ZMQ_TCP(7) 0MQ Manual ZMQ_TCP(7)
NAME
zmq_tcp - 0MQ unicast transport using TCP
SYNOPSIS
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.
ADDRESSING
A 0MQ endpoint is a string consisting of a transport:// followed by an
address. The transport specifies the underlying protocol to use. The
address specifies the transport-specific address to connect to.
For the TCP transport, the transport is tcp, and the meaning of the
address part is defined below.
Assigning a local address to a socket
When assigning a local address to a socket using zmq_bind() with the
tcp transport, the endpoint shall be interpreted as an interface
followed by a colon and the TCP port number to use.
An interface may be specified by either of the following:
• The wild-card *, meaning all available interfaces.
• The primary IPv4 or IPv6 address assigned to the interface, in its
numeric representation.
• The non-portable interface name as defined by the operating system.
The TCP port number may be specified by:
• A numeric value, usually above 1024 on POSIX systems.
• The wild-card *, meaning a system-assigned ephemeral port.
When using ephemeral ports, the caller should retrieve the actual
assigned port using the ZMQ_LAST_ENDPOINT socket option. See
zmq_getsockopt(3) for details.
Unbinding wild-card address from a socket
When wild-card * endpoint was used in zmq_bind(), the caller should use
real endpoint obtained from the ZMQ_LAST_ENDPOINT socket option to
unbind this endpoint from a socket using zmq_unbind().
Connecting a socket
When connecting a socket to a peer address using zmq_connect() with the
tcp transport, the endpoint shall be interpreted as a peer address
followed by a colon and the TCP port number to use. You can optionally
specify a source_endpoint which will be used as the source address for
your connection; tcp://source_endpoint;'endpoint', see the interface
description above for details.
A peer address may be specified by either of the following:
• The DNS name of the peer.
• The IPv4 or IPv6 address of the peer, in its numeric
representation.
Note: A description of the ZeroMQ Message Transport Protocol (ZMTP)
which is used by the TCP transport can be found at
http://rfc.zeromq.org/spec:15
HWM
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 accomodate 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).
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.
Of course if the receiver is slow, transmitting on a TCP ZMQ socket
will eventually trigger the "mute state" of the socket; simply don’t
rely on the exact HWM value.
Obviously the same considerations apply for the receive HWM (see
ZMQ_RCVHWM).
EXAMPLES
Assigning a local address to a socket.
// 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);
Connecting a socket.
// 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);
SEE ALSO
zmq_bind(3) zmq_connect(3) zmq_pgm(7) zmq_ipc(7) zmq_inproc(7)
zmq_vmci(7) zmq(7)
AUTHORS
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read the 0MQ Contribution Policy at
http://www.zeromq.org/docs:contributing.
0MQ 4.3.4 01/18/2023 ZMQ_TCP(7)
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