The Cisco perimeter router must be configured to protect an enclave connected to an approved gateway by using an inbound filter that only permits packets with destination addresses within the sites address space.

Enclaves with approved gateway connections must take additional steps to ensure there is no compromise on the enclave network or NIPRNet. Without verifying the destination address of traffic coming from the site's approved gateway, the perimeter router could be routing transit data from the internet into the NIPRNet. This could also make the perimeter router vulnerable to a denial-of-service (DoS) attack and provide a back door into the NIPRNet. The DoW enclave must ensure the ingress filter applied to external interfaces on a perimeter router connecting to an approved gateway is secure through filters permitting packets with a destination address belonging to the DoW enclave's address block.