round-trip min/avg/max = 0.5/0.5/0.6 ms A line of
round-trip min/avg/max = 0.5/0.5/0.6 ms A line of output is printed each time a packet is sent and received in return. It shows how much data was sent and how long it took for each package to be received. After you have watched this for a while, type Ctrl+C to stop ping. At that point, it will show you statistics of how many packets were transmitted, received, and lost. If you don t see output that shows packets have been received, it means that you are not contacting the other computer. Try to verify that the names and addresses of the computers that you want to reach are in your /etc/hosts file or that your DNS server is accessible. Next, confirm that the names and IP addresses you have for the other computers that you are trying to reach are correct (the IP addresses are the most critical). Is your Ethernet connection up? Using the ifconfig command, you can determine whether your Ethernet (and other network interfaces) are up and running. Type the following command: # ifconfig The output that appears will be similar to the following: eth Link encap:Ethernet HWaddr 00:90:27:4E:67:35 inet addr:10.0.0.11 Bcast:10.255.255.255 Mask:255.0.0.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:156 errors:0 dropped:0 overruns:0 frame:0 TX packets:104 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 RX bytes:20179 (19.7 Kb) TX bytes:19960 (19.4 Kb) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:3924 Metric:1 RX packets:56 errors:0 dropped:0 overruns:0 frame:0 TX packets:56 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 RX bytes:3148 (3.0 Kb) TX bytes:3148 (3.0Kb) In this example, there are currently two network interfaces up on the current computer. The first section shows your Ethernet interface (eth0) and its hardware address, Ethernet hardware address, IP address (inet addr), broadcast address, and network mask. The next lines provide information on packets that have been sent, along with the number of errors and collisions that have occurred. Note The lo entry is for loopback. This enables you to run TCP/IP commands on your local system without having a physical network up and running. I describe this and other network interfaces in more detail in Chapter 16. If your eth0 interface does not appear, it may still be configured properly, but not running at the moment. Try to start the eth0 interface by typing the following: # ifconfig eth0 up After this, type ifconfig again to see if eth0 is now running. If it is, it may be that eth0 is simply not configured to start automatically at boot time. You can change it so Ethernet starts at boot-time (which I recommend), using the Network Configuration window (described earlier in this chapter). Tip If your network interfaces are not running at all, you can try to start them from the network initialization script. This interface reads parameters and basically runs ifconfig for all network interfaces on your computer. Type the following to restart your network:
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