Testing the Loopback
The figure shows the first step in the testing sequence. The ping command is used to verify the internal IP configuration on a local host. This test is accomplished by using the ping command on a reserved address called the loopback (127.0.0.1). The loopback address, 127.0.0.1, is defined by the TCP/IP protocol as a reserved address that routes packets back to the host.
Ping commands are entered into a command line on the local host using the syntax:
C:\> ping 127.0.0.1
The reply from this command would look something like this:
Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
Ping statistics for 127.0.0.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms
The result indicates that four test packets of 32 bytes each were sent and returned from host 127.0.0.1 in a time of less than 1 ms. This successful ping request verifies that the network interface card, drivers, and the TCP/IP implementation are all functioning correctly.
Practice testing a loopback address by entering commands in Figure 2.