In Mac OS X, how can I check to see if a computer is on the network?

In Mac OS X, to see if a computer is on the network, use the Network Utility to ping the remote host. A ping is a small packet of data sent to the remote host and then sent back by the recipient computer. If the computer is not on the network, it will not be able to respond to the packet.

To use the Network Utility:

1. From the Applications folder, open the Utilities folder, and then open the Network Utility application.
   
   
2. In the Network Utility window, click the Ping tab.
   
   
3. In the first field, enter the IP address or domain name of the computer you want to ping.
   
   
4. Select Send only ___ pings.
   
   
5. In the Send only ___ pings box, type the number of packets you would like the Network Utility to send. The default is ten, which should be sufficient in all but the most congested network conditions.
   
   
6. Click Ping.

The Network Utility will begin pinging the host. If the host is on the network, the packets will be listed in the Network Utility as they are returned. If no packets are returned, then either the computer is off the network or there are network problems between your computer and the remote host. For a more definitive answer, use the Network Utility's traceroute function, which will attempt to determine where the network difficulty is occurring.

To use the traceroute function:

1. In the Network Utility window, click the Traceroute tab.
   
   
2. In the first field, enter the IP address or domain name of the remote host.
   
   
3. Click Trace.

Note: In some cases, a computer will respond to a ping but will be unreachable by other network tools, such as telnet, rlogin, or web browsers.

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