-WPAD lets you use many methods to automatically specify a proxy server configuration file on the network - [DHCP], [DNS], or manual specification. The file is a .PAC (Proxy Auto Configuration) file, which is defined in Netscape's [definition of PAC files|http://home.netscape.com/eng/mozilla/2./relnotes/demo/proxy-live.html]. 

-!The Easy Method 

-Step 1: if all your clients are something.yourdomain.tla (the connection suffix is assigned with DHCP - if you're unsure, and running Windows, run ' ipconfig' from a command prompt) 

-Step 2: set your gateway machine up so that it has a CNAME for wpad.yourdomain.tla pointing to server.yourdomain.tla 

-Step 3: Copy something like this into your HTTP root as wpad.dat: 

-<verbatim>  

- function FindProxyForURL(url, host)  

- {  

- if(shExpMatch(url, "!https:*") || isPlainHostName(host) || \  

- dnsDomainIs(host, ".yourdomain.tla") || dnsDomainIs(host, ".youralias.tla"))  

- { 

- } else { 

- }  

- }  

-</verbatim>  

-Step 4: Check you can access it by going ~http://wpad.yourdomain.tla/wpad.dat.  

-(Optional) Step 5: Make Apache serve it with the correct MIME type (x-ns-proxy-autoconfig) using a virtual host in your [Apache] configuration file ( /etc /apache /httpd .conf):  

-<verbatim >  

-<VirtualHost ip.ad.dr.es>  

- ServerName wpad.yourdomain.tla  

- ServerAlias ip.ad.dr.ess  

- AddType application/x-ns-proxy-autoconfig .dat  

- </VirtualHost >  

- </verbatim > 

-(The alias is added because MSIE 6.00.2800.1106 on Win98SE does not look up the hostname.) 

-If your DomainName is machine.something.meta.net.nz then InternetExplorer will request the following urls* until it finds a [WPAD] configuration file. 

-* ~ http://wpad .something .meta .net .nz /wpad .dat  

-* ~ http://wpad .meta .net.nz /wpad.dat  

-* ~http://wpad .net .nz/wpad.dat  

-Warning: Beware that Internet Explorer 5.5+ may cache your wpad file and not recognize future changes you make to it -- this feature is referred to as Automatic Proxy Result Cache ([MS Knowledge Base 271361|KB :271361]). If you turn off "Automatically detect settings", save the change, restart IE, turn it back on, and restart IE again, then it will force a refresh of the wpad.dat file from your webserver (If you're lucky. It seems IE 6 refuses to flush even then) . Here is a [Google Groups' |http://groups.google.com/groups?q=squid+wpad.dat+doesn%27t+work&hl=en&lr=&ie=UTF-8&oe=UTF-8& selm=b6239t%24mif%241%40FreeBSD.csie.NCTU.edu.tw&rnum=3 ] discussion of the issue . 

-The DHCP method (the MicrosoftCorporation "preferred option", which like most MSFT'isms, doesn't actually work) . Add the following to your /etc/dhcpd.conf 

- option option-252 "http://wpad.host.co.nz/proxy.pac"; 

-With ISC DHCP v3+, ' option-#' options don't work, You have to do this in the global section of your configuration: 

- option wpad-url code 252 = text; (define a new option) 

- option wpad-url "http://wpad.my.domain.tld/proxy.pac\n"; (use new option) 

-You might like to try using an IP address there instead; there has been a report that a DNS domain doesn't work, but no indication on what version of dhcpd. 

-__NOTE__ :  

-It seems tha IE eats the last character of the URL given in option 252. You have to append a space there (or any other character) to get it working: 

- option wpad-url "http://wpad.my.domain.tld/proxy.pac "; 

-or if you're configuring a Windows DHCP server, right click on the server and click "Set predefined options" to add 252 as a String value (it's not in there by defult. See [here |http://support.microsoft.com/default.aspx?scid=kb;EN-US;252898] for more.) 

-The DNS method(s). Add all or some of the follwing entries to your DNS zone file. 

- $ORIGIN host.co.nz.  

- wpad IN A 192.168..254  

- IN TXT "service: wpad:!http://wpad.host.co.nz:80/proxy.pac"  

- wpad.tcp IN SRV 0 0 80 wpad.host.co.nz. 

-See also:  

- var proxy_yes = "PROXY proxy.i.zmi.at:3128; DIRECT";  

- var proxy_no = "DIRECT"; 

- // WARNING: The "dnsDomainIs" is a check of which DNS domain the _client_  

- // is inside. It's not a check for where the client wants to go!!!  

- // if (dnsDomainIs( host,"zmi.at") { return proxy_no; } 

- // Proxy if PC is on local LAN - doesn't work with Konqueror!  

- // So this test is for Internet Explorer and compatible only  

- if (isInNet(myIpAddress(), "10...", "255...") || isInNet(myIpAddress(), "192.168..", "255.255..")) {  

- if (url.substring(, 5) == "http:" ||  

- url.substring(, 4) == "ftp:" ||  

- url.substring(, 7) == "gopher:")  

- return proxy_yes;  

- else  

- return proxy_no;  

- }  

- // Konqueror comes until here:  

- if (url.substring(, 5) == "http:" ||  

- url.substring(, 4) == "ftp:" ||  

- url.substring(, 7) == "gopher:")  

- return proxy_yes;  

- else  

- return proxy_no; 

-  

- Now you even can differentiate between Konqueror and Internet Explorer , and could give them different proxies. If you want to download the running config, visit ! http://zmi.at/wpad.dat 

-wpad.com does actually exist and is owned by Duane Wessles, the author of [Web Caching|http://www.oreilly.com/catalog/webcaching/]. There 's no wpad.dat there.  

-I mailed him a while back asking about it , and he constantly gets between 10 and 40 hits per second depending on the time of day . The 404 logs for that site are at http: //www .life-gone-hazy .com/~snmp/http_status .cgi if you 're interested.