Validating with login server
If you are connecting using a SQL Server alias created in the local client, then the protocol specified in the alias will only be used. Connecitivity flow when using TCP/IP Protocol While making connections using TCP/IP protocol, the client driver will check whether the instance is DEFAULT instance (MSSQLSERVER is the instance name for default instance) and if yes, the connection is made directly to port 1433 using TCP protocol to the target SQL Server Instance.
If this works then it could be a firewall blocking connections from passive node and other clients.It will be a good step to stop Firewall service and give it a try.If you are interested in adding Exception to firewall, add exception for Port 1434-UDP for SQL Browser and Port xxxx-TCP for SQL Server.There are other things like authentication and authorization to complete a login successfully. Authentication: It means that the username and password you specified in the connection is valid.If you are using Windows authentication and SQL Server server running with any of two mode "Mixed Mode" or "Windows-only" authentication, SQL Server will request Local Security Authority Subsystem Service (LSASS) to verify the credentials of the specified user.