Connection listeners allow connections to a database server using a specific network protocol, address, or port.
A connection listener listens on a particular address for connection attempts from specified network protocols. The database server can have listeners for shared memory, HTTP, HTTPS, and TCP/IP. All connection listeners except for shared memory listen on an IP address and a specific port. When you start a database server, use the -x or -xs database server option to tell the database server which type of connection attempts or web requests to listen for.
If the IP addresses change on the computer where the database server is running, then the database server responds by automatically starting or stopping connection listeners as necessary. For example, if a database server is running on a laptop and the laptop then connects to a new wireless network, the database server detects the change and starts a connection listener on the new IP address. Or, if the laptop disconnects from a network, then the database server detects the disconnection and shuts down the appropriate connection listeners.
Connection listeners can also be manually started and stopped without stopping and restarting the database server by running the sp_start_listener and sp_stop_listener system procedures, or by using the Listeners tab for the database server in SQL Central.