Steps to resolve:
Whether the 1:sql server has been started.
2: Check whether the SQL Server server is turning on the TCP/IP protocol. The default port for listening is 1433
3:ping the database server. See if the network is accessible
4:telnet Server IP 1433, check whether the firewall causes the port to not pass
5: Whether the server allows remote connections
6: If the IP can ping, but the machine name Ping does not pass, then the host file needs to be changed.
7: If the database is connected using the ip+ port, then it can be connected at this time. However, if you use the server name \ Instance name and server name\instance name to connect, you will also need to check the following actions:
A: the SQL server Browser service is turned on by the server and client.
B: Firewall modification: Allow 1434 ports to use the UDP protocol through the firewall (the SQL Server Browser service uses the UDP protocol and the default 1434 port)
The database should now be able to connect. If the last step is not yet. Please leave a message below.
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SQL Server server name \ Instance name cannot connect to server name\instance name