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5. Communication between browsers and Squid

Most web browsers available today support proxying and are easily configured to use a Squid server as a proxy. Some browsers support advanced features such as lists of domains or URL patterns that shouldn't be fetched through the proxy, or JavaScript automatic proxy configuration.

5.1 Netscape manual configuration

Select Network Preferences from the Options menu. On the Proxies page, click the radio button next to Manual Proxy Configuration and then click on the View button. For each protocol that your Squid server supports (by default, HTTP, FTP, and gopher) enter the Squid server's hostname or IP address and put the HTTP port number for the Squid server (by default, 3128) in the Port column. For any protocols that your Squid does not support, leave the fields blank.

Here is a screen shot of the Netscape Navigator manual proxy configuration screen.

5.2 Netscape automatic configuration

Netscape Navigator's proxy configuration can be automated with JavaScript (for Navigator versions 2.0 or higher). Select Network Preferences from the Options menu. On the Proxies page, click the radio button next to Automatic Proxy Configuration and then fill in the URL for your JavaScript proxy configuration file in the text box. The box is too small, but the text will scroll to the right as you go.

Here is a screen shot of the Netscape Navigator automatic proxy configuration screen.

You may also wish to consult Netscape's documentation for the Navigator JavaScript proxy configuration

Here is a sample auto configuration JavaScript from Oskar Pearson:

//We ( run a central cache for our customers that they
//access through a firewall - thus if they want to connect to their intranet
//system (or anything in their domain at all) they have to connect
//directly - hence all the "fiddling" to see if they are trying to connect
//to their local domain.

//Replace each occurrence of with your domain name
//and if you have some kind of intranet system, make sure
//that you put it's name in place of "internal" below.

//We also assume that your cache is called "", and
//that it runs on port 8080. Change it down at the bottom.

//(C) Oskar Pearson and the Internet Solution (

    function FindProxyForURL(url, host)
            //If they have only specified a hostname, go directly.
            if (isPlainHostName(host))
                    return "DIRECT";

            //These connect directly if the machine they are trying to
            //connect to starts with "intranet" - ie http://intranet
            //Connect  directly if it is intranet.*
            //If you have another machine that you want them to
            //access directly, replace "internal*" with that
            //machine's name
            if (shExpMatch( host, "intranet*")||
                            shExpMatch(host, "internal*"))
                return "DIRECT";

            //Connect directly to our domains (NB for Important News)
            if (dnsDomainIs( host,"")||
            //If you have another domain that you wish to connect to
            //directly, put it in here
                return "DIRECT";

            //So the error message "no such host" will appear through the
            //normal Netscape box - less support queries :)
            if (!isResolvable(host))
                    return "DIRECT";

            //We only cache http, ftp and gopher
            if (url.substring(0, 5) == "http:" ||
                            url.substring(0, 4) == "ftp:"||
                            url.substring(0, 7) == "gopher:")

            //Change the ":8080" to the port that your cache
            //runs on, and "" to the machine that
            //you run the cache on
                    return "PROXY; DIRECT";

            //We don't cache WAIS
            if (url.substring(0, 5) == "wais:")
                    return "DIRECT";

                    return "DIRECT";

5.3 Lynx and Mosaic configuration

For Mosaic and Lynx, you can set environment variables before starting the application. For example (assuming csh or tcsh):

        % setenv http_proxy
        % setenv gopher_proxy
        % setenv ftp_proxy

For Lynx you can also edit the lynx.cfg file to configure proxy usage. This has the added benefit of causing all Lynx users on a system to access the proxy without making environment variable changes for each user. For example:


5.4 Redundant Proxy Auto-Configuration

There's one nasty side-effect to using auto-proxy scripts: if you start the web browser it will try and load the auto-proxy-script.

If your script isn't available either because the web server hosting the script is down or your workstation can't reach the web server (e.g. because you're working off-line with your notebook and just want to read a previously saved HTML-file) you'll get different errors depending on the browser you use.

The Netscape browser will just return an error after a timeout (after that it tries to find the site '' if the script you use is called 'proxy.pac').

The Microsoft Internet Explorer on the other hand won't even start, no window displays, only after about 1 minute it'll display a window asking you to go on with/without proxy configuration.

The point is that your workstations always need to locate the proxy-script. I created some extra redundancy by hosting the script on two web servers (actually Apache web servers on the proxy servers themselves) and adding the following records to my primary nameserver:

        proxy   CNAME           proxy1
                CNAME           proxy2
The clients just refer to 'http://proxy/proxy.pac'. This script looks like this:

function FindProxyForURL(url,host)
        // Hostname without domainname or host within our own domain?
        // Try them directly:
        // actually lives before the firewall, so
        // make an exception:
        if ((isPlainHostName(host)||dnsDomainIs( host,"")) &&
                !localHostOrDomainIs(host, ""))
                return "DIRECT";

        // First try proxy1 then proxy2. One server mostly caches '.com'
        // to make sure both servers are not
        // caching the same data in the normal situation. The other
        // server caches the other domains normally.
        // If one of 'm is down the client will try the other server.
        else if (shExpMatch(host, "*.com"))
                return "PROXY; PROXY; DIRECT";
        return "PROXY; PROXY; DIRECT";

I made sure every client domain has the appropriate 'proxy' entry. The clients are automatically configured with two nameservers using DHCP.

-- Rodney van den Oever

5.5 Proxy Auto-Configuration with URL Hashing

The Sharp Super Proxy Script page contains a lot of good information about hash-based proxy auto-configuration scripts. With these you can distribute the load between a number of caching proxies.

5.6 Microsoft Internet Explorer configuration

Select Options from the View menu. Click on the Connection tab. Tick the Connect through Proxy Server option and hit the Proxy Settings button. For each protocol that your Squid server supports (by default, HTTP, FTP, and gopher) enter the Squid server's hostname or IP address and put the HTTP port number for the Squid server (by default, 3128) in the Port column. For any protocols that your Squid does not support, leave the fields blank.

Here is a screen shot of the Internet Explorer proxy configuration screen.

Microsoft is also starting to support Netscape-style JavaScript automated proxy configuration. As of now, only MSIE version 3.0a for Windows 3.1 and Windows NT 3.51 supports this feature (i.e., as of version 3.01 build 1225 for Windows 95 and NT 4.0, the feature was not included).

If you have a version of MSIE that does have this feature, elect Options from the View menu. Click on the Advanced tab. In the lower left-hand corner, click on the Automatic Configuration button. Fill in the URL for your JavaScript file in the dialog box it presents you. Then exit MSIE and restart it for the changes to take effect. MSIE will reload the JavaScript file every time it starts.

5.7 Netmanage Internet Chameleon WebSurfer configuration

Netmanage WebSurfer supports manual proxy configuration and exclusion lists for hosts or domains that should not be fetched via proxy (this information is current as of WebSurfer 5.0). Select Preferences from the Settings menu. Click on the Proxies tab. Select the Use Proxy options for HTTP, FTP, and gopher. For each protocol that enter the Squid server's hostname or IP address and put the HTTP port number for the Squid server (by default, 3128) in the Port boxes. For any protocols that your Squid does not support, leave the fields blank.

Take a look at this screen shot if the instructions confused you.

On the same configuration window, you'll find a button to bring up the exclusion list dialog box, which will let you enter some hosts or domains that you don't want fetched via proxy. It should be self-explanatory, but you might look at this screen shot just for fun anyway.

5.8 Opera 2.12 proxy configuration

Select Proxy Servers... from the Preferences menu. Check each protocol that your Squid server supports (by default, HTTP, FTP, and Gopher) and enter the Squid server's address as hostname:port (e.g. or Click on Okay to accept the setup.


-- Hume Smith

5.9 How do I tell Squid to use a specific username for FTP urls?

Insert your username in the host part of the URL, for example:
Squid should then prompt you for your account password. Alternatively, you can specify both your username and password in the URL itself:
However, we certainly do not recommend this, as it could be very easy for someone to see or grab your password.

5.10 Configuring Browsers for WPAD

by Mark Reynolds

You may like to start by reading the Expired Internet-Draft that describes WPAD.

After reading the 8 steps below, if you don't understand any of the terms or methods mentioned, you probably shouldn't be doing this. Implementing wpad requires you to fully understand:

  1. web server installations and modifications.
  2. squid proxy server (or others) installation etc.
  3. Domain Name System maintenance etc.
Please don't bombard the squid list with web server or dns questions. See your system administrator, or do some more research on those topics.

This is not a recommendation for any product or version. As far as I know IE5 is the only browser out now implementing wpad. I think wpad is an excellent feature that will return several hours of life per month. Hopefully, all browser clients will implement it as well. But it will take years for all the older browsers to fade away though.

I have only focused on the domain name method, to the exclusion of the DHCP method. I think the dns method might be easier for most people. I don't currently, and may never, fully understand wpad and IE5, but this method worked for me. It may work for you.

But if you'd rather just have a go ...

  1. Create a standard netscape auto proxy config file. The sample provided there is more than adequate to get you going. No doubt all the other load balancing and backup scripts will be fine also.
  2. Store the resultant file in the document root directory of a handy web server as wpad.dat (Not proxy.pac as you may have previously done.)

    Andrei Ivanov notes that you should be able to use an HTTP redirect if you want to store the wpad.dat file somewhere else. You can probably even redirect wpad.dat to proxy.pac:

    Redirect /wpad.dat

  3. If you do nothing more, a url like should bring up the script text in your browser window.
  4. Insert the following entry into your web server mime.types file. Maybe in addition to your pac file type, if you've done this before.
            application/x-ns-proxy-autoconfig       dat
    And then restart your web server, for new mime type to work.
  5. Assuming Internet Explorer 5, under Tools, Internet Options, Connections, Settings or Lan Settings, set ONLY Use Automatic Configuration Script to be the URL for where your new wpad.dat file can be found. i.e. Test that that all works as per your script and network. There's no point continuing until this works ...
  6. Create/install/implement a DNS record so that resolves to the host above where you have a functioning auto config script running. You should now be able to use as the Auto Config Script location in step 5 above.
  7. And finally, go back to the setup screen detailed in 5 above, and choose nothing but the Automatically Detect Settings option, turning everything else off. Best to restart IE5, as you normally do with any Microsoft product... And it should all work. Did for me anyway.
  8. One final question might be 'Which domain name does the client (IE5) use for the wpad... lookup?' It uses the hostname from the control panel setting. It starts the search by adding the hostname "WPAD" to current fully-qualified domain name. For instance, a client in would search for a WPAD server at If it could not locate one, it would remove the bottom-most domain and try again; for instance, it would try next. IE 5 would stop searching when it found a WPAD server or reached the third-level domain,

Anybody using these steps to install and test, please feel free to make notes, corrections or additions for improvements, and post back to the squid list...

There are probably many more tricks and tips which hopefully will be detailed here in the future. Things like wpad.dat files being served from the proxy server themselves, maybe with a round robin dns setup for the WPAD host.

5.11 Configuring Browsers for WPAD with DHCP

You can also use DHCP to configure browsers for WPAD. This technique allows you to set any URL as the PAC URL. For ISC DHCPD, enter a line like this in your dhcpd.conf file:

        option wpad code 252 = text;
        option wpad "";

Replace the hostname with the name or address of your own server.

Ilja Pavkovic notes that the DHCP mode does not work reliably with every version of Internet Explorer. The DNS name method to find wpad.dat is more reliable.

Another user adds that IE 6.01 seems to strip the last character from the URL. By adding a trailing newline, he is able to make it work with both IE 5.0 and 6.0:<

        option wpad "\n";

5.12 IE 5.0x crops trailing slashes from FTP URL's

by Reuben Farrelly

There was a bug in the 5.0x releases of Internet Explorer in which IE cropped any trailing slash off an FTP URL. The URL showed up correctly in the browser's ``Address:'' field, however squid logs show that the trailing slash was being taken off.

An example of where this impacted squid if you had a setup where squid would go direct for FTP directory listings but forward a request to a parent for FTP file transfers. This was useful if your upstream proxy was an older version of Squid or another vendors software which displayed directory listings with broken icons and you wanted your own local version of squid to generate proper FTP directory listings instead. The workaround for this is to add a double slash to any directory listing in which the slash was important, or else upgrade to IE 5.5. (Or use Netscape)

5.13 IE 6.0 SP1 fails when using authentication

When using authentication with Internet Explorer 6 SP1, you may encounter issues when you first launch Internet Explorer. The problem will show itself when you first authenticate, you will receive a "Page Cannot Be Displayed" error. However, if you click refresh, the page will be correctly displayed.

This only happens immediately after you authenticate.

This is not a Squid error or bug. Microsoft broke the Basic Authentication when they put out IE6 SP1.

There is a knowledgebase article ( KB 331906) regarding this issue, which contains a link to a downloadable "hot fix." They do warn that this code is not "regression tested" but so far there have not been any reports of this breaking anything else. The problematic file is wininet.dll. Please note that this hotfix is included in the latest security update.

Lloyd Parkes notes that the article references another article, KB 312176. He says that you must not have the registry entry that KB 312176 encourages users to add to their registry.

According to Joao Coutinho, this simple solution also corrects the problem:

Another possible workaround to these problems is to make the ERR_CACHE_ACCESS_DENIED larger than 1460 bytes. This should trigger IE to handle the authentication in a slightly different manner.

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