The mechanism by which one would would block a URL requires protocol level filtering - this is nothing at all to do with DNS or IP routing. That you mention DNS and routing in your question makes me think that you are a bit out of your depth here.
Without a grasp of the technologies, you are more likely to make your network less secure by adding stuff to it than improving it's security. I would strongly recommend you spend some time learning about basic network technologies.
There are lots of products available off the shelf to do URL filtering (e.g. dansguardian, websense) but for these to be of any use your network needs to be configured to force all traffic which might be subject to a filtering policy though it - and that means you need to know how to configure stuff like firewalls, DHCP, port translation, HTTP proxies and/or browser configuration scripts, even before considering the complications of SSL. There are multiple ways to achieve this funneling - if you ask a more specific question the you may get a more specific answer.