The TCP/IP Protocols Ethernet - a LAN protocol, used to send packets between two hosts connected to a single network. IP - Internet Protocol. used to perform basic routing of packets between two hosts on an internetwork. May sit on top of Ethernet, Token-ring, FDDI, PPP and so on. ICMP - Internet Control Message Protocol. Complements the IP protocol by allowing sending control messages from hosts or gateways along the route of a packet back to the sending host. TCP - Transport Control Protocol. Allows forming a connection between two hosts, and guarantees that traffic sent on this "stream" is reliable (packets arrive in the order sent, no packet gets lost, data arrives in-tact by using a checksum). UDP - User Datagram Protocol. A user-level protocol that adds only ports to the basic IP addresses. leaves all handling of ordering, checksumming to the user application.