Not sure if this is exactly ASP.NET, but that's the technology I'm using.

Just got handed a project, one of the requirements is that I verify the IP address of the user against a table of possible addresses. This I can do with SERVER_ADDR, but, I don't think that's exactly what they mean.

For example, if the client site dials an ISP, it could be a range of addresses. I think they expect that only certain machines on their site can access my web site. Someone told me it could "NAT out" to their address, but unsure how to do this this or if it's even really feasible.

Anyone know what I'm talking about and have any suggestions? Can I really tell their original location, or is that hidden from me? If so, I'll be happy telling them that I can only see the IP address as revealed to me, but would just like to know if it's possible to "drill down".

Thanks,
Mike