Very slow connection to SQL Server 2005 only if using ADO.NET with SqlClient

Question

I have a brand new server with Windows 2008 Server 64 bit + SQL Server 2005 Standard Edition SP3.

When I try to open a connection to this server from a client in the same domain (Windows XP, .Net 3.5), it takes around 20 seconds to open the connection.

After opening the connection, everything is fast as usual.

When using a MDAC 2.8 connection, or ADO.NET OleDb, there is no problem at all.

How can I find the reason for the slow connection?

Answer 1

The problem was the firewall running on the server. I added an exception for port 1433 and the problem was gone.

Possible explanation: maybe when using OLEDB the connection tries Name Pipes first, bypassing the firewall rules.