1udp(7P) Protocols udp(7P)
2
6 udp, UDP - Internet User Datagram Protocol
7
9 #include <sys/socket.h>
10 #include <netinet/in.h>
13 s = socket(AF_INET, SOCK_DGRAM, 0);
16 s = socket(AF_INET6, SOCK_DGRAM, 0);
19 t = t_open("/dev/udp", O_RDWR);
22 t = t_open("/dev/udp6", O_RDWR);
25
28 UDP is a simple datagram protocol which is layered directly above the
29 Internet Protocol ("IP") or the Internet Protocol Version 6 ("IPv6").
30 Programs may access UDP using the socket interface, where it supports
31 the SOCK_DGRAM socket type, or using the Transport Level Interface
32 ("TLI"), where it supports the connectionless (T_CLTS) service type.
33 Within the socket interface, UDP is normally used with the sendto(),
36 sendmsg(), recvfrom(), and recvmsg() calls (see send(3SOCKET) and
37 recv(3SOCKET)). If the connect(3SOCKET) call is used to fix the desti‐
38 nation for future packets, then the recv(3SOCKET) or read(2) and
39 send(3SOCKET) or write(2) calls may be used.
40 UDP address formats are identical to those used by the Transmission
43 Control Protocol ("TCP"). Like TCP, UDP uses a port number along with
44 an IPor IPv6 address to identify the endpoint of communication. The UDP
45 port number space is separate from the TCP port number space, that is,
46 a UDP port may not be "connected" to a TCP port. The bind(3SOCKET) call
47 can be used to set the local address and port number of a UDP socket.
48 The local IP or IPv6 address may be left unspecified in the bind() call
49 by using the special value INADDR_ANY for IP, or the unspecified
50 address (all zeroes) for IPv6. If the bind() call is not done, a local
51 IP or IPv6 address and port number will be assigned to the endpoint
52 when the first packet is sent. Broadcast packets may be sent, assuming
53 the underlying network supports this, by using a reserved "broadcast
54 address" This address is network interface dependent. Broadcasts may
55 only be sent by the privileged user.
56 Note that no two UDP sockets can be bound to the same port unless the
59 bound IP addresses are different. IPv4 INADDR_ANY and IPv6 unspecified
60 addresses compare as equal to any IPv4 or IPv6 address. For example, if
61 a socket is bound to INADDR_ANY or unspecified address and port X, no
62 other socket can bind to port X, regardless of the binding address.
63 This special consideration of INADDR_ANY and unspecified address can be
64 changed using the SO_REUSEADDR socket option. If SO_REUSEADDR is set
65 on a socket doing a bind, IPv4 INADDR_ANY and IPv6 unspecified address
66 do not compare as equal to any IP address. This means that as long as
67 the two sockets are not both bound to INADDR_ANY/unspecified address or
68 the same IP address, the two sockets can be bound to the same port.
69 If an application does not want to allow another socket using the
72 SO_REUSEADDR option to bind to a port its socket is bound to, the
73 application can set the socket level option SO_EXCLBIND on a socket.
74 The option values of 0 and 1 represent enabling and disabling the
75 option, respectively. Once this option is enabled on a socket, no
76 other socket can be bound to the same port.
77 IPv6 does not support broadcast addresses; their function is supported
80 by IPv6 multicast addresses.
81 Options at the IP level may be used with UDP. See ip(7P) or ip6(7P).
84 Additionally, there is one UDP-level option of interest to IPsec Key
85 Management applications (see ipsec(7P)and pf_key(7P)):
86 UDP_NAT_T_ENDPOINT
88 If this boolean option is set, datagrams sent via this socket will
90 have a non-ESP marker inserted between the UDP header and the data.
91 Likewise, inbound packets that match the endpoint's local-port will
92 be demultiplexed between ESP or the endpoint itself if a non-ESP
93 marker is present. This option is only available on IPv4 sockets
94 (AF_INET), and the application must have sufficient privilege to
95 use PF_KEY sockets to also enable this option.
96 There are a variety of ways that a UDP packet can be lost or corrupted,
100 including a failure of the underlying communication mechanism. UDP
101 implements a checksum over the data portion of the packet. If the
102 checksum of a received packet is in error, the packet will be dropped
103 with no indication given to the user. A queue of received packets is
104 provided for each UDP socket. This queue has a limited capacity. Arriv‐
105 ing datagrams which will not fit within its high-water capacity are
106 silently discarded.
107 UDP processes Internet Control Message Protocol ("ICMP") and Internet
110 Control Message Protocol Version 6 ("ICMP6") error messages received in
111 response to UDP packets it has sent. See icmp(7P) and icmp6(7P).
112 ICMP "source quench" messages are ignored. ICMP "destination unreach‐
115 able," "time exceeded" and "parameter problem" messages disconnect the
116 socket from its peer so that subsequent attempts to send packets using
117 that socket will return an error. UDP will not guarantee that packets
118 are delivered in the order they were sent. As well, duplicate packets
119 may be generated in the communication process.
120 ICMP6 "destination unreachable" packets are ignored unless the enclosed
123 code indicates that the port is not in use on the target host, in which
124 case, the application is notified. ICMP6 "parameter problem" notifica‐
125 tions are similarly passed upstream. All other ICMP6 messages are
126 ignored.
127
129 read(2), write(2), bind(3SOCKET), connect(3SOCKET), recv(3SOCKET),
130 send(3SOCKET), icmp(7P), icmp6(7P), inet(7P), inet6(7P), ip(7P),
131 ipsec(7P), ip6(7P), pf_key(7P), tcp(7P)
132 Postel, Jon, RFC 768, User Datagram Protocol, Network Information Cen‐
135 ter, SRI International, Menlo Park, Calif., August 1980
136 Huttunen, A., Swander, B., Volpe, V., DiBurro, L., Stenberg, M., RFC
139 3948, UDP Encapsulation of IPsec ESP Packets, The Internet Society,
140 2005.
141
143 A socket operation may fail if:
144 EISCONN A connect() operation was attempted on a socket on
146 which a connect() operation had already been per‐
147 formed, and the socket could not be successfully dis‐
148 connected before making the new connection.
149 EISCONN A sendto() or sendmsg() operation specifying an
152 address to which the message should be sent was
153 attempted on a socket on which a connect() operation
154 had already been performed.
155 ENOTCONN A send() or write() operation, or a sendto() or
158 sendmsg() operation not specifying an address to which
159 the message should be sent, was attempted on a socket
160 on which a connect() operation had not already been
161 performed.
162 EADDRINUSE A bind() operation was attempted on a socket with a
165 network address/port pair that has already been bound
166 to another socket.
167 EADDRNOTAVAIL A bind() operation was attempted on a socket with a
170 network address for which no network interface exists.
171 EINVAL A sendmsg() operation with a non-NULL msg_accrights
174 was attempted.
175 EACCES A bind() operation was attempted with a "reserved"
178 port number and the effective user ID of the process
179 was not the privileged user.
180 ENOBUFS The system ran out of memory for internal data struc‐
183 tures.
184SunOS 5.11 4 July 2006 udp(7P)