about HTTP server redirect

Hi,

I have apache http server A and two other machine B and C. B is the production server and C is the test server. Http server A is in separate machine.

Now, users will send request via Http server A to production server B.
if any page or link is not found then Http server redirect the link to
test server C (test server keeps same contents like B).

I don't know how do I do that, Can any one give me any idea?

Thanks