Ping

Short for Packet InterNet Groper, Ping is a utility that uses ICMP echo request and echoes reply messages to verify connectivity between hosts. Ping can be used with both IPv4 and IPv6 hosts.To test connectivity to another host on a local network or remote network, an echo request is sent to the address of destination host using this command. If the host at the particular address receives the echo request, it responds with an echo reply. As each echo reply is received, ping gives feedback on the time between when the echo request was sent and when the echo reply was received. This time can be determining the performance of the network.

Ping has a timeout value for the reply. If a reply is not received within this period, its provides a message which indicates that a response was not received from the destination host. This typically indicates that there is a problem with the remote host or with the network. In some cases, it may be caused due to security features which block ping messages on the network.

Once all the ping requests are sent, the utility provides a detailed summary that shows the success rate, losses and average round-trip time to the destination.

Pinging the Loopback Addresses

If a host is unable to connect the resources, then it can troubleshoot by using the ping command to test connectivity. The very first test for which we can use ping utility is the internal configuration of IPv4 or IPv6 on the local host. To perform this test, we ping the local loopback address of 127.0.0.1 for IPv4 and (::1 )for IPv6.

A response from 127.0.0.1 for IPv4, or (::1) for IPv6, indicates that TCP/IP is properly installed on the host. But this response is not an indication that the addresses, masks, or gateways are properly configured. It is also not indicate anything about the status of the lower layer of the network stack. This simply tests IP down through the network layer of IP. An error message indicates that TCP/IP is not operational on the host. The Figure below shows the pining of loopback addresses both for IPv4 and IPv6.

Testing Connectivity to the Local LAN

Ping can also be used to test the capability of a host to communicate on the local network. This is generally done by pinging the IP address of the gateway of the host. A successful ping to the gateway shows that the host and the router interface serving as the gateway are both operating on the local network.

For this test, the gateway address is mostly used because the router is normally for all time operational. If the gateway address does not respond, a ping can be sent to the IP address of another host on the local network that is known to be operational.

If one of the both gateway or another host responds; then the local host can effectively communicate over the local network. If the gateway does not respond but another host responds; this could point to a problem with the router interface serving as the gateway.

It is also possible that the wrong gateway address has been configured on the host. Another option is that the router interface may be fully operational but have security applied to it that prevents it from processing or responding to ping requests. The figure below you can see when i am pinging my local network.

Testing Connectivity to Remote Network

Ping can also test the capability of a local host to communicate across an internetwork. The local host can ping an operational IPv4 host of a remote network.

If this ping is successful, the operation of a large portion of the internetwork can be verified. A successful ping across the internetwork verify communication on the local network; the function of the router serving as the gateway; and the function of all other routers that might be in the path between the local network and the network of the remote host.

furthermore, the functionality of the remote host can also be verified. If the remote host could not communicate outside of its local network, it would not have responded. The figure below I am pinging my remote network. 

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