Correct port identification in a network host connection

The invention creates a registry database 101, 102 of services and the numbers of the ports that the service listener is associated with. The registry may include the protocol used by the service and additional information (such as URI, URL). Users may explicitly query the database 105 with service/protocol information 106. Alternatively if the user attempts to connect to an incorrect port using the wrong protocol or similar 103, information can be extracted 104 and used to query the registry. The query information is used to search the registry 107 and return an error 109, reply suggesting the correct port to use for a service 110 or automatically connect to the correct port for the service 111. The disclosure includes an example application to IBMs (rtm) Customer Information Control System (CICS (rtm)).