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RFC 8013 - Forwarding and Control Element Separation (ForCES) In

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Internet Engineering Task Force (IETF)                  D. Joachimpillai
Request for Comments: 8013                                       Verizon
Category: Standards Track                                  J. Hadi Salim
ISSN: 2070-1721                                        Mojatatu Networks
                                                           February 2017

           Forwarding and Control Element Separation (ForCES)
                Inter-FE Logical Functional Block (LFB)


   This document describes how to extend the Forwarding and Control
   Element Separation (ForCES) Logical Functional Block (LFB) topology
   across Forwarding Elements (FEs) by defining the inter-FE LFB class.
   The inter-FE LFB class provides the ability to pass data and metadata
   across FEs without needing any changes to the ForCES specification.
   The document focuses on Ethernet transport.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Conventions . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Scope and Use Cases . . . . . . . . . . . . . . . . .   4
     3.1.  Assumptions . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Sample Use Cases  . . . . . . . . . . . . . . . . . . . .   4
       3.2.1.  Basic IPv4 Router . . . . . . . . . . . . . . . . . .   4  Distributing the Basic IPv4 Router  . . . . . . .   6
       3.2.2.  Arbitrary Network Function  . . . . . . . . . . . . .   7  Distributing the Arbitrary Network Function . . .   8
   4.  Inter-FE LFB Overview . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Inserting the Inter-FE LFB  . . . . . . . . . . . . . . .   8
   5.  Inter-FE Ethernet Connectivity  . . . . . . . . . . . . . . .  10
     5.1.  Inter-FE Ethernet Connectivity Issues . . . . . . . . . .  10
       5.1.1.  MTU Consideration . . . . . . . . . . . . . . . . . .  10
       5.1.2.  Quality-of-Service Considerations . . . . . . . . . .  11
       5.1.3.  Congestion Considerations . . . . . . . . . . . . . .  11
     5.2.  Inter-FE Ethernet Encapsulation . . . . . . . . . . . . .  12
   6.  Detailed Description of the Ethernet Inter-FE LFB . . . . . .  13
     6.1.  Data Handling . . . . . . . . . . . . . . . . . . . . . .  13
       6.1.1.  Egress Processing . . . . . . . . . . . . . . . . . .  14
       6.1.2.  Ingress Processing  . . . . . . . . . . . . . . . . .  15
     6.2.  Components  . . . . . . . . . . . . . . . . . . . . . . .  16
     6.3.  Inter-FE LFB XML Model  . . . . . . . . . . . . . . . . .  17
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   8.  IEEE Assignment Considerations  . . . . . . . . . . . . . . .  21
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     10.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   In the ForCES architecture, a packet service can be modeled by
   composing a graph of one or more LFB instances.  The reader is
   referred to the details in the ForCES model [RFC5812].

   The ForCES model describes the processing within a single Forwarding
   Element (FE) in terms of Logical Functional Blocks (LFBs), including
   provision for the Control Element (CE) to establish and modify that
   processing sequence, and the parameters of the individual LFBs.

   Under some circumstances, it would be beneficial to be able to extend
   this view and the resulting processing across more than one FE.  This
   may be in order to achieve scale by splitting the processing across
   elements or to utilize specialized hardware available on specific

   Given that the ForCES inter-LFB architecture calls for the ability to
   pass metadata between LFBs, it is imperative to define mechanisms to
   extend that existing feature and allow passing the metadata between
   LFBs across FEs.

   This document describes how to extend the LFB topology across FEs,
   i.e., inter-FE connectivity without needing any changes to the ForCES
   definitions.  It focuses on using Ethernet as the interconnection
   between FEs.

2.  Terminology and Conventions

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.2.  Definitions

   This document depends on the terms (below) defined in several ForCES
   documents: [RFC3746], [RFC5810], [RFC5811], [RFC5812], [RFC7391], and

      Control Element (CE)

      Forwarding Element (FE)

      FE Model

      LFB (Logical Functional Block) Class (or type)

      LFB Instance

      LFB Model

      LFB Metadata

      ForCES Component

      LFB Component

      ForCES Protocol Layer (ForCES PL)

      ForCES Protocol Transport Mapping Layer (ForCES TML)

3.  Problem Scope and Use Cases

   The scope of this document is to solve the challenge of passing
   ForCES-defined metadata alongside packet data across FEs (be they
   physical or virtual) for the purpose of distributing the LFB

3.1.  Assumptions

   o  The FEs involved in the inter-FE LFB belong to the same Network
      Element (NE) and are within a single administrative private
      network that is in close proximity.

   o  The FEs are already interconnected using Ethernet.  We focus on
      Ethernet because it is commonly used for FE interconnection.
      Other higher transports (such as UDP over IP) or lower transports
      could be defined to carry the data and metadata, but these cases
      are not addressed in this document.

3.2.  Sample Use Cases

   To illustrate the problem scope, we present two use cases where we
   start with a single FE running all the LFBs functionality and then
   split it into multiple FEs achieving the same end goals.

3.2.1.  Basic IPv4 Router

   A sample LFB topology depicted in Figure 1 demonstrates a service
   graph for delivering a basic IPv4-forwarding service within one FE.
   For the purpose of illustration, the diagram shows LFB classes as
   graph nodes instead of multiple LFB class instances.

   Since the purpose of the illustration in Figure 1 is to showcase how
   data and metadata are sent down or upstream on a graph of LFB
   instances, it abstracts out any ports in both directions and talks
   about a generic ingress and egress LFB.  Again, for illustration
   purposes, the diagram does not show exception or error paths.  Also
   left out are details on Reverse Path Filtering, ECMP, multicast
   handling, etc.  In other words, this is not meant to be a complete
   description of an IPv4-forwarding application; for a more complete
   example, please refer to the LFBLibrary document [RFC6956].

   The output of the ingress LFB(s) coming into the IPv4 Validator LFB
   will have both the IPv4 packets and, depending on the implementation,

   a variety of ingress metadata such as offsets into the different
   headers, any classification metadata, physical and virtual ports
   encountered, tunneling information, etc.  These metadata are lumped
   together as "ingress metadata".

   Once the IPv4 validator vets the packet (for example, it ensures that
   there is no expired TTL), it feeds the packet and inherited metadata
   into the IPv4 unicast LPM (Longest-Prefix-Matching) LFB.

                      |    |
           IPv4 pkt   |    | IPv4 pkt     +-----+             +---+
       +------------->|    +------------->|     |             |   |
       |  + ingress   |    | + ingress    |IPv4 |   IPv4 pkt  |   |
       |   metadata   |    | metadata     |Ucast+------------>|   +--+
       |              +----+              |LPM  |  + ingress  |   |  |
     +-+-+             IPv4               +-----+  + NHinfo   +---+  |
     |   |             Validator                   metadata   IPv4   |
     |   |             LFB                                    NextHop|
     |   |                                                     LFB   |
     |   |                                                           |
     |   |                                                  IPv4 pkt |
     |   |                                               + {ingress  |
     +---+                                                  + NHdetails}
     Ingress                                                metadata |
      LFB                                +--------+                  |
                                         | Egress |                  |
                                      <--+        |<-----------------+
                                         |  LFB   |

             Figure 1: Basic IPv4 Packet Service LFB Topology

   The IPv4 unicast LPM LFB does an LPM lookup on the IPv4 FIB using the
   destination IP address as a search key.  The result is typically a
   next-hop selector, which is passed downstream as metadata.

   The NextHop LFB receives the IPv4 packet with associated next-hop
   (NH) information metadata.  The NextHop LFB consumes the NH
   information metadata and derives a table index from it to look up the
   next-hop table in order to find the appropriate egress information.
   The lookup result is used to build the next-hop details to be used
   downstream on the egress.  This information may include any source
   and destination information (for our purposes, which Media Access
   Control (MAC) addresses to use) as well as egress ports.  (Note: It
   is also at this LFB where typically, the forwarding TTL-decrementing
   and IP checksum recalculation occurs.)

   The details of the egress LFB are considered out of scope for this
   discussion.  Suffice it to say that somewhere within or beyond the
   Egress LFB, the IPv4 packet will be sent out a port (e.g., Ethernet,
   virtual or physical).  Distributing the Basic IPv4 Router

   Figure 2 demonstrates one way that the router LFB topology in
   Figure 1 may be split across two FEs (e.g., two Application-Specific
   Integrated Circuits (ASICs)).  Figure 2 shows the LFB topology split
   across FEs after the IPv4 unicast LPM LFB.

    |                            +----+                           |
    | +----------+               |    |                           |
    | | Ingress  |    IPv4 pkt   |    | IPv4 pkt     +-----+      |
    | |  LFB     +-------------->|    +------------->|     |      |
    | |          |  + ingress    |    | + ingress    |IPv4 |      |
    | +----------+    metadata   |    |   metadata   |Ucast|      |
    |      ^                     +----+              |LPM  |      |
    |      |                      IPv4               +--+--+      |
    |      |                     Validator              |         |
    |                             LFB                   |         |
                                                   IPv4 packet +
                                                 {ingress + NHinfo}
      FE2                                               |
    |                                                   V         |
    |             +--------+                       +--------+     |
    |             | Egress |     IPv4 packet       | IPv4   |     |
    |       <-----+  LFB   |<----------------------+NextHop |     |
    |             |        |{ingress + NHdetails}  | LFB    |     |
    |             +--------+      metadata         +--------+     |

             Figure 2: Split IPv4 Packet Service LFB Topology

   Some proprietary interconnections (for example, Broadcom HiGig over
   XAUI [brcm-higig]) are known to exist to carry both the IPv4 packet
   and the related metadata between the IPv4 Unicast LFB and IPv4NextHop
   LFB across the two FEs.

   This document defines the inter-FE LFB, a standard mechanism for
   encapsulating, generating, receiving, and decapsulating packets and
   associated metadata FEs over Ethernet.

3.2.2.  Arbitrary Network Function

   In this section, we show an example of an arbitrary Network Function
   that is more coarsely grained in terms of functionality.  Each
   Network Function may constitute more than one LFB.

    |                            +----+                           |
    | +----------+               |    |                           |
    | | Network  |   pkt         |NF2 |    pkt       +-----+      |
    | | Function +-------------->|    +------------->|     |      |
    | |    1     |  + NF1        |    | + NF1/2      |NF3  |      |
    | +----------+    metadata   |    |   metadata   |     |      |
    |      ^                     +----+              |     |      |
    |      |                                         +--+--+      |
    |      |                                            |         |
    |                                                   |         |

         Figure 3: A Network Function Service Chain within One FE

   The setup in Figure 3 is typical of most packet processing boxes
   where we have functions like deep packet inspection (DPI), NAT,
   Routing, etc., connected in such a topology to deliver a packet
   processing service to flows.  Distributing the Arbitrary Network Function

   The setup in Figure 3 can be split across three FEs instead of as
   demonstrated in Figure 4.  This could be motivated by scale-out
   reasons or because different vendors provide different functionality,
   which is plugged-in to provide such functionality.  The end result is
   having the same packet service delivered to the different flows
   passing through.

      FE1                        FE2
      +----------+               +----+               FE3
      | Network  |   pkt         |NF2 |    pkt       +-----+
      | Function +-------------->|    +------------->|     |
      |    1     |  + NF1        |    | + NF1/2      |NF3  |
      +----------+    metadata   |    |   metadata   |     |
           ^                     +----+              |     |
           |                                         +--+--+

       Figure 4: A Network Function Service Chain Distributed across
                               Multiple FEs

4.  Inter-FE LFB Overview

   We address the inter-FE connectivity requirements by defining the
   inter-FE LFB class.  Using a standard LFB class definition implies no
   change to the basic ForCES architecture in the form of the core LFBs
   (FE Protocol or Object LFBs).  This design choice was made after
   considering an alternative approach that would have required changes
   to both the FE Object capabilities (SupportedLFBs) and the
   LFBTopology component to describe the inter-FE connectivity
   capabilities as well as the runtime topology of the LFB instances.

4.1.  Inserting the Inter-FE LFB ne 15

   The distributed LFB topology described in Figure 2 is re-illustrated
   in Figure 5 to show the topology location where the inter-FE LFB
   would fit in.

   As can be observed in Figure 5, the same details passed between IPv4
   unicast LPM LFB and the IPv4 NH LFB are passed to the egress side of
   the inter-FE LFB.  This information is illustrated as multiplicity of
   inputs into the egress inter-FE LFB instance.  Each input represents
   a unique set of selection information.

    | +----------+               +----+                           |
    | | Ingress  |    IPv4 pkt   |    | IPv4 pkt     +-----+      |
    | |  LFB     +-------------->|    +------------->|     |      |
    | |          |  + ingress    |    | + ingress    |IPv4 |      |
    | +----------+    metadata   |    |   metadata   |Ucast|      |
    |      ^                     +----+              |LPM  |      |
    |      |                      IPv4               +--+--+      |
    |      |                     Validator              |         |
    |      |                      LFB                   |         |
    |      |                                  IPv4 pkt + metadata |
    |      |                                   {ingress + NHinfo} |
    |      |                                            |         |
    |      |                                       +..--+..+      |
    |      |                                       |..| |  |      |
    |                                            +-V--V-V--V-+    |
    |                                            |   Egress  |    |
    |                                            |  Inter-FE |    |
    |                                            |   LFB     |    |
    |                                            +------+----+    |
                                Ethernet Frame with:    |
                                IPv4 packet data and metadata
                                {ingress + NHinfo + Inter-FE info}
     FE2                                                |
    |                                                +..+.+..+    |
    |                                                |..|.|..|    |
    |                                              +-V--V-V--V-+  |
    |                                              | Ingress   |  |
    |                                              | Inter-FE  |  |
    |                                              |   LFB     |  |
    |                                              +----+------+  |
    |                                                   |         |
    |                                         IPv4 pkt + metadata |
    |                                          {ingress + NHinfo} |
    |                                                   |         |
    |             +--------+                       +----V---+     |
    |             | Egress |     IPv4 packet       | IPv4   |     |
    |       <-----+  LFB   |<----------------------+NextHop |     |
    |             |        |{ingress + NHdetails}  | LFB    |     |
    |             +--------+      metadata         +--------+     |

         Figure 5: Split IPv4-Forwarding Service with Inter-FE LFB

   The egress of the inter-FE LFB uses the received packet and metadata
   to select details for encapsulation when sending messages towards the
   selected neighboring FE.  These details include what to communicate
   as the source and destination FEs (abstracted as MAC addresses as
   described in Section 5.2); in addition, the original metadata may be
   passed along with the original IPv4 packet.

   On the ingress side of the inter-FE LFB, the received packet and its
   associated metadata are used to decide the packet graph continuation.
   This includes which of the original metadata and on which next LFB
   class instance to continue processing.  In Figure 5, an IPv4NextHop
   LFB instance is selected and the appropriate metadata is passed to

   The ingress side of the inter-FE LFB consumes some of the information
   passed and passes it the IPv4 packet alongside with the ingress and
   NHinfo metadata to the IPv4NextHop LFB as was done earlier in both
   Figures 1 and 2.

5.  Inter-FE Ethernet Connectivity

   Section 5.1 describes some of the issues related to using Ethernet as
   the transport and how we mitigate them.

   Section 5.2 defines a payload format that is to be used over
   Ethernet.  An existing implementation of this specification that runs
   on top of Linux Traffic Control [linux-tc] is described in [tc-ife].

5.1.  Inter-FE Ethernet Connectivity Issues

   There are several issues that may occur due to using direct Ethernet
   encapsulation that need consideration.

5.1.1.  MTU Consideration

   Because we are adding data to existing Ethernet frames, MTU issues
   may arise.  We recommend:

   o  Using large MTUs when possible (example with jumbo frames).

   o  Limiting the amount of metadata that could be transmitted; our
      definition allows for filtering of select metadata to be
      encapsulated in the frame as described in Section 6.  We recommend
      sizing the egress port MTU so as to allow space for maximum size
      of the metadata total size to allow between FEs.  In such a setup,
      the port is configured to "lie" to the upper layers by claiming to
      have a lower MTU than it is capable of.  Setting the MTU can be
      achieved by ForCES control of the port LFB (or some other

      configuration.  In essence, the control plane when explicitly
      making a decision for the MTU settings of the egress port is
      implicitly deciding how much metadata will be allowed.  Caution
      needs to be exercised on how low the resulting reported link MTU
      could be: for IPv4 packets, the minimum size is 64 octets [RFC791]
      and for IPv6 the minimum size is 1280 octets [RFC2460].

5.1.2.  Quality-of-Service Considerations

   A raw packet arriving at the inter-FE LFB (from upstream LFB class
   instances) may have Class-of-Service (CoS) metadata indicating how it
   should be treated from a Quality-of-Service perspective.

   The resulting Ethernet frame will be eventually (preferentially)
   treated by a downstream LFB (typically a port LFB instance) and their
   CoS marks will be honored in terms of priority.  In other words, the
   presence of the inter-FE LFB does not change the CoS semantics.

5.1.3.  Congestion Considerations

   Most of the traffic passing through FEs that utilize the inter-FE LFB
   is expected to be IP based, which is generally assumed to be
   congestion controlled [UDP-GUIDE].  For example, if congestion causes
   a TCP packet annotated with additional ForCES metadata to be dropped
   between FEs, the sending TCP can be expected to react in the same
   fashion as if that packet had been dropped at a different point on
   its path where ForCES is not involved.  For this reason, additional
   inter-FE congestion-control mechanisms are not specified.

   However, the increased packet size due to the addition of ForCES
   metadata is likely to require additional bandwidth on inter-FE links
   in comparison to what would be required to carry the same traffic
   without ForCES metadata.  Therefore, traffic engineering SHOULD be
   done when deploying inter-FE encapsulation.

   Furthermore, the inter-FE LFB MUST only be deployed within a single
   network (with a single network operator) or networks of an adjacent
   set of cooperating network operators where traffic is managed to
   avoid congestion.  These are Controlled Environments, as defined by
   Section 3.6 of [UDP-GUIDE].  Additional measures SHOULD be imposed to
   restrict the impact of inter-FE-encapsulated traffic on other
   traffic; for example:

   o  rate-limiting all inter-FE LFB traffic at an upstream LFB

   o  managing circuit breaking [circuit-b]

   o  Isolating the inter-FE traffic either via dedicated interfaces or

5.2.  Inter-FE Ethernet Encapsulation

   The Ethernet wire encapsulation is illustrated in Figure 6.  The
   process that leads to this encapsulation is described in Section 6.
   The resulting frame is 32-bit aligned.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      | Destination MAC Address                                       |
      | Destination MAC Address       |   Source MAC Address          |
      | Source MAC Address                                            |
      | Inter-FE ethertype            | Metadata length               |
      | TLV encoded Metadata ~~~..............~~                      |
      | TLV encoded Metadata ~~~..............~~                      |
      | Original packet data ~~................~~                     |

                    Figure 6: Packet Format Definition

   The Ethernet header (illustrated in Figure 6) has the following

   o  The Destination MAC Address is used to identify the Destination
      FEID by the CE policy (as described in Section 6).

   o  The Source MAC Address is used to identify the Source FEID by the
      CE policy (as described in Section 6).

   o  The ethertype is used to identify the frame as inter-FE LFB type.
      Ethertype ED3E (base 16) is to be used.

   o  The 16-bit metadata length is used to describe the total encoded
      metadata length (including the 16 bits used to encode the metadata

   o  One or more 16-bit TLV-encoded metadatum follows the Metadata
      length field.  The TLV type identifies the metadata ID.  ForCES
      metadata IDs that have been registered with IANA will be used.

      All TLVs will be 32-bit-aligned.  We recognize that using a 16-bit
      TLV restricts the metadata ID to 16 bits instead of a ForCES-
      defined component ID space of 32 bits if an Index-Length-Value
      (ILV) is used.  However, at the time of publication, we believe
      this is sufficient to carry all the information we need; the TLV
      approach has been selected because it saves us 4 bytes per
      metadatum transferred as compared to the ILV approach.

   o  The original packet data payload is appended at the end of the
      metadata as shown.

6.  Detailed Description of the Ethernet Inter-FE LFB

   The Ethernet inter-FE LFB has two LFB input port groups and three LFB
   output ports as shown in Figure 7.

   The inter-FE LFB defines two components used in aiding processing
   described in Section 6.1.

     Inter-FE LFB   |                 |
     Encapsulated   |             OUT2+--> Decapsulated Packet
     -------------->|IngressInGroup   |       + metadata
     Ethernet Frame |                 |
                    |                 |
     raw Packet +   |             OUT1+--> Encapsulated Ethernet
     -------------->|EgressInGroup    |           Frame
     Metadata       |                 |
                    |    EXCEPTIONOUT +--> ExceptionID, packet
                    |                 |           + metadata

                          Figure 7: Inter-FE LFB

6.1.  Data Handling

   The inter-FE LFB (instance) can be positioned at the egress of a
   source FE.  Figure 5 illustrates an example source FE in the form of
   FE1.  In such a case, an inter-FE LFB instance receives, via port
   group EgressInGroup, a raw packet and associated metadata from the
   preceding LFB instances.  The input information is used to produce a
   selection of how to generate and encapsulate the new frame.  The set
   of all selections is stored in the LFB component IFETable described
   further below.  The processed encapsulated Ethernet frame will go out
   on OUT1 to a downstream LFB instance when processing succeeds or to
   the EXCEPTIONOUT port in the case of failure.

   The inter-FE LFB (instance) can be positioned at the ingress of a
   receiving FE.  Figure 5 illustrates an example destination FE in the
   form of FE1.  In such a case, an inter-FE LFB receives, via an LFB
   port in the IngressInGroup, an encapsulated Ethernet frame.
   Successful processing of the packet will result in a raw packet with
   associated metadata IDs going downstream to an LFB connected on OUT2.
   On failure, the data is sent out EXCEPTIONOUT.

6.1.1.  Egress Processing

   The egress inter-FE LFB receives packet data and any accompanying
   metadatum at an LFB port of the LFB instance's input port group
   labeled EgressInGroup.

   The LFB implementation may use the incoming LFB port (within the LFB
   port group EgressInGroup) to map to a table index used to look up the
   IFETable table.

   If the lookup is successful, a matched table row that has the IFEInfo
   details is retrieved with the tuple (optional IFETYPE, optional
   StatId, Destination MAC address (DSTFE), Source MAC address (SRCFE),
   and optional metafilters).  The metafilters lists define a whitelist
   of which metadatum are to be passed to the neighboring FE.  The
   inter-FE LFB will perform the following actions using the resulting

   o  Increment statistics for packet and byte count observed at the
      corresponding IFEStats entry.

   o  When the MetaFilterList is present, walk each received metadatum
      and apply it against the MetaFilterList.  If no legitimate
      metadata is found that needs to be passed downstream, then the
      processing stops and the packet and metadata are sent out the
      EXCEPTIONOUT port with the exceptionID of EncapTableLookupFailed

   o  Check that the additional overhead of the Ethernet header and
      encapsulated metadata will not exceed MTU.  If it does, increment
      the error-packet-count statistics and send the packet and metadata
      out the EXCEPTIONOUT port with the exceptionID of FragRequired

   o  Create the Ethernet header.

   o  Set the Destination MAC address of the Ethernet header with the
      value found in the DSTFE field.

   o  Set the Source MAC address of the Ethernet header with the value
      found in the SRCFE field.

   o  If the optional IFETYPE is present, set the ethertype to the value
      found in IFETYPE.  If IFETYPE is absent, then the standard inter-
      FE LFB ethertype ED3E (base 16) is used.

   o  Encapsulate each allowed metadatum in a TLV.  Use the metaID as
      the "type" field in the TLV header.  The TLV should be aligned to
      32 bits.  This means you may need to add a padding of zeroes at
      the end of the TLV to ensure alignment.

   o  Update the metadata length to the sum of each TLV's space plus 2
      bytes (a 16-bit space for the Metadata length field).

   The resulting packet is sent to the next LFB instance connected to
   the OUT1 LFB-port, typically a port LFB.

   In the case of a failed lookup, the original packet and associated
   metadata is sent out the EXCEPTIONOUT port with the exceptionID of
   EncapTableLookupFailed [RFC6956].  Note that the EXCEPTIONOUT LFB
   port is merely an abstraction and implementation may in fact drop
   packets as described above.

6.1.2.  Ingress Processing

   An ingressing inter-FE LFB packet is recognized by inspecting the
   ethertype, and optionally the destination and source MAC addresses.
   A matching packet is mapped to an LFB instance port in the
   IngressInGroup.  The IFETable table row entry matching the LFB
   instance port may have optionally programmed metadata filters.  In
   such a case, the ingress processing should use the metadata filters
   as a whitelist of what metadatum is to be allowed.

   o  Increment statistics for packet and byte count observed.

   o  Look at the metadata length field and walk the packet data,
      extracting the metadata values from the TLVs.  For each metadatum
      extracted, in the presence of metadata filters, the metaID is
      compared against the relevant IFETable row metafilter list.  If
      the metadatum is recognized and allowed by the filter, the
      corresponding implementation Metadatum field is set.  If an
      unknown metadatum ID is encountered or if the metaID is not in the
      allowed filter list, then the implementation is expected to ignore
      it, increment the packet error statistic, and proceed processing
      other metadatum.

   o  Upon completion of processing all the metadata, the inter-FE LFB
      instance resets the data point to the original payload (i.e.,
      skips the IFE header information).  At this point, the original
      packet that was passed to the egress inter-FE LFB at the source FE
      is reconstructed.  This data is then passed along with the
      reconstructed metadata downstream to the next LFB instance in the

   In the case of a processing failure of either ingress or egress
   positioning of the LFB, the packet and metadata are sent out the
   EXCEPTIONOUT LFB port with the appropriate error ID.  Note that the
   EXCEPTIONOUT LFB port is merely an abstraction and implementation may
   in fact drop packets as described above.

6.2.  Components

   There are two LFB components accessed by the CE.  The reader is asked
   to refer to the definitions in Figure 8.

   The first component, populated by the CE, is an array known as the
   "IFETable" table.  The array rows are made up of IFEInfo structure.
   The IFEInfo structure constitutes the optional IFETYPE, the
   optionally present StatId, the Destination MAC address (DSTFE), the
   Source MAC address (SRCFE), and an optionally present array of
   allowed metaIDs (MetaFilterList).

   The second component (ID 2), populated by the FE and read by the CE,
   is an indexed array known as the "IFEStats" table.  Each IFEStats row
   carries statistics information in the structure bstats.

   A note about the StatId relationship between the IFETable table and
   the IFEStats table -- an implementation may choose to map between an
   IFETable row and IFEStats table row using the StatId entry in the
   matching IFETable row.  In that case, the IFETable StatId must be
   present.  An alternative implementation may map an IFETable row to an
   IFEStats table row at provisioning time.  Yet another alternative
   implementation may choose not to use the IFETable row StatId and
   instead use the IFETable row index as the IFEStats index.  For these
   reasons, the StatId component is optional.

6.3.  Inter-FE LFB XML Model

  <LFBLibrary xmlns="urn:ietf:params:xml:ns:forces:lfbmodel:1.1"
            <synopsis>Arbitrary Packet</synopsis>
                   Ethernet frame with encapsulated IFE information



         <synopsis>Basic stats</synopsis>
          <component componentID="1">
           <synopsis>The total number of bytes seen</synopsis>

          <component componentID="2">
           <synopsis>The total number of packets seen</synopsis>

          <component componentID="3">
           <synopsis>The total number of packets with errors</synopsis>


          <synopsis>Describing IFE table row Information</synopsis>
             <component componentID="1">
                   The ethertype to be used for outgoing IFE frame
             <component componentID="2">
                   The Index into the stats table
             <component componentID="3">
                       The destination MAC address of the destination FE
             <component componentID="4">
                       The source MAC address used for the source FE
             <component componentID="5">
                       The allowed metadata filter table
               <array type="variable-size">



      <LFBClassDef LFBClassID="18">
           This LFB describes IFE connectivity parameterization


            <inputPort group="true">
                     The input port group of the egress side.
                     It expects any type of Ethernet frame.

            <inputPort  group="true">
                     The input port group of the ingress side.
                     It expects an interFE-encapsulated Ethernet frame.



                  The output port of the egress side


                The output port of the Ingress side

              The exception handling path



        <component componentID="1" access="read-write">
              The table of all inter-FE relations
           <array type="variable-size">

       <component componentID="2" access="read-only">
          The stats corresponding to the IFETable table



                        Figure 8: Inter-FE LFB XML

7.  IANA Considerations

   IANA has registered the following LFB class name in the "Logical
   Functional Block (LFB) Class Names and Class Identifiers" subregistry
   of the "Forwarding and Control Element Separation (ForCES)" registry

   | LFB Class  |  LFB   |   LFB   |      Description      | Reference |
   | Identifier | Class  | Version |                       |           |
   |            |  Name  |         |                       |           |
   |     18     |  IFE   |   1.0   |     An IFE LFB to     |    This   |
   |            |        |         |  standardize inter-FE |  document |
   |            |        |         |     LFB for ForCES    |           |
   |            |        |         |    Network Elements   |           |

     Logical Functional Block (LFB) Class Names and Class Identifiers

8.  IEEE Assignment Considerations

   This memo includes a request for a new Ethernet protocol type as
   described in Section 5.2.

9.  Security Considerations

   The FEs involved in the inter-FE LFB belong to the same NE and are
   within the scope of a single administrative Ethernet LAN private
   network.  While trust of policy in the control and its treatment in
   the datapath exists already, an inter-FE LFB implementation SHOULD
   support security services provided by Media Access Control Security
   (MACsec) [ieee8021ae].  MACsec is not currently sufficiently widely
   deployed in traditional packet processing hardware although it is
   present in newer versions of the Linux kernel (which will be widely
   deployed) [linux-macsec].  Over time, we expect that most FEs will be
   able to support MACsec.

   MACsec provides security services such as a message authentication
   service and an optional confidentiality service.  The services can be
   configured manually or automatically using the MACsec Key Agreement
   (MKA) over the IEEE 802.1x [ieee8021x] Extensible Authentication
   Protocol (EAP) framework.  It is expected that FE implementations are
   going to start with shared keys configured from the control plane but
   progress to automated key management.

   The following are the MACsec security mechanisms that need to be in
   place for the inter-FE LFB:

   o  Security mechanisms are NE-wide for all FEs.  Once the security is
      turned on, depending upon the chosen security level (e.g.,
      Authentication, Confidentiality), it will be in effect for the
      inter-FE LFB for the entire duration of the session.

   o  An operator SHOULD configure the same security policies for all
      participating FEs in the NE cluster.  This will ensure uniform
      operations and avoid unnecessary complexity in policy
      configuration.  In other words, the Security Association Keys
      (SAKs) should be pre-shared.  When using MKA, FEs must identify
      themselves with a shared Connectivity Association Key (CAK) and
      Connectivity Association Key Name (CKN).  EAP-TLS SHOULD be used
      as the EAP method.

   o  An operator SHOULD configure the strict validation mode, i.e., all
      non-protected, invalid, or non-verifiable frames MUST be dropped.

   It should be noted that given the above choices, if an FE is
   compromised, an entity running on the FE would be able to fake inter-
   FE or modify its content, causing bad outcomes.

10.  References

10.1.  Normative References

              IEEE, "IEEE Standard for Local and metropolitan area
              networks Media Access Control (MAC) Security", IEEE
              802.1AE-2006, DOI 10.1109/IEEESTD.2006.245590,

              IEEE, "IEEE Standard for Local and metropolitan area
              networks - Port-Based Network Access Control.", IEEE
              802.1X-2010, DOI 10.1109/IEEESTD.2010.5409813,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5810]  Doria, A., Ed., Hadi Salim, J., Ed., Haas, R., Ed.,
              Khosravi, H., Ed., Wang, W., Ed., Dong, L., Gopal, R., and
              J. Halpern, "Forwarding and Control Element Separation
              (ForCES) Protocol Specification", RFC 5810,
              DOI 10.17487/RFC5810, March 2010,

   [RFC5811]  Hadi Salim, J. and K. Ogawa, "SCTP-Based Transport Mapping
              Layer (TML) for the Forwarding and Control Element
              Separation (ForCES) Protocol", RFC 5811,
              DOI 10.17487/RFC5811, March 2010,

   [RFC5812]  Halpern, J. and J. Hadi Salim, "Forwarding and Control
              Element Separation (ForCES) Forwarding Element Model",
              RFC 5812, DOI 10.17487/RFC5812, March 2010,

   [RFC7391]  Hadi Salim, J., "Forwarding and Control Element Separation
              (ForCES) Protocol Extensions", RFC 7391,
              DOI 10.17487/RFC7391, October 2014,

   [RFC7408]  Haleplidis, E., "Forwarding and Control Element Separation
              (ForCES) Model Extension", RFC 7408, DOI 10.17487/RFC7408,
              November 2014, <http://www.rfc-editor.org/info/rfc7408>.

10.2.  Informative References

              Broadcom, "HiGig", <http://www.broadcom.com/products/

              Fairhurst, G., "Network Transport Circuit Breakers", Work
              in Progress, draft-ietf-tsvwg-circuit-breaker-15, April

              Dubroca, S., "MACsec: Encryption for the wired LAN",
              Netdev 11, Feb 2016.

   [linux-tc] Hadi Salim, J., "Linux Traffic Control Classifier-Action
              Subsystem Architecture", Netdev 01, Feb 2015.

   [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

   [RFC3746]  Yang, L., Dantu, R., Anderson, T., and R. Gopal,
              "Forwarding and Control Element Separation (ForCES)
              Framework", RFC 3746, DOI 10.17487/RFC3746, April 2004,

   [RFC6956]  Wang, W., Haleplidis, E., Ogawa, K., Li, C., and J.
              Halpern, "Forwarding and Control Element Separation
              (ForCES) Logical Function Block (LFB) Library", RFC 6956,
              DOI 10.17487/RFC6956, June 2013,

   [tc-ife]   Hadi Salim, J. and D. Joachimpillai, "Distributing Linux
              Traffic Control Classifier-Action Subsystem", Netdev 01,
              Feb 2015.

              Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", Work in Progress, draft-ietf-tsvwg-
              rfc5405bis-19, October 2016.


   The authors would like to thank Joel Halpern and Dave Hood for the
   stimulating discussions.  Evangelos Haleplidis shepherded and
   contributed to improving this document.  Alia Atlas was the AD
   sponsor of this document and did a tremendous job of critiquing it.
   The authors are grateful to Joel Halpern and Sue Hares in their roles
   as the Routing Area reviewers for shaping the content of this
   document.  David Black put in a lot of effort to make sure the
   congestion-control considerations are sane.  Russ Housley did the
   Gen-ART review, Joe Touch did the TSV area review, and Shucheng LIU
   (Will) did the OPS review.  Suresh Krishnan helped us provide clarity
   during the IESG review.  The authors are appreciative of the efforts
   Stephen Farrell put in to fixing the security section.

Authors' Addresses

   Damascane M. Joachimpillai
   60 Sylvan Rd
   Waltham, MA  02451
   United States of America

   Email: damascene.joachimpillai@verizon.com

   Jamal Hadi Salim
   Mojatatu Networks
   Suite 200, 15 Fitzgerald Rd.
   Ottawa, Ontario  K2H 9G1

   Email: hadi@mojatatu.com


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