UDP(4) BSD Programmer's Manual UDP(4)NAMEudp - Internet User Datagram Protocol
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
int
socket(AF_INET, SOCK_DGRAM, 0);
DESCRIPTION
UDP is a simple, unreliable datagram protocol which is used to support
the SOCK_DGRAM abstraction for the Internet protocol family. UDP sockets
are connection-less, and are normally used with the sendto and recvfrom
calls, though the connect(2) call may also be used to fix the destination
for future packets (in which case the recv(2) or read(2) and send(2) or
write(2) system calls may be used).
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
(i.e. 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(4). In
particular, the destination address used to deliver a received IP data-
gram is available via the ancillary data provided with the recvmsg() sys-
tem call when the IP_RECVDSTADDR option is enabled.
SYSCTL VARIABLES
Some UDP options can be read or written via the sysctl(3) facility.
Variables specific to UDP are:
CTL_NET, PF_INET, IPPROTO_UDP
These variables are used to get or set various global TCP options.
Fourth level name Type Changeable
UDPCTL_CHECKSUM integer yes
UDPCTL_RECVSPACE integer yes
UDPCTL_SENDMAX integer yes
UDPCTL_STATS struct no
UDPCTL_CHECKSUM
Returns 1 when UDP checksums are being computed and checked.
Disabling UDP checksums is strongly discouraged.
UDPCTL_RECVSPACE
Returns the default value (in bytes) of buffering available per-
socket for received UDP datagrams. This value may be changed on
a per-socket basis by manipulating the SO_RCVBUF parameter with
setsockopt(2).
UDPCTL_SENDMAX
Returns the default value for the maximum per-socket size (in
bytes) for transmitted UDP datagrams. This value may be changed
on a per-socket basis by manipulating the SO_SNDBUF parameter
with setsockopt(2).
UDPCTL_STATS
Returns the struct udpstat containing statistics about UDP pro-
cessing.
DIAGNOSTICS
A socket operation may fail with one of the following errors returned:
[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 al-
ready connected;
[ENOTCONN] when trying to send a datagram, but no destination ad-
dress is specified, and the socket hasn't been connect-
ed;
[ENOBUFS] when the system runs out of memory for an internal data
structure;
[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 net-
work address for which no network interface exists.
SEE ALSOgetsockopt(2), recv(2), send(2), socket(2), intro(4), inet(4),
ip(4)HISTORY
The udp protocol appeared in 4.2BSD.
4.2 Berkeley Distribution June 5, 1993 2