Cabletron Systems NB20E User manual

NB20E and NB25 E
TWO PORT ETHERNET BRIDGES
USER’S MANUAL
CABLETRON SYSTEMS, P.O. BOX 6257, ROCHESTER, NH 03867-6257

i
NOTICE
Cabletron Systems reserves the right to make changes in specifications
and other information contained in this document without prior notice.
The reader should in all cases consult Cabletron Systems to determine
whether any such changes have been made.
The hardware, firmware, or software described in this manual is subject to
change without notice.
IN NO EVENT SHALL CABLETRON SYSTEMS BE LIABLE FOR
ANY INCIDENTAL, INDIRECT, SPECIAL, OR CONSEQUENTIAL
DAMAGES WHATSOEVER (INCLUDING BUT NOT LIMITED TO
LOST PROFITS) ARISING OUT OF OR RELATED TO THIS
MANUAL OR THE INFORMATION CONTAINED IN IT, EVEN IF
CABLETRON SYSTEMS HAS BEEN ADVISED OF, KNOWN, OR
SHOULD HAVE KNOWN, THE POSSIBILITY OF SUCH DAMAGES.
© Copyright May 1990 by:
Cabletron Systems Inc.
P.O. Box 6257, E. Rochester, NH 03867-6257
All Rights Reserved
Printed in the United States of America
Order Number: 9030040-02 May 90
Remote LANVIEW , LANVIEW , NB25E , NB20E , and LAN-MD are
trademarks of Cabletron Systems Inc.

FCC NOTICE
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FCC NOTICE
This device complies with Part 15 of the FCC rules. Operation is subject
to the following two conditions: (1) this device may not cause harmful
interference, and (2) this device must accept any interference received,
including interference that may cause undesired operation.
WARNING: This equipment uses and generates and can radiate radio
frequency energy and if not installed properly and used in accordance
with the instruction manual, may cause interference to radio
communications. It has been tested and found to comply with the limits
for a Class A digital device pursuant to Subpart J, of Part 15, of the FCC
rules., which are designed to provide reasonable protection against such
interference in a commercial environment. Operation of this equipment in
a residential area is likely to cause interference in which case the user at
his own expense will be required to correct the interference.
If this equipment does cause interference to radio or television, which can
be determined by turning the equipment off and on, the user is
encouraged to try to correct the interference by one or more of the
following measure:
• Re-orient the receiving antenna.
• Relocate the antenna with respect to the bridge.
• Move the bridge away from the receiver.
• Plug the bridge into a different outlet so that the bridge and the
receiver are on different branch circuits.
If necessary, the user should consult the dealer or an experienced radio/
television technician for additional suggestions. The user may find the
following booklet prepared by the Federal Communication Commission
helpful:
“How to Identify and Resolve Radio TV Interference Problems”
This booklet is available from the U.S. Government Printing Office,
Washington, D.C. 20401- Stock No. 004-000-00345-4

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CONTENTS
CHAPTER 1 INTRODUCTION
1.1 USING THIS MANUAL................................................................1-1
1.2 GETTING HELP..........................................................................1-2
1.3 THE NB20E AND NB25E TWO PORT ETHERNET BRIDGE ....1-2
1.4 THE BRIDGE FILTERING METHOD..........................................1-3
1.5 MULTIPLE BRIDGE ENVIRONMENTS......................................1-5
1.5.1 The Root Bridge..............................................................1-5
1.5.2 Primary and Redundant Data Paths...............................1-6
1.6 REMOTE LANVIEW....................................................................1-7
1.7 RELATED MANUALS..................................................................1-8
CHAPTER 2 INSTALLATION REQUIREMENTS/
SPECIFICATIONS
2.1 LOCATION REQUIREMENTS....................................................2-1
2.2 NETWORK REQUIREMENTS....................................................2-1
2.3 OPERATING SPECIFICATIONS ................................................2-2
CHAPTER 3 INSTALLINGTHE NB20E OR NB25E BRIDGE
3.1 UNPACKING THE NB20E OR NB25E BRIDGE.........................3-1
3.2 INSTALLING THE BRIDGE.........................................................3-1
3.2.1 Installing the Rack Mount Brackets ................................3-2
3.2.2 Cable Support Installation...............................................3-3
3.2.3 Connecting The Bridge To The Network ........................3-3
3.2.4 Setting The Mode Switches............................................3-4
3.2.5 Connecting The NB20E or NB25E To
The Power Source.........................................................3-5
CHAPTER 4 TESTING AND LANVIEW
4.1 INSTALLATION CHECK-OUT.....................................................4-1
4.2 USING LANVIEW........................................................................4-2
4.3 USING THE FORWARD BROADCAST SWITCH.......................4-3
4.4 USING THE ROOT SWITCH ......................................................4-4

CONTENTS
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1-1
CHAPTER 1
INTRODUCTION
Welcome to the Cabletron Systems NB20E™ and NB25E™ Two Port
Ethernet Bridges User's Manual. We have designed this user’s manual to
serve as a simple installation and reference guide for the NB20E and
NB25E, and to explain the capabilities and special features of each
individual bridge. With the appropriate design, the Cabletron Systems
NB25E or NB20E can dramatically improve network performance and
bandwidth efficiency on heavily utilized network segments.
You should read through this manual to gain a full understanding of the
NB20E and NB25E Bridges and their capabilities.
1.1 USINGTHIS MANUAL
Chapter 1, Introduction , discusses the capabilities of Cabletron Systems'
NB20E or NB25E Two Port Ethernet Bridge. An explanation of the
bridge filtering process and a discussion of bridge functionality in
multi-bridge environments are also included. The chapter concludes with
a list of related manuals.
Chapter 2,
Installation Requirements/Specifications , contains a list of
hardware, software, location and environmental requirements that must be
met before you install either bridge.
Chapter 3,
Installing the NB20E or NB25E Bridge , contains
instructions for installing the NB20E or the NB25E Two Port Ethernet
Bridge.
Chapter 4,
Testing and Troubleshooting , provides procedures for testing
and troubleshooting the installation of the NB20E or the NB25E Bridge.
Instructions for using LANVIEW™, Cabletron Systems’built-in visual
diagnostic and status monitoring system, are also included.
We assume that you have a general working knowledge of Ethernet or
IEEE 802.3 type data communications networks and their physical layer
components.

INTRODUCTION
1-2
1.2 GETTING HELP
If you need additional support related to the Cabletron Systems NB20E or
NB25E Two Port Ethernet Bridge, or if you have any questions,
comments or suggestions related to this manual, feel free to contact
Cabletron Systems' Technical Support at:
Cabletron Systems Inc.
P.O. Box 6257
E. Rochester, NH 03867-6257
Phone: [phone]
1.3 THE NB20E AND NB25ETWO PORT ETHERNET
BRIDGE
With the Cabletron Systems NB20E or NB25E Two Port Ethernet Bridge,
you can dramatically increase the performance of two 10 Mbit per second
Ethernet networks efficiently and economically, regardless of the media
type. The bridges are designed to increase the efficiency of bandwidth use
across a LAN by building a list of local node addresses as it learns which
nodes are located on each side of the bridge. This list is called the Source
Address Table. The bridge uses the Source Address Table to determine
which data packets should be allowed to cross the bridge, keeping local
traffic local.
The NB20E Bridge uses a software filter database to check destination
addresses against its Source Address Table. The NB25E Bridge uses a
higher performance hardware filter database. Both bridges are equipped
with a feature called Aging Time, that continually makes space for new
entries into the Source Address Table by deleting addresses that are not
frequently used.
The NB20E and NB25E are designed to function in multiple-bridge
environment. As IEEE 802.1 compliant bridging units, the bridges
incorporate a Spanning Tree Algorithm to detect potential data loops in
the network. Spanning TreeAlgorithm is a hierarchy (or tree) of priorities
that is established between bridges.
The NB20E and NB25E can be controlled and managed by Cabletron
Systems' Remote LANVIEW™ - Network Control Management for the
Cabletron Systems' NB20E and NB25E. Remote LANVIEW provides the
most complete network management system for Ethernet networks in the
industry today. With Remote LANVIEW, a bridge can be managed

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.

INTRODUCTION
1-4
Figure 1-1 Bridging Method
In this example, when NodeA sends a packet to Node B, the bridge learns
Node A’s source address and adds the address to the Source Address
Table, indicating that the node is on LAN 1. If Node C subsequently sends
a packet to Node A, Node A’s address will be detected in the Source
Address Table for LAN 1 and the packet will not be forwarded across the
bridge to LAN 2. At the same time, the bridge will learn Node C’s source
address and add it to the SourceAddress Table, indicating that the node is
on LAN 1.
If the destination address of a packet is located on a different segment, the
bridge will forward the packet across the bridge. If Node B sends a packet
to Node A, the bridge will compare the destination address of the packet
against the addresses in the SourceAddress Table. It will then detect Node
A as being on the other side of the bridge and forward the packet through
the bridge to LAN 1. The bridge will store the address of Node B to
indicate that Node B is on LAN 2.
If no packets are sent from a source address in a five minute interval, that
address will be deleted from the bridge’s Source Address Table.
TT
TT
NODE A NODE C
LAN 1
LAN 2
NODE B