Running Linux, 5th Edition

Network Diagnostics Tools

There are a number of useful tools that can help you diagnose network problems. We discuss three of them here that are generally helpful; a host of others for diagnosing particular problems are available as well.

ping

The first tool we look at is called ping. ping sends so-called ICMP packets to the server that you specify, the server returns them, and the ping determines the time the round trip took. This is useful to get an idea of the quality of your Internet connection, but we most often use it to see whether we can get a connection somewhere at all. For example, to see whether you have an Internet connection, just ping any computer on the Internet. For example:

    kalle@tigger:~> ping www.oreilly.com
    PING www.oreilly.com (208.201.239.36) 56(84) bytes of data.
    64 bytes from www.oreillynet.com (208.201.239.36): icmp_seq=1 ttl=46 time=280 ms
    64 bytes from www.oreillynet.com (208.201.239.36): icmp_seq=2 ttl=46 time=250 ms
    64 bytes from www.oreillynet.com (208.201.239.36): icmp_seq=3 ttl=46 time=244 ms

    --- www.oreilly.com ping statistics ---
    3 packets transmitted, 3 received, 0% packet loss, time 2001ms
    rtt min/avg/max/mdev = 244.976/258.624/280.430/15.586 ms

Notice that we pressed Ctrl-C here after a few seconds—it is not very nice to use the opposite server for this purpose for too long. What can you see from this? Well, first of all, you can see that you are actually able to contact a computer on the Internet. Since you did not type in the numerical IP address, ...