HP-UX Reference (11i v1 00/12) - 4 File Formats (vol 8)
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STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man4/!!!intro.4
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t
tun(4) tun(4)
NAME
tun - IP network tunnel driver
SYNOPSIS
#include <net/tun.h>
open("/dev/tun
n", mode);
DESCRIPTION
When IP packets are written to /dev/tunn or /dev/tunn+M, they will be received by the kernel’s IP
layer on the network interface dun. When the kernel’s IP layer sends packets to the IP interface dun,
they will be available for reading on /dev/tunn or /dev/tunn+M.
Instead of having hardware and an associated kernel interface that support network functions, the tun
driver allows a network interface to be implemented as a user-space process. While talking to the same set
of tunnel drivers on the same system, different network interface processes can implement different IP
encapsulation methods, such as RFC 877 for use over CCITT X.25-based public data networks, or RFC 1055
SLIP or RFC 1548/1332PPP for use over dedicated lines and dialup modems.
The tun driver provides support for a pair of devices collectively known as an IP tunnel. The two devices
comprising a tunnel are known as the inbound and outbound sides, similar to the pairing between
/dev/ttyn (the inbound terminal) and /dev/cun (the outbound ‘auto-call unit’ available on many sys-
tems). The outbound side’s minor device number is that of the inbound side plus M, though they together
appear to IP as one interface. If both the inbound and outbound sides of a tunnel device are open, packets
received from IP are delivered to only the inbound side. On HP-UX systems, M is 64.
If a TCP packet received from IP is part of a telnet, rlogin, or FTP command stream, it will be put in a fast
queue. All packets in the fast queue are delivered to the user before any packets in the normal queue.
Config
pseudo-device tun[n]
Ioctls
A few special
ioctls are provided for use on the /dev/tun* devices to supply the functionality needed
by applications programs to emulate real hardware interfaces. The complete list of supported
ioctls is:
TUIOSPTPT Set or clear the IFF_POINTOPOINT
in the associated network interface.
TUIOSADRMD Set or clear ‘address mode’, in which packets read are prefaced with four octets contain-
ing the destination IP address in network byte order. The third argument is a pointer
to an integer containing either a zero or a one, indicating whether ‘address mode’ should
be cleared or set, respectively. If both ‘address mode’ and ‘packed buffer mode’ are set,
each packet’s length will come first, followed by the packet’s destination address, fol-
lowed by the packet itself.
TUIOGADRMD Get the current status of ‘address mode’.
TUIOSPKBMD Set or clear ‘packed buffer mode’ where multiple packets are encoded in single
read/write buffers. The third argument is a pointer to an integer containing either a
zero or a one, indicating whether ‘packed buffer mode’ should be cleared or set, respec-
tively. If set (1), each packet is preceded by four octets representing the next packet’s
length in octets. The following packet will then be aligned to the next multiple of four
octets. If cleared (0), packets will be delivered one per read(3) from the tunnel device.
If both ‘address mode’ and ‘packed buffer mode’ are set, each packet’s length will come
first, followed by the packet’s address, followed by the packet itself.
TUIOGPKBMD Get the current status of ‘packed buffer mode’.
TUIOSPKMAX Set the max number of IP frames to send back in a packet buffer read.
TUIOGPKMAX Get the PKMAX value.
TUIOSPKPAD Set the number of long word zeroes to put on the front of each packet read in packed
buffer mode.
TUIOGPKPAD Get the number of pad words.
TUIOSNAME Set the interface name (may only be invoked by the superuser).
Section 4−−360 − 1 − HP-UX Release 11i: December 2000
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