Common TCP/IP problems

Unable to map service name

Cause: The specified service name is not defined in your /etc/services file.

Unable to resolve host name

Cause: The specified host name is not defined.

Connection Refused

Cause: No one is listening at the target address. This indicates that the server program is not running on the specified host system or it is using a different port number.

Fix: Check that client and server use the same port number or start the server program.

Address already in use

Cause: The port number the server program wants to use is already in use. Either the server is already active, another server is using the same port number (caused by bad service name/port number mapping) or there are still sockets stuck in TIME_WAIT state.

Fix: Check the port number the server program wants to use. If there are sockets in TIME_WAIT state (probably caused by a crashed server process) you need to terminate all client processes and wait for a minute until the operating system releases the port. You can use netstat to check for used sockets.