This question does not specify which IP address should be spoofed. Perhaps an explanation of WCCP and caching
will answer the question.
With WCCP enabled, the traffic passing through the 3640 router will be redirected to the CacheEngine. The CacheEngine
will then check to see if it has the objects being requested. If so it will "spoof" the web-servers address, and
respond to the client. In this way the client thinks it is getting a response from the web-server.
If the CacheEngine does not have the object requested in its cache, then it will retrieve this content from the web-server and
then "spoof" the web-servers address and response to the client. The connection from the CacheEngine to the web-server
will use the IP address of the CacheEngine and NOT the address of the original client making the request. The result
of this is that the web-server will only see requests from one ip address for the entire organization using that CacheEngine.
