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Login problem with sessions and IP Match

#4
[eluser]1stInter[/eluser]
Hi,

It's a very common issue indeed, but for a different reason than a company using two different IP addresses - although that explanation is absolutely correct as well.

A number of ISPs (and companies) are using Proxy Servers to reduce their external bandwidth, and by bringing content closer to their users they are able to reduce cost and improve the user experience.

The client makes the request to the proxy server, and the proxy server makes the request to your server. If a client is sent to two different proxy servers then the IP address shown will be different.

Using Load Balancing, the user may be directed to any one of several proxy servers, and the IP address may therefore change even during the same page load. For instance, in load balancing a "Round Robin" method is often used, so the first query goes to server 1, the second to server 2. But if a page loads 2 graphics images and an iframe the requests will go like this: Server 1 initial HTML, Server 2 first graphic, Server 1 second graphic, Server 2 iframe etc etc.

AOL in particular has always been a problem - see AOL Proxy Information for more information on their system.

This is transparent to the user, by the way - the ISP intercepts the traffic and redirects it seamlessly to the proxy servers and there's absolutely nothing the client can do to stop it.

The upshot is that you CANNOT use the IP address to keep track of session details - even if you make an exception for AOL users there are lots and lots of IPs who implement this, and the information isn't publicly available so exceptions can be made.

Note that you can sometimes see an HTTP header called X-Forwarded-For which contains the internal IP - however this header is definitely NOT included for all clients. See Wikipedia for more information.

Regards
Steve


Messages In This Thread
Login problem with sessions and IP Match - by El Forum - 12-13-2008, 01:01 AM
Login problem with sessions and IP Match - by El Forum - 12-13-2008, 01:27 AM
Login problem with sessions and IP Match - by El Forum - 12-13-2008, 01:37 AM
Login problem with sessions and IP Match - by El Forum - 12-13-2008, 05:04 AM

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