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$ ipconfig /all
DNS Servers . . . . . . . . . . . . : a.b.c.d

Why do I have two DNS servers listed? Is it something like try second in case first fails?

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up vote 10 down vote accepted

Yep, exactly correct, redundancy.

Most big DNS providers always give two addresses in the event that one fails.

Google - Configure your network settings to use the IP addresses and as your DNS servers or

OpenDNS - and

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+1 - In Windows the terminology is "Primary DNS" and "Backup DNS" – JNK Sep 10 '10 at 14:37
I like the public verizon DNS too, and – JNK Sep 10 '10 at 14:37
@JNK +1, also as a side note, on Windows, if you click the advanced button then the DNS tab, you can have a lot more than two! (I am sure you will be able to do this in other operating systems as well!) – William Hilsum Sep 10 '10 at 14:38
@JNK: 4.2.2.[1-5], and isn't it owned by Level3? – grawity Sep 10 '10 at 19:43
@grawity - it may be now, when I used it before it was a verizon public. – JNK Sep 10 '10 at 19:58

Google has a program that they have released that will run speed tests on all of the most popular DNS servers including your ISP's.

This maybe be of some use to you if you wish to tweak your DNS settings.

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