= easy reading
= requires a little effort
= technical
updated 8/2003
Routers, by definition, route data from one network to
another. Therefore, the Internet would come to a halt without routers. The
routers used to route Internet traffic are a lot more powerful and
sophisticated than the ones used in the homes and small businesses, but the
idea remains the same. The main difference is scale. Internet routers have
to handle huge amounts of traffic. Therefore, they have to be
"smarter."
You may have heard the word NAT associated with routers. NAT stands for Network
Address Translation. A NAT router has two ends. One end interacts with the DSL/cable modem and
obtains whatever public IP address (simply stated as IP from now on) the modem (or to be more precise, the ISP)
gives it, regardless of whether this IP is always the same (static) or
different each time a user dials into the ISP (dynamic). The router then
translates that public IP to at least one private IP, usually one starts
with 192.168. This private IP is
given to a computer that is connected to the router at the other end. This computer therefore
can have access to the Internet through the router.
Why go through all
this hassle of translation? Well, it's all about a lack of available IP
addresses and security. Hackers outside your home network cannot, at least not directly, access this computer because
they can only
access the router. Private IPs are non-routable, meaning the computers
with them cannot transmit to and receive data from the Internet without having their IPs
re-translated to the assigned public routable IP by the router. Therefore,
think of the router as a doorman where all delivery packages have to go
through. The FedEx person never comes into contact with the residents behind
the door. Needless to say, it is imperative to keep the password to the
router secret. In fact, if you could modify the default settings of the
router, do so. This way, hackers have to guess what type of a router it is
before they can start hacking. This is even more evidently so with routers
that are also wireless access points.
Ok, now some routers also act as DHCP servers. (What does DHCP stand for
is not important in this article because its full name, unlike that of
NAT, does not provide an easy clue for its purpose.) DHCP is a piece of
software that runs in the router that the router uses to give out
any IP address a client computer connected to it wants. Remember, any
computer that wants to access the Internet or connect to another computer
within your local network has to have an IP, public or private.
You can have multiple
computers connected to a router through the router's various Ethernet ports. In
this setup, all these computers can share that single public IP, and
therefore the DSL connection! The router keeps what is called a routing
table in its flash-based memory. This table has basically 2 entries: the
globally unique MAC address of the network card used by the computer and the private IP
given to it by the DHCP server of the router. Through this routing
table, the router knows what computer requests what data from the Internet
and relays the incoming requested data to that computer.
For more info on routers, check out these links:
Routers are a great invention in networking. The fact that you can get one
for about 30 dollars is amazing to me. Of course, there are a lot more to
routers than NAT and DHCP. There are things like firewall and port
forwarding. But that is another story.
http://snipurl.com/ah5o
