DNS Web Filter Troubleshooting: Bark for Schools

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Paola
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This article discusses frequent troubleshooting solutions specific to the DNS web filter. If you are troubleshooting the Chrome web filtering extension or Chrome web monitoring extension, refer to this guide instead.

Domain Exceptions

When adding exceptions for particular domains or categories in your Bark DNS web filter policies, you can expect to see the changes reflected in your network/computers within a few minutes.

Clearing your Cache

If you are encountering issues with content filtering, such as blocking not working according to your policy, we ask that you first clear both your system cache and browser cache. Instructions to do this are below:

Browser Cache

Google Chrome (Windows and Mac):

  1. In a new tab, type the following into the address bar and hit enter:
    chrome://net-internals/#dns
  2. Click the button labeled clear host cache.

Firefox:

  1. Type about:config in Firefox’s address bar and acknowledge the warning that appears
  2. Find an entry called network.dnsCacheExpiration and set it’s value to 0
    (If there’s no such entry, create a new integer item with the name above and a value of 0)
  3. Now go back and change the value to 3600

Safari (Windows and Mac):

  1. Resetting the DNS Cache in Windows and Mac automatically flushes the DNS cache on Safari. Nothing to do here!

Operating System Cache

Windows 7

  1. Press ⊞ Win + X
  2. Right-click Command Prompt and select Run as Administrator.
  3. Run the following command and hit enter:
    ipconfig /flushdns

Mac OSX 10.9 and Later:

  1. Launch the Terminal application
  2. Run the following command and hit enter:
    sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

Mac OSX 10.8 and Earlier:

  1. Launch Terminal (under Applications/Utilities)
  2. Run the following command and hit enter:
    sudo killall -HUP mDNSResponder

Linux (Ubuntu)

  1. Open a terminal window.
  2. Run the following command and hit enter:
    sudo service network-manager restart

 

Advanced Troubleshooting - Transparent DNS Proxy

Before testing for a suspected transparent DNS proxy as the reason for not experiencing content filtering, refer to "Clearing Your Cache" above, which is the reason for most false alarms when content filtering does not appear to be working.

When the Bark DNS web filter is properly analyzing web traffic, you should see the requests on the DNS web filter reports on the super admin's Bark dashboard, as seen below:

If you're seeing 0 requests, verify that there's no caching issue, that your public IP matches the one entered into the DNS filter setup, and that you've correctly pointed your gateway's settings to Bark's provided IP addresses.

If still no luck, let's see if a transparent proxy could be the culprit.

What is it?

A transparent DNS proxy is the practice of intercepting DNS requests destined for a specific recursive DNS server (like Bark's DNS Filter), and sending the DNS requests to a completely different DNS server.

 

Who is typically proxied?

  • Most "hardwired" ISPs (cable, DSL, fiber) in North America and Europe are not using transparent DNS proxies.
  • Satellite ISPs and Telecom providers (3G/4G/LTE) are commonly using transparent DNS proxies for performance reasons.

 

How do I identify if I have a transparent DNS proxy?

After you are sure that your settings are correct in the Bark DNS filter policies and your network is correctly pointing to our Bark IPs, visit DNS Leak Test or Whoismydns in your web browser.

If the domain names correspond to your Internet Service Provider, your requests are being proxied by your ISP.

If the requests correspond to some other address (like 8.8.8.8) then is is likely that you have a firewall/security appliance on your network that has a legacy firewall rule that you will need to change.

 

How do I reach the Bark for Schools team?

We have an incredible team behind the scenes here at Bark. For technical questions, we can be reached here. Our team is happy to help!