kerneltap.hh

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// -*- c-basic-offset: 4 -*-
#ifndef CLICK_KERNELTAP_HH
#define CLICK_KERNELTAP_HH
#include "kerneltun.hh"
CLICK_DECLS

/*
=c

KernelTap(ADDR/MASK [, GATEWAY, I<keywords> ETHER, MTU, HEADROOM, IGNORE_QUEUE_OVERFLOWS])

=s comm

interface to /dev/tap or ethertap (user-level)

=d

Reads Ethernet packets from and writes Ethernet packets to a /dev/tun* or
/dev/tap* device.  This allows a user-level Click to hand packets to the
virtual Ethernet device.  KernelTap will also transfer packets from the
virtual Ethernet device.

KernelTap allocates a /dev/tun* or tap* device (this might fail) and runs
ifconfig(8) to set the interface's local (i.e., kernel) address to ADDR and
the netmask to MASK.  If a nonzero GATEWAY IP address (which must be on the
same network as the tun) is specified, then KernelTap tries to set up a
default route through that host.

Keyword arguments are:

=over 8

=item ETHER

Ethernet address. Specifies the fake device's Ethernet address. Default is
00:01:02:03:04:05. On Linux, you must supply an ETHER argument, and use that
address as the destination Ethernet address for all packets sent to the tap
element; otherwise, Linux will ignore your packets. On FreeBSD, there is no
way to set the Ethernet address, and any ETHER argument is silently ignored,
but it is safe to use any destination Ethernet address for packets sent to the
tap.

=item MTU

Integer.  The interface's maximum transmission unit, not including the
Ethernet header.  Default is 1500; some operating systems do not allow it to
be set.

=item HEADROOM

Integer.  The number of bytes left empty before the packet data (to leave room
for additional encapsulation headers).  Default is 0.

=item IGNORE_QUEUE_OVERFLOWS

Boolean.  If true, don't print more than one error message when there are
queue overflow errors (ENOBUFS) when sending or receiving packets via the tun
device.  Default is false.

=back

KernelTap accepts the same arguments as KernelTun.

=n

Linux will send ARP queries to the fake device. You must respond to these
queries in order to receive any IP packets, but you can obviously respond
with any Ethernet address you'd like. Here is one common idiom:

  tap0 :: KernelTap(192.0.0.1/8)
       -> fromhost_cl :: Classifier(12/0806, 12/0800);
  fromhost_cl[0] -> ARPResponder(0.0.0.0/0 1:1:1:1:1:1) -> tap0;
  fromhost_cl[1] -> ... // IP packets

An error like "could not allocate a /dev/tap* device : No such file or
directory" usually means that you have not enabled /dev/tap* in your
kernel.

=a ToHost, KernelTun, ifconfig(8) */

class KernelTap : public KernelTun { public:

    KernelTap();

    const char *class_name() const	{ return "KernelTap"; }

};

CLICK_ENDDECLS
#endif