Hubs, Switches and Routers - What's the Difference?
By Steve Leytus
The backbone of a computer network uses three types of devices to interconnect
computers - hubs, switches and routers. Each is important and serves a different
role in facilitating communication between networked computers.
From the outside these devices may look similar - small, metal boxes with
multiple connectors or ports where ethernet cables are attached (routers may
also expose other types of connectors).
The terms "hub", "switch", and "router" are often used interchangeably and
misused - in fact, the devices are quite different. Hubs are used to simply
interconnect individual computers. Switches do the same (but more efficiently).
However, routers interconnect different networks (as opposed to individual machines).
Network Hub
Compared to switches and routers, hubs are the least expensive, simplest
device on the network. All data that enters one port of the hub is sent out all
the other ports. Hence, all computers connected to the same hub see each other's
network communications.
The hub doesn't pay any attention to the transmitted data, it simply passes
it along to its other ports. A hub's value lies in the fact it is inexpensive and
offers a quick and easy way to connect computers in a small network.
Network Switch
The job of a switch is similar to a hub's - but it does it more efficiently.
Each packet of data (ethernet frame) that is transmitted on the network has a
source and destination MAC address. A switch has the ability to remember the
address of each computer attached to its ports and will act as a traffic cop -
only passing transmitted data to the destination machine and not all the others.
This can have a significant positive affect on network performance because it
eliminates unnecessary transmissions and frees-up network bandwidth. A switch
can be thought of as the central component of a single network. It is used to
interconnect devices on the network and to deliver layer 2 (OSI model) frames.
A switch differs from a hub in that it does not retransmit frames to all other
devices - rather, a switch makes a direct link between the transmitting and
receiving devices.
Network Router
Compared to switches, routers are slow and relatively expensive. A router is
an intelligent device that interconnects two or more networks for the purpose of
delivering layer 3 (OSI model) packets. Since there may be more than one
possible path, a router takes into account multiple criteria when determining
which path to send the data packets.
The fact that switches and routers operate at different layers of the OSI model
indicates they rely on different information (contained in the frames or packets)
to send data from a source to a destination.
An important difference between switched and routed networks is switched
networks do not block broadcasts. As a result, switches can be overwhelmed by
broadcast storms. Routers block LAN broadcasts, so a broadcast storm only
affects the broadcast domain from which it originated. Since routers block
broadcasts, they also provide a higher level of security than switches.
Analogy
Here's an analogy to help explain the difference between a router and switch - a
corporation's mail room. When an employee sends a letter it may (a) be delivered
to its final destination by the company's internal mail delivery system or, (b)
taken to the local Post Office (if the recipient resides outside the company). A
switch represents the corporation's mail room, and a router the local Post Office.
A switch does not look inside the mail or examine the type of mail being
delivered. The only logic behind a switch is a table of MAC addresses (one for
each computer on the network) and which port a destination MAC is connected.
That is, the switch stores a table of company employees and their office numbers
and is responsible for delivering internal mail directly to employees. So, if
mail arrives at the switch that is destined for an employee then a switch knows
how to deliver it.
A router, on the other hand, is responsible for delivering mail destined for
individuals outside the company. In addition, routers can look inside the mail
and delivery rules can be applied based on the mail's contents. This feature
allows routers to play an important role in network security.
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