| 1 | .\" Copyright (c) 1983, 1991 The Regents of the University of California. |
| 2 | .\" All rights reserved. |
| 3 | .\" |
| 4 | .\" Redistribution and use in source and binary forms, with or without |
| 5 | .\" modification, are permitted provided that the following conditions |
| 6 | .\" are met: |
| 7 | .\" 1. Redistributions of source code must retain the above copyright |
| 8 | .\" notice, this list of conditions and the following disclaimer. |
| 9 | .\" 2. Redistributions in binary form must reproduce the above copyright |
| 10 | .\" notice, this list of conditions and the following disclaimer in the |
| 11 | .\" documentation and/or other materials provided with the distribution. |
| 12 | .\" 3. All advertising materials mentioning features or use of this software |
| 13 | .\" must display the following acknowledgement: |
| 14 | .\" This product includes software developed by the University of |
| 15 | .\" California, Berkeley and its contributors. |
| 16 | .\" 4. Neither the name of the University nor the names of its contributors |
| 17 | .\" may be used to endorse or promote products derived from this software |
| 18 | .\" without specific prior written permission. |
| 19 | .\" |
| 20 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND |
| 21 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| 22 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| 23 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE |
| 24 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
| 25 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
| 26 | .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| 27 | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| 28 | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
| 29 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| 30 | .\" SUCH DAMAGE. |
| 31 | .\" |
| 32 | .\" @(#)tcp.4 6.5 (Berkeley) 3/28/91 |
| 33 | .\" |
| 34 | .Dd March 28, 1991 |
| 35 | .Dt TCP 4 |
| 36 | .Os BSD 4.2 |
| 37 | .Sh NAME |
| 38 | .Nm tcp |
| 39 | .Nd Internet Transmission Control Protocol |
| 40 | .Sh SYNOPSIS |
| 41 | .Fd #include <sys/socket.h> |
| 42 | .Fd #include <netinet/in.h> |
| 43 | .Ft int |
| 44 | .Fn socket AF_INET SOCK_STREAM 0 |
| 45 | .Sh DESCRIPTION |
| 46 | The |
| 47 | .Tn TCP |
| 48 | protocol provides reliable, flow-controlled, two-way |
| 49 | transmission of data. It is a byte-stream protocol used to |
| 50 | support the |
| 51 | .Dv SOCK_STREAM |
| 52 | abstraction. TCP uses the standard |
| 53 | Internet address format and, in addition, provides a per-host |
| 54 | collection of |
| 55 | .Dq port addresses . |
| 56 | Thus, each address is composed |
| 57 | of an Internet address specifying the host and network, with |
| 58 | a specific |
| 59 | .Tn TCP |
| 60 | port on the host identifying the peer entity. |
| 61 | .Pp |
| 62 | Sockets utilizing the tcp protocol are either |
| 63 | .Dq active |
| 64 | or |
| 65 | .Dq passive . |
| 66 | Active sockets initiate connections to passive |
| 67 | sockets. By default |
| 68 | .Tn TCP |
| 69 | sockets are created active; to create a |
| 70 | passive socket the |
| 71 | .Xr listen 2 |
| 72 | system call must be used |
| 73 | after binding the socket with the |
| 74 | .Xr bind 2 |
| 75 | system call. Only |
| 76 | passive sockets may use the |
| 77 | .Xr accept 2 |
| 78 | call to accept incoming connections. Only active sockets may |
| 79 | use the |
| 80 | .Xr connect 2 |
| 81 | call to initiate connections. |
| 82 | .Pp |
| 83 | Passive sockets may |
| 84 | .Dq underspecify |
| 85 | their location to match |
| 86 | incoming connection requests from multiple networks. This |
| 87 | technique, termed |
| 88 | .Dq wildcard addressing , |
| 89 | allows a single |
| 90 | server to provide service to clients on multiple networks. |
| 91 | To create a socket which listens on all networks, the Internet |
| 92 | address |
| 93 | .Dv INADDR_ANY |
| 94 | must be bound. The |
| 95 | .Tn TCP |
| 96 | port may still be specified |
| 97 | at this time; if the port is not specified the system will assign one. |
| 98 | Once a connection has been established the socket's address is |
| 99 | fixed by the peer entity's location. The address assigned the |
| 100 | socket is the address associated with the network interface |
| 101 | through which packets are being transmitted and received. Normally |
| 102 | this address corresponds to the peer entity's network. |
| 103 | .Pp |
| 104 | .Tn TCP |
| 105 | supports one socket option which is set with |
| 106 | .Xr setsockopt 2 |
| 107 | and tested with |
| 108 | .Xr getsockopt 2 . |
| 109 | Under most circumstances, |
| 110 | .Tn TCP |
| 111 | sends data when it is presented; |
| 112 | when outstanding data has not yet been acknowledged, it gathers |
| 113 | small amounts of output to be sent in a single packet once |
| 114 | an acknowledgement is received. |
| 115 | For a small number of clients, such as window systems |
| 116 | that send a stream of mouse events which receive no replies, |
| 117 | this packetization may cause significant delays. |
| 118 | Therefore, |
| 119 | .Tn TCP |
| 120 | provides a boolean option, |
| 121 | .Dv TCP_NODELAY |
| 122 | (from |
| 123 | .Aq Pa netinet/tcp.h , |
| 124 | to defeat this algorithm. |
| 125 | The option level for the |
| 126 | .Xr setsockopt |
| 127 | call is the protocol number for |
| 128 | .Tn TCP , |
| 129 | available from |
| 130 | .Xr getprotobyname 3 . |
| 131 | .Pp |
| 132 | Options at the |
| 133 | .Tn IP |
| 134 | transport level may be used with |
| 135 | .Tn TCP ; |
| 136 | see |
| 137 | .Xr ip 4 . |
| 138 | Incoming connection requests that are source-routed are noted, |
| 139 | and the reverse source route is used in responding. |
| 140 | .Sh DIAGNOSTICS |
| 141 | A socket operation may fail with one of the following errors returned: |
| 142 | .Bl -tag -width [EADDRNOTAVAIL] |
| 143 | .It Bq Er EISCONN |
| 144 | when trying to establish a connection on a socket which |
| 145 | already has one; |
| 146 | .It Bq Er ENOBUFS |
| 147 | when the system runs out of memory for |
| 148 | an internal data structure; |
| 149 | .It Bq Er ETIMEDOUT |
| 150 | when a connection was dropped |
| 151 | due to excessive retransmissions; |
| 152 | .It Bq Er ECONNRESET |
| 153 | when the remote peer |
| 154 | forces the connection to be closed; |
| 155 | .It Bq Er ECONNREFUSED |
| 156 | when the remote |
| 157 | peer actively refuses connection establishment (usually because |
| 158 | no process is listening to the port); |
| 159 | .It Bq Er EADDRINUSE |
| 160 | when an attempt |
| 161 | is made to create a socket with a port which has already been |
| 162 | allocated; |
| 163 | .It Bq Er EADDRNOTAVAIL |
| 164 | when an attempt is made to create a |
| 165 | socket with a network address for which no network interface |
| 166 | exists. |
| 167 | .El |
| 168 | .Sh SEE ALSO |
| 169 | .Xr getsockopt 2 , |
| 170 | .Xr socket 2 , |
| 171 | .Xr intro 4 , |
| 172 | .Xr inet 4 , |
| 173 | .Xr ip 4 |
| 174 | .Sh HISTORY |
| 175 | The |
| 176 | .Nm |
| 177 | protocol stack appeared in |
| 178 | .Bx 4.2 . |