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_ether4
node, using the
lower
hook.
nomatch
Typically this hook would also be connected to an
ng_ether4
type node using the
upper
hook.
Aq 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
Vt 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
Vt 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.
