Today most routers have become something of a Swiss Army knife,
combining the features and functionality of a router and switch/hub into
a single unit. So conversations regarding these devices can be a bit
misleading — especially to someone new to computer networking.
The functions of a router, hub and a switch are all quite different from
one another, even if at times they are all integrated into a single
device.
Let's start with the hub and the switch since these two devices have
similar roles on the network. Each serves as a central connection for
all of your network equipment and handles a data type known as frames.
Frames carry your data. When a frame is received, it is amplified and
then transmitted on to the port of the destination PC. The big
difference between these two devices is in the method in which frames
are being delivered.
In a hub, a frame is passed along or
"broadcast" to every one of its ports. It doesn't matter that the frame
is only destined for one port. The hub has no way of distinguishing
which port a frame should be sent to. Passing it along to every port
ensures that it will reach its intended destination. This places a lot
of traffic on the network and can lead to poor network response times.
Additionally, a 10/100Mbps hub must share its
bandwidth
with each and every one of its ports. So when only one PC is
broadcasting, it will have access to the maximum available bandwidth.
If, however, multiple PCs are broadcasting, then that bandwidth will
need to be divided among all of those systems, which will degrade
performance.
A switch, however, keeps a record of the
MAC addresses
of all the devices connected to it. With this information, a switch can
identify which system is sitting on which port. So when a frame is
received, it knows exactly which port to send it to, without
significantly increasing network response times. And, unlike a hub, a
10/100Mbps switch will allocate a full 10/100Mbps to each of its ports.
So regardless of the number of PCs transmitting, users will always have
access to the maximum amount of bandwidth. It's for these reasons why a
switch is considered to be a much better choice then a hub.
Routers are completely different devices. Where a hub or switch is
concerned with transmitting frames, a router's job, as its name implies,
is to route
packets
to other networks until that packet ultimately reaches its destination.
One of the key features of a packet is that it not only contains data,
but the destination address of where it's going.
A router is typically connected to at least two networks, commonly two Local Area Networks (
LANs) or Wide Area Networks (
WAN) or a LAN and its
ISP's network . for example, your PC or workgroup and EarthLink. Routers are located at
gateways,
the places where two or more networks connect. Using headers and
forwarding tables, routers determine the best path for forwarding the
packets. Router use protocols such as
ICMP to communicate with each other and configure the best route between any two hosts.
Today, a wide variety of services are integrated into most broadband
routers. A router will typically include a 4 - 8 port Ethernet switch
(or hub) and a Network Address Translator (
NAT).
In addition, they usually include a Dynamic Host Configuration Protocol
(DHCP) server, Domain Name Service (DNS) proxy server and a hardware
firewall to protect the LAN from malicious intrusion from the Internet.
All routers have a WAN Port that connects to a
DSL or
cable modem
for broadband Internet service and the integrated switch allows users
to easily create a LAN. This allows all the PCs on the LAN to have
access to the Internet and Windows file and printer sharing services.
Some routers have a single WAN port and a single LAN port and are
designed to connect an existing LAN hub or switch to a WAN. Ethernet
switches and hubs can be connected to a router with multiple PC ports to
expand a LAN. Depending on the capabilities (kinds of available ports)
of the router and the switches or hubs, the connection between the
router and switches/hubs may require either straight-thru or crossover
(null-modem) cables. Some routers even have
USB ports, and more commonly, wireless access points built into them.
Some of the more high-end or business class routers will also
incorporate a serial port that can be connected to an external dial-up
modem, which is useful as a backup in the event that the primary
broadband connection goes down, as well as a built in LAN printer server
and printer port.
Besides the inherent protection features
provided by the NAT, many routers will also have a built-in,
configurable, hardware-based firewall. Firewall capabilities can range
from the very basic to quite sophisticated devices. Among the
capabilities found on leading routers are those that permit configuring
TCP/UDP ports for games, chat services, and the like, on the LAN behind
the firewall.
So, in short, a hub glues together an Ethernet
network segment, a switch can connect multiple Ethernet segments more
efficiently and a router can do those functions plus route
TCP/IP packets between multiple LANs and/or WANs; and much more of course.
