NAME
udp —
Internet User Datagram
Protocol
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
int
socket(
AF_INET,
SOCK_DGRAM,
0);
int
socket(
AF_INET6,
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 connectionless, and are normally used with the
sendto(2) and
recvfrom(2) 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.
There are two UDP-level
setsockopt(2)/
getsockopt(2)
options.
UDP_OPTIONS
may be used to change the default
behavior of the socket. For example:
setsockopt(s, IPPROTO_UDP, UDP_OPTIONS, NULL, 0);
The
UDP_ENCAP
option can be used to encapsulate ESP
packets in UDP. There are two valid encapsulation options:
UDP_ENCAP_ESPINUDP_NON_IKE from draft-ietf-ipsec-nat-t-ike-00/01 and
UDP_ENCAP_ESPINUDP from draft-ietf-ipsec-udp-encaps-06 defined in
<netinet/udp.h>.
Options at the IP transport level may be used with UDP; see
ip(4) or
ip6(4).
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 already connected;
-
-
- [
ENOTCONN
]
- when trying to send a datagram, but no destination address
is specified, and the socket hasn't been connected;
-
-
- [
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 network
address for which no network interface exists.
SEE ALSO
getsockopt(2),
recv(2),
send(2),
socket(2),
inet(4),
inet6(4),
intro(4),
ip(4),
ip6(4),
rfc6056(7),
sysctl(7)
User Datagram Protocol,
RFC, 768,
August 28, 1980.
Requirements for Internet Hosts --
Communication Layers, RFC,
1122, October 1989.
HISTORY
The
udp protocol appeared in
4.2BSD.