Starting from v10.0 release Trustwave Secure Web Gateway introduces URL Rewriting feature that allows the proxy to direct URLs to a specified alternate location. 

Caching functionality is required to use URL Rewriting functionality and it could be deployed in two modes: Server mode and Client mode.

This article describes the differences taking place in the background when the system is set to use URL Rewriting in Server mode vs Client mode.

Below setting will redirect any request for http://www.m86security.com to go to http://www.iconfactory.com .

This configuration is used for demo purposes only and gains no performance benefits at all.

As the browser sends a request to the proxy (frame 252 below) the requested URL would be automatically rewritten to go to alternate location, 

as shown in frame 262 in details:

In this case, the browser is not aware of this change and redirection is being performed on the proxy (Server) side.

Now, the configuration is set to perform same URL Rewriting in Client mode:

Frame 78 - Trustwave caching component responds with HTTP 302 Moved Temporarily code, with location details as shown below.

Frame 80 - Trustwave proxy component returns same HTTP 302 code to the client.

Frame 81 - consequent request from the client to go to alternate location as specified by proxy.

HTTP 302 code is the major difference in this case meaning that the browser is aware of this change.

It should issue another request for URL as specified in location field of HTTP 302 response and the redirection is performed on the client side.