Reading some docs (probably outdated) about traffic analysis, I see talking about different hostname on each request of a single user. Is this still true? These docs bring AOL as an example. I have no idea if some ISPs work that way nowadays. Could you tell me if these are outdated informations or not? Are there ISPs that use this mechanism these days. Hope this isn't a stupid issue, but I'm really curious. Thanks.

Assuming I understood your query correctly:

Most ISPs (just about all) give each user their own IP address for the duration of the connection.

However, many ISPs (especially the larger ones including AOL) intercept their users' browsing requests and redirect it through a transparent proxy or caching engine.

This can reduce the numbers of measured "unique hits" to the site.

Take the following scenario:

10 people were visiting my site from the same area, same ISP and using the same operating system and browser. Because of these transparent caching engines they could all appear to be the one users as far as the statistics are concerned.

These CEs will usually send a header HTTP_X_FORWARDED_FOR indicating who they are making the request on behalf of, but this is rarely logged by the destination site.

I hope this clears up some things :)

--Shaun

Thank you very much. Really great answer, thanks.

Reading your original question again, the opposite can also apply.

One user browsing your site can appear to be several different users if there are load-balanced caching engines.

For example, if I'm browsing from a corporation that has 5 load balanced CEs. Even though I'm just the one person browsing, my sequential requests could appear to come from any of xx.xx.xx.20 xx.xx.xx.21 xx.xx.xx.22, etc. - and change with every request.

I've actually experienced this before. I was using WHT a while back from a certain place where my IP changed every time. I was trying to vote on a poll and it was causing great difficulty.

--Shaun

Yes, indeed, your second post replys more to what I was meaning with my first post. But your first reply answered also another issue for me(always related). So, you have covered my issues with one shot (thread). Thanks a lot Shaun. :)