Why doesn't OpenDNS allow keyword blocking?

[georgekolasa1]

If I want to block reddit.com/r/gaming via OpenDNS, then I have to block all of reddit.com

Why isn't there an option to block by keyword? (i.e. any site that has the word "gaming" in it) 

Is there some technical limitation behind this?

[rotblitz]

Because a keyword "gaming" wouldn't catch reddit.com/r/gaming in DNS.  The domain name system (DNS) doesn't know anything about URLs, "sites" or any other objects except domain names.  So a DNS service like OpenDNS just sees the domain name reddit.com with the DNS query, because you don't send any other or more information to them.

So, it's not a technical limitation, but simply how DNS works.  Here is a simplified flow:

1. Your browser raises a DNS query for www.reddit.com to obtain its IP address(es).  Else it cannot connect.
2. OpenDNS responds with the IP address information for www.reddit.com
3. Your browser is now able to establish a connection to www.reddit.com and requests to read https://www.reddit.com/r/gaming - OpenDNS is out of scope here because already over.