Essential System Administration, 3rd Edition

Network Testing and Troubleshooting

Once network configuration is complete, you will need to test network connectivity and address any problems that may arise. Here is an example testing scheme:

• Verify that the network hardware is working by examining any status lights on the adapter and switch or hub.

• Check basicnetwork connectivity using the ping command. Be sure to use IP addresses instead of hostnames so you are not dependent on DNS.

• Test name resolution using ping with hostnames or nslookup (see Section 8.1).

• Check routing by pinging hosts beyond the local subnet (but inside the firewall).

• Test higher-level protocol connectivity by using telnet to a remote host. If this fails, be sure that inetd is running, that the telnet daemon is enabled, and that the remote host from which you are attempting to connect is allowed to do so (inetd is discussed in Chapter 8).

• If appropriate, verify that other protocols are working. For example, use a browser to test the web server and/or proxy setup. If there are problems, verify that the browser itself is configured properly by attempting to view a local page.

• Test any network servers that are present on the local system (see Chapter 8).

The first step is to test the network setup and connection with the ping command. ping is a simple utility that will tell you whether the connection is working and the basic setup is correct. It takes a remote hostname or IP address as its argument:^[21]

$ ping hamlet PING hamlet: 56 data bytes 64 bytes from 192.0.9.3: ...