|  | 4.4 | Basic Networking Testing
| 4.4.3 | Testing the network layer using the ping command
As an aid to diagnosing basic network connectivity, many network protocols support an echo protocol, which is a test to determine whether protocol packets are being routed. The ping command sends a packet to the destination host and then waits for a reply packet from that host. Results from this echo protocol can help evaluate the path-to-host reliability, delays over the path, and whether the host can be reached or is functioning. In the Figure, the ping target 172.16.1.5 responded successfully to all five datagrams sent. The exclamation points (!) indicate each successful echo. If you instead receive one or more periods (.) on your display, the application on your router timed out waiting for a given packet echo from the ping target. You can use the ping user EXEC command to diagnose basic network connectivity. ping uses the ICMP (Internet Control Message Protocol).
| Lab Activity
| In this lab you will use ICMP or Internet Control Message Protocol. ICMP will give you the ability to diagnose basic network connectivity. Using ping xxx.xxx.xxx.xxx will send an ICMP packet to the specified host and then wait for a reply packet from that host. You can ping the host name of a router but you must have a static host lookup table in the router or DNS server for name resolution to IP addresses.