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NB-30 Bridging
3-2 Bridging Basics
About Transparent Bridging
Transparent bridges are most common in Ethernet networks. Individual
Transparent bridges monitor packet trafÞc on attached network segments to learn
where end stations reside in relation to each segment by mapping the Source
Address of each received frame to the port (and segment) it was detected on. This
information gets stored in the bridgeÕs Filtering Database.
When in the Forwarding state, the bridge compares a packetÕs destination address
to the information in the Filtering Database to determine if the packet should be
forwarded to another network segment or Þltered (i.e., not forwarded). A bridge
Þlters a packet if it determines that the packetÕs destination address exists on the
same side of the bridge as the source address.
If two or more bridges are connected to the same Ethernet LAN segmentÑplaced
in parallelÑonly a single bridge must be allowed to forward data frames onto
that segment. If two or more bridges were forwarding data frames onto the same
Ethernet segment, the network would soon be ßooded.
With a data loop in the topology, bridges would erroneously associate a single
source address with multiple bridge ports, and keep proliferating data by
forwarding packets in response to the ever-changing (but incorrect) information
stored in their Filtering Database.
To avoid such data storms, Transparent bridges communicate with one another
on the network by exchanging Bridge Protocol Data Units (BPDUs) to determine
the network topology and collectively implement a Spanning Tree Algorithm
(STA) that selects a controlling bridge for each LAN segment; this ensures that
only a single data route exists between any two end stations and that topology
information remains current.
Viewing and Managing Bridging Interfaces
With SPECTRUM Element Manager, you can view and manage each bridging
interface supported by your NB-30. You manage your bridge by using the
following windows:
¥ The Bridge Status window provides you with basic information about the
current status of the NB-30Õs bridging interfaces, allows you to conÞgure each
interface, and lets you enable or disable bridging across the bridge. The Bridge
Status window also lets you access further windows to conÞgure bridging at
the NB-30 (see Bridge Status, page 3-3).
¥ Bridge StatisticsÑincluding the Performance Graph, Bridge Summary
Statistics and the Ethernet and Remote Port Statustics windowsÑgraphically
display the trafÞc passing between your bridged networks, and let you
compare and contrast trafÞc processed by each interface (see Bridge Statistics,
page 3-9).