4.2.5 Connection Transport Protocols

For programs that use the MySQL client library (for example, mysql and mysqldump), MySQL supports connections to the server based on several transport protocols: TCP/IP, Unix socket file, named pipe, and shared memory. This section describes how to select these protocols, and how they are similar and different.

• Transport Protocol Selection

• Transport Support for Local and Remote Connections

• Interpretation of localhost

• Encryption and Security Characteristics

• Connection Compression

Transport Protocol Selection

For a given connection, if the transport protocol is not specified explicitly, it is determined implicitly. For example, connections to localhost result in a socket file connection on Unix and Unix-like systems, and a TCP/IP connection to 127.0.0.1 otherwise. For additional information, see Section 4.2.4, “Connecting to the MySQL Server Using Command Options”.

To specify the protocol explicitly, use the --protocol command option. The following table shows the permissible values for --protocol and indicates the applicable platforms for each value. The values are not case-sensitive.

--protocol Value	Transport Protocol Used	Applicable Platforms
TCP	TCP/IP	All
SOCKET	Unix socket file	Unix and Unix-like systems
PIPE	Named pipe	Windows
MEMORY	Shared memory	Windows

Transport Support for Local and Remote Connections

TCP/IP transport supports connections to local or remote MySQL servers.

Socket-file, named-pipe, and shared-memory transports support connections only to local MySQL servers. (Named-pipe transport does allow for remote connections, but this capability is not implemented in MySQL.)

Interpretation of localhost

If the transport protocol is not specified explicitly, localhost is interpreted as follows:

• On Unix and Unix-like systems, a connection to localhost results in a socket-file connection.

• Otherwise, a connection to localhost results in a TCP/IP connection to 127.0.0.1.

If the transport protocol is specified explicitly, localhost is interpreted with respect to that protocol. For example, with --protocol=TCP, a connection to localhost results in a TCP/IP connection to 127.0.0.1 on all platforms.

Encryption and Security Characteristics

TCP/IP and socket-file transports are subject to TLS/SSL encryption, using the options described in Command Options for Encrypted Connections. Named-pipe and shared-memory transports are not subject to TLS/SSL encryption.

A connection is secure by default if made over a transport protocol that is secure by default. Otherwise, for protocols that are subject to TLS/SSL encryption, a connection may be made secure using encryption:

• TCP/IP connections are not secure by default, but can be encrypted to make them secure.

• Socket-file connections are secure by default. They can also be encrypted, but encrypting a socket-file connection makes it no more secure and increases CPU load.

• Named-pipe connections are not secure by default, and are not subject to encryption to make them secure. However, the named_pipe_full_access_group system variable is available to control which MySQL users are permitted to use named-pipe connections.

• Shared-memory connections are secure by default.

If the require_secure_transport system variable is enabled, the server permits only connections that use some form of secure transport. Per the preceding remarks, connections that use TCP/IP encrypted using TLS/SSL, a socket file, or shared memory are secure connections. TCP/IP connections not encrypted using TLS/SSL and named-pipe connections are not secure.

See also Configuring Encrypted Connections as Mandatory.

Connection Compression

All transport protocols are subject to use of compression on the traffic between the client and server. If both compression and encryption are used for a given connection, compression occurs before encryption. For more information, see Section 4.2.6, “Connection Compression Control”.