Cabletron Systems 9H42X-XX An Overview of Bridge Management

Bridging

5-2 An Overview of Bridge Management

return a response to the source node that contains the route information ﬁeld

indicating which bridge paths the explorer packets took. In future communication

between the two nodes, the original source node will append the best route to the

destination node in a Routing Information Field (RIF) of its data frames, so that a

bridge on the network will simply have to examine the RIF to verify whether it is

a part of the route process.

Transparent bridges are most common in Ethernet networks. Individual

Transparent bridges monitor packet trafﬁc on attached network segments to learn

their network segment location in terms of which bridge port receives packets

originating from a particular station (determined via the packet’s Source Address

ﬁeld). This information gets stored in the bridge’s Filtering Database. When in the

Forwarding state, the bridge compares a packet’s destination address to the

information in the Filtering Database to determine if the packet should be

forwarded to another network segment or ﬁltered (i.e., not forwarded). A bridge

ﬁlters a packet if it determines that the packet’s destination address exists on the

same side of the bridge as the source address.

Transparent bridges in a network communicate with one another by exchanging

Bridge Protocol Data Units, or BPDUs, and collectively implement a Spanning

Tree Algorithm (STA) to determine the network topology, to ensure that only a

single data route exists between any two end stations, and to ensure that the

topology information remains current.

An Overview of Bridge Management

With SPECTRUM Element Manager, you can view and manage bridging across

the 9H42x-xx module — and at each bridging interface — by using the following

windows:

• The Bridge Status window provides you with basic information about the

current status of the 9H42x-xx module’s bridging interfaces, and allows you to

enable or disable bridging at each interface of the switch. The Bridge Status

window also lets you access further windows to conﬁgure bridging at the

9H42x-xx module.

• The Performance Graph, Statistics, and I/F Statistics windows graphically

display the trafﬁc passing between bridged networks, and let you compare

and contrast trafﬁc processed by each interface. Performance graphs are

described beginning on page 5-7; the statistics windows are described in

Chapter 4.

• The Spanning Tree window shows bridge port information and protocol

parameters relating to the Spanning Tree Algorithm (the method of

determining the controlling bridge when a series of bridges are placed in

parallel).