I appreciate answers to help me troubleshot remote connection issue after DNS and DCHP server down I got today.
I have 2 instances on a same server. I open 1433 and 1435 for SQL connection throuth firewall. I also open 1434 for UDP through firewall. I configure TCP and Named Pipes enabled. Before today, remote computers could connect to both instances by IP and instance name.
Today DNS and DCHP server down for a while. After DNS and DCHP server up again, remote computers can only connect both instance by IP. SSMS and ODBC can find instance names, but cannot logon. I got SQL Server error 6.Thanks in advance.
I would suggest disabling named pipes on whatever client you are using for testing but only becuase I think the TCP connection is easier to understand / troubleshoot. I would run open a comment prompt on your test client and run ipconfig /flushdns
first, followed by nslookup <name of server>
Name of server should NOT include the instance name, the nslookup should respond with the IP address of the server. If it does then try the SQL connection again. If nslookup fails then DNS is still not working, in this case I'd start by checking the eventlogs on the DNS server. If nslookup works then there is someother issue with SQL Server. (Try a reboot?)