+-----------------+
  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 a 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 labelled EgressInGroup.

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

If lookup is successful, a matched table row which has the InterFEinfo details is retrieved with the tuple {optional IFEtype, optional StatId, Destination MAC address(DSTFE), Source MAC address(SRCFE), 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 tuple:

• Increment statistics for packet and byte count observed at corresponding IFEStats entry.
• When MetaFilterList is present, then walk each received Metadatum and apply against the MetaFilterList. If no legitimate metadata is found that needs to be passed downstream then the processing stops and send the packet and metadata out the EXCEPTIONOUT port with exceptionID of EncapTableLookupFailed [RFC6956].
• 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 exceptionID of FragRequired [RFC6956].
• Create the Ethernet header
• Set the Destination MAC address of the Ethernet header with value found in the DSTFE field.
• Set the Source MAC address of the Ethernet header with value found in the SRCFE field.
• If the optional IFETYPE is present, set the Ethernet type to the value found in IFETYPE. If IFETYPE is absent then the standard Inter-FE LFB Ethernet type is used (XXX: Note to editor, to be updated).
• 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 padding of zeroes to ensure alignment.
• Update the Metadata length to the sum of each TLV's space plus 2 bytes (for the Metadata length field 16 bit space).

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 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.

• Increment statistics for packet and byte count observed.
• Look at the metadata length field and walk the packet data extracting from the TLVs the metadata values. 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 is 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 the implementation is expected to ignore it, increment the packet error statistic and proceed processing other Metadatum.
• 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 graph.

In the case of processing failure of either ingress or egress positioning of the LFB, the packet and metadata are sent out the EXCEPTIONOUT LFB port with 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: optional IFETYPE, optionally present StatId, Destination MAC address(DSTFE), Source MAC address(SRCFE), 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 which carries statistics information in the structure bstats.

A note about the StatId relationship between the IFETable table and 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. Alternative implementation may map at provisioning time an IFETable row to IFEStats table row. 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"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       provides="IFE">
  <frameDefs>

     <frameDef>
	 <name>PacketAny</name>
	  <synopsis>Arbitrary Packet</synopsis>
     </frameDef>
     <frameDef>
	 <name>InterFEFrame</name>
	 <synopsis>
		 Ethernet Frame with encapsulate IFE information
	 </synopsis>
     </frameDef>

  </frameDefs>

  <dataTypeDefs>

    <dataTypeDef>
       <name>bstats</name>
       <synopsis>Basic stats</synopsis>
    <struct>
	<component componentID="1">
	 <name>bytes</name>
	 <synopsis>The total number of bytes seen</synopsis>
	 <typeRef>uint64</typeRef>
	</component>

	<component componentID="2">
	 <name>packets</name>
	 <synopsis>The total number of packets seen</synopsis>
	 <typeRef>uint32</typeRef>
	</component>

	<component componentID="3">
	 <name>errors</name>
	 <synopsis>The total number of packets with errors</synopsis>
	 <typeRef>uint32</typeRef>
	</component>
    </struct>

   </dataTypeDef>

     <dataTypeDef>
        <name>IFEInfo</name>
	<synopsis>Describing IFE table row Information</synopsis>
        <struct>
           <component componentID="1">
             <name>IFETYPE</name>
	     <synopsis>
		 the ethernet type to be used for outgoing IFE frame
	     </synopsis>
	     <optional/>
             <typeRef>uint16</typeRef>
           </component>
           <component componentID="2">
             <name>StatId</name>
	     <synopsis>
		 the Index into the stats table
	     </synopsis>
	     <optional/>
             <typeRef>uint32</typeRef>
           </component>
           <component componentID="3">
             <name>DSTFE</name>
	     <synopsis>
		     the destination MAC address of destination FE
	     </synopsis>
             <typeRef>byte[6]</typeRef>
           </component>
           <component componentID="4">
             <name>SRCFE</name>
	     <synopsis>
		     the source MAC address used for the source FE
	     </synopsis>
             <typeRef>byte[6]</typeRef>
           </component>
           <component componentID="5">
             <name>MetaFilterList</name>
	     <synopsis>
		     the allowed metadata filter table
	     </synopsis>
	     <optional/>
             <array type="variable-size">
               <typeRef>uint32</typeRef>
             </array>
            </component>


        </struct>
     </dataTypeDef>

  </dataTypeDefs>

  <LFBClassDefs>
    <LFBClassDef LFBClassID="18">
      <name>IFE</name>
      <synopsis>
         This LFB describes IFE connectivity parameterization
      </synopsis>
      <version>1.0</version>

	<inputPorts>

	  <inputPort group="true">
	   <name>EgressInGroup</name>
	   <synopsis>
		   The input port group of the egress side.
		   It expects any type of Ethernet frame.
	   </synopsis>
	   <expectation>
		<frameExpected>
		<ref>PacketAny</ref>
		</frameExpected>
	   </expectation>
	  </inputPort>

	  <inputPort  group="true">
	   <name>IngressInGroup</name>
	   <synopsis>
		   The input port group of the ingress side.
		   It expects an interFE encapsulated Ethernet frame.
	    </synopsis>
	   <expectation>
		<frameExpected>
		<ref>InterFEFrame</ref>
		</frameExpected>
	   </expectation>
	</inputPort>

       </inputPorts>

       <outputPorts>

         <outputPort>
           <name>OUT1</name>
           <synopsis>
                The output port of the egress side.
           </synopsis>
           <product>
              <frameProduced>
                <ref>InterFEFrame</ref>
              </frameProduced>
           </product>
        </outputPort>

        <outputPort>
          <name>OUT2</name>
          <synopsis>
              The output port of the Ingress side.
          </synopsis>
          <product>
             <frameProduced>
               <ref>PacketAny</ref>
             </frameProduced>
          </product>
       </outputPort>

       <outputPort>
         <name>EXCEPTIONOUT</name>
         <synopsis>
            The exception handling path
         </synopsis>
         <product>
            <frameProduced>
              <ref>PacketAny</ref>
            </frameProduced>
            <metadataProduced>
              <ref>ExceptionID</ref>
            </metadataProduced>
         </product>
      </outputPort>

   </outputPorts>

   <components>

      <component componentID="1" access="read-write">
         <name>IFETable</name>
         <synopsis>
            the table of all InterFE relations
         </synopsis>
         <array type="variable-size">
            <typeRef>IFEInfo</typeRef>
         </array>
      </component>

     <component componentID="2" access="read-only">
       <name>IFEStats</name>
       <synopsis>
        the stats corresponding to the IFETable table
       </synopsis>
       <typeRef>bstats</typeRef>
     </component>

  </components>

 </LFBClassDef>
</LFBClassDefs>

</LFBLibrary>