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Name:Alex Dybenko

Location:Moscow, Russia

Thursday, May 22, 2008

Why SQL Server drops connection

Some days ago my client asked me why 2 workstations loosing connection every 30 minutes. Only restart of PC (!) helps to run application again! First guess was that something wrong with network for these PCs, but no, network was ok. Finally he noticed that DNS settings are different, both DNS servers are the same, one - local server and other – external, but in other order. Don’t know which one exactly caused this problem, but certainly this is not a good configuration, I would better leave only one, local server, as DNS server, and let it decide how to deal with external DNS requests.

Anyway – another option is to run Cliconfg and create an alias to SQL Server using TCP/IP library and its IP address, this always works fine for me.

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Anonymous Anonymous said...

As a network infrastructure person, I can tell you that it is not good practice to have an external DNS in Local clients TCP/IP configuration.

The reason for this is that, if for what ever reason the internal DNS Server is not available, or alternatively, just busy, then Windows will fall to the next DNS Server.

What this means is that when you look up COMPANYSERVER it will no longer append a .local (or what ever your internal FQDN is) to the lookup, instead, it will append a or a .com to the lookup request, and suddenly you are trying to connect to external machines

Windows doesn't then fall back to the initial DNS Server until the first one fails a request.

DNS Should be configured with forwarders, (if required in your network) and the client machines should only have internal DNS Servers to manage requests.

If you want a redundant DNS server, then create a new Internal DNS Server.

Hope this explains why this was happening.

Anthony Moore

1:30 AM  
Blogger Alex Dybenko said...

Thanks for explanation, Anthony!

6:51 AM  

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