Testing Network Connectivity

A few tools can help you determine whether the network can send data between computers; these tools test the network protocols as well as low-level network hardware layers.

ping

ping is a fundamental tool for testing TCP/IP network connectivity. Because most Windows XP Professional networks use the Internet (TCP/IP) protocol for file and printer sharing services, as well as for Internet access, most Windows XP Professional users can use the ping test to confirm that their network cabling, hardware, and the TCP/IP protocol are all functioning correctly. ping sends several data packets to a specified computer and waits for the other computer to send the packets back. By default, it sends four packets and prints the results of the four tests.

To see whether the network can carry data between a pair of computers, use the ipconfig command (described previously) to find the IP address of the two computers. Then, on one computer, open a Command Prompt window by choosing Start, All Programs, Accessories, Command Prompt.

Next, type the following command:

 ping 127.0.0.1 

This command tests the networking software of the computer itself, by sending packets to the special internal IP address 127.0.0.1; this test has the computer send data to itself. It should print the following:

 Reply from 127.0.0.1: bytes=32 time<10ms TTL=128 Reply from 127.0.0.1: bytes=32 time<10ms TTL=128 Reply from 127.0.0.1: bytes=32 time<10ms TTL=128 Reply from 127.0.0.1: bytes=32 time<10ms TTL=128 

If it doesn't, the TCP/IP protocol itself is incorrectly installed or configured; check the computer's IP address configuration, or, if that seems correct, remove and reinstall the Internet Protocol from Local Area Connection in Network Connections. (I have to say, in more than 10 years of working with PC networks, I've never seen this test fail.)

If your computer can send data to itself, try another computer on your LAN. Find its IP address by running ipconfig on that computer, and then issue the ping command again on the first computer, as in this example:

 ping 192.168.0.23 

Of course, you should use the other computer's real IP address in place of 192.168.0.23. You should get four replies as before:

 Reply from 192.168.0.23: bytes=32 time<10ms TTL=32 Reply from 192.168.0.23: bytes=32 time<10ms TTL=32 Reply from 192.168.0.23: bytes=32 time<10ms TTL=32 Reply from 192.168.0.23: bytes=32 time<10ms TTL=32 

These replies indicate that you have successfully sent data to the other machine and received it back.

If, on the other hand, the ping command returns Request timed out, the packets either didn't make it to the other computer or were not returned. In either case, you have problem with your cabling, network adapter or the TCP/IP protocol setup.

You can use ping to determine which computers can send to which other computers on your LAN or across wide area networks (WANs) or the Internet. ping works when given a computer's IP address or its network name.

NOTE

If you enter a computer name, and ping can't determine the computer's IP address, the problem isn't necessarily a wiring problemit could be that the DNS or WINS name lookup systems are not working correctly. Try using an IP address with ping in this case to help determine what the problem really is.