Solved: Flushing the DNS cache - ipconfig /flushdns question

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tjamnz

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Jun 15, 2004
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Hello, I was wondering when to flush the DNS cache or why it may be necessary to do so?

I found documentation that states: XP remembers negative (DNS unable to resolve) entries for a few minutes, and that as long as a negative entry sits there, you will continue to get a cannot find server error.

The reason im asking... is becuase it is my understanding that as long as you type in (example) www.google.com... my pc will attempt to resolve that url to an ip address by contacting my isp's DNS server. And if my isp's dns server is down it wont be able to resolve the url, so therefore I wont have a cached ip address for google.com, nor will my pc be able to resolve until my isp's dsn servers are back online. hence... the "page cannot be found error"

At this point Im not sure what a "negative entry" might be, how a negative entry is created, and why i really would ever need to flush my dns cache anyways? (im assumming my browser will try to resolve this until its successful every time i type the url into my address bar and hit "enter")

I do realize that I can bypass dns if I directly type an ip address into my address bar, which i suppose could come in handy. I remember one ocassion when my comcast dns servers were down for a few hours... but i could surf by manually typing in ip's. I just happened to have a few written down at the time.

DNS is interesting.

thanks for any info on flushdns command
 
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Aug 25, 2006
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A negative entry in your DNS cache would actually not be the result of not being able to contact your DNS server. Rather it would be the result of your DNS server not being able to resolve your query and returning an negative result to your computer. For example if you were to send a query to your dns server for the host name "doesnotexist.nodomain.com" which didnt exist, then moments later you added an A record for that host to your zone. It is possible that you may still not be able to find it because your computer could be caching a negative result. It could be this situation where flushing your local dns cache might be usefull.
 

tjamnz

Thread Starter
Joined
Jun 15, 2004
Messages
775
This makes sense, but since when can a dns server in general not resove a query? And even if it cant, Its DNS job to find another DNS server that can resolve, if it doesnt know the answer. Must be a rare error indeed.

thanks
 
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