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OpenDNS’s SmartCache is basically a DNS optimization feature which allows Open DNS nameservers to return the last known good IP address for a domain whose authoritative nameservers are currently not responding.

In order to get a bigger picture of why OpenDNS needs to contact the authoritative nameservers, you must read my earlier article titled What is a DNS and how does it work?.

In a real-world situation, An authoritative nameserver for a domain can be down or not responding for multiple reasons. Some prominent ones are

1.) Authoritative DNS nameserver has crashed and needs to be brought up again.

2.) Authoritative DNS nameserver is going through a Distributed DOS attack and that has caused it to crash.( Read: How a Distributed Denial of Service Attack on your DNS Server can bring down your Website)

3.) There are routing issues with the ISP which hosts the Authoritative DNS nameserver and therefore the server is currently not pingable.

When an authoritative DNS server is not reachable and the local nameserver doesnt have a fresh record of the domain in its cache, it serves a timeout or an error/no-response to the client and the website won’t load. So in reality, even though the webserver hosting the website is up and running fine, the website cannot be reached from the browser ( basically, because the DNS is not responding, the browser doesn’t know which IP address to connect to). OpenDNS’s Smartcache tries to get rid of this issue by handing out to the client, the last know good IP address instead of the error or no-response.

In order to setup OpenDNS SmartCache, follow the steps below ( i am assuming that you already have a OpenDNS account and have also added your network to it).

1.)  Log in to your OpenDNS account.

2.)  Go to the Settings tab.

3.)  Select the network you want to enable SmartCache for.

4.) Choose Advanced Settings.

5.) Select “Enable SmartCache on this Network” at the top.

Once you have followed the above steps, OpenDNS will return back the last known good-ip address to the client.

Also Read: [How-To] Block Specific Domains Using OpenDNS

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Related posts:

1. [How-To] Block Specific Domains Using OpenDNS
2. Google introduces Public DNS Resolver to help Speed up browsing
3. How does a DNS work?
4. [Security] How a Distributed Denial of Service Attack on your DNS Server can bring down your Website
5. Open DNS: A big DNS Cache