BGP finds an optimal path across autonomous systems. √

An IP address is a physical hardware address that a network interface uses to identify itself. √

In the CSMA/CD protocol used in Ethernet, the receiver of a unicast frame sends an ACK if the frame is received correctly. x

The idea of summarizing routing table entries in a smaller number of routes is called "subnetting". x

The filtering database on a bridge stores a mapping of IP address to bridge port number. x