ATL Telecom AM30 - Manual (Page 117)

ATL Telecom User Guide
AM30
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7
Configuring Bridging
The ROUTER can be configured to act as a bridging device between your LAN and your ISP.
Bridges are devices that enable two or more networks to communicate as if they are two
segments of the same physical LAN. This chapter describes how to configure the ROUTER to
operate as a bridge.
Note
Before changing your bridge configuration, check with your
ISP to determine the type of connection they use to
exchange data with their customer’s DSL modems (such as
Ethernet bridging or IP routing).
Overview of Bridges
A bridge is a device used to connect two or more networks so they can exchange data. A
bridge learns the unique manufacturer-
assigned hardware IDs of each computer or device on both (or all) networks it is attached
to. It learns that some of the IDs represent computers attached via one of the device's
interfaces and others represent computers connected via other interfaces. For example, the
hardware IDs of your home computers are attached via the Ethernet port, and the
hardware IDs of your ISP's computers are attached via the WAN (DSL) port. It stores the ID
list and the interface associated with each ID in its bridge forwarding table.
When the bridge receives a data packet, it compares its destination hardware ID to the
entries in the bridge forwarding table. When the packet's ID matches one of the entries, it
forwards the packet through the interface that connects to the corresponding network.
Note that the bridge does not send the data directly to the receiving computer, but
broadcasts it to the receiving network, making it available to any node on that network. On
the receiving network, a LAN protocol such as Ethernet takes over, helping the packet
reaches its destination.
When the bridge does not recognize a packet’s destination hardware ID, it broadcasts the
packet through all of its interfaces – to each network it is attached to.