In this hour you learned about the Internet layer protocols IP, ARP, RARP, and ICMP. IP provides a hardware-independent addressing system for delivering data over the network. You learned about binary and dotted decimal IP address formats and about the IP address classes A, B, C, D, and E. You also learned about ARP, a protocol that resolves IP addresses to physical addresses. RARP is the opposite of ARP, a protocol that lets a diskless computer query a server for its own IP address. ICMP is a protocol used for diagnosis and testing.