Workshop

There’s also an interactive mode that’s most helpful for resolving complex DNS issues. I’ll go into this
feature in Hour 19, “Internet/Intranet Troubleshooting.”
Pole Position
Sometimes a UNIX networking problem won’t be in the higher-level services and programs—in other
words, there will be times when it’s not the “people behind the telephone,” but rather the telephone or
phone system itself. In order to make this determination, you can use a couple techniques and commands.
When nothing seems to be working, you might have to find the UNIX console (the terminal that’s hardwired
to the server) and log in from there. If the console isn’t responsive, the UNIX server has locked up.
This doesn’t have anything to do with the network—it’s a rare occurrence, but it does happen. Your only
option here is to wince, turn the server off, and hope that it reboots okay.
Assuming that the console is working, it’s time to roll up your sleeves and see why your UNIX server
can’t be seen from the network. Let’s work from the inside out, assuming that, like Dr. Freud, all analysis
begins with the self. The basic notion here is that you need a network card to get to anything. Let’s check
that first:
# ifconfig -a
lo Link encap:Local Loopback
inet addr:127.0.0.1 Bcast:127.255.255.255 Mask:255.0.0.0
UP BROADCAST LOOPBACK RUNNING MTU:2000 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0
TX packets:37231 errors:0 dropped:0 overruns:0
eth0 Link encap:10Mbps Ethernet HWaddr 00:00:C0:82:26:94
inet addr:167.195.160.6 Bcast:167.195.160.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:816928 errors:0 dropped:0 overruns:0
TX packets:654019 errors:0 dropped:0 overruns:0
Interrupt:10 Base address:0x350 Memory:c8000-cc000
The key things to look for are the words up and running. If you don’t see them, something has caused
your network card to go down. Some network cards will go down due to a bad port on a hub, so try
switching the port. A reboot may be in order, or you may indeed have a bad network card. You can also
try netstat -i to check the error count and/or run ethstat to see what types of errors you might be
getting. This may point to a network problem rather than UNIX problem.