ATL Telecom AM30 - Manual (Page 83)

ATL Telecom User Guide
AM30
8
3
Configuring IP Routes
You can use Configuration Manager 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 0.)
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.