It depends on what you're trying to do. For instance, how certain do you
need to be that the request is from one of your customers? Is this some form
of authentication?

You might consider having the customer include some data signed via XML
Digital Signature. This data would be signed in such a way that if you are
able to verify the signature, it will imply that only your customer could
have signed it. .NET 2.0 includes the new SignedXml class in the
System.Security.Cryptography.Xml namespace. It makes it much easier to
generate and verify digital signatures.

Basically, the network isn't going to do this job for you. Speaking at a
somewhat network-theoretical level, your desire to identify your customer is
pretty much an Application-layer function. That means that it's something
between your Application and the customer's Application. You can't depend on
something from the Network layer to do this for you. The Network layer has
the right to do anything it wants with Network-layer data like the IP
Address.

So, if _you_ want to be certain who _your_ customer is, then _you_ have to
do it.

John