OpenDNS
OpenDNS is an alternative DNS service.
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DNS in Linux
Your ISP (usually) provides working DNS servers, and a router may also add an extra DNS server in case you have your own cache server. Switching between DNS servers does not represent a problem for Windows users, because if a DNS server is slow or does not work it will immediately switch to a better one. However, Linux usually takes longer to timeout, which could be the reason why you are getting a delay.
Use dig (provided by package dnsutils) before any changes, repeat after making the adjustments in the section below and compare the query time(s):
$ dig www5.yahoo.com
You can also specify a nameserver:
$ dig @ip.of.name.server www5.yahoo.com
Using OpenDNS
Edit /etc/resolv.conf and add the OpenDNS nameservers to the top of the file so they are used first, optionally removing already listed servers in order to only use OpenDNS:
# OpenDNS nameservers nameserver 208.67.222.222 nameserver 208.67.220.220
Several network management applications, such as wicd, have an option for a third DNS server. You should not duplicate one of the first two OpenDNS nameservers as it will resort back to 0.0.0.0. OpenDNS has two servers which can be used for this third option:
208.67.222.220 208.67.220.222
Protect /etc/resolv.conf
See Resolv.conf#Preserve_DNS_settings for how to preserve your settings in resolv.conf.
dhclient
If you use dhclient, you will need to add to (or create) to /etc/dhclient.conf:
prepend domain-name-servers 127.0.0.1;
Pdnsd
See Pdnsd#OpenDNS.
Fixing problems with Google
OpenDNS hijacks Google-searches by routing all queries through their own servers first. This can be annoying because Google searches may slow down noticeably and it also breaks Google's FeelingLucky feature (e.g., entering digg in your adress bar will open www.digg.com). For the latter, there is a Firefox-addon that brings back the original behaviour. A more elegant solution is to redirect all queries for Google exclusively to your ISP's DNS Server. This can be done with dnsmasq (see Speeding up DNS with dnsmasq for more information).