The firewall IPD behaves as an Ethernet switch. That is, addresses are learned on both ports and when an Ethernet Unicast packet arrives at either port, it is forwarded only if the packet contains a destination address for the opposite side. The firewall IPD rules then take over and determine which Unicast packets should be dropped or rejected based on protocol, address, port, or packet rate. Based on the configuration rules, the firewall IPD forwards, drops, or rejects Multicast and Broadcast packets. The firewall IPD performs some packet checks to detect illegal or malformed packets and discards these packets if found. This is similar to a standard Ethernet switch that drops packets with CRC errors. The firewall IPD is transparent to the discovery packets that the Network Device Command Center (NDCC) uses to discover DeltaV Smart Switches.