WPAD detection in Internet Explorer
Hello again, I spent a lot of time recently troubleshooting WPAD detection using DHCP 252 option. In doing so, the information I collected may be useful to those deciding how to implement proxy auto-discovery in corporate networks. Proxy Auto-Disover configuration files , wpad.dat files, provide central administration for proxy connections to the Internet.
What I would like to talk about today is the order in which IE will search out a proxy auto-configuration file when using Automatically Detect setting (default) setting in IE. Internet Explorer goes down a list of predefined detection methods:
1. DHCP (252 option)
2. DNS A record query/queries
3. NetBios
NOTE: Only applies when 'Automatically detect settings' in Internet Options -> connections -> Lan Connections is the only option checked. Other options for configuring IE connection settings include Automatic Configuration Scripts and manually specifying a proxy server.
Now, if DHCP is configured to provide the WPAD location, IE stops the detection and will make a GET request for the wpad.dat file and no further searching is done. This is true even if the DHCP 252 option is incorrect and a correct entry is configured as a DNS record.
If DHCP 252 is not configured, IE will continue until it either exhausts the search or gets a response:
1. BootP request to DHCP for the 252 option containing the path to the wpad.dat file
if DHCP 252 is not configured:
2. DNS A query for “wpad.<dns suffix>” ex. wpad.domainname.com
if the DNS query fails:
3. A Netbios query for a machine named WPAD occurs
If Netbios fails:
4. A direct connection is attempted
If this attempt fails, the user is presented with the Cannot display the webpage or similar message.
The wpad.dat detection (steps 1 thru 3) occur when "Detecting proxy settings..." is displayed in the status bar in the lower left corner of the Internet Explorer window.
Example of a detection order:
- If a domain suffix is north.corp.contoso.com
IE will perform the following queries:
wpad.north.corp.contoso.com
wpad.corp.contoso.com
wpad.contoso.com
NOTE: If a domain suffix search order has been specified, the first domain in the list will be used instead.
As you can see, there is overhead associated with the detection method. If you do not have a wpad solution, there is no reason to have this option enabled. Disabling it can reduce network traffic as well as the initial page load times for Internet Explorer. Disabling this option forces IE to attempt a direct connection to the internet immediately, which it would eventually get to if no wpad files were found.
Another great Blog brought to you by Aurthur Anderson, an IE Senior Escalation Engineer.
Regards,
The IE Support Team
Comments
- Anonymous
January 22, 2009
How can I check current WPAC status?I mean, I have "automatic detection" enabled, but how can I know if my PC has actually received a configuration set ? - Anonymous
January 27, 2009
Hey Alejendro!Well, there are several ways to tell, but I don't think I can do the answer justice in just a comment. Tell you what, we will put together a follow-up blog to answer your question. How does that sound?Regards,The IE Support Team - Anonymous
May 14, 2009
Hello, i have similar question as Alejandro, i find the wpad.dat files in the cache and can verify its correct, but its not working on all stations, is there anyway to "debug" it. - Anonymous
June 10, 2009
The comment has been removed - Anonymous
August 19, 2009
The comment has been removed - Anonymous
September 13, 2009
We use a VPN Citrix Access Gateway and with "autoconf proxy" activated, it seems that IE doesn't detect the new connectoide VPN and don't get the .dat file. - Anonymous
November 09, 2009
Quote "by Alejandro GrijalbaHow can I check current WPAC status?I mean, I have "automatic detection" enabled, but how can I know if my PC has actually received a configuration set ?Tuesday, January 27, 2009 11:35 PM by Brent GoodpasterHey Alejendro!Well, there are several ways to tell, but I don't think I can do the answer justice in just a comment. Tell you what, we will put together a follow-up blog to answer your question. How does that sound? "Hello Brent,Please can you provide a link to the post with your answer, as I too an interested in seeing what cached WPAD file IE is reading.Many thanksChris - Anonymous
February 23, 2010
The comment has been removed - Anonymous
February 23, 2010
Fyi I found this:"Alejendro, this blogs for you! "http://blogs.msdn.com/askie/archive/2009/02/18/how-can-i-tell-if-ie-has-received-a-wpad-configuration-file-when-automatic-detection-is-enabled.aspx - Anonymous
April 11, 2010
To know more about "Automatically detect settings and WPAD and option 252" refer to the following blog:https://blogs.msdn.com/anshu/archive/2010/04/06/internet-explorer-and-wpad.aspx - Anonymous
September 08, 2013
Hello, I have this question: should wpad record be CNAME or HOST(A) record ? On official TechNet Library it is written CNAME.Bye,Luca - Anonymous
September 11, 2013
The comment has been removed - Anonymous
December 02, 2013
Hi, I met a puzzled problem. I am working on a WinINet application. My machine(Win7, x64, and IE8,IE9,IE10, 32bit) is in the domain, and wpad is configured, and "Automatically detect settings" is selected. I found for some urls, WinINet control doesn't get "INTERNET_STATUS_RESOLVING_NAME" and "INTERNET_STATUS_CONNECTING_TO_SERVER" message in InternetSetStatusCallback function. If I unselect the "Automatically detect settings", it is normal. Could you give some advice? - Anonymous
January 13, 2014
I am also having the issue and noticed that on the machines that has the issue, they also have Vmware installed. When I disable the vmnet adapters, the wpad detections works quickly in ie9. Also, installing IE11 and then uninstall IE11 makes IE9 work with wpad. - Anonymous
February 23, 2015
We discovered an issue with the 'Automatically Detect setting' in Internet Explorer 11 in combination with Windows 7 when we switched off NetBIOS over TCP/IP. Users auto-loading multiple sites were suddely experiencing load issues: 'Page can not be displayed' on Internet sites and popups for logon credentials for Internet sites. After unselecting the 'Automatically Detect setting' the auto-loading of sites was ok again..We no WPAD infrastructure in place and use a proxy.pac file for configuring the proxy settings. Therefore we don't need the 'Automatically Detect setting'.Still, it looks like an intersting bug in Internet Explorer 11. IE 11 in combination with Windows 8 doesn't show the issue.Is anyone else experiencing this?