ListenAddress

ListenAddress is a configuration directive used by network servers to specify the network interface address on which the service should listen for incoming connections. It designates the binding address and, in some implementations, the listening port. Address values may be IPv4 addresses, IPv6 addresses, or hostnames that resolve to an address. A key use is to restrict a service to a limited network interface (for example, localhost only) or to expose it on multiple interfaces.

In software that supports it, ListenAddress can be repeated to bind to several addresses. If no ListenAddress is configured, the service will typically bind to all available interfaces on the default port. Some implementations allow specifying a port per ListenAddress, separate from the global Port setting.

In OpenSSH's sshd_config, ListenAddress can be used to specify the addresses the daemon should bind to. For example, ListenAddress 127.0.0.1 binds only to the loopback interface, while ListenAddress 0.0.0.0 binds to all IPv4 interfaces. An optional port can be provided as a second token after the address, e.g., ListenAddress 0.0.0.0 2222. The exact syntax and support may vary by software.

Security considerations include that binding to fewer addresses limits exposure, whereas binding to all interfaces may increase the service's surface unless other protections exist.

See also: Bind address, sshd_config, Listen directive.