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⟩