What are you trying to block? Are you hoping that the router is smart enough to block certain types of sites with a filter (family filter or porn filter or similar), or are you trying to block specific sites that you know and that you specifically enter into the router? Why are you trying to block the sites and from whom are you trying to prevent them from loading? If it is for Windows based computers, it could be done via the Hosts file - just set the particular sites to resolve to localhost 127.0.0.1