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-Universal TUN/TAP device driver.
-Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
-
- Linux, Solaris drivers
- Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
-
- FreeBSD TAP driver
- Copyright (c) 1999-2000 Maksim Yevmenkin <m_evmenkin@yahoo.com>
-
- Revision of this document 2002 by Florian Thiel <florian.thiel@gmx.net>
-
-1. Description
- TUN/TAP provides packet reception and transmission for user space programs.
- It can be seen as a simple Point-to-Point or Ethernet device, which,
- instead of receiving packets from physical media, receives them from
- user space program and instead of sending packets via physical media
- writes them to the user space program.
-
- In order to use the driver a program has to open /dev/net/tun and issue a
- corresponding ioctl() to register a network device with the kernel. A network
- device will appear as tunXX or tapXX, depending on the options chosen. When
- the program closes the file descriptor, the network device and all
- corresponding routes will disappear.
-
- Depending on the type of device chosen the userspace program has to read/write
- IP packets (with tun) or ethernet frames (with tap). Which one is being used
- depends on the flags given with the ioctl().
-
- The package from http://vtun.sourceforge.net/tun contains two simple examples
- for how to use tun and tap devices. Both programs work like a bridge between
- two network interfaces.
- br_select.c - bridge based on select system call.
- br_sigio.c - bridge based on async io and SIGIO signal.
- However, the best example is VTun http://vtun.sourceforge.net :))
-
-2. Configuration
- Create device node:
- mkdir /dev/net (if it doesn't exist already)
- mknod /dev/net/tun c 10 200
-
- Set permissions:
- e.g. chmod 0666 /dev/net/tun
- There's no harm in allowing the device to be accessible by non-root users,
- since CAP_NET_ADMIN is required for creating network devices or for
- connecting to network devices which aren't owned by the user in question.
- If you want to create persistent devices and give ownership of them to
- unprivileged users, then you need the /dev/net/tun device to be usable by
- those users.
-
- Driver module autoloading
-
- Make sure that "Kernel module loader" - module auto-loading
- support is enabled in your kernel. The kernel should load it on
- first access.
-
- Manual loading
- insert the module by hand:
- modprobe tun
-
- If you do it the latter way, you have to load the module every time you
- need it, if you do it the other way it will be automatically loaded when
- /dev/net/tun is being opened.
-
-3. Program interface
- 3.1 Network device allocation:
-
- char *dev should be the name of the device with a format string (e.g.
- "tun%d"), but (as far as I can see) this can be any valid network device name.
- Note that the character pointer becomes overwritten with the real device name
- (e.g. "tun0")
-
- #include <linux/if.h>
- #include <linux/if_tun.h>
-
- int tun_alloc(char *dev)
- {
- struct ifreq ifr;
- int fd, err;
-
- if( (fd = open("/dev/net/tun", O_RDWR)) < 0 )
- return tun_alloc_old(dev);
-
- memset(&ifr, 0, sizeof(ifr));
-
- /* Flags: IFF_TUN - TUN device (no Ethernet headers)
- * IFF_TAP - TAP device
- *
- * IFF_NO_PI - Do not provide packet information
- */
- ifr.ifr_flags = IFF_TUN;
- if( *dev )
- strncpy(ifr.ifr_name, dev, IFNAMSIZ);
-
- if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ){
- close(fd);
- return err;
- }
- strcpy(dev, ifr.ifr_name);
- return fd;
- }
-
- 3.2 Frame format:
- If flag IFF_NO_PI is not set each frame format is:
- Flags [2 bytes]
- Proto [2 bytes]
- Raw protocol(IP, IPv6, etc) frame.
-
-Universal TUN/TAP device driver Frequently Asked Question.
-
-1. What platforms are supported by TUN/TAP driver ?
-Currently driver has been written for 3 Unices:
- Linux kernels 2.2.x, 2.4.x
- FreeBSD 3.x, 4.x, 5.x
- Solaris 2.6, 7.0, 8.0
-
-2. What is TUN/TAP driver used for?
-As mentioned above, main purpose of TUN/TAP driver is tunneling.
-It is used by VTun (http://vtun.sourceforge.net).
-
-Another interesting application using TUN/TAP is pipsecd
-(http://perso.enst.fr/~beyssac/pipsec/), a userspace IPSec
-implementation that can use complete kernel routing (unlike FreeS/WAN).
-
-3. How does Virtual network device actually work ?
-Virtual network device can be viewed as a simple Point-to-Point or
-Ethernet device, which instead of receiving packets from a physical
-media, receives them from user space program and instead of sending
-packets via physical media sends them to the user space program.
-
-Let's say that you configured IPX on the tap0, then whenever
-the kernel sends an IPX packet to tap0, it is passed to the application
-(VTun for example). The application encrypts, compresses and sends it to
-the other side over TCP or UDP. The application on the other side decompresses
-and decrypts the data received and writes the packet to the TAP device,
-the kernel handles the packet like it came from real physical device.
-
-4. What is the difference between TUN driver and TAP driver?
-TUN works with IP frames. TAP works with Ethernet frames.
-
-This means that you have to read/write IP packets when you are using tun and
-ethernet frames when using tap.
-
-5. What is the difference between BPF and TUN/TAP driver?
-BPF is an advanced packet filter. It can be attached to existing
-network interface. It does not provide a virtual network interface.
-A TUN/TAP driver does provide a virtual network interface and it is possible
-to attach BPF to this interface.
-
-6. Does TAP driver support kernel Ethernet bridging?
-Yes. Linux and FreeBSD drivers support Ethernet bridging.