Networking

ping

Most network administrators are very familiar with the ping utility and are likely to use it on an almost daily basis. The basic function of the ping command is to test the connectivity between the two devices on a network. All the command is designed to do is determine whether the two computers can see each other and to notify you of how long the round-trip takes to complete.

Although ping is most often used on its own, a number of switches can be used to assist in the troubleshooting process. Table 3 shows some of the commonly used switches with ping on a Windows system.

Table 3 ping Command Switches

Option

Description

ping -t

Pings a device on the network until stopped

ping -a

Resolves addresses to hostnames

ping -n count

Specifies the number of echo requests to send

ping -r count

Records route for count hops

ping -s count

Timestamp for count hops

ping -w timeout

Timeout in milliseconds to wait for each reply

ping works by sending ICMP echo request messages to another device on the network. If the other device on the network hears the ping request, it automatically responds with an ICMP echo reply. By default, the ping command on a Windows-based system sends four data packets; however, using the -t switch, a continuous stream of ping requests can be sent.

ping is perhaps the most widely used of all network tools; it is primarily used to verify connectivity between two network devices. On a good day, the results from the ping command will be successful, and the sending device will receive a reply from the remote device. Not all ping results are that successful, and to be able to effectively use ping, you must be able to interpret the results of a failed ping command.

The Destination Host Unreachable Message

The Destination Host Unreachable error message means that a route to the destination computer system cannot be found. To remedy this problem, you might need to examine the routing information on the local host to confirm that the local host is correctly configured, or you might need to make sure that the default gateway information is correct. The following is an example of a ping failure that gives the Destination host unreachable message:

Pinging 24.67.54.233 with 32 bytes of data:
Destination host unreachable.
Destination host unreachable.
Destination host unreachable.
Destination host unreachable.
Ping statistics for 24.67.54.233:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
Approximate round trip times in milli-seconds:
    Minimum = 0ms, Maximum =  0ms, Average =  0ms