Cabletron Systems NB20E - Manual (Page 9)

INTRODUCTION
1-3
according to the specific needs of a network manager. The network
manager's ability to set up parameters within Remote LANVIEW ensures
optimal performance for each bridge, and hence, each network. For
example, a network manager can manage and monitor: the flow of traffic
through a bridge, the status of a database, the bridge protocol and port
parameters, and the bridge setup.
Both bridges also incorporate Cabletron Systems' LANVIEW Status
Monitoring and Diagnostics Systems. Should a problem arise,
LANVIEW's LEDs will help you to diagnose problems, such as power
failures or cable faults. Individual or separate LEDs advise you that: the
bridge is on line and operational, the bridge is receiving or transmitting
data packets, or the bridge is detecting a collision signal from an
individual segment.
The NB20E or NB25E Bridge interconnects networks consisting of
Ethernet Version 1, Version 2, and/or IEEE 802.3 equipment. The bridge
has two AUI ports so it can be connected directly to any of Cabletron’s
many Ethernet transceivers for data transmission over various media
including twisted pair, fiber optic, and/or thick or thin Ethernet coaxial
cable.
1.4 THE BRIDGE FILTERING METHOD
The Cabletron Systems NB20E and NB25E prevent unnecessary network
traffic from passing through the bridge, by implementing a filtering
process. This process begins with the creation of a list of local node
addresses in a table referred to as the Source Address Table.
When the NB20E or NB25E first goes on line, the bridge initially
forwards all packets through the bridge. As the bridge receives a packet, it
learns the address of the sending node from the packet and stores that
address in its Source Address Table, indicating the segment on which the
address resides. In this manner, the bridge learns the address of each node
on each side of the bridge and is able to use the addresses stored in the
table to compare the destination address of each subsequent packet that
travels to the bridge. If the destination address of a packet is located on
the same segment (local segment) as the sending node, the packet is not
forwarded across the bridge.
Figure 1-1 provides an illustration of the filtering process.