Understanding Network Hardware
Switches have become inexpensive and are blazingly fast. For local area network
(LAN) connections, switches make more sense than hubs, partly because of their cost
and their relative simplicity. In fact, purchasing bridges has become difficult, as switches
now dominate the market.
Additionally, most new networks eschew hubs in favor of a 100 percentswitched
approach. In fact, it's virtually impossible to purchase hubs any longer, because
manufacturers typically offer only switches. (You may still be able to purchase very
small hubs, with four to eight ports, but even in these small applications, switches are
preferable and not much more expensive.)
It's important that you understand the difference between hubs and switches, because
you may still encounter hubs installed in existing networks. For new networks, you will
use switches exclusively. Doing so dramatically reduces the opportunity for network
packet collisions, which are more likely in a hub arrangement.
Bridges are, in a nutshell, more intelligent versions of repeaters. Bridges can connect
two network segments together, but they have the intelligence to pass traffic from one
segment to another only when that traffic is destined for the other segment. Bridges are used
to segment networks into smaller pieces. Some bridges can span different networking
systems and media, such as from coaxial Thin Ethernet to twisted-pair Token Ring.
As you might recall, repeaters operate at the physical layer (layer 1) of the OSI
networking model. Bridges operate one layer higher, at the data-link layer (layer 2).
Bridges examine the media access control (MAC) address of each packet they encounter
to determine whether they should forward the packet to the other network. Bridges
contain address information about all the parts of your network, through either a static
routing table that you program or a dynamic, learning-tree system that discovers all the
devices and addresses on the network automatically.
Is It Better to Use Fewer Large Switches or More Small Switches?
Larger switches that can host hundreds of connections within a single chassis are
generally more powerful than their smaller 24-port siblings, and they tend to
have more built-in redundancy, such as redundant power supplies in the unit and
so forth. However, sometimes it's easier and less expensive to build a network
using smaller 24-port switches. You can simply purchase an extra 24-port unit as
a hot-swap backup (a backup unit that can be quickly swapped in to take the place
of a failed unit) that you can manually implement at a moment's notice. The only
real disadvantage to this approach is that the redundancy is not automatic. If one
24-port switch fails, you'll need to move its connections to the backup switch. In
contrast, a larger unit can switch to redundant features automatically. As always,
consider such trade-offs carefully for your particular company and its needs.