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ng_ether - Ethernet netgraph node type
The ether netgraph node type allows Ethernet interfaces to interact with
the netgraph(4) networking subsystem. Once the ng_ether module is loaded
into the kernel, a node is automatically created for each Ethernet
interface in the system. Each node will attempt to name itself with the
same name as the associated interface.
Three hooks are supported: lower, upper, and orphans. The hook name
divert may be used as an alias for lower, and is provided for backward
compatibility. In reality, the two names represent the same hook.
The lower hook is a connection to the raw Ethernet device. When
connected, all incoming packets are forwarded to this hook, instead of
being passed to the kernel for upper layer processing. Writing to this
hook results in a raw Ethernet frame being transmitted by the device.
Normal outgoing packets are not affected by lower being connected.
The upper hook is a connection to the upper protocol layers. When
connected, all outgoing packets are forwarded to this hook, instead of
being transmitted by the device. Writing to this hook results in a raw
Ethernet frame being received by the kernel just as if it had come in
over the wire. Normal incoming packets are not affected by upper being
The orphans hook is equivalent to lower, except that only unrecognized
packets (that would otherwise be discarded) are written to the hook,
while other normal incoming traffic is unaffected. Unrecognized packets
written to upper will be forwarded back out to orphans if connected.
In all cases, frames are raw Ethernet frames with the standard 14 byte
Ethernet header (but no checksum).
When no hooks are connected, upper and lower are in effect connected
together, so that packets flow normally upwards and downwards.
This node type supports the following hooks:
lower Connection to the lower device link layer.
upper Connection to the upper protocol layers.
orphans Like lower, but only receives unrecognized packets.
This node type supports the generic control messages, plus the following:
Returns the name of the associated interface as a NUL-terminated
ASCII string. Normally this is the same as the name of the node.
Returns the global index of the associated interface as a 32 bit
Returns the device’s unique six byte Ethernet address.
Sets the device’s unique six byte Ethernet address. This control
message is equivalent to using the SIOCSIFLLADDR ioctl(2) system
Enable or disable promiscuous mode. This message includes a
single 32 bit integer flag that enables or disables promiscuous
mode on the interface. Any non-zero value enables promiscuous
Get the current value of the node’s promiscuous flag. The
returned value is always either one or zero. Note that this flag
reflects the node’s own promiscuous setting and does not
necessarily reflect the promiscuous state of the actual
interface, which can be affected by other means (e.g., bpf(4)).
Sets the automatic source address override flag. This message
includes a single 32 bit integer flag that causes all outgoing
packets to have their source Ethernet address field overwritten
with the device’s unique Ethernet address. If this flag is set
to zero, the source address in outgoing packets is not modified.
The default setting for this flag is disabled.
Get the current value of the node’s source address override flag.
The returned value is always either one or zero.
Join Ethernet multicast group. This control message is
equivalent to using the SIOCADDMULTI ioctl(2) system call.
Leave Ethernet multicast group. This control message is
equivalent to using the SIOCDELMULTI ioctl(2) system call.
Detach from underlying Ethernet interface and shut down node.
Upon receipt of the NGM_SHUTDOWN control message, all hooks are
disconnected, promiscuous mode is disabled, and the source address
override flag is re-enabled, but the node is not removed. Node can be
shut down only using NGM_ETHER_DETACH control message. If the interface
itself is detached (e.g., because of PC Card removal), the node
disappears as well.
This command dumps all unrecognized packets received by the “fxp0”
interface to standard output decoded in hex and ASCII:
nghook -a fxp0: orphans
This command sends the contents of sample.pkt out the interface “fxp0”:
cat sample.pkt | nghook fxp0: orphans
These commands insert an ng_tee(4) node between the lower and upper
protocol layers, which can be used for tracing packet flow, statistics,
ngctl mkpeer fxp0: tee lower right
ngctl connect fxp0: lower upper left
arp(4), netgraph(4), netintro(4), ifconfig(8), ngctl(8), nghook(8)
Julian Elischer 〈julian@FreeBSD.org〉
Archie Cobbs 〈archie@FreeBSD.org〉
The automatic KLD module loading mechanism that works for most other
Netgraph node types does not work for the ether node type, because ether
nodes are not created on demand; instead, they are created when Ethernet
interfaces are attached or when the KLD is first loaded. Therefore, if
the KLD is not statically compiled into the kernel, it is necessary to
load the KLD manually in order to bring the ether nodes into existence.