You're starting to get into homework territory. Id recommend actually learning what youre doing before pressing forward before you get into oopsies-this-net-admin-isn't-an-idiot-and-reaches-for-his-phone-to-dial-the-local-FBI-office-territory.
If it's a wifi network as seems implied, you'd deauth them by send deauth packets. Aircrack does this just fine and guides abound if you google enough. Will say sending deauth packets to mac address you intend to use has amusing results(amusing for me, not for you trying it) so I highly do not recommend it.
For the filter, couldve been a timed thing, temporary, or maybe you were just plain wrong about why you couldn't connect. As for hacking the dns server, depends on what the goal is by hack. As in different attacks net you different types of access with different degrees of success. If this is a wifi network I will say from experience that at least half of the wifi routers ive come across has had a webserver with either http basic auth or a simple web portal(okay like all of them, but half vulnerable to what im describing next). The basic auth tend to give you some hint about the model of the wifi router and a web portal tends to outright state it, and its simple from there to look up a default username and password for the device. Most prevalent ive seen is good ole admin:admin, especially on linksys routers. This will let you in the admin page and reconfigure the wifi router. Most of the time at least. Other times you're mostly SOL unless you know the ISP that provisioned the device. I've yet to come across a leased wifi router that did not have a maintence backdoor for telnet/ssh, but finding the username and password tends to be slightly more involved than a simple google search(though once you got one, you know itll be good for like ever, pwned out of the box).
and proxx what can I say, I seem to have been in a generous mood lately.
