# DNS Server Question



## SPS-1 (Oct 21, 2008)

I am running Windows 7 and using Cogeco cable. I was unable to reach a particular web-site last nite. This has happened before. When I ran the Windows diagnostics, it came back with "your DNS server may be unavailable". My attempt to ping the web-site seemed to show good status. My system was set to "Obtain DNS server automatically". I changed that to use Cogeco's DNS server as primary, and Googles DNS server as alternate. I re-booted my computer, and then I was able to reach the web site. But I really don't understand what is going on here. If I check off "obtain DNS server automatically", what DNS server is it using ? Should a computer normally be set to "obtain automatically", or to specified DNS server ?


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## hyunelan2 (Aug 14, 2007)

Automatic vs. specified depends on what you want. Typically automatic will be assigned to you by the DHCP server (your ISP) to use their DNS. If the server they tell you to use is not working, you will have some issues. Another time you could want to use a specified DNS, is like your Google example. You may choose to use a better/faster/more-available server than what your ISP would typically assign. Here's another example of when you might specify. Comcast. I have Comcast business class internet for work uses. There are a different set of DNS servers used by that than what DNS servers are specified for Comcast home use. I can set my DNS at home to use the Comcast Business DNS servers, which are less busy than the home DNS servers. Though, now I use Google DNS for just about everything (8.8.8.8 and 8.8.4.4).


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## Ironlight (Apr 13, 2011)

SPS-1 said:


> I was unable to reach a particular web-site last nite. This has happened before.


In a nutshell, if this has happened before then your provider's DNS service is unreliable. You're perfectly fine setting your own choice of DNS server. Using your provider's _may _offer advantages in terms of speed (it's right there on your network) but if it's not performing well by all means change it permanently.


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## SPS-1 (Oct 21, 2008)

Thanks. I think I understand it better now. 8.8.8.8 is the DNS server I have as alternate.


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## pyper (Jul 1, 2009)

In addition to what others have said, at work I have a firewall set up, and one of the functions it performs is DNS cache. So all the PCs on our network are specified to look to the firewall for DNS. It keeps a cache of frequently used numbers, so it can speed things up.

Thanks for the tip about Google, I think I might set the firewall to look there. That's a nice advantage of the firewall -- only one place to make a change. It's called ipcop -- it's an opensource linux product that runs on an old PC.


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## diyorpay (Sep 21, 2010)

I listen to Steve Gibson and Leo Laporte on Security Now podcast.

Steve provides this interesting tool:

http://www.grc.com/dns/benchmark.htm


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