Why is WPAD not caching? RRS feed

  • Question

  • Hi,

    We use a WPAD file hosted on a Websense appliance and use IE11 on Windows 7 x64.

    We are seeing some performance issues with the Websense delivery of WPAD and have discovered that every computer is making a large amount of calls to the websense appliance to retrieve WPAD.dat. (Up to 1000 per machine in some cases)

    We have worked with Websense and found that they were returning a 'no-cache' option in the WPAD response header. Via a patch we have had this removed.

    However I still can't find a cached WPAD file on my machine that I am using for testing and have checked all the registry entries I can think of related to caching.

    Does anyone have any ideas?

    For reference, the WPAD.dat is (edited of course):


    // Start of Script

    function FindProxyForURL(url, host)

    // Convert everything to lower case
    var lhost = host.toLowerCase();
    host = lhost;

    //Local Networking Match
    if (isPlainHostName(host) ||
    shExpMatch(host, "localhost.*") ||
    shExpMatch(host, "*") ||
    shExpMatch(host, "*.local") ||
    isInNet(dnsResolve(host), "", "") ||
    isInNet(dnsResolve(host), "", "") ||
    isInNet(dnsResolve(host), "", "") ||
    isInNet(dnsResolve(host), "", ""))
    return "DIRECT";

    //Host Matching
    if (dnsDomainIs(host, "*") ||
    dnsDomainIs(host, "*") ||
    dnsDomainIs(host, "*") ||)
    return "DIRECT";

    //Expression Matching
    //if (shExpMatch(url, "*"))
    //return "DIRECT";

    // Default - Use Proxy 
    return "PROXY"; 

    // End of function

    We use DNS to point to the Websense appliance.

    Any suggestions / ideas welcomed.

    Tuesday, June 28, 2016 11:12 AM

All replies

  • Hi AdrianColes,

    Based on my knowledge and search, usually the wpad.dat file will be cached if we haven`t set a "cache control"header .
    Here is a link for reference,this link may be useful to troubleshoot this issue (Pay attention to "What else IE will do in WPAD detection?" part) :
    Insight WPAD proxy settings on IE

    Have you set this group policy "disable cache of auto-proxy scripts" in this path :User Configuration > Administrative Templates > Windows Components > Internet Explorer > Disable caching of Auto-Proxy scripts ?

    We can try the following steps to have a check:
    1.Clear the Internet cache and then have a  check .
    2.Reset the Internet Explorer 11 and then have a check.

    Hope it will be helpful to you

    Please mark the reply as an answer if you find it is helpful.

    If you have feedback for TechNet Support, contact

    Wednesday, June 29, 2016 10:51 AM
  • Hi,

    Still racking my brains with this one.

    EnableAutoproxyResultCache is set to either 1 or not present from all machines so should be caching.

    I have also deleted the proxy cache from the registry here:

    HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\DefaultConnectionSettings

    HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\SavedLegacySettings

    Still no joy.

    Have tried a vanilla install of Windows 7 and still not caching.

    Can anyone come up with any ideas of what to check? Struggling with this one for months now.

    PS. I've checked and the WPAD response header does not have a 'no-cache' option in it.

    Friday, July 22, 2016 8:36 AM
  • Anyone?


    Thursday, July 28, 2016 3:22 PM
  • Hey, This you ever find a solution for this?
    The response from Microsoft regarding this issue was not very helpful..

    IE11 Proxy PAC File Caching does not work (9242413)

    By design

    Steps to reproduce

    On a Windows 7 (x64) machine, fully patched and updated:
    Configure IE11 to use a proxy autoconfiguration script from a webserver.
    Use wireshark to see IE requesting the PAC file over and over again when browsing different webpages

    Ibrahim O. ‎Oct‎ ‎19‎, ‎2016 2016-10-19T16:13:03.247Z Microsoft Edge Team

    Thank you for providing your feedback on IE11.
    We are not accepting feedback on Internet Explorer through this portal any longer (unless security related). We welcome any feedback you have on Microsoft Edge using this website. This item will be closed as By Design since IE feature bugs are not being worked unless security related.
    All the best,
    The MS Edge Team 

    Monday, October 24, 2016 1:40 PM