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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 connected.
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.
|Connection to the lower device link layer.|
|Connection to the upper protocol layers.|
|Like lower, but only receives unrecognized packets.|
|NGM_ETHER_GET_IFNAME ( getifname)|
|Returns the name of the associated interface as a NUL-terminated ASCII string. Normally this is the same as the name of the node.|
|NGM_ETHER_GET_IFINDEX ( getifindex)|
|Returns the global index of the associated interface as a 32 bit integer.|
|NGM_ETHER_GET_ENADDR ( getenaddr)|
|Returns the device's unique six byte Ethernet address.|
|NGM_ETHER_SET_ENADDR ( setenaddr)|
|Sets the device's unique six byte Ethernet address. This control message is equivalent to using the SIOCSIFLLADDR ioctl(2) system call.|
|NGM_ETHER_SET_PROMISC ( setpromisc)|
|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 mode.|
|NGM_ETHER_GET_PROMISC ( getpromisc)|
|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)).|
|NGM_ETHER_SET_AUTOSRC ( setautosrc)|
|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.|
|NGM_ETHER_GET_AUTOSRC ( getautosrc)|
|Get the current value of the node's source address override flag. The returned value is always either one or zero.|
|NGM_ETHER_ADD_MULTI ( addmulti)|
|Join Ethernet multicast group. This control message is equivalent to using the SIOCADDMULTI ioctl(2) system call.|
|NGM_ETHER_DEL_MULTI ( delmulti)|
|Leave Ethernet multicast group. This control message is equivalent to using the SIOCDELMULTI ioctl(2) system call.|
|NGM_ETHER_DETACH ( detach)|
|Detach from underlying Ethernet interface and shut down node.|
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, etc.:
ngctl mkpeer fxp0: tee lower right ngctl connect fxp0: lower upper left
|NG_ETHER (4)||June 23, 2011|
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|“||On two occasions I have been asked [by members of Parliament], 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.||”|
|— Charles Babbage|