Packets forwarded to unused Static IP addresses?

Hi all,

It recently came to our attention that our business IP Gateway (SMB) is passing packets for our static IP addresses that are not in use. We have a /29 assigned from Comcast and are only using three of them. For the others that arent being used, attempts to connect to those addresses are passed through the gateway, even though they are not set up anywhere.

This caused a scenario where traffic from the internet, destined for one of the unassigned static IPs, hit a test router with a default gateway of another part of our network and it sent that traffic, sourced from an Iranian IP address, all over our network and eventually died on a firewall.

We have removed the test router, thus stopping this behavior, but the gateway should not be passing traffic for Static Ips not set up. Is there any way to stop that behavior?