<OT> How do ISPs work?

[vu pham]

Tony Alfrey wrote:
[...]
> Question:  Is this actually possible, i.e. that an ISP could give 
> selective web access to a particular web browser?  Does a web browser 
> somehow encode within its packets some identification?

Web browsers send many properties in their HTTP requests. One of the 
properties is "User-Agent".

On my desktop, Firefox set the following value for User-Agent:

Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.14) Gecko/20080416 
Fedora/2.0.0.14-1.fc8 Firefox/2.0.0.14

The web designers use this field to know what kind of browsers are 
accessing the server, and select the proper html/javascript codes to 
send out.

I may be wrong, please correct me.

Vu