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     ng_etf — Ethertype filtering netgraph node type


     #include <netgraph.h>
     #include <netgraph/ng_etf.h>


     The etf node type multiplexes and filters data between hooks on the basis
     of the ethertype found in an Ethernet header, presumed to be in the first
     14 bytes of the data.  Incoming Ethernet frames are accepted on the
     downstream hook and if the ethertype matches a value which the node has
     been configured to filter, the packet is forwarded out the hook which was
     identified at the time that value was configured.  If it does not match a
     configured value, it is passed to the nomatch hook.  If the nomatch hook
     is not connected, the packet is dropped.

     Packets travelling in the other direction (towards the downstream hook)
     are also examined and filtered.  If a packet has an ethertype that
     matches one of the values configured into the node, it must have arrived
     in on the hook for which that value was configured, otherwise it will be
     discarded.  Ethertypes of values other than those configured by the
     control messages must have arrived via the nomatch hook.


     This node type supports the following hooks:

     downstream  Typically this hook would be connected to a ng_ether(4) node,
                 using the lower hook.

     nomatch     Typically this hook would also be connected to an ng_ether(4)
                 type node using the upper hook.

     ⟨any legal name⟩
                 Any other hook name will be accepted and can be used as the
                 match target of an ethertype.  Typically this hook would be
                 attached to a protocol handling node that requires and
                 generates packets with a particular set of ethertypes.


     This node type supports the generic control messages, plus the following:

           This command returns a struct ng_etfstat containing node statistics
           for packet counts.

           Sets the a new ethertype filter into the node and specifies the
           hook to and from which packets of that type should use.  The hook
           and ethertype are specified in a structure of type struct

               struct ng_etffilter {
                       char       matchhook[NG_HOOKSIZ];     /* hook name */
                       u_int16_t  ethertype;                 /* catch these */


     Using ngctl(8) it is possible to set a filter in place from the command
     line as follows:

         cat <<DONE >/tmp/xwert
         # Make a new ethertype filter and attach to the Ethernet lower hook.
         # first remove left over bits from last time.
         shutdown ${ETHER_IF}:lower
         mkpeer ${ETHER_IF}: etf lower downstream
         # Give it a name to easily refer to it.
         name ${ETHER_IF}:lower etf
         # Connect the nomatch hook to the upper part of the same interface.
         # All unmatched packets will act as if the filter is not present.
         connect ${ETHER_IF}: etf: upper nomatch
         ngctl -f /tmp/xwert

         # something to set a hook to catch packets and show them.
         echo "Unrecognised packets:"
         nghook -a etf: newproto &
         # Filter two random ethertypes to that hook.
         ngctl 'msg etf: setfilter { matchhook="newproto" ethertype=${MATCH1} }
         ngctl 'msg etf: setfilter { matchhook="newproto" ethertype=${MATCH2} }


     This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
     when all hooks have been disconnected.


     netgraph(4), ng_ether(4), ngctl(8), nghook(8)


     The ng_etf node type was implemented in FreeBSD 5.0.


     Julian Elischer ⟨