# nng_tcp(7) Manual Page

## NAME

nng_tcp - TCP/IP transport

## SYNOPSIS

    #include <nng/transport/tcp/tcp.h>

    int nng_tcp_register(void);

## DESCRIPTION

The tcp transport provides communication support between sockets across a TCP/IP network. Both IPv4 and IPv6 are supported when the underlying platform also supports it.

### Registration

This transport is generally built-in to the core of NNG, so no extra steps to use it should be necessary.

### URI Format

This transport uses URIs using the scheme `tcp://`, followed by an IP address or hostname, followed by a colon and finally a TCP port number. For example, to contact port 80 on the localhost either of the following URIs could be used: `tcp://127.0.0.1:80` or `tcp://localhost:80`.

A URI may be restricted to IPv6 using the scheme `tcp6://`, and may be restricted to IPv4 using the scheme `tcp4://`.

| Specifying `tcp6://` may not prevent IPv4 hosts from being used with IPv4-in-IPv6 addresses, particularly when using a wildcard hostname with listeners. The details of this varies across operating systems.

| Both `tcp6://` and `tcp4://` are specific to NNG, and might not be understood by other implementations.

| We recommend using either numeric IP addresses, or names that are specific to either IPv4 or IPv6 to prevent confusion and surprises.

When specifying IPv6 addresses, the address must be enclosed in square brackets (`[]`) to avoid confusion with the final colon separating the port.

For example, the same port 80 on the IPv6 loopback address (`::1`) would be specified as `tcp://[::1]:80`.

The special value of 0 (`INADDR_ANY`) can be used for a listener to indicate that it should listen on all interfaces on the host. A short-hand for this form is to either omit the address, or specify the asterisk (`*`) character. For example, the following three URIs are all equivalent, and could be used to listen to port 9999 on the host:

1. `tcp://0.0.0.0:9999`

2. `tcp://*:9999`

3. `tcp://:9999`

The entire URI must be less than `NNG_MAXADDRLEN` bytes long.

### Socket Address

When using an `nng_sockaddr` structure, the actual structure is either of type `nng_sockaddr_in` (for IPv4) or `nng_sockaddr_in6` (for IPv6).

### Transport Options

The following transport options are supported by this transport, where supported by the underlying platform.

- `NNG_OPT_LOCADDR`

- `NNG_OPT_REMADDR`

- `NNG_OPT_TCP_KEEPALIVE`

- `NNG_OPT_TCP_NODELAY`

- `NNG_OPT_URL`

## SEE ALSO

nng_options(5), nng_sockaddr(5), nng_sockaddr_in(5), nng_sockaddr_in6(5), nng_tcp_options(5), nng(7)