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〉