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NG_ETHER(4) Device Drivers Manual NG_ETHER(4)

ng_ether — Ethernet netgraph node type

#include <netgraph/ether/ng_ether.h>

The ng_ether netgraph node type allows Ethernet interfaces to interact with the netgraph(4) networking subsystem. Once the ng_ether module is loaded in 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. All ng_ether nodes are persistent for as long as the interface itself exists.

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 diverted out this hook. 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 diverted out this hook. 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 connected.

The orphans hook is equivalent to lower, except that only unrecognized packets (that would otherwise be discarded) are written to the hook, and normal incoming traffic is unaffected. At most one of orphans and lower may be connected at any time.

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:

Connection to the lower device link layer.
Connection to the upper protocol layers.
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 integer.
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 call.
Enable or disable promiscuous mode. This message includes a single 32 bit integer flag that enables or disables promiscuous mode on the interface.
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 enabled.
Get the current value of the node's source address override flag. The returned value is always either one or zero.

This node is persistent for as long as the interface exists. Upon receipt of a NGM_SHUTDOWN control message, all hooks are disconnected, promiscuous mode is disabled, and the source address override flag is reenabled, but the node is not removed. If the interface itself is detached (e.g., because of PCCARD 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 foo.pkt out the interface fxp0:

cat foo.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, etc.:

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 ng_ether node type, because ng_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 ng_ether nodes into existence.

June 26, 2000 DragonFly-5.6.1