LAN Segmentation Using Switches

LAN Segmentation Using Switches
Ethernet is the most popular type of network in the world and will continue to be so,
ensured by the low cost of implementation coupled with the huge installed base of equipment.
It is therefore important for you to understand how hubs and switches work within
an Ethernet network.
By using
switched Ethernet
in layer 2 of your network, you no longer have to share bandwidth
with the different departments in the corporation. With hubs, all devices have to share the
same bandwidth (collision domain), which can cause havoc in today’s networks. This makes a
switched Ethernet LAN much more scalable than one based on shared Ethernet.
Hubs are layer 1 devices. The best way to think of them is as multi-port repeaters,
repeating everything that comes their way, including runt frames, giant frames,
and frames failing the frame check sequence at the end.
Even though layer 2 switches break the network into smaller collision domains, the network
is still one large broadcast domain. Nowadays, switched Ethernet has largely replaced
shared hubs in the networking world because each connection from a host to the switch is in
its own collision domain. This is often referred to as
micro-segmentation
(as opposed to
segmentation
, where a legacy bridge may have created only two LAN segments). Remember that,
with shared hubs, the network was one large collision domain and one large broadcast
domain, whereas layer 2 switches break up collision domains on each port, but all ports are
still considered, by default, to be in one large broadcast domain. Only virtual LANs, covered
in Chapter 14, “VLANs, Trunks, and VTP,” break up broadcast domains in a layer 2
switched network.
Switched Ethernet is a good way to allocate dedicated 10Mbps, 100Mbps, or 1000Mbps
connections to each user. By also running full-duplex Ethernet, you can theoretically double the
throughput on each link. In the next sections, we’ll discuss how Ethernet is used in your network,
the differences between the Ethernet types, and the half- and full-duplex options.