| 9.2 |  | Network Testing |
| 9.2.5 |  | Layer 3 troubleshooting using ping |

| The ping utility is used to test network connectivity. As an aid to diagnosing basic network connectivity, many network protocols support an echo protocol. Echo protocols are used to test 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. The ping output displays the minimum, average, and maximum times it takes for a ping packet to find a specified system and return. The ping command uses Internet Control Message Protocol (ICMP) to verify the hardware connection and the logical address of the network layer. Figure is a table showing the various ICMP message types. This is a very basic testing mechanism for network connectivity. In Figure , the ping target 172.16.1.5 responded successfully to all five datagrams sent. The exclamation points (!) indicate each successful echo. If one or more periods (.) instead of exclamations are received on a display, the application on the router timed out waiting for a given packet echo from the ping target.
Command | Purposes
Router#ping [protocol] {host | address} | Invokes a diagnostic tool for testing connectivity
The ping command tests network connections by sending ICMP echo requests to a target host and times replies. When testing a connection, ping tracks the number of packets sent, the number of replies received, and the percentage of packets lost. It also tracks the amount of time required for the packets to reach the destination, and for replies to be received. This information allows verification of communication between a workstation and other hosts, and whether information was lost. The ping command can be invoked from both user EXEC mode and privileged EXEC mode. The ping command can be used to confirm basic network connectivity on AppleTalk, ISO Connectionless Network Service (CLNS), IP, Novell, Apollo, VINES, DECnet, or XNS networks. The use of an extended ping command directs the router to perform a more extensive range of test options. To use extended ping, type ping at the command line, then press the Enter key without entering an IP address. Prompts will appear each time the Enter key is pressed, allowing the specification of many more options than with standard ping. It is a good idea to use the ping command when the network is functioning properly to see how the command works under normal conditions and so that there is something to compare against when troubleshooting.
| Lab Activity e-Lab Activity: Layer 3 Troubleshooting Using ping In this lab, the students will use the ping command to send ICMP echo requests to an adjacent router.
| Web Links Using the Extended ping and Extended traceroute Commands http://www.cisco.com/en/US/tech/ tk826/ tk365/technologies_ tech_ note09186a0080093f22.shtml