When 'Bypass Proxy for Local addresses' (or whatever) is selected do the following: - If local subnet give local dns priority, if fails try proxy, if fails google search. If not local subnet but on the 'reserved for private use' IP ranges give local dns priority, if fails try proxy, if failes try google.

• Pac File Bypass Proxy For Local Addresses Brighton Michigan
• Pac File Bypass Proxy For Local Addresses Brighton Ma
• Pac File Bypass Proxy For Local Addresses Brighton Michigan

This page includes a PAC file example which has been proven to be flexible, easy to update, while still providing accurate results. Proxy bypass rules for private IP networks, internal hostnames, and hosts with.local domain extension. Setting up Proxy.pac files in IIS7 for proxy use If you want the clients to connect using an automatic configuration script to connect to your proxy server, which will work if it is accessible, and won’t work from else where, e.g. Laptop users at home.

Unable to find a definite answer in regards to my question. I was wondering if it was possible to poison the pac file to point to loopback address so that the traffic dies out. Seems that the traffic I am pointing to 127.0.0.1 is still going towards the proxy. Was wondering if I am doing this wrong and if I need to put 'return Proxy 127.0.0.1'.

The reason I want to poison this towards loopback is because the traffic is blocked but to lower the CPU utilization of my proxy I want to let this traffic die out locally (on the computer) as it keeps being denied on the proxy. Causing high CPU.

1 Answer

Yes the block return string needs to start with 'PROXY' and it should also have a port number.

I generally use something like this as a skeleton:

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A proxy auto-config (PAC) file defines how web browsers and other user agents can automatically choose the appropriate proxy server (access method) for fetching a given URL.

A PAC file contains a JavaScriptfunction “FindProxyForURL(url, host)”. This function returns a string with one or more access method specifications. These specifications cause the user agent to use a particular proxy server or to connect directly.

Multiple specifications provide a fall-back when a proxy fails to respond. The browser fetches this PAC file before requesting other URLs. The URL of the PAC file is either configured manually or determined automatically by the Web Proxy Autodiscovery Protocol.

• 2The PAC File
  • 2.1Limitations

Context[edit]

Modern web browsers implement several levels of automation; users can choose the level that is appropriate to their needs. The following methods are commonly implemented:

• Automatic proxy selection: Specify a host-name and a port number to be used for all URLs. Most browsers allow you to specify a list of domains (such as localhost) that will bypass this proxy.
• Proxy auto-configuration (PAC): Specify the URL for a PAC file with a JavaScript function that determines the appropriate proxy for each URL. This method is more suitable for laptop users who need several different proxy configurations, or complex corporate setups with many different proxies.
• Web Proxy Autodiscovery Protocol (WPAD): Let the browser guess the location of the PAC file through DHCP and DNS lookups.

The PAC File[edit]

The Proxy auto-config file format was originally designed by Netscape in 1996 for the Netscape Navigator 2.0^[1] and is a text file that defines at least one JavaScript function, FindProxyForURL(url, host), with two arguments: url is the URL of the object and host is the host-name derived from that URL. Syntactically it is the same string as between :// and the first : or / after that.^[2]

By convention, the PAC file is normally named proxy.pac. The WPAD standard uses wpad.dat.

To use it, a PAC file is published to a HTTP server, and client user agents are instructed to use it, either by entering the URL in the proxy connection settings of the browser or through the use of the WPAD protocol. The URL may also reference a local file as for example: file:///etc/proxy.pac.

Even though most clients will process the script regardless of the MIME type returned in the HTTP reply, for the sake of completeness and to maximize compatibility, the HTTP server should be configured to declare the MIME type of this file to be either application/x-ns-proxy-autoconfig or application/x-javascript-config.

There is little evidence to favor the use of one MIME type over the other. It would be, however, reasonable to assume that application/x-ns-proxy-autoconfig will be supported in more clients than application/x-javascript-config as it was defined in the original Netscape specification, the latter type coming into use more recently.

A very simple example of a PAC file is:

This function instructs the browser to retrieve all pages through the proxy on port 8080 of the server proxy.example.com. Should this proxy fail to respond, the browser contacts the Web-site directly, without using a proxy. The latter may fail if firewalls, or other intermediary network devices, reject requests from sources other than the proxy—a common configuration in corporate networks.

A more complicated example demonstrates some available JavaScript functions to be used in the FindProxyForURL function:

Limitations[edit]

PAC Character-Encoding[edit]

The encoding of PAC scripts is generally unspecified, and different browsers and network stacks have different rules for how PAC scripts may be encoded. In general, wholly ASCII PAC scripts will work with any browser or network stack. Mozilla Firefox 66 and later additionally supports PAC scripts encoded as UTF-8.^[3]

DnsResolve[edit]

Pac File Bypass Proxy For Local Addresses Brighton Michigan

The function dnsResolve (and similar other functions) performs a DNS lookup that can block the browser for a long time if the DNS server does not respond.

myIpAddress[edit]

The myIpAddress function has often been reported to give incorrect or unusable results, e.g. 127.0.0.1, the IP address of the localhost.It may help to remove on the system's host file (e.g. /etc/hosts on Linux) any lines referring to the machine host-name, while the line 127.0.0.1 localhost can, and should, stay.

Security[edit]

In 2013, researchers began warning about the security risks of proxy auto-config.^[4] The threat involves using a PAC to redirect the victim's browser traffic to an attacker-controlled server instead.

Old Microsoft problems[edit]

Caching of proxy auto-configuration results by domain name in Microsoft's Internet Explorer 5.5 or newer limits the flexibility of the PAC standard. In effect, you can choose the proxy based on the domain name, but not on the path of the URL. Alternatively, you need to disable caching of proxy auto-configuration results by editing the registry, a process described by de Boyne Pollard (listed in further reading).

It is recommended to always use IP addresses instead of host domain names in the isInNet function for compatibility with other Windows components which make use of the Internet Explorer PAC configuration, such as .NET 2.0 Framework. For example,

The current convention is to fail over to direct connection when a PAC file is unavailable.

Shortly after switching between network configurations (e.g. when entering or leaving a VPN), dnsResolve may give outdated results due to DNS caching.

For instance, Firefox usually keeps 20 domain entries cached for 60 seconds. This may be configured via the network.dnsCacheEntries and network.dnsCacheExpiration configuration variables. Flushing the system's DNS cache may also help, which can be achieved e.g. in Linux with sudo service dns-clean start or in Windows with ipconfig /flushdns.

On Internet Explorer 9, isInNet('localHostName', 'second.ip', '255.255.255.255') returns true and can be used as a workaround.

The myIpAddress function assumes that the device has a single IPv4 address. The results are undefined if the device has more than one IPv4 address or has IPv6 addresses.

Others[edit]

Further limitations are related to the JavaScript engine on the local machine.

Apple OS X v10.10 and above operating system in some cases can ignore .pac file to use it in native Cocoa apps such as Safari web browser.^[5]

Advanced functionality[edit]

More advanced PAC files can reduce load on proxies, perform load balancing, fail over, or even black/white listing before the request is sent through the network.One can return multiple proxies:

Pac File Bypass Proxy For Local Addresses Brighton Ma

References[edit]

1. ^'Navigator Proxy Auto-Config File Format'. Netscape Navigator Documentation. March 1996. Archived from the original on 2007-06-02. Retrieved 2013-07-05.Cite uses deprecated parameter deadurl= (help)
2. ^https://developer.mozilla.org/en-US/docs/Web/HTTP/Proxy_servers_and_tunneling/Proxy_Auto-Configuration_(PAC)_file
3. ^'Bug 1492938 - Proxy autoconfig scripts should be loaded as UTF-8 if they are valid UTF-8, otherwise as Latin-1 (a byte is a code point)'. Retrieved 2019-04-10.
4. ^Lemos, Robert (2013-03-06). 'Cybercriminals Likely To Expand Use Of Browser Proxies'. Retrieved 2016-04-20.
5. ^'Safari and several other apps won't connect to proxy server'. CERN.

Further reading[edit]

de Boyne Pollard, Jonathan (2004). 'Automatic proxy HTTP server configuration in web browsers'. Frequently Given Answers. Retrieved 2013-07-05.

External links[edit]

• 'Proxy Auto-Configuration (PAC) file'. 2019-01-27.

• 'Using the Client Autoconfiguration File'. Netscape Proxy Server Administrator's Guide: Chapter 11. 1998-02-25. Archived from the original on 2004-08-10.Cite uses deprecated parameter deadurl= (help)

• 'Chapter 26 - Using Automatic Configuration, Automatic Proxy, and Automatic Detection'. Microsoft TechNet. Retrieved 2013-07-05.

• 'Proxy Auto Config for Firefox (PAC). Fully working examples including anti-ad and anti-adult filter rules'. 2012-05-12.

Pac File Bypass Proxy For Local Addresses Brighton Michigan