Chapter 3
9E312/9E423 Module Bridging
Bridge management overview; the Bridge Status window — viewing the window, field definitions, enabling and disabling bridging; the Bridge Performance Graphs — field definitions, configuring the graphs, bridge detail breakdown, bridge port detail background; the Bridge Spanning Tree window — fields defined, changing bridge Spanning Tree parameters; the Filtering Database window — field definitions, configuring the filtering database; the Duplex Modes window — field definitions, setting the duplex mode; the port Source Addressing window
Bridging Basics
Your
Bridges are used in local area networks to connect two or more network segments and to control the flow of packets between the segments. Ideally, bridges forward packets to another network segment only when necessary.
Bridges are also used to increase the fault tolerance in a local area network by creating redundant bridge paths between network segments. In the event of a bridge or bridge segment failure, an alternate bridge path will be available to network traffic, without significant interruption to its flow.
The method a bridge uses to forward packets, choose a bridge path, and ensure that a sending station’s messages take only one bridge path depends on the bridge’s type: Transparent (generally used in Ethernet or FDDI environments) or Source Routing (generally used in Token Ring environments).
Transparent bridging relies on a “Filtering Database” to make forwarding decisions. The source addresses of data coming into each bridge interface are read and stored in a Filtering Database that associates each address with the interface it was detected on. When a packet is received by the bridge, it can then compare the destination address of the packet to the addresses in the Filtering Database, and determine which bridge interface to send the packet to.