NG_ETF(4)

NAME
ng_etf - Ethertype filtering netgraph node type

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

DESCRIPTION
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.

HOOKS
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.

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

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

NGM_ETF_SET_FILTER
    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 ng_etffilter:

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

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

    #!/bin/sh
    ETHER_IF=fxp0
    MATCH1=0x834
    MATCH2=0x835
    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 ${ETHER_IF}: etf: upper nomatch
    DONE
    ngctl -f /tmp/xwert
    # something to set a hook to catch packets and show them.
    echo "Unrecognised packets:"
    nghook -a etf: newproto &
    # Filter two random ethertypes to that hook.
    ngctl 'msg etf: setfilter { matchhook="newproto" ethertype=${MATCH1} }
    ngctl 'msg etf: setfilter { matchhook="newproto" ethertype=${MATCH2} }
    DONE

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

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

HISTORY
The ng_etf node type was implemented in FreeBSD 5.0.

AUTHORS
Julian Elischer <julian@FreeBSD.org>