Unable to connect SSMS, Microsoft SQL Server, Error: 53

Question

SQL Server Management Studio is not connecting on my database server machine at production server.

Whereas production sites accessing database. When I tried to connect database from SSMS, I get this error:

Cannot connect to 111.11.11.11.

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 53)

I was using this SSMS last couple of years,n this SSMS is running fine since more then year on production database server ni didn't closed ever, now when i connecting this SSMS but facing this issue, whereas my sites which accessing this database is working fine.

I also tried to access database from sqlcmd but no luck n facing facing this error:

HResult 0x35, Level 16, State 1
Named Pipes Provider: Could not open a connection to SQL Server [53].
Sqlcmd: Error: Microsoft SQL Server Native Client 10.0 : A network-related or instance-specific error has occurred while establishing a connection to SQL Server.
Server is not found or not accessible. Check if instance name is correct and if SQL Server is configured to allow remote connections. For more information see SQL Server Books Online..

Answer 1

I thinks we resolved the issues. 1. Active Directory server was not behaving, so 2. SQL server couldn't run without credentials and 3. they found another SQL server issue and fixed it.

We started looking into the SQL connections that my team had found and it lead us to find that the Active Directory server had basically crashed. It was allowing us to log in however it wasn't able to access the majority of the AD functionality. We ended up rebooting the AD server which corrected the issue however we were still seeing issues with the SQL cluster manager and SQL itself was rejecting connections on a somewhat regular basis.

After the AD server was rebooted we were able to log into the SQL cluster manager but with limited capabilities, since it had been erroring due to the AD issue we restarted the cluster service to see if this would correct the issue. This caused the SQL service to fail over to the passive server and caused SQL to start rejecting even more connections than it had been. The cluster service started working with this restart however the SQL connections were getting worse. We found that the IPv6 protocol was enabled for the SQL service which causes problems, like the ones we were seeing, in SQL clusters, to disable this we had to reboot the 2 SQL servers. We rebooted them one at a time and once they were back up everything was working properly.