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UDP(4) NetBSD Kernel Interfaces Manual UDP(4)
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by Kimmo Suominen.
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udp -- Internet User Datagram Protocol
socket(AF_INET, SOCK_DGRAM, 0);
socket(AF_INET6, SOCK_DGRAM, 0);
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
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 is one valid encapsulation option: UDP_ENCAP_ESPINUDP from RFC3948
defined in <netinet/udp.h>.
Options at the IP transport level may be used with UDP; see ip(4) or
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 net-
work 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
[ENOBUFS] when the system runs out of memory for an internal data
[ENOTCONN] when trying to send a datagram, but no destination
address is specified, and the socket hasn't been con-
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,
The udp protocol appeared in 4.2BSD.
NetBSD 9.0 May 31, 2018 NetBSD 9.0