Help: Return different IP address based on source IP

[Dr Yufan Hu]

Hello,

I have a wired situation I would like to seek advice.

We have a web server running at www.foo.com and we have a very large group
of potential users that are behind somebody's firewall. We can however
setup a host within that firewall to do http forwarding for all these
users through a host named as fwd.foo.com. Due to marketing reason I do
not want these users to use the name fwd.foo.com instead of www.foo.com.
The simplest way of doing this is to return the address for fwd.foo.com
when the name server for these group of users query our name server for
www.foo.com. 

I think the easiest way is to set up a secondary on these firewall DNS
servers to use different master data. However, due to some political
reason the server admin refuses to provide such service to us (although
the network owner allow us to setup a host inside the firewall).

My question is: is it possible, in Bind 8 or with some assistant tools, to
detect that the query comes from the DNS serving the users behind the
firewall and return IP address for fwd.foo.com for queries for www.foo.com?
More general, is it possible to return different IP address for a name
based on the source IP address of the query?

Thanks in advnace.

Yufan