D-Link DFL-1600 User Manual page 225

20.3. Why VPN in Firewalls
Figure 20.6: VPN Deployment Scenario 6
No special routes need to be added to hosts participating in the VPN
Can seamlessly integrate VPN and firewall policies
Drawbacks
The integrated Security Gateway may make the firewall less stable.
However, it does not add another piece of hardware to the chain of
points that may fail.
This solution provides the highest degree of functionality & security and is
chosen by D-Link's design. All normal modes of operation are supported,
and all traffic may be inspected and logged by the firewall.
D-Link Firewalls User's Guide
205