This is a comment on OpenDNS and other public DNS services, such as Google DNS.
First, DNS simply resolves the human-readable name of an Internet server, such as www.apple.com, to the numerical address by which that server can be reached. The process is analogous to looking up a phone number by name. There is
no chance that changing DNS servers will have any effect on a network problem not related to name resolution.
There are two valid reasons why you might want to use a public DNS service:
- The DNS servers provided by your ISP are misconfigured or don't perform well.
- You have a use for the filtering controls provided by OpenDNS and others.
Although some DNS services are often touted as being faster than others, there's no evidence that the claim is true in any meaningful sense. Most likely there is no noticeable difference in performance among the DNS servers available to you, and under some conditions public DNS will significantly
slow down network performance.
Content-distribution networks, such as the one used by Apple, rely on the location of the DNS server to optimize performance. If your query goes to a distant DNS server, you may get slow downloads of Apple content, among other things. This issue is more likely to affect you if you're outside the U.S.
Why using Google DNS / OpenDNS is a bad idea
ISP's do not intentionally redirect valid DNS queries, though it sometimes happens because of a misconfiguration. Your ISP may, and OpenDNS certainly will, redirect invalid queries to ad sites, in violation of published standards for DNS.
The claims on the OpenDNS website that it "blocks" malware attacks such as Flashback are false advertising. A name service does not and cannot block anything. All it can do is to selectively block queries. It's trivial for a malware attacker to evade such blocks. It's just as easy to evade the parental controls offered by OpenDNS. You may consider those filtering features useful, despite their limitations.
There is one exception to the rule that OpenDNS and Google DNS don't improve performance. The "prefetching" performed by modern web browsers, including Safari, may confuse some DNS servers, with the effects described in this Apple Support article:
Slow or partial webpage loading, or webpage cannot be found
The article suggests testing OpenDNS, Google DNS, or another third-party DNS service as a possible way to overcome the problem.
If you need to switch DNS providers because of a misconfiguration of your ISP's servers, the change will most likely only need to be temporary. The problem may be resolved automatically within a matter of hours.
If you intend to use public DNS on a long-term basis, you should be aware of the privacy implications. As a user of the free service, you are not an OpenDNS customer, and the company — a for-profit corporation — doesn't have a contract with you. The marketers to whom OpenDNS sells information are its customers.
OpenDNS will know, and store, the address of every Internet server you use from now on. This is from its
privacy policy:
When you use our Services, OpenDNS stores certain DNS, IP address and related information about you to improve the quality of our Service, to provide you with Services and for internal business and analysis purposes.
Concerning personal information, the policy states:
...[I]t is disclosed to entities that perform marketing services on our behalf or to other entities with whom we have joint marketing agreements...
You can't opt out of those disclosures. Read the privacy policy carefully and draw your own conclusions. The privacy policy of Google DNS seems to be somewhat more benign, but again, you should decide that for yourself.
Linked below is a brief. somewhat outdated, critique of OpenDNS on a Harvard Law School blog, with a response from the company's founder:
OpenDNS and Firefox Search
