FromDevice.u Element Documentation

FromDevice.u -- Click element; reads packets from network device (user-level)

FromDevice(DEVNAME [, keywords SNIFFER, PROMISC, SNAPLEN, FORCE_IP, CAPTURE, BPF_FILTER, OUTBOUND])

Ports: no inputs, 1 output
Processing: push
Drivers: userlevel
Package: userlevel (core)

This manual page describes the user-level version of the FromDevice element. For the Linux kernel module element, read the FromDevice manual page. Reads packets from the kernel that were received on the network controller named DEVNAME. User-level FromDevice behaves like a packet sniffer by default. Packets emitted by FromDevice are also received and processed by the kernel. Thus, it doesn't usually make sense to run a router with user-level Click, since each packet will get processed twice (once by Click, once by the kernel). Install firewalling rules in your kernel if you want to prevent this, for instance using the KernelFilter element or FromDevice's SNIFFER false argument. Under Linux, a FromDevice element will not receive packets sent by a ToDevice element for the same device. Under other operating systems, your mileage may vary. Sets the packet type annotation appropriately. Also sets the timestamp annotation to the time the kernel reports that the packet was received. Keyword arguments are:

SNIFFER

Boolean. Specifies whether FromDevice should run in sniffer mode. In non-sniffer mode, FromDevice installs KernelFilter filtering rules to block the kernel from handling any packets arriving on device DEVNAME. Default is true (sniffer mode).

PROMISC

Boolean. FromDevice puts the device in promiscuous mode if PROMISC is true. The default is false.

SNAPLEN

Unsigned. On some systems, packets larger than SNAPLEN will be truncated. Defaults to 2046.

FORCE_IP

Boolean. If true, then output only IP packets. (Any link-level header remains, but the IP header annotation has been set appropriately.) Default is false.

CAPTURE

Word. Defines the capture method FromDevice will use to read packets from the kernel. Linux targets generally support PCAP and LINUX; other targets support only PCAP. Defaults to LINUX on Linux targets (unless you give a BPF_FILTER), and PCAP elsewhere.

BPF_FILTER

String. A BPF filter expression used to select the interesting packets. Default is the empty string, which means all packets. If CAPTURE is not PCAP, then any filter expression is ignored with a warning.

OUTBOUND

Boolean. If true, then emit packets that the kernel sends to the given interface, as well as packets that the kernel receives from it. Default is false.

  FromDevice(eth0) -> ...

FromDevice sets packets' extra length annotations as appropriate.

count (read-only)

Returns the number of packets read by the device.

reset_counts (write-only)

Resets "count" to zero.

kernel_drops (read-only)

Returns the number of packets dropped by the kernel, probably due to memory constraints, before FromDevice could get them. This may be an integer; the notation "<d", meaning at most d drops; or "??", meaning the number of drops is not known.

encap (read-only)

Returns a string indicating the encapsulation type on this link. Can be `IP', `ETHER', or `FDDI', for example.

ToDevice.u, FromDump, ToDump, KernelFilter, FromDevice

Generated by 'click-elem2man' from '../elements/userlevel/fromdevice.hh' on 18/Sep/2007.