Sunday, August 24, 2014

DNS - The Internet's Phone Book

My earlier post about filtering Internet content for kids bringing home their school iPads may have created more questions than answers for some parents. The big confusion seems to step from what a Domain Name System (DNS) server is, and how it helps filter out objectionable content.

Let's go waaaaay back in time, back to the birth of the initial global network called ARPANET. Back in the day - and even now - you could reach a remote computer by using its numeric address. To connect to a remote computer, your machine may connect to "" and send along some pretty data. Those numeric addresses could be a pain to remember however - so shortcuts were created that mapped a human-recognizable name (like "BubbaComp") to the numeric address (like ""). Solutions were eventually engineered that let people share these lists... that way everyone could have this helpful list of shortcuts. This convention kept evolving as users continued to join the global network, up to today. Now when you type in "" your computer is smart enough to look up this shortcut name and find out the numeric address is Your computer always talks to, however you talk to your browser using

This operates just like a phone book. No one remembers people's phone numbers anymore... or at least I don't. Instead you look up a person's name in your personal address book or the big dead-tree phone book on your front stoop, then communicate using the phone number in the book. Connecting to sites over the Internet works in the very same way.

What if you didn't want your kids visiting certain sites? You could employ the same trick as you might to stop them from calling certain people over the phone - edit the phone book. If your kids can't look up a person's name and find their phone number, they can't call the person. If you edit the Internet's phone book and remove objectionable sites, your kids can't visit the objectionable site on their device of choice. That's exactly what OpenDNS allows you to do - use a phone book that only has acceptable web sites within it.

What if a kid memorizes a phone number tho? Your plan falls apart a bit in that case. DNS filtering has the same limitation - if your kids memorize the IP address of a site (or share an underground DNS server), then they can go directly to the site and bypass your sanctioned "phone book."

If your kids go to a site that has a wide variety of content (like YouTube), you can't filter out specific types of content within the site. Just like calling a party line on the phone... if you allow access to the party line, you can't control anything past the initial dial.

Hopefully that helps explain why OpenDNS is only your first line of filtering. Lemme know in the comments if I can clarify further!

Saturday, August 23, 2014

Web Filtering at Home

[Updated to include an OpenDNS how-to]

Now that iPads are standard issue for a lot of schools, a few parents have asked me how they can block inappropriate material at home. While the schools themselves filter at the network level, as soon as the student comes home the network is wide open.

In all honesty, you can't filter out 100% of all objectionable content. It's hard to have software determine if a YouTube stream is showing questionable video. However, you can audit, track and block some obviously adult sites. The traditional options to perform web filtering include:
  • Software applications or parental controls on the device itself
  • Filtering devices on the router or wireless access point
  • External Internet services that block DNS requests

Software applications give you the most control on a per-device level and can block errant applications as well (like anti-virus software), however you have to install them on each and every device. They also have the benefit of blocking things no matter what network they are attached to. They usually require a medium-level effort to circumvent, and it is sometimes hard to get a report on what the actual activity has been or if any sites had to be blocked.

Filtering devices provide filtering for the entire network and do not rely on software to be installed on the device, which is nice. This solution is the hardest to circumvent, so long as you properly lock down your wireless access point. This solution cares less about applications however, and can’t really tell how appropriate actual content on a site is. It also only controls those devices on your network, and often doesn’t have fine-grained controls.

External Internet services filter your entire network, just like a filtering device would, however it is hosted out on the Internet rather than being something installed or managed inside your house. This option often doesn’t give you much (if any) per-device controls, however they often do a great job of letting you pick what and how many sites to filter out. These solutions often provide reporting as well, letting you see what was viewed by devices on the network. This solution also can’t tell you about the actual content on the site, but just the URL that was visited. This solution is the easiest to circumvent, although this can be mitigated by locking users out of the administrative settings of a device (e.g. not letting users change network settings on an iPad).

What I chose for the house was an external Internet service via OpenDNS. This was easy to set up since I just had to create an account and make a few minor tweaks to our wireless access point, and it gives me some nice reporting on what was blocked. For example, lately I saw a lot of adult sites being blocked and found an iOS application was loading them in the background.

OpenDNS has a Getting Started Guide on their site, but here's an abbreviated version of the steps for setting up OpenDNS on your home network:
  1. First, load up the settings console for your wireless router. Check your user guide for how to do this - usually it involves loading up a web page at and entering a username and password.
  2. Next, find the "Internet" or "WAN" settings page within your wireless router. This is in your router's user guide as well. It may look something like:
  3. Change the DNS Servers from the automatic settings to the values "" and ""
  4. Click on "Apply" or "Save" or whatever floats your router's boat.
  5. Create a new account at
  6. Part of your account creation process will be linking your local network to your OpenDNS account. Once your local network joins OpenDNS, it will begin monitoring what sites are requested.
  7. After you create your account, you will be taken to the OpenDNS dashboard. At that point you can decide how much filtering you want to apply to your network - from sites that are obviously adult-only to sites that are adult in theme (fashion magazines, for example).

I'll post a subsequent entry on what OpenDNS actually does in hopes of helping explain why this kind of filtering is useful and its limitations. While this might seem like rocket surgery at first, hopefully this helps you learn how to be a steward of your Internet connection... just like you have to monitor & maintain your sump pump before the basement floods.