121
GB
Appendix C: Networks and Routing Basics
This chapter provides an overview of IP networks, routing, and firewalls. This is by no
means a complete overview! If you are looking for more information, you can use your
favorite search engine to find information on the internet about the internet. Suffice to
say, there is plenty.
Basic Router Concepts
Even though the amount of bandwidth in your local area network (LAN) can be provided easily
and relatively inexpensively, the price of the connection to the internet is much higher. Because
of this expense, Internet access is usually provided by a slower-speed wide-area network (WAN)
link such as a cable or DSL modem. To use this WAN link efficiently, a mechanism must be in
place for selecting and transmitting only the data traffic meant for the Internet. The function of
selecting and forwarding this data is performed by a router.
What is a Router?
A router splits the information meant for your network and meant for other networks, so
the available bandwidth is used efficiently. The router sends data based on network layer
information in the data and on routing tables maintained by the router. The routing
tables are built by gathering and exchanging information with other routers in the
network. The router builds up a logical picture of the overall network. Using this
information, the router chooses the best path for forwarding network traffic. Routers
vary in performance and scale, number of routing protocols supported, and types of
physical WAN connection they support.
Routing Information Protocol
One of the protocols used by a router to build and maintain a picture of the network is
the Routing Information Protocol (RIP). Using RIP, routers periodically update one
another and check for changes to add to the routing table.
IP Addresses and the Internet
For a computer to communicate with other computers and Web servers on the Internet,
it must have a unique IP address. An IP address (IP stands for Internet Protocol) is a unique
number that identifies the location of your computer on a network.
Basically, it works like your street address — as a way to find out exactly where you are
and deliver information to you. The IP address is written as 4 numbers between 0 and
255, such as "192.168.0.12".
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