Tracking Users By IP Address

Richie Hindle richie at
Thu Oct 7 15:02:01 CEST 2004

> Assuming that each visitor will have a unique IP address is probably
> not 100% accurate but will have a reasonably low margin of error !!

> If I expected many visitors
> from corporate environments, I'd not think this approach would
> have a "reasonably low margin of error".  Almost any such
> environment will have a firewall and masquerade multiple users
> as the same address.

Some (many? all? negligibly few? I don't know) proxy firewalls will tell
you which internal address the request came from, so you can combine the
two to get a unique address for that user. is a useful tool for checking your HTTP headers
(thanks, Alan!).  From where I am at the moment, that tells me:

  Remote IP Address: 

The combination of those IP addresses world-wide-uniquely identifies
this PC, even though it's behind a firewall.

I can't speak for the other billion PCs in similar situations.  8-)

Richie Hindle
richie at

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