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About six months ago my vendor installed SQL Server 2008 R2 into a clustered pair of servers, DB01 and DB02.

I've been logging on, periodically, to DB01 to audit some of the data contained in the database instance.

I've been using SSMS the whole time, and for six months there have been no problems.

Suddenly yesterday, I am unable to connect using SSMS.

I get the following error:

Cannot connect to DB01.

Additional information:

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)(Microsoft SQL Server, Error: 53.)

This is very confusing, very little has changed since the last time I've logged in to SSMS.

TCP/IP is enabled on SQL Server, as are named pipes.

One thing I know has changed is that for the CLIENT machines that hit it, the TcpTimedWaitDelay parameter has been set to 30, and the MaxUserPort has been set to 10000.

But that's on the client machines only.

Could there be an issue arising from from these parameters not being mirrored on the database servers?

Could there be an issue arising from these two boxes sharing an IP for the clustering? The database is normally accessed through a shared IP, where DB02 takes the IP if DB01 fails.

I've considered restarting the SQL Server service but that scares the bejeezus out of me.

What if this issue spreads to the application currently using the databases?

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migrated from stackoverflow.com Jul 27 '13 at 13:26

This question came from our site for professional and enthusiast programmers.

    
TCP/IP connections yield this: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 0 - An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full.) (Microsoft SQL Server, Error: 10055) – Garrett Johnson Jul 23 '13 at 17:42
up vote 3 down vote accepted

As I posted in the comments, a couple of possibilities exist for that error, mainly lack of memory for additional TCP connections (generally in conjunction with 32-bit OSes), or lack of TCP ports. Both issues (and possible solutions) are outlined here on the SQL Protocols blog:

Understanding the error "An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full."

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