What is the meaning of the different network error messages?
If the error occurs at the SAPGUI, you should always select "Show detailed error messages" to get more information.
Error messages can be divided into two groups:
1. Errors during connection establishment
Partner not reached - Connection refused
"Connection refused" means that the target host was reached but no process accepted the network request on the respective target port. Target host and port are typically displayed as "<hostname>:<port>".
This error can be caused by the usage of the wrong TCP-port (sometimes presented only by the instance number, e.g. "00") or the fact that the target server process was simply not running at that time. In rare error situations the target server process can also somehow be blocked completely for some long time and therefore was unable to accept the network request.
Check your client connection parameter configuration and check if your target server process is running and listening to the specified port.
Partner not reached - Connection timed out
The target host could not be reached within a given span of time. Possible reasons for this might be that the IP address of the target server does not exist, the target server host is currently not running or the client could not reach the server due to a missing route or a blocking firewall between them. Check your network and your target servers availability.
Hostname unknown - <host name> not found
This error is generated if the operating system was not able to resolve the target host name into an IP address. Check the host name resolution on the source host.
Service unknown - <service name> not found
This error is generated if the operating system was not able to resolve the target service name into a TCP-port number. Check the service name resolution on the source host.
2. Errors after the connection was established
If this error message occurs without any additional error information (see below) it just means that the remote host has closed the connection unexpectedly. This is not necessarily an error.
Connection broken - Connection reset by peer
This error is generated by the operating system if the connection was interrupted by an incoming TCP packet with the flag bit "RST" set.
This error can be caused by a crash of the remote program or if the remote program closed the connection without reading all data from the network connection.
It can also be caused by a genuine "network error" like a physically interrupted connection, a faulty network device or a firewall.
On Microsoft Windows this error can have two different meanings (see "Connection broken - Connection timed out").
Check the partner program for crashes or unexpected termination.
Connection broken - Connection timed out
On Microsoft Windows this error is shown as "Connection reset by peer".
This error is thrown if at least one network packet was sent to the target host but not acknowledged in time. It occurs dependent on the operating system and connection speed after 1-20 minutes.
This error can be caused by a physical network error, a firewall idle timeout or a "black hole router".
More detailed information can be found in SAP note 155147.
Check for your network between the client and the server.