natd redirect_port changes source address?

[Matthew Rench]

I recently setup ipfw and natd on my freebsd box. I added the appropriate
command line options to make natd forward 4 tcp ports on the external
address to a box on the internal subnet. This appears to work, except that
natd is rewriting the original source address such that connections to the
internal box appear to come from my external IP address.

Is this behavior normal for natd, or do I have something configured
incorrectly? Previously, I was using a cisco 675 to do natd, and the source
address was not modified during translation. I would much prefer that the
source address not be modified, as this makes it impossible for the internal
box to know who is connecting.

Thanks for any help,
mdr
-- 
Matthew D. Rench