Blocking MAC id's

Is it possible to detect and block MAC id's on a website. For example, my current method of banning a person is disabling their user ID, and blocking their IP from accessing our site. Both are easy enough to get around(change your IP and register a new user). I'm looking for a better option. Anybody have an ideas on this?

My understanding is the MAC id should not be available to me unless I'm on the same ethernet segment as the device I wish to block. Is this correct? If so that would make it impossible to collect using PHP or any other web language correct?

Yeah I think you are right Poly. I believe you would only be able to do that if you are on the same LAN as the user. MAC addresses are not included in the TCP/IP packets routed off the user's local network because that is a layer that is below it. I believe the layers are something like:

Application Layer (HTTP, FTP, SFTP, SSH, etc)
Transport Layer (TCP)
Internet Layer (IP)
Link Layer (usually Ethernet)

As far as a better option, you might block a range of IP addresses if they seem related. If not, you might be able to detect if they are using the same computer by setting cookies, although that could be easily broken through by just deleting the cookie.

The user(s) you are trying to ban, do they typically conduct the same behavior? It could be possible to detect that behavior with a script and auto ban that way.

I've done some research and apparently using ActiveX and Javascript you can do client/server communication that will tell you the users MAC, but its only compatible with IE, and the user has an option of declining it. So I am inclined to agree that its not possible.

Unfortunately its a wide array of reasons. I might still look at setting up a script to auto ban for the most common stuff.