TRENDnet TDM-E400 - Manual (Page 106)

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10
Configuring IP Routes
You can use Web Configuration to define specific routes for your
Internet and network data. This chapter describes basic routing
concepts and provides instructions for creating routes.
Note that most users do not need to define IP routes.
Overview of IP Routes
The essential challenge of a router is: when it receives data
intended for a particular destination, which next device should it
send that data to? When you define IP routes, you provide the rules
that a computer uses to make these decisions.
IP routing versus telephone switching
IP routing decisions are similar to those made by switchboards that
handle telephone calls.
When you dial a long distance telephone number, you are first
connected to a switchboard operated by your local phone service
carrier. All calls you initiate go first to this main switchboard.
If the phone number you dialed is outside your calling area, the
switchboard opens a connection to a higher-level switchboard for
long distance calls. That switchboard looks at the area code you
dialed and connects you with another switchboard that serves that
area. This new switchboard, in turn, may look at the prefix in the
number you dialed (the middle set of three numbers) and connect to
a more localized switchboard that handles numbers with that prefix.
This final switchboard can then look at the last four digits of the
phone number to open a connection with the person or company
you dialed.
In comparison, when your computer initiates communication over
the Internet, such as viewing a web page connecting to an web
server, the data it sends out includes the IP address of the
destination computer (the “phone number”). All your outgoing
requests first go to the same router at your ISP (the first
“switchboard”). That router looks at the network ID portion of the
destination address (the “area code”) and determines which next
router to send the request to. After several such passes, the request
arrives at a router for the destination network, which then uses the
host ID portion of the destination IP address (the local “phone
number”) to route the request to the appropriate computer. (The
network ID and host ID portions of IP addresses are explained in
Appendix A.)
With both the telephone and the computer, all transactions are
initially sent to the same switchboard or router, which serves as a
gateway to other higher- or lower-level devices. No single device
knows at the outset the eventual path the data will take, but each
uses a specific part of the destination address/phone number to
make a decision about which device to connect to next.