From Bridges to Switches
Switches can be useful for solving network problems
Figure 52.1. Hubs do nothing to limit network traffic on the LAN.
When this older LAN was first installed, there was more than adequate bandwidth available and users were satisfied with the response time. Over time, however, each server was replaced with a more powerful model, and some of the end users' workstations were
Network traffic has increased considerably, users are dissatisfied, and the network administrator must take action. Because the main problem is the traffic exchanged between the servers and the high-performance end-
Figure 52.2. A switch can be used to isolate high bandwidth network nodes.
Throughout this book, I keep emphasizing that hubs are now legacy devices. For large networks, this is true. If you're using a small inexpensive hub for a SOHO network and you don't experience a slow network response time, there is no reason to "switch." However, when contemplating any new network installations or an upgrade, there's
Indeed, you'll find it difficult to find larger hubs on the market anymore, except by
An exception to this rule is that in a larger LAN, you might still use a hub (connected upstream to a switch) for a few users whose bandwidth is minimal. In that case, replacing a
This layout gives each node that is connected to the switch a full 10Mbps network connection or more likely 100Mbps, depending on your hardware. If you can't afford to replace older 10Mbps network cards (which is a possibility in a large network with a few hundred or thousands of computers), you might not need to worry. Most modern switches support autosensing, so they can detect both 10Mbps as well as 100Mbps traffic, and you can thus connect both types of network adapter cards to the switch. Even switches that support autosensing don't always work with older network adapters, so you can use the management software that
Each connection on a switch is a broadcast domain with only two end nodes: the connected workstation or server and the switch. In this solution, the server nodes were equipped with
The servers and high-performance workstations should also notice better performance, but their network traffic is no longer broadcast on the segments of the other moderate users, effectively isolating this traffic. For example, in Figure 52.3, you can see another solution discussed a paragraph or so earlier. Here, a hub is used for the workstations that use the network only moderately.
Figure 52.3. Traffic on the hub is not hampered by the traffic generated by the other high-performance servers and workstations.
Here each of the three servers that are responsible for much of the bandwidth use has been placed on a separate port on the switch. Again, full-duplex network adapters were installed to further increase the available bandwidth to each server. The three high-performance workstations also were placed on separate switch ports so that their network use does not directly interfere with other nodes. A hub was retained for connecting moderate network users. Because these nodes do not generate a lot of network communications, placing them on a hub connected to the switch should allow them fast communications among