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I have an (allegedly) 15mbps cable connection from Comcast with a pretty standard setup - cable modem plugged in to Netgear router, which serves one PC via an ethernet cable and several laptops via wireless.

The problem is that, on the desktop only (running Vista), DNS frequently fails. It will work fine for half an hour or so, and then I'll start getting DNS lookup errors, even on sites I've been actively browsing - but not all sites at once, some still work. If I run a command shell as an admin and run ipconfig /flushdns then everything starts working fine again for another period of time. But it is extremely annoying.

All the settings, on both the PC and the router, have "Automatically acquire DNS Server address from ISP" set. And it seems to work fine on all the other computers on the network.

Very puzzled. Any help would be appreciated, I just don't know networking that well.

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migrated from Jul 20 '09 at 16:40

This question came from our site for system and network administrators.

up vote 4 down vote accepted

I can't tell you what your EXACT problem is but I can tell you that I've had this very same problem with Comcast DNS in the past. Everything works fine one minute then suddently poof... only about half the stuff resolves.

In the end I just got tired of Comcast's DNS and changed all of our workstations to use OpenDNS instead:

The IP addresses are:

This will probably fix your problem. It did for us!

Good luck!

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But it will create many other problems: for instance, OpenDNS name servers lie, they rewrite "No such domain" answers to the IP address of an advertisment Web site, they block some domains, they sell data about your queries, etc. – bortzmeyer Jul 21 '09 at 9:51

Just an idea: You could start ipconfig /all in the command line and see if your provider offered you several DNS server IP addresses which are used round robin by your operating system.

If you see more than one DNS server IPs try to resolve e.g. with each of those IPs like this nslookup <DNSSERVERIP> and check if there is a problem with one of the DNS servers. If you find a broken DNS server, report it to your provider (and temporarily disable "Automatically acquire DNS Server address from ISP" by configuring the working servers manually).

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Can you connect Internet connection to some other host other than the Vista machine giving problem? If things work fine with other machine (say laptop) then it is problem with Vista. Then you can try re-installation or if Vista supports some kind of repair.

Since ipconfig /flushdns command is working. It is most likely a local problem. A DNS server problem should not get solved by flushing DNS at end host.

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When I had a provider with a bad DNS server, annoying things would happen like: lookup an address. It fails. Try again, it works. The server also seemed to have a variable length of time to respond to the same query. That made me think the entire service offering was pointing to a non-load balanced IP, or that the subnet was congested and losing packets.

My observation is that the very large providers have a tendency to neglect DNS servers. The reason is pretty obvious, when you have a large number of less sophisticated end users, they are not going to accurately detect and describe problems with the DNS server. Most of them do not know what DNS server is. Then you call tech support, and you find out they do not know what a DNS server is either!

I have noticed that the more specialized providers actually answer the phone, and fix DNS problems.

If you are getting broadband on a very large provider (cable or phone company), you should configure your own caching DNS server, especially if you have never done it. Consider it a learning opportunity :) Or if you actually want a network that works without filling in the infrastructure gaps, get off the big vendor.

There is a lot of DNS caching these days, in the OS and many applications. It insulates ISPs from a lot of there intermitent problems. But nothing will work more consistently and robustly than an actually DNS server.

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