Skip to Main Content
Web Caching
book

Web Caching

by Duane Wessels
June 2001
Intermediate to advanced content levelIntermediate to advanced
320 pages
9h 18m
English
O'Reilly Media, Inc.
Content preview from Web Caching

Web Proxy Auto-Discovery

As I mentioned earlier, proxy auto-configuration usually requires the user to manually enter a URL in the proxy configuration window. Recent efforts by browser developers seek to eliminate that step. This new feature is called web proxy auto-discovery, or WPAD. WPAD is designed to let browsers automatically learn the auto-configuration URL with no assistance from the user.

WPAD uses a number of protocols and services to find the auto-configuration URL. The preferred protocol is DHCP (Dynamic Host Configuration Protocol). If DHCP fails, the user-agent may try the Service Location Protocol (SLP, RFC 2068) next. If SLP fails as well, it queries the DNS for A, SRV, and TXT records. A client that implements WPAD must support at least the DHCP and DNS A record queries. Support for SLP is optional.

Using the DNS is likely to be the simplest and most popular approach for network administrators. The first step is to select an HTTP server and place a proxy auto-configuration script there under the name /wpad.dat. Then the administrator needs only to add a DNS entry for a host named wpad. For example, if wpad.company.com is an alias for company.com’s web server, and the wpad.dat file is installed there, all of the company’s web browsers can automatically configure themselves.

WPAD was submitted to the IETF as an Internet Draft in December of 1999. Unfortunately, it has not yet been updated or moved beyond that stage, and the draft is now expired. Even so, Microsoft’s ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Web Caching and Replication

Web Caching and Replication

Michael Rabinovich, Oliver Spatscheck
NGINX Unit Cookbook

NGINX Unit Cookbook

Derek DeJonghe
NGINX Cookbook

NGINX Cookbook

Tim Butler

Publisher Resources

ISBN: 156592536XCatalog PageErrata