Workshop

(see Figure 4.2).
Figure 4.2 An Ethernet hub with 32 ports requires no more than five guesses.
Unlike a shared Token-Ring (where all hubs are connected in a circle, as shown in Figure 4.3), each
Ethernet hub is connected to another in a straight line (as shown in Figure 4.4). This means that if you
isolate one, you isolate those below it. You can handle this by bypassing the hub you want to isolate and
plugging directly into the next hub in the chain. However, be careful that your “cascade” hub is clearly
labeled before you start unplugging things.
Figure 4.3 A Token-Ring network.
Figure 4.4 An Ethernet network.
When you find the port that’s causing the problem—and even when you first find the hub that has the
problem port—make sure you perform a “control” experiment on it (that is, put it back into the main
network and make sure it’s still causing the problem).
If you isolate the hub that has the “network glue” on it—that is, the server or the router that connects you
to the server—the other hubs won’t be able to “see” any of the network and will remain “down.” If you
suspect this hub, it’s best to divide and conquer on a port level rather than taking out the entire hub (that
is, after verifying that the server or router is okay). If you don’t, you’ll keep the server or router from
talking to the rest of the workstations on the segment, and you’ll assume that taking this hub out does not
fix the problem (because the stations will still be unable to reach the server or router). In fact, the problem
might be with one of the stations on the server hub, which you’ll find if you take them out by port rather
than by the entire hub.