udp(7tcp)

udp -- Internet User Datagram Protocol

Synopsis

Programmer's interface:

#include <sys/types.h>
#include  <sys/socket.h>
#include  <netinet/in.h>

s = socket(AF_INET, SOCK_DGRAM, 0);
s = socket(AF_INET6, SOCK_DGRAM, 0);

#include <paths.h>
#include <fcntl.h>
#include <netinet/ip_var.h>
#include <netinet/udp.h>
#include <netinet/udp_var.h>

fd = open(_PATH_UDP, flags);
fd = open(_PATH_UDPIPV6, flags);

Description

UDP is a simple, unreliable datagram protocol that is used to support the SOCK_DGRAM abstraction for the Internet protocol family. UDP sockets are connectionless, and are normally used with the sendto and recvfrom calls; the connect(3sock) call may also be used to fix the destination for future packets (in which case the recv(3sock), or read(2) and send(3sock), or write(2) system/library calls may be used). In addition, UDP is available as TLI connectionless transport via the special file /dev/inet/udp.

UDP address formats are identical to those used by TCP. In particular, UDP provides a port identifier in addition to the normal Internet address format. Note that the UDP port space is separate from the TCP port space (that is, a UDP port may not be ``connected'' to a TCP port). In addition, broadcast packets may be sent (assuming the underlying network supports this) by using a reserved ``broadcast address''; this address is network interface dependent.

Options at the IPv4 transport level may be used with UDP if AF_INET is specified; see ip(7tcp). Options at the IPv6 transport level may be used with UDP if AF_INET6 is specified; see ipv6(7tcp).

The UDP driver may also be accessed by opening it directly. Network related statistics can be obtained by issuing the following ioctls, defined in <netinet/ip_var.h> and <netinet/udp_var.h>, to the driver:

SIOCSMGMT: to set the inpcb associated with the end-point as a management inpcb (to distinguish it from others, when network statistics are gathered) and link it in the list of management inpcbs.
SIOCGUDPSTATS: to extract UDP statistics. The structure udpstat is passed as an argument to the I_STR ioctl call.
STIOCGUDB: to fetch the entire UDP table. It is a transparent ioctl and functions similar to STIOCBTCB, see tcp(7tcp).

Diagnostics

A socket operation may fail with one of the following errors returned:

[EADDRINUSE]: when an attempt is made to create a socket with a port which has already been allocated
[EADDRNOTAVAIL]: when an attempt is made to create a socket with a network address for which no network interface exists.
[EISCONN]: when trying to establish a connection on a socket which already has one, or when trying to send a datagram with the destination address specified and the socket is already connected
[ENOMEM]: when the system runs out of memory for an internal data structure
[ENOSR]: when the system runs out of STREAMS
[ENOTCONN]: when trying to send a datagram, but no destination address is specified, and the socket has not been connected
[ENXIO]: when no more UDP devices are available

An ioctl operation may fail with the errno set to one of the following:

[EINVAL]: when an invalid argument is passed to the driver, or when the command in the copyresp structure is not valid, or when the ioc_count is not TRANSPARENT for a transparent ioctl
[ENXIO]: when the associated file descriptor is no longer open/valid.

References

getsockopt(3sock), if(7tcp), inconfig(1Mtcp), inet(7tcp), ip(7tcp), recv(3sock), send(3sock), socket(3sock), streamio(7), tcp(7tcp)

``User Datagram Protocol (UDP) parameters'' on the inconfig(1Mtcp) manual page

RFC 768, RFC 1122