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 refers to a ping. 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 packet sent from Google to Alice's computer.

To complete this level, you must send 4 more ICMP echo requests (pings) from Alice to Google. Proceed as before, by adding a new packet in the Timeline Editor. Remember to add the new transport layer header.

Hint: use the 'repeat' feature in the Editor to send the same packet many times!

Level Objectives