Overview

In a multi-server environment, one slave server has a permanently red icon and the message: "Unable to connect to the node", although the synchronization between the servers seems to work. Disconnecting and reconnecting the server only resolves the issue temporarily as after a while the error manifests again.

Root Cause

The Multinode.Transfers.log shows the following error:

2020-10-08,16:24:42,020,1,"#0000AC5C","#00000004","error ","Multinode.Transfers","Error: Call to slave Failed. Error Message: Could not connect to net.tcp://<server>:9096/Configuration. The connection attempt lasted for a time span of 00:00:00. TCP error code 10060: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond <IP address>:9096."

This indicates that there is a communication issue between the servers, caused by an environmental factor.

Solution

Since this is an environmental issue, the only solution is to ensure clear communication between the servers.

GFI MailEssentials is using ports 9095 and 9096 to synchronize the servers. Try to telnet between the servers on ports 9095 and 9096 by running the commands below in a Command Prompt opened as Administrator:

telnet <server IP> 9095
telnet <server IP> 9096

1. In case of a successful connection, a blank screen will show up, meaning that the computer port is open:
   
   
2. A failed connection will be accompanied by an error message. It can indicate either a closed port or the fact that the indicated remote server is not listening on the provided port:
   

If this communication cannot be established, make sure that there are no firewall rules or any external applications that may be blocking ports 9095 and 9096 on both servers.