So far we have seen very basic packets. These packets have shown only the source (who sent the packet) and the destination (who received the packet). In this level, we will see a more complex packet that will give the recipient information about how to respond.

Pause the simulation to view the packet sent from Alice's computer to Google. There is a new header under the transport layer. The header, proto defines the protocol that will be run on this layer. The protocol listed is ICMP, which is used to ping computers. When a computer receives a packet with an ICMP echo request (ping) they respond by sending back a packet with an ICMP echo (pong). Resume the simulation and notice the response packet sent from Google to Alice's computer.

Level Objectives

• To complete this level, you must send 4 more ICMP echo requests from Alice to Google. Proceed as before, by clicking the + to add new packets. Remember to fill in the new transport layer header proto header field.