Chapter 6 Configuring Ip Routes; Overview Of Ip Routes; Comparing Ip Routing To Telephone Switching - ZyXEL Communications Prestige 623 series User Manual

Prestige 623 Series Dual-link ADSL Router
Chapter 6
Configuring IP Routes
This chapter describes basic routing concepts and provides instructions for creating routes
6.1

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 Prestige uses to
make these decisions.
Most users do not need to define IP routes.

6.1.1 Comparing IP Routing to 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 a 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.
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.
Configuring IP Routes 6-1