We have MSSQL 2008 R2 running on windows 2008 r2 it's being hit by 2 server 2008 r2 webservers running asp.net. Both are joined to an active directory domain and use integrated authentication to connect to sql server. The IIS Application pool has the username/password setup on it. This has been working flawlessly for the last year or so.

We recently wanted to spin up new webservers and I configured a new Windows 2012 R2 running the exact same website and configured IIS Application pool with the same username/password. The site connects and works great when I'm doing my testing. But as soon as I bring any real load onto the server I see IIS start to hang and request start piling up.

I took a memory dump and used the new DebugDiag 2.0 analysis on it and saw that the requests were hanging on opening a sql connection:

This thread is trying to open a data base connection

The connection String is Data Source=;Failover Partner=;Initial Catalog=XXXX;Integrated Security=True;Max Pool Size=6000;Connect Timeout=30;Network Library=dbmssocn;Application Name=EntityFrameworkMUE and the connection timeout is set to be 30 seconds.

Within the analysis I see quite a few exceptions:

Connection Timeout Expired. The timeout period elapsed while attempting to consume the pre-login handshake acknowledgement. This could be because the pre-login handshake failed or the server was unable to respond back in time. This failure occured while attempting to connect to the Principle server. The duration spent while attempting to connect to this server was - [Pre-Login] initialization=3342; handshake=0;

Any ideas on what to try?

2 Answers 2


We ended up solving the issue in our environment by removing Integrated Security, and went with specifying user id and password in the connection string. Never did find the root cause.



It's quite possible that TCP/IP is enabled for the IPv4 address of the SQL server but not the IPv6 and your new servers are attempting to speak IPv6.

Try enabling IPv6 on the SQL server.

In SQL Server Config Manager

  • Open the node SQL Server Network Configuration
  • Click Protocols for MYSQLINSTANCE
  • On the right side, right click TCP/IP
  • Click Properties
  • Select the IP Addresses tab
  • For each listed IP address, ensure Active and Enabled are both Yes.

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