ABOUT THIS GUIDE
Finding Speciﬁc Information in This Guide 12
What to Expect from This Guide 12
Related Documentation 15
Help Systems 15
PART I BEFORE TROUBLESHOOTING
NETWORK TROUBLESHOOTING OVERVIEW
Introduction to Network Troubleshooting 19
About Connectivity Problems 19
About Performance Problems 20
Solving Connectivity and Performance Problems 20
Network Troubleshooting Framework 21
Troubleshooting Strategy 23
Recognizing Symptoms 24
User Comments 24
Network Management Software Alerts 24
Analyzing Symptoms 25
Understanding the Problem 25
Identifying and Testing the Cause of the Problem 26
Sample Problem Analysis 27
Equipment for Testing 28
Solving the Problem 29
YOUR NETWORK TROUBLESHOOTING TOOLBOX
Transcend Applications 31
Transcend Central 32
Status View 32
Status Watch 32
MAC Watch 33
Web Reporter 33
LANsentry Manager 33
Trafﬁx Manager 34
Device View 35
Network Management Platforms 35
3Com SmartAgent Embedded Software 36
Other Commonly Used Tools 38
Strategies for Using Ping 39
Tips on Interpreting Ping Messages 40
FTP and TFTP 40
Cable Testers 42
STEPS TO ACTIVELY MANAGING YOUR NETWORK
Designing Your Network for Troubleshooting 43
Positioning Your SNMP Management Station 44
Using Probes 45
Monitoring Business-critical Networks 47
FDDI Backbone Monitoring 48
Internet WAN Link Monitoring 48
Switch Management Monitoring 48
Using Telnet, Serial Line, and Modem Connections 49
Using Communications Servers 50
Setting Up Redundant Management 51
Other Tips on Network Design 52
Management Station Conﬁguration 52
More Tips 52
Preparing Devices for Management 53
Conﬁguring Management Parameters 53
Conﬁguring Traps 53
Conﬁguring Transcend Software 54
Monitoring Devices 54
Setting Thresholds and Alarms 54
Setting Thresholds in Status Watch 55
Setting Thresholds and Alarms in LANsentry Manager 55
Reﬁning Alarm Settings 56
Setting Alarms Based on a Baseline 57
Other Tips for Setting Thresholds and Alarms 57
Knowing Your Network 58
Knowing Your Network’s Conﬁguration 58
Site Network Map 58
Logical Connections 60
Device Conﬁguration Information 60
Other Important Data About Your Network 61
Identifying Your Network’s Normal Behavior 62
Baselining Your Network 62
Identifying Background Noise 63
PART II NETWORK CONNECTIVITY PROBLEMS AND SOLUTIONS
Manager-to-Agent Communication Overview 67
Understanding the Problem 67
Identifying the Problem 67
Solving the Problem 68
Checking Management Conﬁgurations 68
Manager-to-Agent Communication Reference 69
IP Address 69
Gateway Address 69
Subnetwork Mask 69
SNMP Community Strings 69
SNMP Traps 72
FDDI Connectivity Overview 73
Understanding the Problem 73
Identifying the Problem 75
Solving the Problem 76
Monitoring FDDI Connections 77
Status Watch 77
Making Your FDDI Connections More Resilient 77
Implementing Dual Homing 77
Installing an Optical Bypass Unit 79
FDDI Connectivity Reference 79
Peer Wrap Condition 79
Twisted Ring Condition 80
Undesired Connection Attempt Event 80
PART III NETWORK PERFORMANCE PROBLEMS AND SOLUTIONS
Bandwidth Utilization Overview 85
Understanding the Problem 85
Identifying the Problem 85
Solving the Problem 86
Identifying Utilization Problems 86
Status Watch 86
Generating Historical Utilization Reports 88
Web Reporter 88
Bandwidth Utilization Reference 89
ATM Utilization 89
Ethernet Utilization 89
FDDI Utilization 90
Token Ring Utilization 90
Broadcast Storms Overview 93
Understanding the Problem 93
Identifying the Problem 93
Solving the Problem 94
Identifying a Broadcast Storm 94
Status Watch 94
Trafﬁx Manager 96
Disabling the Offending Interface 97
MAC Watch 97
Correcting Spanning Tree Misconﬁgurations 98
Device View 98
Broadcast Storms Reference 99
Broadcast Packets 99
Multicast Packets 99
Duplicate Addresses Overview 101
Understanding the Problem 101
Identifying the Problem 101
Solving the Problem 101
Finding Duplicate MAC Addresses 102
MAC Watch 102
Status Watch 103
Finding Duplicate IP Addresses 103
MAC Watch 104
LANsentry Manager 104
Duplicate Addresses Reference 105
Duplicate MAC Addresses 105
Duplicate IP Addresses 106
ETHERNET PACKET LOSS
Ethernet Packet Loss Overview 107
Understanding the Problem 107
Identifying the Problem 108
Solving the Problem 108
Checking for Packet Loss 109
Status Watch 109
LANsentry Manager Network Statistics Graph 111
Device View 114
Ethernet Packet Loss Reference 115
Alignment Errors 115
CRC Errors 116
Excessive Collisions 116
FCS Errors 116
Late Collisions 116
Nonstandard Ethernet Problems 117
Receive Discards 118
Too Long Errors 118
Too Short Errors 118
Transmit Discards 118
FDDI RING ERRORS
FDDI Ring Errors Overview 119
Understanding the Problem 119
Identifying the Problem 119
Solving the Problem 120
Identifying Ring Errors 121
Status Watch 121
FDDI Ring Errors Reference 121
Elasticity Buffer Error Condition 121
Frame Error Condition 121
Frames Not Copied Condition 122
Link Error Condition 122
MAC Neighbor Change Event 122
NETWORK FILE SERVER TIMEOUTS
Network File Server Timeout Overview 123
Understanding the Problem 123
Identifying the Problem 124
Solving the Problem 124
Checking for Obvious Errors 124
Ping and Telnet 124
LANsentry Manager Alarms View 124
LANsentry Manager Statistics View 125
LANsentry Manager History View 125
Reproducing the Fault While Monitoring the Network 126
LANsentry Manager Top-N Graph 126
LANsentry Manager Packet Capture 126
LANsentry Manager Packet Decode 127
MAC Watch 128
LANsentry Manager Packet Decode 128
Correcting the Fault 129
Network File Server Timeouts Reference 129
Network File System (NFS) Protocol 129
PART IV REFERENCE
SNMP IN NETWORK TROUBLESHOOTING
SNMP Operation 133
Manager/Agent Operation 133
SNMP Messages 134
Trap Reporting 134
SNMP MIBs 136
MIB Tree 136
RMON MIB 139
RMON2 MIB 140
3Com Enterprise MIBs 141
ABOUT THIS GUIDE
About This Guide provides an overview of this guide, describes guide
conventions, tells you where to look for speciﬁc information, and lists
other publications that may be useful.
This guide helps you to troubleshoot connectivity and performance
problems on your network using Transcend® software and other tools.
This guide is intended for network administrators who understand
networking technologies and how to integrate networking devices. You
should have a working knowledge of:
s Transmission Control Protocol/Internet Protocol (TCP/IP)
s Simple Network Management Protocol (SNMP)
s Network management platforms (especially HP OpenView Network
Node Manager from Hewlett-Packard)
s 3Com devices on your network
You should also be familiar with the interface and features of the
Transcend management software you have installed.
With subsequent releases of Transcend management software, this
guide will be updated with new troubleshooting information and
additional Transcend troubleshooting tools. The most current version of
this guide is on the 3Com Web site: www.3Com.com.
12 ABOUT THIS GUIDE
Finding Speciﬁc This guide, which is available online (in PDF and HTML formats) and on
Information in paper, is designed to be used online. For the online version,
This Guide cross-references to other sections are indicated with links in blue,
underlined text, which you can click. You can print any pages as
Table 1 provides guidelines for navigating through this document.
Table 1 Guidelines for Finding Speciﬁc Information in This Guide
If you are looking for See
An introduction to network troubleshooting, Part I: Before Troubleshooting
information about troubleshooting tools, and (page 17)
guidelines for getting ready for management
Note: This part is recommended
reading for users who are new to
Specific troubleshooting scenarios that will help Part II: Network Connectivity
you solve real network problems Problems and Solutions (page
Part III: Network Performance
Problems and Solutions (page
Useful background information to help you with Part IV: Reference (page 131)
What to Expect This guide demonstrates how to troubleshoot problems on your
from This Guide network with the help of Transcend management software and other
tools. It also shows you how to use Transcend software to move
beyond day-to-day troubleshooting to proactive network management.
This guide does not help you identify and correct problems with
installation and use of Transcend software. For that type of
s The Transcend Management Software Installation Guide (for help
with installation and startup problems)
s The help or user guide for a speciﬁc application (for information
about troubleshooting application problems)
This guide focuses on technologies that are important for
troubleshooting your network and shows how these technologies are
applied using Transcend management software. For additional
information, see the resources listed in Information Resources (page
Conventions Table 2, Table 3, and Table 4 list conventions that are used throughout
Table 2 Notice Icons
Icon Notice Type Description
Information note Important features or instructions
Caution Information to alert the user to potential damage
to a program, system, or device
Warning Information to alert the user to potential personal
Table 3 Troubleshooting Icons
Icon Type Points out
Troubleshooting Where a troubleshooting procedure begins
Troubleshooting Tips and other useful information for performing a
tip troubleshooting task or working with a Transcend
management software tool
14 ABOUT THIS GUIDE
Table 4 Text Conventions
Syntax The word “syntax” means you must evaluate the syntax
provided and supply the appropriate values. Placeholders
for values you must supply appear in angle brackets.
Enable RIPIP by using the following syntax:
SETDefault !<port> -RIPIP CONTrol = Listen
In this example, you must supply a port number for
Commands The word “command” means you must enter the
command exactly as shown in text and press the Return or
Enter key. Example:
To remove the IP address, enter the following
SETDefault !0 -IP NETaddr = 0.0.0.0
Screen displays This typeface represents information as it appears on the
The words “enter” When you see the word “enter” in this guide, you must
and “type” type something, and then press the Return or Enter key.
Do not press the Return or Enter key when an instruction
simply says “type.”
[Key] names Key names appear in text in one of two ways:
s Referred to by their labels, such as “the Return key” or
“the Escape key”
s Written with brackets, such as [Return] or [Esc].
If you must press two or more keys simultaneously, the key
names are linked with a plus sign (+). Example:
Menu commands Menu commands or button names appear in italics.
and buttons Example:
From the Help menu, select Contents.
Words in italicized Italics emphasize a point or denote new terms at the place
type where they are defined in the text.
Words in boldface Bold text denotes key features.
Related Documentation 15
Related This guide is complemented by other 3Com documents and
Documentation comprehensive help systems.
Documents The following documents are shipped with your Transcend software on
the compact disc entitled Transcend Enterprise Manager Online
Documentation Set for Windows NT v1.0 and Windows v.6.1:
s Transcend Management Software Installation Guide
(A paper version is also shipped with the product.)
s Transcend Management Software Getting Started Guide
(A paper version is also shipped with the product.)
s Transcend Management Software Transcend Central User Guide
s Transcend Management Software Status View User Guide
s Transcend Management Software LANsentry Manager User Guide
s Transcend Management Software ATMvLAN Manager User Guide
s Transcend Management Software Device View User Guide
Also, see the Transcend Trafﬁx Manager User Guide, shipped with the
Trafﬁx Manager software.
Help Systems Each Transcend application contains a help system that describes how
to use all the features of the application. Help includes window
descriptions, instructions, conceptual information, and troubleshooting
tips for that application.
You can access help from:
s The Help menu in any application by selecting Help Topics (in the
Help Topics window, you can view the Contents and Index)
s A Help button in windows and dialog boxes
s Your 3Com/Transcnd/Help directory (or the directory that you have
set for your Transcend software installation)
Network Troubleshooting Overview (page 19)
Your Network Troubleshooting Toolbox (page 31)
Steps to Actively Managing Your Network (page 43)
These sections introduce you to the concepts and practice of network
s Introduction to Network Troubleshooting (page 19)
s Network Troubleshooting Framework (page 21)
s Troubleshooting Strategy (page 23)
Introduction to Network troubleshooting means recognizing and diagnosing
Network networking problems with the goal of keeping your network running
Troubleshooting optimally. As a network administrator, your primary concern is
maintaining connectivity of all devices (a process often called fault
management). You also continually evaluate and improve your
network’s performance. Because serious networking problems can
sometimes begin as performance problems, paying attention to
performance can help you address issues before they become serious.
About Connectivity Connectivity problems occur when end stations cannot communicate
Problems with other areas of your local or wide-area network. Using
management tools, you can often ﬁx a connectivity problem before the
user even notices it. Connectivity problems include:
s Loss of connectivity — Immediately correct any connectivity
breaks. When users cannot access areas of your network, your
organization’s effectiveness is impaired.
s Intermittent connectivity — If connectivity is erratic, investigate
the problem immediately. Although users have access to network
resources some of the time, they are still facing periods of
downtime. Intermittent connectivity problems could indicate that
your network is on the verge of a major break.
s Timeout problems — Timeouts cause loss of connectivity, but are
often associated with poor network performance.
20 NETWORK TROUBLESHOOTING OVERVIEW
About Performance Your network has performance problems when it is not operating as
Problems effectively as it should. For example, response times may be slow, the
network may not be as reliable as usual, and users may be complaining
that it takes them longer to do their work. Some performance
problems are intermittent, like instances of duplicate addresses. Other
problems can indicate a growing strain on your network, such as
consistently high utilization rates.
If you regularly check your network for performance problems, you can
extend the usefulness of your existing network conﬁguration and plan
network enhancements, instead of waiting for a performance problem
to adversely affect the users’ productivity.
Solving Connectivity When troubleshooting your network, you employ tools and knowledge
and Performance already at your disposal. With an in-depth understanding of your
Problems network, you can use network software tools, such as Ping (page 38),
and network devices, such as Analyzers (page 41), to locate problems,
and then make corrections, such as swapping equipment or
reconﬁguring segments, based on your analysis.
Transcend® management software provides another set of tools for
network troubleshooting. These tools have graphical user interfaces
that make managing and troubleshooting your network easier. With
Transcend Applications (page 31), you can:
s Baseline your network’s normal status so that you can use it as a
basis for comparison when troubleshooting
s Precisely monitor network events
s Be immediately notiﬁed of critical problems on your network, such
as a device losing connectivity
s Establish alert thresholds that warn you of potential problems so
that you can correct problems before they affect your network
s Resolve problems by disabling ports or reconﬁguring devices
See Your Network Troubleshooting Toolbox (page 31) for details about
each troubleshooting tool.
Network Troubleshooting Framework 21
Network The International Standards Organization (ISO) Open Systems
Troubleshooting Interconnect (OSI) reference model is the foundation of all network
Framework communications. This seven-layer structure provides a clear picture of
how network communications work.
Protocols (rules) govern communications between the layers of a single
system and among several systems. In this way, devices made by
different manufacturers or using different designs can use different
protocols and still be about to communicate.
Understanding how network troubleshooting ﬁts into the framework of
the OSI model will help you to identify at what layer problems are
located and which type of troubleshooting tools you might want to
use. For example, unreliable packet delivery could be caused by a
problem with the transmission media or with a router conﬁguration. If
you are receiving high rates of FCS Errors (page 116) and Alignment
Errors (page 115), which you can monitor with Status Watch, then the
problem is probably located at the physical layer and not the network
layer. Figure 1 shows how to troubleshoot the layers of the OSI model.
The data that network management tools can collect as it relates to the
OSI model layers is described in Table 5.
Table 5 Network Data and the OSI Model Layers
Layer Data Collected Transcend Tool Used
Application Protocol information and other s LANsentry Manager (page 33)
Remote Monitoring (RMON)
Presentation s Traffix Manager (page 34)
and RMON2 data
(for more detail)
Network Routing information s Status Watch (page 32)
s LANsentry® Manager
(for more detail)
s Traffic Manager
(for more detail)
Data Link Traffic counts and other packet s Status Watch
s LANsentry Manager
(for more detail)
Physical Error counts s Status Watch
22 NETWORK TROUBLESHOOTING OVERVIEW
Presentation manager, agent, rlogin, FTP
Layer 6 proxy agent
Transport TCP UDP
LLC LLC LLC
Layer 2 Probes
MAC MAC MAC
PHY PHY PHY
Cable Status Watch
Physical Ethernet Token testing
Layer 1 Ring PMD tools
Figure 1 OSI Reference Model and Network Troubleshooting
For information about network troubleshooting tools, see Your Network
Troubleshooting Toolbox (page 31).
Troubleshooting Strategy 23
Troubleshooting How do you know when you are having a network problem? The
Strategy answer to this question depends on your site’s network conﬁguration
and on your network’s normal behavior. See Knowing Your Network
(page 58) for more information.
If you notice changes on your network, ask the following questions:
s Is the change expected or unusual?
s Has this event ever occurred before?
s Does the change involve a device or network path for which you
already have a backup solution in place?
s Does the change interfere with vital network operations?
s Does the change affect one or many devices or network paths?
Once you have an idea of how the change is affecting your network,
you can categorize it as critical or noncritical. Both of these categories
need resolution (except for changes that are one-time occurrences); the
difference between the categories is the time you have to ﬁx the
Using a strategy for network troubleshooting helps you to approach a
problem methodically and resolve it with minimal disruption to the
network users. A good approach to problem resolution is:
s Recognizing Symptoms (page 24)
s Understanding the Problem (page 25)
s Identifying and Testing the Cause of the Problem (page 26)
s Solving the Problem (page 29)
24 NETWORK TROUBLESHOOTING OVERVIEW
Recognizing The ﬁrst step to resolving any problem is to identify and interpret the
Symptoms symptoms. You may discover network problems in several ways. You
may have users complaining that the network seems slow or that they
cannot connect to a server. You may pass your network management
station and notice that a node icon is red. Your beeper may go off and
display the message: WAN connection down.
While you can often solve networking problems before users notice a
change in their environment, you invariably get feedback from your
users about how the network is running, such as:
“I can’t print.”
“I can’t access the application server.”
“It’s taking me much longer to copy ﬁles across the network than it
“I can’t log on to a remote server.”
“When I send e-mail to our other site, I get a routing error message.”
“My system freezes whenever I try to Telnet.”
Network Management Software Alerts
Network management software, as described in Your Network
Troubleshooting Toolbox (page 31), can alert you to areas of your
network that need attention. For example:
s The application displays red (Warning) icons.
s Your weekly Top-N utilization report (which provides you with a
table of the top ten ports showing the highest utilization rates)
shows that one port is experiencing much higher utilization levels
s You receive an e-mail message from your network management
station that the threshold for broadcast and multicast packets has
These signs usually provide additional information about the problem,
allowing you to focus on the right area.
Troubleshooting Strategy 25
When confronted with a symptom, ask yourself these types of
questions to narrow the location of the problem and to get more data
s To what degree is the network not acting normally (for example,
does it now take one minute to perform a task that normally takes
s On what subnetwork is the user located?
s Is the user trying to reach a server, end station, or printer on the
same subnetwork or on a different subnetwork?
s Are many users complaining that the network is operating slowly or
that a speciﬁc network application is operating slowly?
s Are many users reporting network logon failures?
s Are the problems intermittent? For example, some ﬁles may print
with no problems, while other printing attempts generate error
messages, make users lose their connections, and cause systems to
Understanding the Networks are designed to move packets of data from a transmitting
Problem device to a receiving device. When communication becomes
problematic, you must determine why packets are not traveling as
expected and then ﬁnd a solution. The two most common causes for
packets not moving reliably from source to destination are:
s The physical connection breaks (that is, a cable is unplugged or
s A network device is not working properly and cannot send or
receive some or all packets.
Network management software can easily locate and report a physical
connection break (layer 1 problem). You will ﬁnd it harder to determine
why a network device is not working as expected, which is often
related to a layer 2 or a layer 3 problem.
26 NETWORK TROUBLESHOOTING OVERVIEW
When trying to determine why a network device is not working
properly, check ﬁrst for:
s Valid service — Is the device conﬁgured properly for the type of
service it is supposed to provide? For example, has Quality of Service
(QoS), the deﬁnition of the transmission parameters, been
s Restricted access — Is an end station supposed to be able to
connect with a speciﬁc device or is that connection restricted? For
example, is a ﬁrewall set up preventing that device from accessing
certain network resources?
s Correct conﬁguration — Is there a misconﬁguration of IP address,
network mask, gateway, or broadcast address? Network problems
are commonly caused by misconﬁguration of newly connected or
conﬁgured devices. See Manager-to-Agent Communication (page
67) for more information.
Identifying and After you develop a possible theory about what is causing the problem,
Testing the Cause of you must test your theory. The test must conclusively prove or disprove
the Problem your theory.
A general rule of troubleshooting is that, if you cannot reproduce a
problem, then no problem exists unless it happens again on its own.
However, if the problem is intermittent and you cannot replicate it, you
can conﬁgure your network management software to catch the event
For example, with LANsentry Manager (page 33), you can set alarms
and automatic packet capture ﬁlters to monitor your network and
inform you when the problem occurs again. See Conﬁguring Transcend
Software (page 54) for more information.
Although network management tools can provide a great deal of
information about problems and their general location, you may still
need to swap equipment or replace components of your network setup
until you locate the exact trouble spot.
After testing your theory, you should either ﬁx the problem as
described in Solving the Problem (page 29) or develop another theory
Troubleshooting Strategy 27
Sample Problem Analysis
This section illustrates the analysis phase of a typical troubleshooting
On your network, a user reports that she cannot access her mail server.
You need to establish two areas of information:
s What you know — In this case, the workstation cannot
communicate with the server.
s What you do not know and need to test —
s Can the workstation communicate with the network at all, or is
the problem limited to communication with the server? Test by
sending a Ping (page 38) or by connecting to other devices.
s Is the workstation the only device that is unable to communicate
with the server, or do other workstations have the same
problem? Test connectivity at other workstations.
s If other workstations cannot communicate with the server, can
they communicate with other network devices? Again, test the
The analysis process follows these steps:
1 Can the workstation communicate with any other device on the
s If no, then go to test 2.
s If yes, determine if it is only the server that is unreachable.
s If only the server cannot be reached, this suggests a server
problem. Conﬁrm by doing test 2.
s If other devices cannot be reached, this suggests a connectivity
problem in the network. Conﬁrm by doing test 3.
2 Can other workstations communicate with the server?
s If no, then most likely it is a server problem. Go to test 3.
s If yes, then the problem is that the workstation is not
communicating with the subnetwork. (This situation can be caused
by workstation issues or a network issue with that speciﬁc station.)
3 Can other workstations communicate with other network devices?
s If no, then the problem is likely a network problem.
s If yes, the problem is likely a server problem.
28 NETWORK TROUBLESHOOTING OVERVIEW
When you determine whether the problem is with the server,
subnetwork, or workstation, you can further analyze the problem, as
s For a problem with the server, examine whether the server is
running, if it is properly connected to the network, and if it is
s For a problem with the subnetwork, examine any device on the
path between the users and the server.
s For a problem with the workstation, examine whether the
workstation can access other network resources and if it is
conﬁgured to communicate with that particular server.
Equipment for Testing
To help identify and test the cause of problems, have available:
s A laptop computer loaded with a terminal emulator, IP stack, TFTP
server, CD-ROM drive (with which you can read the online
documentation), and some key network management applications,
such as LANsentry Manager. With the laptop computer, you can
plug into any subnetwork to gather and analyze data about the
s A spare managed hub to swap for any hub that does not have
management. Swapping in a managed hub allows you to quickly
spot which port is generating the errors.
s A single port probe to insert in the network if you are having a
problem where you do not have management capability.
s Console cables for each type of connector, labeled and stored in a
Troubleshooting Strategy 29
Solving the Problem Many device or network problems are straightforward to resolve, but
others yield misleading symptoms. If one solution does not work,
continue with another.
A solution often involves:
s Upgrading software or hardware (for example, upgrading to a new
version of agent software or installing Gigabit Ethernet devices)
s Balancing your network load by analyzing:
s What users communicate with which servers
s What the user trafﬁc levels are in different segments of your
Based on these ﬁndings, you can decide how to redistribute
s Adding segments to your LAN (for example, adding a new switch
where utilization is continually high)
s Replacing faulty equipment (for example, replacing a module that
has port problems or replacing a network card that has a faulty
jabber protection mechanism)
To help solve problems, have available:
s Spare hardware equipment (such as modules and power supplies),
especially for your critical devices
s A recent backup of your device conﬁgurations to reload if ﬂash
memory gets corrupted (which can sometimes happen when there is
a power outage)
The Transcend application suite Network Admin Tools allows you to
save and reload your software conﬁgurations to devices.
A robust network troubleshooting toolbox consists of items (such as
network management applications, hardware devices, and other
software) essential for recognizing, diagnosing, and solving networking
problems. It contains:
s Transcend Applications (page 31)
s Network Management Platforms (page 35)
s 3Com SmartAgent Embedded Software (page 36)
s Other Commonly Used Tools (page 38)
Transcend Transcend® management software is optimized for managing 3Com
Applications devices and their attached networks. However, some applications, such
as LANsentry® Manager, can manage any vendor’s networking
equipment that complies with the Remote Monitoring (RMON) MIB.
This section describes these Transcend applications, which you can use
to troubleshoot your network:
s Transcend Central (page 32)
s Status View (page 32)
s LANsentry Manager (page 33)
s Trafﬁx Manager (page 34)
s Device View (page 35)
This guide primarily focuses on using these applications to troubleshoot
32 YOUR NETWORK TROUBLESHOOTING TOOLBOX
Transcend Central Transcend Central, an asset management and device grouping
application, is your starting point for understanding what your network
consists of and for controlling the Transcend network management
troubleshooting tools. Transcend Central is available as both a native
Windows application and a Java application that you can access using a
Using Transcend Central for troubleshooting, you can:
s Display an inventory of device, module, and port information.
s Group devices to make your troubleshooting tasks easier. Managing
a collection of devices allows you to simultaneously perform the
same tasks on each device in a group and to locate physical or
logical problems on your network.
s Launch Transcend applications, including some of your primary
Transcend troubleshooting tools:
s Status View (page 32), which includes Status Watch and MAC
Watch (from the native version) and Web Reporter (from the Java
s LANsentry Manager (page 33)
s Device View (page 35)
Status View The Status View applications manage 3Com devices and their attached
networks. Status View applications primarily poll for MIB-II (page 138)
Check the Status View help to see which 3Com devices are supported
by each Status View application.
Status Watch is a performance monitoring application that allows you
to monitor the operational status of your network devices and quickly
identify any problems that require your attention.
Transcend Applications 33
MAC Watch is an address collection and discovery application that:
s Polls managed devices for all MAC addresses
s Polls managed devices and routers for IP addresses to perform
MAC-to-IP address translation
s Allows you to disable troublesome ports
Web Reporter is a data-reporting application that runs in a World Wide
Web (WWW) browser. It generates reports from data collected by the
Status Watch and MAC Watch applications, allowing you to compare
network statistics against a baseline
LANsentry Manager LANsentry Manager is a set of integrated applications that displays and
explores the real-time and historical data captured by RMON-compliant
devices (probes) on the network. LANsentry Manager uses SNMP
polling to gather RMON and RMON2 data from the probes.
Use LANsentry Manager to:
s Monitor current performance of network segments
s See trends over time
s Spot signs of current problems
s Conﬁgure alarms to monitor for speciﬁc events
s Capture packets and display their contents
LANsentry Manager works with any device (from 3Com or other
vendors) that supports the RMON MIB (page 139) or the RMON2 MIB
34 YOUR NETWORK TROUBLESHOOTING TOOLBOX
Trafﬁx Manager Trafﬁx™ Manager is a performance-monitoring application that provides
information about layer 3 conversations between nodes. It helps you to
assess trafﬁc patterns on your network. Trafﬁx Manager:
s Monitors all the stations seen by the RMON2–compliant probes
deployed on your network
s Captures and stores RMON and RMON2 data for your network’s
protocols and applications
s Displays trafﬁc between stations in user-deﬁned views of the
s Graphs current or historical data on the devices selected
s Delivers reports for user-speciﬁed stations and time periods as
postscript to your printer or as HTML to your web server
s Launches LANsentry Manager tools for in-depth analysis of a station
or a conversation between stations
You can use Trafﬁx Manager to:
s Know your network — Understand overall ﬂow patterns and
interactions between systems and see how your network is really
being used at the application level
s Optimize your network — Gain an insight into trafﬁc and
application usage trends to help you optimize the use and
placement of current network resources and make wise decisions
about capacity planning and network growth
Trafﬁx Manager works with any device (from 3Com or other vendors)
that supports the RMON2 MIB (page 140).
Network Management Platforms 35
Device View The Device View application is a device conﬁguration tool. When
troubleshooting your network, you can use Device View to check or
change a device’s conﬁguration and upgrade a device’s agent software.
You can also use Device View to look at a device’s statistics and to set
Device View manages only 3Com devices.
See the Device View help for which 3Com devices are supported by
You can also use Transcend Upgrade Manager, which is one of the
Network Admin Tools applications, to perform bulk software upgrades
Network As part of your troubleshooting toolbox, your network management
Management platform is the ﬁrst place that you go to view the overall health of your
Platforms network. With the platform, you can understand the logical
conﬁguration of your network and conﬁgure views of your network to
understand how devices work together and the role they play in the
users’ work. The network management platform that supports your
Transcend software installation can provide valuable troubleshooting
For example, Transcend Enterprise Manager ‘97 for Windows NT
software is integrated with HP OpenView Network Node Manager
Version 5.01, which runs on Windows NT Version 4.0. Network Node
Manager (NNM) provides a number of functions useful in
It automatically discovers all the devices on your network and creates a
database that contains information about each device. NNM updates
the database when new devices are added or when existing devices are
modiﬁed or deleted.
Using this device database, NNM creates a default map that displays a
graphical representation of your network. Each device on your network
appears as a symbol (icon) on the map. You can conﬁgure views of
your network to show devices on the same subnetworks or ﬂoors.
36 YOUR NETWORK TROUBLESHOOTING TOOLBOX
You can use NNM to monitor network performance and to diagnose
network performance and connectivity problems. You can:
s Take a snapshot of your network in its normal state. The snapshot
records the state of your network at a particular instant. If you later
have network performance problems, you can compare the current
state of your network to the snapshot.
s Quickly determine the connectivity status of a device by noting the
color of its map symbol. Red usually means a device disconnection.
s Diagnose connectivity problems by determining whether two devices
can communicate. If they can communicate, then examine the route
between the devices, the number of packets sent and lost, and the
roundtrip time between the two devices.
s Manage MIB information (for example, collecting and storing MIB
data for trend analysis and graphing) using MIB queries. NNM
compiles MIBs and lets you navigate up and down the MIB Tree
(page 136) to retrieve MIB objects from devices. You can set
thresholds for MIB data and generate events when a threshold is
s Conﬁgure the software to act on certain events. The Event
Categories window informs you of any unexpected events (which
arrive in the form of traps).
For more information, see the HP documentation shipped with your
3Com SmartAgent Traditional SNMP management places the burden of collecting network
Embedded management information on the management station. In this
Software traditional model, software agents collect information about
throughput, record errors or packet overﬂows, and measure
performance based on established thresholds. Through a polling
process, agents pass this information to a centralized network
management station whenever they receive an SNMP query.
Management applications then make the data useful and alert the user
if there are problems on the device.
For more information about traditional SNMP management, see SNMP
Operation (page 133).
3Com SmartAgent Embedded Software 37
As a useful companion to traditional network management methods,
3Com’s SmartAgent® technology places management intelligence into
the software agent that runs within a 3Com device. This scalable
solution reduces the amount of computational load on the
management station and helps minimize management-related network
SmartAgent software, which uses the RMON MIB (page 139), is
self-monitoring, collecting and analyzing its own statistical, analytical,
and diagnostic data. In this way, you can conduct network
management by exception — that is, you are only notiﬁed if a problem
occurs. Management by exception is unlike traditional SNMP
management, in which the management software collects all data from
the device through polling.
SmartAgent software works autonomously and reports to the network
management station whenever an exceptional network event occurs.
The software can also take direct action without involving the
management station. Devices that contain SmartAgent software may be
s Perform broadcast throttling to minimize the ﬂow of broadcast
trafﬁc on your network
s Monitor the ratio of good to bad frames
s Switch a resilient link pair to the standby path if the primary path
s Report if trafﬁc on vital segments drops below minimum usage
s Disable a port for ﬁve seconds to clear problems, and then
automatically reconnect it
To conﬁgure these advanced SmartAgent software features, see your
The Transcend applications LANsentry Manager (page 33) and
Trafﬁx Manager (page 34) make RMON data collected by the
SmartAgent software more usable by summarizing and correlating
38 YOUR NETWORK TROUBLESHOOTING TOOLBOX
Other Commonly These commonly used tools can also help you troubleshoot your
Used Tools network:
s Network software, such as Ping (page 38), Telnet (page 40), and FTP
and TFTP (page 40). You can use these applications to troubleshoot,
conﬁgure and upgrade your system.
s Network monitoring devices, such as Analyzers (page 41) and Probes
s Tools, such as Cable Testers (page 42), for working on physical
Many of the tools discussed in this section are only useful in TCP/IP
Ping Packet Internet Groper (Ping) allows you to quickly verify the
connectivity of your network devices. Ping sends a packet from one
device, attempts to transmit it to a station on the network, and listens
for the response to ensure that it was correctly received. You can
validate connections on the parts of your network by pinging different
s A successful response tells you that a valid network path exists
between your station and the remote host and that the remote host
s Slower response times than normal can tell you that the path is
congested or obstructed.
s A failed response indicates that a connection is broken somewhere;
use the message to help locate the problem. See Tips on
Interpreting Ping Messages (page 40).
Some network devices, like the CoreBuilder® 5000, must be conﬁgured
to be able to respond to Ping messages. If you are not receiving
responses from a device, ﬁrst check that it is set up to be a Ping
Other Commonly Used Tools 39
Strategies for Using Ping
Follow these strategies for using Ping:
s Ping devices when your network is operating normally so that you
have a performance baseline for comparison. See Identifying Your
Network’s Normal Behavior (page 62) for more information.
s Ping by IP address when:
s You want to test devices on different subnetworks. This method
allows you to Ping your network segments in an organized way,
rather than having to remember all the hostnames and locations.
s Your DNS server is down and your system cannot look up host
names properly. You can Ping with IP addresses even if you
cannot access hostname information.
s Ping by hostname when you want to identify DNS server problems.
s To troubleshoot problems involving large packet sizes, Ping the
remote host repeatedly, increasing the packet size each time.
s To determine if a link is erratic, perform a continuous Ping (using
PING -t on Windows NT or ping -s on UNIX), which provides you
with the time that it took the device to respond to each Ping.
s To determine a route taken to a destination, use the trace route
function (tracert) on Windows 95 and Windows NT.
s Consider creating a Ping script that periodically sends a Ping to all
necessary networking devices. If a Ping failure message is received,
the script can perform some action to notify you of the problem,
such as paging you.
s Use the Ping functions of your network management platform. For
example, in your HP Openview map, selecting a device and
right-clicking provides access to Ping functions.
40 YOUR NETWORK TROUBLESHOOTING TOOLBOX
Tips on Interpreting Ping Messages
Use the following Ping failure messages to troubleshoot problems:
s No reply from <destination> — Shows that the destination routes
are available but that there is a problem with the destination itself.
s <destination> is unreachable — Shows that your system does not
know how to get to the destination. This message means either that
routing information to a different subnetwork is unavailable or that
a device on the same subnetwork is down.
s ICMP host unreachable from gateway — Indicates that your
system can transmit to the target address using a gateway, but the
gateway cannot forward the packet properly because either a device
is misconﬁgured or the gateway is down.
Telnet Telnet, which is a login and terminal emulation program for
Transmission Control Protocol/Internet Protocol (TCP/IP) networks, is a
common way to communicate with an individual device. You log into
the device (a remote host) and use that remote device as if it were a
If you have an out-of-band Telnet connection established with a device,
you can use Telnet to communicate with that device even if the
network goes down. This feature makes Telnet one of the most
frequently used network troubleshooting tools. Usually, all device
statistics and conﬁguration capabilities are accessible by using Telnet to
connect to the device’s console. For more information about setting up
an out-of-band connection, see Using Telnet, Serial Line, and Modem
Connections (page 49).
You can invoke the Telnet application on your local system and set up a
link to a Telnet process running on a remote host. You can then run a
program located on a remote host as if you were working on the
FTP and TFTP Most network devices support either the File Transfer Protocol (FTP) or
the Trivial File Transfer Protocol (TFTP) for downloading updates of
system software. Updating system software is often the solution to
networking problems that are related to agent problems. Also, new
software features may help correct a networking problem.
Other Commonly Used Tools 41
FTP provides ﬂexibility and security for ﬁle transfer by:
s Accepting many ﬁle formats, such as ASCII and binary
s Using data compression
s Providing Read and Write access so that you can display, create, and
delete ﬁles and directories
s Providing password protection
TFTP is a simple version of FTP that does not list directories or require
passwords. TFTP only transfers ﬁles to and from a remote server.
Analyzers An analyzer, often called a Sniffer, is a network device that collects
network data on the segment to which it is attached, a process called
packet capturing. Software on the device analyzes this data, a process
referred to as protocol analysis. Most analyzers can interpret different
types of protocol trafﬁc, such as TCP/IP, AppleTalk, and Banyan Vines
You usually use analyzers for reactive troubleshooting — you see a
problem somewhere on your network and you attach an analyzer to
capture and interpret the data from that area. Analyzers are particularly
helpful in identifying intermittent problems. For example, if your
network backbone has experienced moments of instability that prevent
users from logging onto the network, you can attach an analyzer to
the backbone to capture the intermittent problems when they happen
Probes Like Analyzers (page 41), a probe is a network device that collects
network data. Depending on its type, a probe can collect data from
multiple segments simultaneously. It stores the collected data and
transfers the data to an analysis site when requested. Unlike an
analyzer, probes do not interpret data.
A probe can be either a stand-alone device or an agent in a network
device. The Transcend Enterprise Monitor 500 series and the
SuperStack® II Monitor series are stand-alone RMON probes. LANsentry
Manager and Trafﬁx Manager use data from probes that are compliant
with the RMON MIB (page 139) or the RMON2 MIB (page 140).
42 YOUR NETWORK TROUBLESHOOTING TOOLBOX
You can use a probe daily to check the health of your network. The
Transcend applications can interpret and report this data, alerting you
to possible problems so that you can proactively manage your network.
For example, an RMON2 probe can help you to analyze trafﬁc patterns
on your network. Use this data to make decisions about reconﬁguring
devices and end stations as needed.
Cable Testers Cable testers check the electrical characteristics of the wiring. They are
most commonly used to ensure that building wiring and cables meet
Category 5, 4, and 3 standards. For example, network technologies
such as Fast Ethernet require the cabling to meet Category 5
requirements. Testers are also used to ﬁnd defective and broken wiring
in a building.
STEPS TO ACTIVELY MANAGING
These sections describe the steps you can take to effectively
troubleshoot your network when the need arises:
s Designing Your Network for Troubleshooting (page 43)
s Preparing Devices for Management (page 53)
s Conﬁguring Transcend Software (page 54)
s Knowing Your Network (page 58)
Designing Your Designing your network for troubleshooting facilitates your access to
Network for key devices on your network when your network is experiencing
Troubleshooting connectivity or performance problems. Having adequate management
access depends on these design criteria:
s Position of the management station so that it can gather the
greatest amount of network data through SNMP polling
s Position of probes for distributed management of critical networks
s Ability to communicate with each device even when your
management station cannot access the network
The following sections discuss how to design your network with the
above criteria in mind:
s Positioning Your SNMP Management Station (page 44)
s Using Probes (page 45)
s Monitoring Business-critical Networks (page 47)
s Using Telnet, Serial Line, and Modem Connections (page 49)
s Using Communications Servers (page 50)
s Setting Up Redundant Management (page 51)
s Other Tips on Network Design (page 52)
44 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Positioning Your In a typical LAN, it is best to locate your Windows NT or UNIX
SNMP Management management station directly off the backbone where it can conduct
Station SNMP polling and manage network devices. The backbone is usually
the optimum location for the management station because:
s The backbone is not subject to the failures of individual
subnetworked routers or switches.
s In a partial network outage, the information collected by a
backbone management station is probably more accurate than a
station in a routed subnet.
s The backbone is usually protected with redundant power and
technologies, like FDDI, that correct their own problems. This
redundancy ensures that the backbone remains operational, even
when other areas of the network are having problems.
s The backbone is typically faster and has a higher bandwidth than
other areas of your network, making it a more efﬁcient location for
a management station.
Make sure that the capacity of your backbone can accommodate the
SNMP trafﬁc that is generated by the management applications.
Figure 2 shows a management station that is set up at the network
backbone and polling network devices.
FDDI card or
x network device
x x x
x x x x x x x x x
x = Network devices that you want to poll
Figure 2 SNMP Management at the Backbone
Designing Your Network for Troubleshooting 45
Although SNMP management from the backbone is a good way to
keep track of what is happening on your network, do not rely on it
exclusively. Because SNMP management occurs in-band (that is, SNMP
trafﬁc shares network bandwidth with data trafﬁc), network
troubleshooting using SNMP can become a problem in these ways:
s Very heavy data trafﬁc or a break in the network can make it
difﬁcult or impossible for the management station to poll a device.
s Trafﬁc added to the network by SNMP polling may contribute to
Using Probes To minimize the frequency of SNMP trafﬁc on your network, set up one
or more Probes (page 41) to collect Remote Monitoring (RMON) data
from the network devices. In the distributed model illustrated in
Figure 3, the management station using SNMP polling collects data
from the probes rather than from all the network devices. Distributing
the management over the network ensures you of some continued
data collection even if you have network problems.
Many management applications support data from MIBs other than the
RMON MIBs. For this reason, even if you are using RMON probes, some
SNMP polling to individual devices from a key management station is
always useful for a complete picture of your network.
46 STEPS TO ACTIVELY MANAGING YOUR NETWORK
workstation x Probe
FDDI card or FDDI card or
x network device x network device
x x x
x x x x x x
x x x x = Network devices that you want to poll
Figure 3 Management at the Backbone with as Attached Probe
To extend your remote monitoring capabilities, use embedded RMON
probes or roving analysis (monitoring one port for a period of time,
moving on to another port for a while, and so on). However, with
roving analysis, you cannot see a historical analysis of the ports because
the probe is moving from one port to another.
Some probes, like 3Com’s Enterprise Monitor, are designed to support
the large number of interfaces found in switched environments. The
probe’s high port density supports this multi-segmented switched
environment. The probe’s interfaces can also be used to monitor mirror
(or copy) ports on the switch, which means that all data received and
transmitted on a port is also sent to the probe.
Probes will not indicate which port has caused an error. Only a
managed hub (a hub or switch with an onboard management module)
can provide that level of detail. Probes and a hub’s own management
module complement each other.
Designing Your Network for Troubleshooting 47
Monitoring On business-critical networks, you need to increase your level of
Business-critical management by dedicating probes to the essential areas of your
Networks network. For detailed network management, it is not enough to gather
raw performance ﬁgures — you need to know, at the network and
conversation level, who is generating the trafﬁc and when it is being
generated. For this type of analysis, use reporting tools, such as
Trafﬁx Manager (page 34), and low-level, fault diagnostic tools, such as
LANsentry Manager (page 33).
The three critical areas on this type of network that you should monitor
are discussed in these sections and shown in Figure 4:
s FDDI Backbone Monitoring (page 48)
s Internet WAN Link Monitoring (page 48)
s Switch Management Monitoring (page 48)
Direct connection to the
with FDDI module
Inline monitoring SuperStack II
on Fast Ethernet Enterprise Monitor
x x x
x x x x x x
WAN Monitor 700
x = Network devices that you want to poll
WAN = Possible probe attachment to a switch’s
roving analysis port
Figure 4 Probes Monitoring a Business-critical Network
48 STEPS TO ACTIVELY MANAGING YOUR NETWORK
FDDI Backbone Monitoring
On the FDDI backbone, you need to continually monitor whether it is
being overutilized, and, if so, by what type of trafﬁc. By placing the
SuperStack® II Enterprise Monitor with an FDDI media module directly
at the backbone, you can gather utilization and host matrix
information. This data is used by Trafﬁx™ Manager to provide regular
segment utilization reports and Top-N host reports. In addition, the
probe provides a full range of FDDI performance statistics that can be
recorded with LANsentry® Manager or reported to the management
station by way of SNMP traps.
To ensure management access to the probe, provide a direct
connection to the probe from your management station. This
connection allows you to access probe data even if the ring is unusable
and keeps management trafﬁc off the main ring.
Internet WAN Link Monitoring
The Internet link is a concern for dedicated network management
because it represents an external cost to the company that requires
budgeting and because it is a possible security problem. In a way
similar to monitoring the FDDI backbone, Trafﬁx Manager reports can
indicate whether you are paying for too much bandwidth or whether
you need to purchase more. It can also indicate the level of use on a
workgroup basis for internal billing and highlight the top sites visited by
users. Similarly, you can monitor for unexpected conversations and
You also need to know the error rates on this link and whether you are
experiencing congestion because of circumstances on the Internet
provider’s network. LANsentry Manager can record and display these
statistics and provide a detailed real-time view.
Switch Management Monitoring
The third area of interest in this network is the large number of
switch-to-end station links. When detailed analysis of these devices is
required (for example, if one of the ports on the network suddenly
reports much higher trafﬁc than normal), you need to track the source
of the problem and decide whether you can optimize the trafﬁc path.
In this case, you need a way to view the trafﬁc on the switch port at a
Designing Your Network for Troubleshooting 49
By placing a Superstack II Enterprise Monitor in a central location, you
can easily attach it to the switches that have the most Ethernet ports as
the need arises. Using the roving analysis feature of many 3Com
devices, data from a monitored port can be copied to the port on the
switch to which the SuperStack II is connected. When a problem arises,
roving analysis is activated for a particular switch and LANsentry
Manager or Trafﬁx Manager collects the data from the SuperStack II
Enterprise Monitor. These applications can then monitor the network
data for the devices connected to that switch.
Using Telnet, To minimize your dependency on SNMP management, set up a way to
Serial Line, and reach the console of your key networking devices. Through the console,
Modem Connections you can often view Ethernet, FDDI, ATM, and token ring statistics, view
routing and bridging tables, and check and modify device
These console connections are also key to network troubleshooting
because they can be out-of-band (that is, management using a
dedicated line to a device). If the network goes down, your console
connections are still available.
The types of console connections include:
s Telnet (page 40) — Out-of-band and in-band access using a
network connection. For example, on 3Com’s CoreBuilder 6000
switch, using Telnet you can access the management console by
using a dedicated Ethernet connection to the management module
(out-of-band) and from any network attached to the device
s Serial line — Direct, out-of-band access using a terminal
connection. This type of connection allows you to maintain your
connections to a device if it reboots.
s Modem — Remote, out-of-band access using a modem connection.
Figure 5 shows management of a device through the serial line and
50 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Serial line port Network
Figure 5 Out-of-band Management Using the Serial and Modem Ports
Sometimes, direct access to network devices through out-of-band
management is the only way to examine a network problem. For
example, if your network connections are down, you can Telnet (page
40) to one of your key routers and examine its routing table. The
routing table shows the devices that the router can reach, allowing you
to narrow the area of the problem. You can also Ping (page 38) from
this device to further investigate which areas of the network are down.
Using While out-of-band management keeps you in contact with a particular
Communications device during a network problem, it does not inform you about all the
Servers areas of your network from a central point. You must access each
device separately. To make device management more central, you can
set up a communications server (often called a comm server), through
which you can easily manage all devices conﬁgured to that server from
one management station. See Figure 6. 3Com communication servers
include the C/S 2500 and C/S 3500.
Designing Your Network for Troubleshooting 51
Wiring closet Wiring closet
Serial line port Serial line port
(“Comm” server) Attached LAN
Figure 6 Out-of-band Management with a Communications Server
For optimal beneﬁt, provide two management connections to the
s Connect the comm server to the network (an in-band connection)
so that you can access the devices from anywhere on the network
using reverse Telnet.
s Connect your management workstation directly to one of the serial
ports of the comm server (an out-of-band connection) so that you
can access the devices when the network is down.
Setting Up To add redundancy to your management strategy so that a
Redundant management station can always access the backbone, set up a “buddy
Management system” of management. In this setup, management applications (often
different ones) run on separate management workstations, which are
connected to the backbone through separate network devices or by
using a network card.
This setup allows the management workstations to check on each
other and report any problems with their attached network devices.
The buddy system also provides a backup management connection to
your network if one management station loses connectivity.
52 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Other Tips on This section provides some additional tips for designing your network
Network Design for troubleshooting.
Management Station Conﬁguration
s Conﬁgure the management station to run without any network
connection — including NIS, NFS, and DNS lookups. Because your
management station should run with all network cables pulled out,
do not install Transcend® Enterprise Manager on a network drive.
s Have more than one interface available on the management station,
an arrangement called dual hosting. Connect vital probes to the
second interface to create a private monitoring LAN (one without
regular network trafﬁc) on which network problems will not impair
s Do not give the management station privileges on the network,
such as the ability to log in with no passwords (rsh). Hackers can
easily spot management stations.
s Connect the management station to an uninterruptible power
supply (UPS) to protect the station from events that interrupt power,
such as blackouts, power surges, and brownouts.
s Regularly back up the management station.
s Provide remote access through a modem to the management
station so that you can keep track of your network’s activity
s Use managed hubs to narrow which link is causing an error. Even if
your budget does not allow you to manage all hubs, strategically
install one managed hub for error tracking.
s Keep copies of all conﬁgurations on a ﬁle server and on the
management station. See Knowing Your Network’s Conﬁguration
(page 58) for more information.