As I've shown you in "Hack DNS for lightning-fast Web browsing," there are a number of way you can hack Domain Name System to speed up the way you browse the Web.
DNS, though, can be your foe as well as your friend. DNS problems may stop you from being able to visit Web sites. If you're having problems connecting, it doesn't take much work to see if DNS is the cause, and if it is, to try to fix it.
To find out whether DNS is a potential culprit when you're having trouble connecting to a site, first ping the site to which you can't connect by issuing the ping command at the command prompt, like this:
If the site is live, you'll get an answer like this (Note: text below has line breaks inserted to fit into the Web page display):
Pinging www.computerworld.com [22.214.171.124] with 32 bytes of data: Reply from 126.96.36.199: bytes=32 time=22ms TTL=235 Reply from 188.8.131.52: bytes=32 time=23ms TTL=235 Reply from 184.108.40.206: bytes=32 time=23ms TTL=235 Reply from 220.127.116.11: bytes=32 time=24ms TTL=235 Ping statistics for 18.104.22.168: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 22ms, Maximum = 24ms, Average = 23ms</pre>
If it's not, you'll get a response like this:
Ping request could not find host. Please check the name and try again.</pre>
If you ping a site and it's live but you can't connect to it with your browser, a DNS problem might be the reason. If you suspect you're having a DNS problem, take the following actions:
Check your HOSTS file
If your HOSTS file contains an incorrect or outdated listing, you won't be able to connect. Even if you don't recall adding listings to a HOSTS file, it still might contain listings, because some Internet accelerator utilities edit them without telling you. Open your HOSTS file with Notepad and see if the site you can't connect to is listed there. If it is, delete the entry, and you should be able to connect.
For details about editing a HOSTS file, see "Hack DNS for lightning-fast Web browsing."
Check your DNS settings
Make sure your DNS settings are correct for your ISP or network. If you've changed your DNS settings to use a service such as OpenDNS, for example, you might have entered them incorrectly.
Find out from your ISP or network administrator what your DNS settings are supposed to be, or check the OpenDNS site (or another DNS service) for their server settings. Once you've done that, you'll need to make sure that you've entered the DNS settings properly.
Check the article "Hack DNS for lightning-fast Web browsing" for details about how to change your DNS settings. Then change the DNS servers to the proper ones, or choose "Obtain DNS server address automatically" if your ISP or network administrator tells you to use that setting.
Flush your DNS cache
The problem might be related to your DNS cache, so flush it out. To flush the cache, type ipconfig /flushdns at a command prompt.
Find out if your ISP is having DNS problems
Your ISP could be the source of the problem. One possibility is that one of its DNS servers is down and you're trying to access the downed server. If you know the addresses of the DNS servers, ping each of your ISP's DNS servers, and if any of them don't respond, remove them from your DNS list.
If you don't know the address of the DNS servers and you're supposed to use the choose "Obtain DNS server address automatically" setting, you'll have to call your ISP to see whether its DNS servers are having problems. Alternately, you can use the OpenDNS servers instead of your ISP's DNS servers. For details, see "Hack DNS for lightning-fast Web browsing."
Preston Gralla is a contributing editor for Computerworld and the author of more than 35 books, including Windows Vista in a Nutshell.