router is a device that forwards data packets along networks.
A router is connected to at least two networks, commonly two
LANs or WANs or a LAN and its ISP's network. Routers are located
at gateways, the places where two or more networks connect,
and are the critical device that keeps data flowing between
networks and keeps the networks connected to the Internet.
When data is sent between locations on one network or from
one network to a second network the data is always seen and
directed to the correct location by the router. They accomplish
his by using headers and forwarding tables to determine the
best path for forwarding the data packets, and they use protocols
such as ICMP to communicate with each other and configure
the best route between any two hosts.
The Internet itself is a global network connecting millions
of computers and smaller networks — so you can see how
crucial the role of a router is to our way of communicating
Would I Need a Router?
For most home users, they may want to set-up a LAN (local
Area Network) or WLAN (wireless LAN) and connect all computers
to the Internet without having to pay a full broadband subscription
service to their ISP for each computer on the network. In
many instances, an ISP will allow you to use a router and
connect multiple computers to a single Internet connection
and pay a nominal fee for each additional computer sharing
the connection. This is when home users will want to look
at smaller routers, often called broadband routers that enable
two or more computers to share an Internet connection. Within
a business or organization, you may need to connect multiple
computers to the Internet, but also want to connect multiple
private networks — and these are the types of functions
a router is designed for.
for Home & Small Business
Not all routers are created equal since their job will differ
slightly from network to network. Additionally, you may look
at a piece of hardware and not even realize it is a router.
What defines a router is not its shape, color, size or manufacturer,
but its job function of routing data packets between computers.
A cable modem which routes data between your PC and your ISP
can be considered a router. In its most basic form, a router
could simply be one of two computers running the Windows 98
(or higher) operating system connected together using ICS
(Internet Connection Sharing). In this scenario, the computer
that is connected to the Internet is acting as the router
for the second computer to obtain its Internet connection.
a step up from ICS, we have a category of hardware routers
that are used to perform the same basic task as ICS, albeit
with more features and functions. Often called broadband or
Internet connection sharing routers, these routers allow you
to share one Internet connection between multiple computers.
or ICS routers will look a bit different depending on the
manufacturer or brand, but wired routers are generally a small
box-shaped hardware device with ports on the front or back
into which you plug each computer, along with a port to plug
in your broadband modem. These connection ports allow the
router to do its job of routing the data packets between each
of the the computers and the data going to and from the Internet.
on the type of modem and Internet connection you have, you
could also choose a router with phone or fax machine ports.
A wired Ethernet broadband router will typically have a built-in
Ethernet switch to allow for expansion. These routers also
support NAT (network address translation), which allows all
of your computers to share a single IP address on the Internet.
Internet connection sharing routers will also provide users
with much needed features such as an SPI firewall or serve
as a a DHCP Server.
broadband routers look much the same as a wired router, with
the obvious exception of the antenna on top, and the lack
of cable running from the PCs to the router when it is all
set up. Creating a wireless network adds a bit more security
concerns as opposed to wired networks, but wireless broadband
routers do have extra levels of embedded security. Along with
the features found in wired routers, wireless routers also
provide features relevant to wireless security such as Wi-Fi
Protected Access (WPA) and wireless MAC address filtering.
Additionally, most wireless routers can be configured for
"invisible mode" so that your wireless network cannot
be scanned by outside wireless clients. Wireless routers will
often include ports for Ethernet connections as well. For
those unfamiliar with WiFi and how it works, it is important
to note that choosing a wireless router may mean you need
to beef up your Wi-Fi knowledge-base. After a wireless network
is established, you may possibly need to spend more time on
monitoring and security than one would with a wired LAN.
and wireless routers and the resulting network can claim pros
and cons over each other, but they are somewhat equal overall
in terms of function and performance. Both wired and wireless
routers have high reliability and reasonably good security
(without adding additional products). However —and this
bears repeating — as we mentioned you may need to invest
time in learning more about wireless security. Generally,
going wired will be cheaper overall, but setting up the router
and cabling in the computers is a bit more difficult than
setting up the wireless network. Of course, mobility on a
wired system is very limited while wireless offers outstanding
The chances are very good that you'll never see the MAC address
for any of your equipment because the software that helps
your computer communicate with a network takes care of matching
the MAC address to a logical address. The logical address
is what the network uses to pass information along to your
If you'd like to see the MAC address and logical address used
by the Internet Protocol (IP) for your Windows computer, you
can run a small program that Microsoft provides. Go to the
"Start" menu, click on "Run," and in the
window that appears, type WINIPCFG (IPCONFIG/ALL for Windows
2000/XP). When the gray window appears, click on "More
Info" and you'll get this sort of information:
There's a lot of information here that will vary depending
on exactly how your connection to the Internet is established,
but the physical address is the MAC address of the adapter
queried by the program. The IP address is the logical address
assigned to your connection by your ISP or network administrator.
You'll see the addresses of other servers, including the DNS
servers that keep track of all the names of Internet sites
(so you can type "www.howstuffworks.com" rather
than "220.127.116.11") and the gateway server that
you connect to in order to reach the Internet. When you've
finished looking at the information, click OK. (Note: For
security reasons, some of the information about this connection
to the Internet has been changed. You should be very careful
about giving your computer's information to other people --
with your address and the right tools, an unscrupulous person
could, in some circumstances, gain access to your personal
information and control your system through a "Trojan
The first and most basic job of the router is to know where
to send information addressed to your computer. Just as the
mail handler on the other side of the country knows enough
to keep a birthday card coming toward you without knowing
where your house is, most of the routers that forward an e-mail
message to you don't know your computer's MAC address, but
they know enough to keep the message flowing.
Routers are programmed to understand the most common network
protocols. That means they know the format of the addresses,
how many bytes are in the basic package of data sent out over
the network, and how to make sure all the packages reach their
destination and get reassembled. For the routers that are
part of the Internet's main "backbone," this means
looking at, and moving on, millions of information packages
every second. And simply moving the package along to its destination
isn't all that a router will do. It's just as important, in
today's computerized world, that they keep the message flowing
by the best possible route.
a modern network, every e-mail message is broken up into small
pieces. The pieces are sent individually and reassembled when
they're received at their final destination. Because the individual
pieces of information are called packets and each packet can
be sent along a different path, like a train going through
a set of switches, this kind of network is called a packet-switched
network. It means that you don't have to build a dedicated
network between you and your friend on the other side of the
country. Your e-mail flows over any one of thousands of different
routes to get from one computer to the other.
on the time of day and day of the week, some parts of the
huge public packet-switched network may be busier than others.
When this happens, the routers that make up this system will
communicate with one another so that traffic not bound for
the crowded area can be sent by less congested network routes.
This lets the network function at full capacity without excessively
burdening already-busy areas. You can see, though, how Denial
of Service attacks (described in the next section), in which
people send millions and millions of messages to a particular
server, will affect that server and the routers forwarding
message to it. As the messages pile up and pieces of the network
become congested, more and more routers send out the message
that they're busy, and the entire network with all its users
can be affected.
of the Internet
In order to handle all the users of even a large private network,
millions and millions of traffic packets must be sent at the
same time. Some of the largest routers are made by Cisco Systems,
Inc., a company that specializes in networking hardware. Cisco's
Gigabit Switch Router 12000 series of routers is the sort
of equipment that is used on the backbone of the Internet.
These routers use the same sort of design as some of the most
powerful supercomputers in the world, a design that ties many
different processors together with a series of extremely fast
switches. The 12000 series uses 200-MHz MIPS R5000 processors,
the same type of processor used in the workstations that generate
much of the computer animation and special effects used in
movies. The largest model in the 12000 series, the 12016,
uses a series of switches that can handle up to 320 billion
bits of information per second and, when fully loaded with
boards, move as many as 60 million packets of data every second.
Beyond the computing power of the processors, these routers
can handle so much information because they are very highly
specialized. Relieved of the burden of displaying 3-D graphics
and waiting for mouse input, modern processors and software
can cope with amazing amounts of information.
Even with the computing power available in a very large router,
how does it know which of the many possibilities for outbound
connection a particular packet should take? The answer lies
back in the configuration table. The router will scan the
destination address and match that IP address against rules
in the configuration table. The rules will say that packets
in a particular group of addresses (a group that may be large
or small, depending on precisely where the router is) should
go in a specific direction. Next the router will check the
performance of the primary connection in that direction against
another set of rules. If the performance of the connection
is good enough, the packet is sent, and the next packet handled.
If the connection is not performing up to expected parameters,
then an alternate is chosen and checked. Finally, a connection
will be found with the best performance at a given moment,
and the packet will be sent on its way. All of this happens
in a tiny fraction of a second, and this activity goes on
millions of times a second, around the world, 24 hours every
where and how to send a message is the most important job
of a router. Some simple routers do this and nothing more.
Other routers add additional functions to the jobs they perform.
Rules about where messages from inside a company may be sent
and from which companies messages are accepted can be applied
to some routers. Others may have rules that help minimize
the damage from "denial of service" attacks. The
one constant is that modern networks, including the Internet,
could not exist without the router.