A hub is the least intelligent and most rudimentary
network device. With a hub, traffic or data packets that
come in any port are always sent out to all other ports.
For example, in Figure 17-6, Laptop 1 wants to
communicate to Device 3. The hub replicates and sends
the packet from the laptop to each of the ports. Only
Device 3 responds back, and that response is again
replicated to all ports. Every device connected to the hub
“sees” everything. It is up to the devices themselves to
decide if a packet is for them and whether they should
respond. The hub remains passive and does not really
know or understand the traffic that flows through it.
Figure 17-6 Hub: Every Device Receives Every
Packet
One of the biggest challenges with hubs is that every
frame shows up at every device attached to a hub, instead
of just showing up at the intended destination. This can
be a huge security problem. Another challenge has to do
with performance: Because a hub can receive a lot of
inbound frames, sending out frames can be difficult and
can result in performance issues on the network.