If you are using the proxy server (squid) or content filter (dansguardian) in non-transparent mode you may come across some sites that just do not work because of some weird chaining, authentication, or port manipulation. This howto can help address and resolve these issues. This can often be the case for instance with Sharepoint or Outlook Web Access (OWA).
The web proxy bypass section basically creates firewall rules that intercept listed items while they flow across the firewall and pipe them directly to the site. For transparent mode content filtration and proxy, this means that the packets are snatched before they are redirected to the proxy (3128) or the content filter (8080).
Since non-transparent use of the content filter or the proxy server requires setting the client to push web traffic to the server directly rather than across it, the firewall cannot grab any such packet and manipulate its flow. Moreover, web request packets and proxy web request packets look very different, so even if it could it wouldn't work.
The answer to this problem lies in using both the client that is specifically using the proxy and adding the exception there in addition to the web proxy bypass.
Configure the site you want bypassed in the web proxy bypass section of the the gateway. For servers running ClearOS as their gateway, this is done here: <navigation>Gateway » Proxy and Filtering » Web Proxy » Web Site Bypass</navigation>. If ClearOS is not your Firewall/Gateway, simply allow all clients on the local network to egress to that site.
In the Web Proxy Bypass, specify an name (no spaces or special characters, hyphens and underscores are ok). Add either the Domain Name, IP Address, or CIDR of the site. CIDR is recommended. Click 'Add'.
You can push this setting out to your Windows workstations using this registry setting example:
Windows Registry Editor Version 5.00 [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings] "ProxyOverride"="sharepoint.example.com;<local>"
Create a text file. Copy the code above and paste it into the text file. Save the changes. Rename the text file to something like 'webbypass.reg'. Double click to add to the local machine.
Click on <navigation>Start » Control Panel » Internet Options</navigation>.
Then find the Exemption list <navigation>Connections »LAN Settings…»Advanced</navigation>.
Navigate to the network settings. <navigation>Apple icon (upper left)»Show All»Internet & Wireless»Network</navigation>
Find the proxy settings <navigation>Advanced»Proxies»Bypass proxy settings for these Hosts & Domains</navigation>.