
 functions performed by FEs, such off-loaded functions must be
 expressed as part of the FE model so that the CEs can decide how to
 best take advantage of these off-loaded functions when present on the
 FEs.

5.1. General Router Requirements

 Routers have at least two or more logical interfaces.  When CEs and
 FEs are separated by ForCES within a single NE, some additional
 interfaces are needed for intra-NE communications, as illustrated in
 figure 12.  This NE contains one CE and two FEs.  Each FE has four
 interfaces; two of them are used for receiving and transmitting
 packets to the external world, while the other two are for intra-NE
 connections.  CE has two logical interfaces #9 and #10, connected to
 interfaces #3 and #6 from FE1 and FE2, respectively.  Interface #4
 and #5 are connected for FE1-FE2 communication.  Therefore, this
 router NE provides four external interfaces (#1, 2, 7, and 8).

Yang, et al. Informational [Page 25] RFC 3746 ForCES Framework April 2004

  1. ——————————–

| router NE |

    |   -----------   -----------   |
    |   |   FE1   |   |   FE2   |   |
    |   -----------   -----------   |
    |   1| 2| 3| 4|   5| 6| 7| 8|   |
    |    |  |  |  |    |  |  |  |   |
    |    |  |  |  +----+  |  |  |   |
    |    |  |  |          |  |  |   |
    |    |  | 9|        10|  |  |   |
    |    |  | -------------- |  |   |
    |    |  | |    CE      | |  |   |
    |    |  | -------------- |  |   |
    |    |  |                |  |   |
    -----+--+----------------+--+----
         |  |                |  |
         |  |                |  |
    Figure 12. A router NE example with four interfaces.
 IPv4 routers must implement IP to support its packet forwarding
 function, which is driven by its FIB (Forwarding Information Base).
 This Internet layer forwarding (see RFC 1812 [2] Section 5)
 functionality naturally belongs to FEs in the ForCES architecture.
 A router may implement transport layer protocols (like TCP and UDP)
 that are required to support application layer protocols (see RFC
 1812 [2] Section 6).  One important class of application protocols is
 routing protocols (see RFC 1812 [2] Section 7).  In the ForCES
 architecture, routing protocols are naturally implemented by CEs.
 Routing protocols require that routers communicate with each other.
 This communication between CEs in different routers is supported in
 ForCES by FEs' ability to redirect data packets addressed to routers
 (i.e., NEs), and the CEs' ability to originate packets and have them
 delivered by their FEs.  This communication occurs across the Fp
 reference point inside each router and between neighboring routers'
 external interfaces, as illustrated in Figure 11.

5.2. Link Layer

 Since FEs own all the external interfaces for the router, FEs need to
 conform to the link layer requirements in RFC 1812 [2].  Arguably,
 ARP support may be implemented in either CEs or FEs.  As we will see
 later, a number of behaviors that RFC 1812 mandates fall into this
 category -- they may be performed by the FE and may be performed by
 the CE.  A general guideline is needed to ensure interoperability
 between separated control and forwarding planes.  The guideline we
 offer here is that CEs MUST be capable of these kinds of operations

Yang, et al. Informational [Page 26] RFC 3746 ForCES Framework April 2004

 while FEs MAY choose to implement them.  The FE model should indicate
 its capabilities in this regard so that CEs can decide where these
 functions are implemented.
 Interface parameters, including MTU, IP address, etc., must be
 configurable by CEs via ForCES.  CEs must be able to determine
 whether a physical interface in an FE is available to send packets or
 not.  FEs must also inform CEs of the status change of the interfaces
 (like link up/down) via ForCES.

5.3. Internet Layer Protocols

 Both FEs and CEs must implement the IP protocol and all mandatory
 extensions as RFC 1812 specified.  CEs should implement IP options
 like source route and record route while FEs may choose to implement
 those as well.  The timestamp option should be implemented by FEs to
 insert the timestamp most accurately.  The FE must interpret the IP
 options that it understands and preserve the rest unchanged for use
 by CEs.  Both FEs and CEs might choose to silently discard packets
 without sending ICMP errors, but such events should be logged and
 counted.  FEs may report statistics for such events to CEs via
 ForCES.
 When multiple FEs are involved to process packets, the appearance of
 a single NE must be strictly maintained.  For example, Time-To-Live
 (TTL) must be decremented only once within a single NE.  For example,
 it can be always decremented by the last FE with egress function.
 FEs must receive and process normally any packets with a broadcast
 destination address or a multicast destination address that the
 router has asked to receive.  When IP multicast is supported in
 routers, IGMP is implemented in CEs.  CEs are also required of ICMP
 support, while it is optional for FEs to support ICMP.  Such an
 option can be communicated to CEs as part of the FE model. Therefore,
 FEs can always rely upon CEs to send out ICMP error messages, but FEs
 also have the option of generating ICMP error messages themselves.

5.4. Internet Layer Forwarding

 IP forwarding is implemented by FEs.  When the routing table is
 updated at the CEs, ForCES is used to send the new route entries from
 the CEs to FEs.  Each FE has its own forwarding table and uses this
 table to direct packets to the next hop interface.
 Upon receiving IP packets, the FE verifies the IP header and
 processes most of the IP options.  Some options cannot be processed
 until the routing decision has been made.  The routing decision is
 made after examining the destination IP address.  If the destination

Yang, et al. Informational [Page 27] RFC 3746 ForCES Framework April 2004

 address belongs to the router itself, the packets are filtered and
 either processed locally or forwarded to the CE, depending upon the
 instructions set-up by the CE.  Otherwise, the FE determines the next
 hop IP address by looking in its forwarding table.  The FE also
 determines the network interface it uses to send the packets.
 Sometimes an FE may need to forward the packets to another FE before
 packets can be forwarded out to the next hop.  Right before packets
 are forwarded out to the next hop, the FE decrements TTL by 1 and
 processes any IP options that could not be processed before.  The FE
 performs IP fragmentation if necessary, determines the link layer
 address (e.g., by ARP), and encapsulates the IP datagram (or each of
 the fragments thereof) in an appropriate link layer frame and queues
 it for output on the interface selected.
 Other options mentioned in RFC 1812 [2] for IP forwarding may also be
 implemented at FEs, for example, packet filtering.
 FEs typically forward packets destined locally to CEs.  FEs may also
 forward exceptional packets (packets that FEs do not know how to
 handle) to CEs.  CEs are required to handle packets forwarded by FEs
 for whatever reason.  It might be necessary for ForCES to attach some
 meta-data with the packets to indicate the reasons of forwarding from
 FEs to CEs.  Upon receiving packets with meta-data from FEs, CEs can
 decide to either process the packets themselves, or pass the packets
 to the upper layer protocols including routing and management
 protocols.  If CEs are to process the packets by themselves, CEs may
 choose to discard the packets, or modify and re-send the packets.
 CEs may also originate new packets and deliver them to FEs for
 further forwarding.
 Any state change during router operation must also be handled
 correctly according to RFC 1812.  For example, when an FE ceases
 forwarding, the entire NE may continue forwarding packets, but it
 needs to stop advertising routes that are affected by the failed FE.

5.5. Transport Layer

 The Transport layer is typically implemented at CEs to support higher
 layer application protocols like routing protocols.  In practice,
 this means that most CEs implement both the Transmission Control
 Protocol (TCP) and the User Datagram Protocol (UDP).
 Both CEs and FEs need to implement the ForCES Protocol.  If some
 layer-4 transport is used to support ForCES, then both CEs and FEs
 need to implement the L4 transport and ForCES Protocols.

Yang, et al. Informational [Page 28] RFC 3746 ForCES Framework April 2004

5.6. Application Layer – Routing Protocols

 Interior and exterior routing protocols are implemented on CEs.  The
 routing packets originated by CEs are forwarded to FEs for delivery.
 The results of such protocols (like forwarding table updates) are
 communicated to FEs via ForCES.
 For performance or scalability reasons, portions of the control plane
 functions that need faster response may be moved from the CEs and
 off-loaded onto the FEs.  For example, in OSPF, the Hello protocol
 packets are generated and processed periodically.  When done at the
 CEs, the inbound Hello packets have to traverse from the external
 interfaces at the FEs to the CEs via the internal CE-FE channel.
 Similarly, the outbound Hello packets have to go from the CEs to the
 FEs and to the external interfaces.  Frequent Hello updates place
 heavy processing overhead on the CEs and can overwhelm the CE-FE
 channel as well.  Since typically there are far more FEs than CEs in
 a router, the off-loaded Hello packets are processed in a much more
 distributed and scalable fashion.  By expressing such off-loaded
 functions in the FE model, we can ensure interoperability.  However,
 the exact description of the off-loaded functionality corresponding
 to the off-loaded functions expressed in the FE model are not part of
 the model itself and will need to be worked out as a separate
 specification.

5.7. Application Layer – Network Management Protocol

 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. Summary

 This document defines an architectural framework for ForCES.  It
 identifies the relevant components for a ForCES network element,
 including (one or more) FEs, (one or more) CEs, one optional FE
 manager, and one optional CE manager.  It also identifies the
 interaction among these components and discusses all the major

Yang, et al. Informational [Page 29] RFC 3746 ForCES Framework April 2004

 reference points.  It is important to point out that, among all the
 reference points, only the Fp interface between CEs and FEs is within
 the scope of ForCES.  ForCES alone may not be enough to support all
 desirable NE configurations.  However, we believe that ForCES over an
 Fp interface is the most important element in realizing physical
 separation and interoperability of CEs and FEs, and hence the first
 interface that ought to be standardized.  Simple and useful
 configurations can still be implemented with only CE-FE interface
 being standardized, e.g., single CE with full-meshed FEs.

7. Acknowledgements

 Joel M. Halpern gave us many insightful comments and suggestions and
 pointed out several major issues.  T. Sridhar suggested that the
 AgentX protocol could be used with SNMP to manage the ForCES network
 elements.  Susan Hares pointed out the issue of graceful restart with
 ForCES.  Russ Housley, Avri Doria, Jamal Hadi Salim, and many others
 in the ForCES mailing list also provided valuable feedback.

8. Security Considerations

 The NE administrator has the freedom to determine the exact security
 configuration that is needed for the specific deployment. For
 example, ForCES may be deployed between CEs and FEs connected to each
 other inside a box over a backplane.  In such a scenario, physical
 security of the box ensures that most of the attacks, such as man-
 in-the-middle, snooping, and impersonation, are not possible, and
 hence the ForCES architecture may rely on the physical security of
 the box to defend against these attacks and protocol mechanisms may
 be turned off.  However, it is also shown that denial of service
 attacks via external interfaces as described below in Section 8.1.8
 is still a potential threat, even for such an "all-in-one-box"
 deployment scenario and hence the rate limiting mechanism is still
 necessary.  This is just one example to show that it is important to
 assess the security needs of the ForCES-enabled network elements
 under different deployment scenarios.  It should be possible for the
 administrator to configure the level of security needed for the
 ForCES Protocol.
 In general, the physical separation of two entities usually results
 in a potentially insecure link between the two entities and hence
 much stricter security measurements are required.  For example, we
 pointed out in Section 4.1 that authentication becomes necessary
 between the CE manager and FE manager, between the CE and CE manager,
 and between the FE and FE manager in some configurations.  The
 physical separation of the CE and FE also imposes serious security
 requirements for the ForCES Protocol over the Fp interface.  This
 section first attempts to describe the security threats that may be

Yang, et al. Informational [Page 30] RFC 3746 ForCES Framework April 2004

 introduced by the physical separation of the FEs and CEs, and then it
 provides recommendations and guidelines for the secure operation and
 management of the ForCES Protocol over the Fp interface based on
 existing standard security solutions.

8.1. Analysis of Potential Threats Introduced by ForCES

 This section provides the threat analysis for ForCES, with a focus on
 the Fp interface.  Each threat is described in detail with the
 effects on the ForCES Protocol entities or/and the NE as a whole, and
 the required functionalities that need to be in place to defend the
 threat.

8.1.1. "Join" or "Remove" Message Flooding on CEs

 Threats:  A malicious node could send a stream of false "join NE" or
 "remove from NE" requests on behalf of a non-existent or unauthorized
 FE to legitimate CEs at a very rapid rate, and thereby creating
 unnecessary state in the CEs.
 Effects: If maintaining state for non-existent or unauthorized FEs, a
 CE may become unavailable for other processing and hence suffer from
 a denial of service (DoS) attack similar to the TCP SYN DoS.  If
 multiple CEs are used, the unnecessary state information may also be
 conveyed to multiple CEs via the Fr interface (e.g., from the active
 CE to the stand-by CE) and hence subject multiple CEs to a DoS
 attack.
 Requirement: A CE that receives a "join" or "remove" request should
 not create any state information until it has authenticated the FE
 endpoint.

8.1.2. Impersonation Attack

 Threats: A malicious node can impersonate a CE or FE and send out
 false messages.
 Effects: The whole NE could be compromised.
 Requirement: The CE or FE must authenticate the message as having
 come from an FE or CE on the list of the authorized ForCES elements
 (provided by the CE or FE Manager in the pre-association phase)
 before accepting and processing it.

8.1.3. Replay Attack

 Threat: A malicious node could replay the entire message previously
 sent by an FE or CE entity to get around authentication.

Yang, et al. Informational [Page 31] RFC 3746 ForCES Framework April 2004

 Effect: The NE could be compromised.
 Requirement: A replay protection mechanism needs to be part of the
 security solution to defend against this attack.

8.1.4. Attack during Fail Over

 Threat: A malicious node may exploit the CE fail-over mechanism to
 take over the control of NE.  For example, suppose two CEs, say CE-A
 and CE-B, are controlling several FEs.  CE-A is active and CE-B is
 stand-by.  When CE-A fails, CE-B is taking over the active CE
 position.  The FEs already had a trusted relationship with CE-A, but
 the FEs may not have the same trusted relationship established with
 CE-B prior to the fail-over.  A malicious node can take over as CE-B
 if such a trusted relationship has not been established prior to or
 during the fail-over.
 Effect: The NE may be compromised after such insecure fail-over.
 Requirement: The level of trust between the stand-by CE and the FEs
 must be as strong as the one between the active CE and the FEs.  The
 security association between the FEs and the stand-by CE may be
 established prior to fail-over.  If not already in place, such
 security association must be re-established before the stand-by CE
 takes over.

8.1.5. Data Integrity

 Threats: A malicious node may inject false messages to a legitimate
 CE or FE.
 Effect: An FE or CE receives the fabricated packet and performs an
 incorrect or catastrophic operation.
 Requirement: Protocol messages require integrity protection.

8.1.6. Data Confidentiality

 Threat: When FE and CE are physically separated, a malicious node may
 eavesdrop the messages in transit.  Some of the messages are critical
 to the functioning of the whole network, while others may contain
 confidential business data.  Leaking of such information may result
 in compromise even beyond the immediate CE or FE.
 Effect: Sensitive information might be exposed between the CE and FE.
 Requirement: Data confidentiality between the FE and CE must be
 available for sensitive information.

Yang, et al. Informational [Page 32] RFC 3746 ForCES Framework April 2004

8.1.7. Sharing security parameters

 Threat: Consider a scenario where several FEs are communicating to
 the same CE and sharing the same authentication keys for the Fp
 interface.  If any FE or CE is compromised, all other entities are
 compromised.
 Effect: The whole NE is compromised.
 Recommendation: To avoid this side effect, it's better to configure
 different security parameters for each FE-CE communication over the
 Fp interface.

8.1.8. Denial of Service Attack via External Interface

 Threat: When an FE receives a packet that is destined for its CE, the
 FE forwards the packet over the Fp interface.  A malicious node can
 generate a huge message storm like routing protocol packets etc.
 through the external Fi/f interface so that the FE has to process and
 forward all packets to the CE through the Fp interface.
 Effect: The CE encounters resource exhaustion and bandwidth
 starvation on Fp interface due to an overwhelming number of packets
 from FEs.
 Requirement: Some sort of rate limiting mechanism MUST be in place at
 both the FE and CE.  The Rate Limiter SHOULD be configured at the FE
 for each message type being received through the Fi/f interface.

8.2. Security Recommendations for ForCES

 The requirements document [4] suggested that the ForCES Protocol
 should support reliability over the Fp interface, but no particular
 transport protocol is yet specified for ForCES.  This framework
 document does not intend to specify the particular transport either,
 and so we only provide recommendations and guidelines based on the
 existing standard security protocols [18] that can work with the
 common transport candidates suitable for ForCES.
 We review two existing security protocol solutions, namely IPsec (IP
 Security) [15] and TLS (Transport Layer Security) [14].  TLS works
 with reliable transports such as TCP or SCTP for unicast, while IPsec
 can be used with any transport (UDP, TCP, SCTP) and supports both
 unicast and multicast.  Both TLS and IPsec can be used potentially to
 satisfy all of the security requirements for the ForCES Protocol.  In
 addition, other approaches that satisfy the requirements can be used
 as well, but are not documented here, including the use of L2
 security mechanisms for a given L2 interconnect technology.

Yang, et al. Informational [Page 33] RFC 3746 ForCES Framework April 2004

 When ForCES is deployed between CEs and FEs inside a box or a
 physically secured room, authentication, confidentiality, and
 integrity may be provided by the physical security of the box.  Thus,
 the security mechanisms may be turned off, depending on the
 networking topology and its administration policy.  However, it is
 important to realize that even if the NE is in a single-box, the DoS
 attacks as described in Section 8.1.8 can still be launched through
 the Fi/f interfaces.  Therefore, it is important to have the
 corresponding counter-measurement in place, even for single-box
 deployment.

8.2.1. Using TLS with ForCES

 TLS [14] can be used if a reliable unicast transport such as TCP or
 SCTP is used for ForCES over the Fp interface.  The TLS handshake
 protocol is used during the association establishment or re-
 establishment phase to negotiate a TLS session between the CE and FE.
 Once the session is in place, the TLS record protocol is used to
 secure ForCES communication messages between the CE and FE.
 A basic outline of how TLS can be used with ForCES is described
 below.  Steps 1) through 7) complete the security handshake as
 illustrated in Figure 9, while step 8) is for all further
 communication between the CE and FE, including the rest of the
 messages after the security handshake shown in Figure 9 and the
 steady-state communication shown in Figure 10.
 1) During the Pre-association phase, all FEs are configured with the
    CEs (including both the active CE and the standby CE).
 2) The FE establishes a TLS connection with the CE (master) and
    negotiates a cipher suite.
 3) The FE (slave) gets the CE certificate, validates the signature,
    checks the expiration date, and checks whether the certificate has
    been revoked.
 4) The CE (master) gets the FE certificate and performs the same
    validation as the FE in step 3).
 5) If any of the checks fail in step 3) or step 4), the endpoint must
    generate an error message and abort.
 6) After successful mutual authentication, a TLS session is
    established between the CE and FE.
 7) The FE sends a "join NE" message to the CE.

Yang, et al. Informational [Page 34] RFC 3746 ForCES Framework April 2004

 8) The FE and CE use the TLS session for further communication.
 Note that there are different ways for the CE and FE to validate a
 received certificate.  One way is to configure the FE Manager or CE
 Manager or other central component as CA, so that the CE or FE can
 query this pre-configured CA to validate that the certificate has not
 been revoked.  Another way is to have the CE and FE directly
 configure a list of valid certificates in the pre-association phase.
 In the case of fail-over, it is the responsibility of the active CE
 and the standby CE to synchronize ForCES states, including the TLS
 states to minimize the state re-establishment during fail-over.  Care
 must be taken to ensure that the standby CE is also authenticated in
 the same way as the active CE, either before or during the fail-over.

8.2.2. Using IPsec with ForCES

 IPsec [15] can be used with any transport protocol, such as UDP,
 SCTP, and TCP, over the Fp interface for ForCES.  When using IPsec,
 we recommend using ESP in the transport mode for ForCES because
 message confidentiality is required for ForCES.
 IPsec can be used with both manual and automated SA and cryptographic
 key management.  But IPsec's replay protection mechanisms are not
 available if manual key management is used.  Hence, automatic key
 management is recommended if replay protection is deemed important.
 Otherwise, manual key management might be sufficient for some
 deployment scenarios, especially when the number of CEs and FEs is
 relatively small.  It is recommended that the keys be changed
 periodically, even for manual key management.
 IPsec can support both unicast and multicast transport.  At the time
 this document was published, the MSEC working group was actively
 working on standardizing protocols to provide multicast security
 [17].  Multicast-based solutions relying on IPsec should specify how
 to meet the security requirements in [4].
 Unlike TLS, IPsec provides security services between the CE and FE at
 IP level, so the security handshake, as illustrated in Figure 9
 amounts to a "no-op" when manual key management is used.  The
 following outlines the steps taken for ForCES in such a case.
 1) During the Pre-association phase, all the FEs are configured with
    CEs (including the active CE and standby CE) and SA parameters
    manually.

Yang, et al. Informational [Page 35] RFC 3746 ForCES Framework April 2004

 2) The FE sends a "join NE" message to the CE.  This message and all
    others that follow are afforded security service according to the
    manually configured IPsec SA parameters, but replay protection is
    not available.
 It is up to the administrator to decide whether to share the same key
 across multiple FE-CE communication, but it is recommended that
 different keys be used.  Similarly, it is recommended that different
 keys be used for inbound and outbound traffic.
 If automatic key management is needed, IKE [16] can be used for that
 purpose.  Other automatic key distribution techniques, such as
 Kerberos, may be used as well.  The key exchange process constitutes
 the security handshake as illustrated in Figure 9.  The following
 shows the steps involved in using IKE with IPsec for ForCES.  Steps
 1) to 6) constitute the security handshake in Figure 9.
 1) During the Pre-association phase, all FEs are configured with the
    CEs (including active CE and standby CE), IPsec policy etc.
 2) The FE kicks off the IKE process and tries to establish an IPsec
    SA with the CE (master).  The FE (Slave) gets the CE certificate
    as part of the IKE negotiation.  The FE validates the signature,
    checks the expiration date, and checks whether the certificate has
    been revoked.
 3) The CE (master) gets the FE certificate and performs the same
    check as the FE in step 2).
 4) If any of the checks fail in step 2) or step 3), the endpoint must
    generate an error message and abort.
 5) After successful mutual authentication, the IPsec session is
    established between the CE and FE.
 6) The FE sends a "join NE" message to the CE.  No SADB entry is
    created in FE yet.
 7) The FE and CE use the IPsec session for further communication.
 The FE Manager, CE Manager, or other central component can be used as
 a CA for validating CE and FE certificates during the IKE process.
 Alternatively, during the pre-association phase, the CE and FE can be
 configured directly with the required information, such as
 certificates or passwords etc., depending upon the type of
 authentication that administrator wants to configure.

Yang, et al. Informational [Page 36] RFC 3746 ForCES Framework April 2004

 In the case of fail-over, it is the responsibility of the active CE
 and standby CE to synchronize ForCES states and IPsec states to
 minimize the state re-establishment during fail-over.  Alternatively,
 the FE needs to establish a different IPsec SA during the startup
 operation itself with each CE.  This will minimize the periodic state
 transfer across the IPsec layer though the Fr (CE-CE) Interface.

9. References

9.1. Normative References

 [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [2]  Baker, F., Ed., "Requirements for IP Version 4 Routers", RFC
      1812, June 1995.
 [3]  Floyd, S., "Congestion Control Principles", BCP 41, RFC 2914,
      September 2000.
 [4]  Khosravi, H. and Anderson, T., Eds., "Requirements for
      Separation of IP Control and Forwarding", RFC 3654, November
      2003.

9.2. Informative References

 [5]  Case, J., Mundy, R., Partain, D. and B. Stewart, "Introduction
      and Applicability Statements for Internet Standard Management
      Framework", RFC 3410, December 2002.
 [6]  Daniele, M., Wijnen, B., Ellison, M. and D. Francisco, "Agent
      Extensibility (AgentX) Protocol Version 1", RFC 2741, January
      2000.
 [7]  Chan, K., Seligson, J., Durham, D., Gai, S., McCloghrie, K.,
      Herzog, S., Reichmeyer, F., Yavatkar, R. and A. Smith, "COPS
      Usage for Policy Provisioning (COPS-PR)", RFC 3084, March 2001.
 [8]  Crouch, A. et al., "ForCES Applicability Statement", Work in
      Progress.
 [9]  Anderson, T. and J. Buerkle, "Requirements for the Dynamic
      Partitioning of Switching Elements", RFC 3532, May 2003.
 [10] Leelanivas, M., Rekhter, Y. and R. Aggarwal, "Graceful Restart
      Mechanism for Label Distribution Protocol", RFC 3478, February
      2003.

Yang, et al. Informational [Page 37] RFC 3746 ForCES Framework April 2004

 [11] Moy, J., Pillay-Esnault, P. and A. Lindem, "Graceful OSPF
      Restart", RFC 3623, November 2003.
 [12] Sangli, S. et al., "Graceful Restart Mechanism for BGP", Work in
      Progress.
 [13] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS", Work
      in Progress.
 [14] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
      2246, January 1999.
 [15] Kent, S. and R. Atkinson, "Security Architecture for the
      Internet Protocol", RFC 2401, November 1998.
 [16] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
      RFC 2409, November 1998.
 [17] Hardjono, T. and Weis, B. "The Multicast Group Security
      Architecture", RFC 3740, March 2004.
 [18] Bellovin, S., Schiller, J. and C. Kaufman, Eds., "Security
      Mechanisms for the Internet", RFC 3631, December 2003.

Yang, et al. Informational [Page 38] RFC 3746 ForCES Framework April 2004

10. Authors' Addresses

 L. Lily Yang
 Intel Corp., MS JF3-206,
 2111 NE 25th Avenue
 Hillsboro, OR 97124, USA
 Phone: +1 503 264 8813
 EMail: lily.l.yang@intel.com
 Ram Dantu
 Department of Computer Science,
 University of North Texas,
 Denton, TX 76203, USA
 Phone: +1 940 565 2822
 EMail: rdantu@unt.edu
 Todd A. Anderson
 Intel Corp.
 2111 NE 25th Avenue
 Hillsboro, OR 97124, USA
 Phone: +1 503 712 1760
 EMail: todd.a.anderson@intel.com
 Ram Gopal
 Nokia Research Center
 5, Wayside Road,
 Burlington, MA 01803, USA
 Phone: +1 781 993 3685
 EMail: ram.gopal@nokia.com

Yang, et al. Informational [Page 39] RFC 3746 ForCES Framework April 2004

11. Full Copyright Statement

 Copyright (C) The Internet Society (2004).  This document is subject
 to the rights, licenses and restrictions contained in BCP 78, and
 except as set forth therein, the authors retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
 INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 under such rights might or might not be available; nor does it
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 rights in RFC documents can be found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 to implement this standard.  Please address the information to the
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Yang, et al. Informational [Page 40]

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