The ping is a very helpful utility to test and troubleshoot network devices connectivity. It uses the Internet Control Message Protocol (ICMP). The ping results indicate the source of the problem. It is also a first step in troubleshooting a network failure. So, understanding ping results is very important for the student of networking.
Cisco IOS Ping Indicators
There are several ping results and indicators in IOS for ICMP echo request that was sent. The common indicators for ICMP echo are the following:
! – The mark of exclamation indicates that the ping completed successfully and verifies Layer 3 connectivity along the network path. As shown in Figure below, Karak Router Successfully ping Peshawar router, which IP address is 172.16.0.1
“.” The period indicates that there is some problem in connectivity somewhere along the network path. It also indicates that a router along the network path does not configure a route to the destination. If the ping is not allowed in the device it should also give a reply with “.” Indicator. The first echo request timed out is common in the network If the arp process is required. The figure below shows the ping result from Karak router to laptop 3, where “Karak router” has no route to the network 192.168.1.0/24, so its reply with request timed out “.” Indicators.
U – This indicator shows that a router along the network path responded with an ICMP unreachable message because the router did not have a route configure to the destination address. If the destination blocked the ping request it will also reply with this mark.
Testing the Loopback
To verify the internal IP configuration and protocol stack from the network layer to the physical layer the administrator can also use the ping command instead of putting a signal on the media. The Loopback IP addresses are 127.0.0.1 for IPv4 and ::1 for IPv6. We can examine the ping results for loop back interfaces similar to other interfaces.
The extended ping is one of the best commands offers by Cisco IOS. This is also the extended mode of the ping command. To execute and get extended ping results only enter ping command without destination address in privileged EXEC mode. As shown in the figure below, a series of different prompts are then presented asking different parameters. Pressing Enter without writing something accepts the indicated default values.
The figure below illustrates how to force the source address for a ping to be 192.168.1.1(Router Peshawar); the source address far a standard ping would be 172.16.0.2. The network administrator can verify from Peshawar Router that the Karak Router has a route to 192.168.1.0/24 network.