'\" t
.\"     Title: zmq_tcp
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 03/20/2024
.\"    Manual: 0MQ Manual
.\"    Source: 0MQ 4.3.5
.\"  Language: English
.\"
.TH "ZMQ_TCP" "7" "03/20/2024" "0MQ 4\&.3\&.5" "0MQ Manual"
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.SH "NAME"
zmq_tcp \- 0MQ unicast transport using TCP
.SH "SYNOPSIS"
.sp
TCP is an ubiquitous, reliable, unicast transport\&. When connecting distributed applications over a network with 0MQ, using the TCP transport will likely be your first choice\&.
.SH "ADDRESSING"
.sp
A 0MQ endpoint is a string consisting of a \fItransport\fR:// followed by an \fIaddress\fR\&. The \fItransport\fR specifies the underlying protocol to use\&. The \fIaddress\fR specifies the transport\-specific address to connect to\&.
.sp
For the TCP transport, the transport is tcp, and the meaning of the \fIaddress\fR part is defined below\&.
.SS "Assigning a local address to a socket"
.sp
When assigning a local address to a socket using \fIzmq_bind()\fR with the \fItcp\fR transport, the \fIendpoint\fR shall be interpreted as an \fIinterface\fR followed by a colon and the TCP port number to use\&.
.sp
An \fIinterface\fR may be specified by either of the following:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The wild\-card
*, meaning all available interfaces\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The primary IPv4 or IPv6 address assigned to the interface, in its numeric representation\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The non\-portable interface name as defined by the operating system\&.
.RE
.sp
The TCP port number may be specified by:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
A numeric value, usually above 1024 on POSIX systems\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The wild\-card
*, meaning a system\-assigned ephemeral port\&.
.RE
.sp
When using ephemeral ports, the caller should retrieve the actual assigned port using the ZMQ_LAST_ENDPOINT socket option\&. See \fBzmq_getsockopt\fR(3) for details\&.
.SS "Unbinding wild\-card address from a socket"
.sp
When wild\-card * \fIendpoint\fR was used in \fIzmq_bind()\fR, the caller should use real \fIendpoint\fR obtained from the ZMQ_LAST_ENDPOINT socket option to unbind this \fIendpoint\fR from a socket using \fIzmq_unbind()\fR\&.
.SS "Connecting a socket"
.sp
When connecting a socket to a peer address using \fIzmq_connect()\fR with the \fItcp\fR transport, the \fIendpoint\fR shall be interpreted as a \fIpeer address\fR followed by a colon and the TCP port number to use\&. You can optionally specify a \fIsource_endpoint\fR which will be used as the source address for your connection; tcp://\fIsource_endpoint\fR;\*(Aqendpoint\*(Aq, see the \fIinterface\fR description above for details\&.
.sp
A \fIpeer address\fR may be specified by either of the following:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The DNS name of the peer\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The IPv4 or IPv6 address of the peer, in its numeric representation\&.
.RE
.sp
Note: A description of the ZeroMQ Message Transport Protocol (ZMTP) which is used by the TCP transport can be found at \m[blue]\fBhttp://rfc\&.zeromq\&.org/spec:23\fR\m[]
.SH "HWM"
.sp
For the TCP transport, the high water mark (HWM) mechanism works in conjunction with the TCP socket buffers handled at OS level\&. Depending on the OS and several other factors the size of such TCP buffers will be different\&. Moreover TCP buffers provided by the OS will accommodate a varying number of messages depending on the size of messages (unlike ZMQ HWM settings the TCP socket buffers are measured in bytes and not messages)\&.
.sp
This may result in apparently inexplicable behaviors: e\&.g\&., you may expect that setting ZMQ_SNDHWM to 100 on a socket using TCP transport will have the effect of blocking the transmission of the 101\-th message if the receiver is slow\&. This is very unlikely when using TCP transport since OS TCP buffers will typically provide enough buffering to allow you sending much more than 100 messages\&.
.sp
Of course if the receiver is slow, transmitting on a TCP ZMQ socket will eventually trigger the "mute state" of the socket; simply don\(cqt rely on the exact HWM value\&.
.sp
Obviously the same considerations apply for the receive HWM (see ZMQ_RCVHWM)\&.
.SH "EXAMPLES"
.PP
\fBAssigning a local address to a socket\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
//  TCP port 5555 on all available interfaces
rc = zmq_bind(socket, "tcp://*:5555");
assert (rc == 0);
//  TCP port 5555 on the local loop\-back interface on all platforms
rc = zmq_bind(socket, "tcp://127\&.0\&.0\&.1:5555");
assert (rc == 0);
//  TCP port 5555 on the first Ethernet network interface on Linux
rc = zmq_bind(socket, "tcp://eth0:5555");
assert (rc == 0);
.fi
.if n \{\
.RE
.\}
.PP
\fBConnecting a socket\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
//  Connecting using an IP address
rc = zmq_connect(socket, "tcp://192\&.168\&.1\&.1:5555");
assert (rc == 0);
//  Connecting using a DNS name
rc = zmq_connect(socket, "tcp://server1:5555");
assert (rc == 0);
//  Connecting using a DNS name and bind to eth1
rc = zmq_connect(socket, "tcp://eth1:0;server1:5555");
assert (rc == 0);
//  Connecting using a IP address and bind to an IP address
rc = zmq_connect(socket, "tcp://192\&.168\&.1\&.17:5555;192\&.168\&.1\&.1:5555");
assert (rc == 0);
.fi
.if n \{\
.RE
.\}
.sp
.SH "SEE ALSO"
.sp
\fBzmq_bind\fR(3) \fBzmq_connect\fR(3) \fBzmq_pgm\fR(7) \fBzmq_ipc\fR(7) \fBzmq_inproc\fR(7) \fBzmq_vmci\fR(7) \fBzmq\fR(7)
.SH "AUTHORS"
.sp
This page was written by the 0MQ community\&. To make a change please read the 0MQ Contribution Policy at \m[blue]\fBhttp://www\&.zeromq\&.org/docs:contributing\fR\m[]\&.