I was helping a client to connect to a SQL instance on a server. This was a named instance, and we were getting an error: “…. sql network interface error 26…”. It took me a bit of time, but I finally realized that there was a typo in the long FQDN server name\ instance name combo. This is how I stumbled upon a method to discover all the SQL instances available on a SQL server.
As per Microsoft: “Every time client makes a connection to SQL Server named instance, we will send a SSRP UDP packet to the server machine UDP port 1434. We need this step to know configuration information of the SQL instance, e.g., protocols enabled, TCP port, pipe name etc. Without these information, client does know how to connect the server and it fails with this specified error message. ”
So, querying port 1434 on the server in question, will return info that is required for client connections. Info, such as all the SQL instances on the server. The free Microsoft tool for querying a port can be found at: PortQry Command Line Port Scanner Version 2.0.
General syntax (not for V2): portqry.exe -n servername -p UDP -e 1434
Provide only the server name without any instance names. Version 2 works differently, but as of this writing, the older version is also packed with the download. I am having issues querying a clustered server, so right now I am still experimenting with my new findings.