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86 lines
3.5 KiB
Plaintext
86 lines
3.5 KiB
Plaintext
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tun/tap driver for Mac OS X
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===========================
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This is an experimental IP tunnel/ethertap driver for Mac OS X/Darwin. It
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provides /dev/tunX and /dev/tapX devices. The maximum number of devices can be
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configured at compile time, it is currently set to 16. That should be enough in
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most cases.
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The driver ships as two kernel extensions, one for tap and one for tun. They are
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located in /Library/Extensions and can also be loaded and unloaded by hand. If
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you install the startup item, the system will load them automatically at
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startup (tun and tap startup items get installed in /Library/StartupItems).
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Operation & Programming notes
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=============================
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tapX are ethertap devices which provide an interface to the kernel's ethernet
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layer. Packets can be read from and written to the /dev/tapX character devices
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one at a time (same name as the interface that shows up in ifconfig).
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tunX are IP tunnel devices. These can be used to exchange IP packets with the
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kernel. You will get single packets for each read() and should write() packets
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one at a time to /dev/tunX.
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There are some special ioctls with the tun devices that allow you to have them
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prepend the address family of the packet when reading it from /dev/tunX. Using
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this mode the driver also expects you put this 4-byte address family field
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(network byte order) in front of the packets you write to /dev/tunX.
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Here are the ioctls to setup up address prepending mode (for convenience there
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also is a header called tun_ioctls.h in the source package that you can use)
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Set the int argument to one if you want to have AF prepending, use 0 if you want
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to switch it off.
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#define TUNSIFHEAD _IOW('t', 96, int)
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#define TUNGIFHEAD _IOR('t', 97, int)
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Prepending mode is off by default. Currently it is not recommended to switch the
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mode while packets are in flight on the device.
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The character devices are always visible in the filesystem as /dev/tunX and
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/dev/tapX. The number of available character devices is a compile time constant
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and is currently fixed to 16. Each character devices is associated with a
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network interface of the same name. The network interfaces are only created when
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the corresponding character device is opened by a program and will be removed
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when the character device is closed.
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The character devices currently provide a pretty minimal interface. Whole
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packets are read and written using a singe read/write call. File descriptors
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opened on the devices can also be select()ed and support O_NONBLOCK.
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Asynchronous i/o and some ioctls are currently unimplemented, but implementing
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them shouldn't be very hard. Do it yourself or contact me if you can't live
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without.
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There is another limitation imposed by the Darwin 8 kernel. It concerns the
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poll() system call; Darwin currently does *not* support that for (character)
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devices. Use select() instead.
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The interfaces can be configured using ifconfig, the tap devices also support
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setting the MAC address to be used. Both tun and tap should be ready for IPv6.
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Just setup addresses and routing as you would do with other interfaces.
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Please contact me if you find any bugs or have suggestions.
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Enjoy!
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Mattias
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<mattias.nissler@gmx.de>
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Uninstalling
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============
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The installer packages for OS X currently don't have support for uninstall as
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the installer doesn't provide it. Remove the following directories if you want
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to completely remove the files installed:
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/Library/Extensions/tap.kext
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/Library/Extensions/tun.kext
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/Library/StartupItems/tap
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/Library/StartupItems/tun
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Unload the the kernel extensions or reboot and you're done.
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