Well you need at least one layer to protect from the outside world, and another for insider attacks. Many times they can be invisible to the user. For example m

Well you need at least one layer to protect from the outside world, and another for insider attacks. Many times they can be invisible to the user. For example many places have a policy that all internal services must be Internet hardened, as though they were exposed on the broader 'net (even though they're behind a firewall).