>>4243991 (lb, re:Internet Shutdown Precautions)
ITAnon here...when you're browsing the web, for every webpage you go to (ie, 8ch.net, pronhub.com, or God forbid, google.com), your computer first does a lookup at a publicly accessible DNS server (like google's 8.8.8.8, or L3's 4.4.4.2, but most likely their own ISP's DNS server that gets assigned automagically when their modem connects to the net). These DNS are like the phone books of the Internet. Just as with telephones, everything on the Internet communicates by numbers (IP addresses instead of phone numbers), but it's much easier to remember words than a series of seemingly unrelated numbers. At these DNS servers there are database entries from others' previous lookups, such as a cache for 8ch.net that resolves to 104.18.105.234 and this has a TTL value assigned to it which is specified by the DNS administrator for the 8ch.net domain. When they create the record, they say "hey, this record is good for ~(this TTL)~ many seconds (usually between 3600 and 86400, depending on the purpose of the server and what might be going on with maintenance schedules, migrations, etc...super boring shit that you would find no interest in, unless you're an ITFag), so when someone goes to 8ch.net, their computer looks up the IP for 8ch.net, the public DNS server gives them the address 104.18.105.234 and tells them that record is good for (TTL) many seconds. When that time expires, they need to do another lookup to make sure the IP address hasn't changed." Your computer then uses that IP to navigate the route across the interwebs to the destination server. I could explain that too, but I'd hate for you to die from excitement.
The point of this anon's post was that a way for them to "shutdown" the Internet would be to disable (somehow) DNS lookups, whether that be by a DDoS on as many public DNS servers as they could (highly unlikely because there are literally millions of them), or even through DNS protocol blocking at key(stone?) routers strategically located along the Internet backbone. Lay-people would essentially get cut off once the TTL value expired, but if you had a local cache of your frequently visited sites (ie, yoour own DNS server), you'd still be able to get around, although the pages you go to would probably look messed up because of all of the cross-site scripting and 3rd party advertising that wouldn't be able to communicate their own lookups.
They probably wouldn't shut Internet traffic down altogether, because that would affect interstate commerce, as well as their own communications, but by crippling the vast majority of end-users, they could effectively accomplish the same perceived thing.