udp -- Internet User Datagram Protocol


Programmer's interface:
#include <sys/types.h>
#include  <sys/socket.h>
#include  <netinet/in.h>

s = socket(AF_INET, 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);


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(SSC) call may also be used to fix the destination for future packets (in which case the recv(SSC), or read(S) and send(SSC), or write(S) 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 IP transport level may be used with UDP; see ip(ADMP).

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:

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.

to extract UDP statistics. The structure udpstat is passed as an argument to the I_STR ioctl call.

to fetch the entire UDP table. It is a transparent ioctl and functions similar to STIOCBTCB, see tcp(ADMP).


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

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

when trying to send a datagram, but no destination address is specified, and the socket hasn't been connected

when the system runs out of memory for an internal data structure

when an attempt is made to create a socket with a port which has already been allocated

when an attempt is made to create a socket with a network address for which no network interface exists.
An ioctl operation may fail with the errno set to one of the following:

when no argument/NULL 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

when the associated file descriptor is no longer open/valid.



See also

Intro(ADMP), getsockopt(SSC), inet(ADMP), ip(ADMP), recv(SSC), send(SSC), socket(SSC), streamio(M), tcp(ADMP)

Standards conformance

udp is conformant with:

RFC 768 (STD 6), RFC 1122 (STD 7)

© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003