Connection to remote SQL server breaks when upgrading web server to .net framework 4.6.1

Question

We\'re currently working on updating our asp.net web application (hosted on IIS 7.5) from .net framework v4.5 to v4.6.1. On small lower environments/local development in which S

Answer 1

Update - so it looks like we've found (at the least the solution to) the problem. Turns out -- as the exception suggested -- that by increasing the connection timeout property on our connection string (default is 15 seconds, we set it to 60 seconds), we were able to make a connection to our database through our web app. However, opening this connection takes a prohibitively long time, so we started looking for solutions to make our connection open faster. We've discovered that we have Netbios over TCP/IP enabled on our database server, and that by opening up UDP ports (137, 138) on our network for Netbios access, we were able to open connections to the database way faster, timing at <1 second instead of >15 seconds. We're still not sure why the .net upgrade exposed this problem. By testing with a UDL file, we were able to establish that the network connectivity to our database performs about the same on our web servers on .net 4.5 as on our web servers on .net 4.6.1. So it seems as if our connections were opening so slowly that we were already very close to timing out, and some sort of extra logic/cruft in 4.6.1 put us over the edge. I'll update if we find more clarity on that.

Answer 2

First of all - this issue appears only when you're using Active Directory authentication.

I've managed dirty-fix: add your MSSQL server to your local (machine which can not connect to MSSQL server) hosts file (%windir%\system32\drivers\etc\hosts).

For example: 192.168.0.5 mssqlserver

It realy doesn't matter the name. It also works well if you have multiple SQL servers on one IP address (connecting through NAT).

This dirty-fix will also fix slow loading using SQL Management Studio issue.

Answer 3

The following article describes a new default connection string setting for SQL Server connections in .net 4.6.1.

https://blogs.msdn.microsoft.com/dataaccesstechnologies/2016/05/07/connection-timeout-issue-with-net-framework-4-6-1-transparentnetworkipresolution/

This was to solve one problem in some environments, but also caused the issue you are experiencing in other environments.

Basically, you'll want to add the following your connection string:

TransparentNetworkIPResolution=False;

Answer 4

you might want to check the machine.config and web.config files in the windows\micorsoft.net\framework64\v######\config folders. each version of .NET runs on different config files. Since the same code is used in both environments, it must be from the config inherited from here. I am guessing that the 4.6.1 is set to default the connection string to localhost and since the SQL in local and dev are on the same server it is not an issue. You will probably find that the config in the .NET 4.5 version has a connection string defined beyond localhost.

if 4.5 and 4.61 are using the same config files, then make sure you define a default connection string to be used by the entity framework in that web.config.