4. iii
C
ONTENTS
A
BOUT
T
HIS
G
UIDE
Finding Specific Information in This Guide 12
What to Expect from This Guide 12
Conventions 13
Related Documentation 15
Documents 15
Help Systems 15
P
ART
I B
EFORE
T
ROUBLESHOOTING
N
ETWORK
T
ROUBLESHOOTING
O
VERVIEW
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
5. iv
Y
OUR
N
ETWORK
T
ROUBLESHOOTING
T
OOLBOX
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
Ping 38
Strategies for Using Ping 39
Tips on Interpreting Ping Messages 40
Telnet 40
FTP and TFTP 40
Analyzers 41
Probes 41
Cable Testers 42
S
TEPS
TO
A
CTIVELY
M
ANAGING
Y
OUR
N
ETWORK
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
6. v
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
P
ART
II N
ETWORK
C
ONNECTIVITY
P
ROBLEMS
AND
S
OLUTIONS
M
-
ANAGER
TO
-A
GENT
C
OMMUNICATION
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
7. vi
FDDI C
ONNECTIVITY
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
P
ART
III N
ETWORK
P
ERFORMANCE
P
ROBLEMS
AND
S
OLUTIONS
B
ANDWIDTH
U
TILIZATION
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
8. vii
B
ROADCAST
S
TORMS
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
D
UPLICATE
A
DDRESSES
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
9. viii
E
THERNET
P
ACKET
L
OSS
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
Collisions 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 R
ING
E
RRORS
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
10. ix
N
ETWORK
F
ILE
S
ERVER
T
IMEOUTS
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
Jabbering 129
Network File System (NFS) Protocol 129
11. x
P
ART
IV R
EFERENCE
SNMP
IN
N
ETWORK
T
ROUBLESHOOTING
SNMP Operation 133
Manager/Agent Operation 133
SNMP Messages 134
Trap Reporting 134
Security 135
SNMP MIBs 136
MIB Tree 136
MIB-II 138
RMON MIB 139
RMON2 MIB 140
3Com Enterprise MIBs 141
I
NFORMATION
R
ESOURCES
Books 143
URLs 144
I
NDEX
12. A
BOUT
T
HIS
G
UIDE
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:
n
Transmission Control Protocol/Internet Protocol (TCP/IP)
n
Simple Network Management Protocol (SNMP)
n
Network management platforms (especially HP OpenView Network
Node Manager from Hewlett-Packard)
n
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.
13. 12 ABOUT THIS GUIDE
Finding Specific
Information in
This Guide
This guide, which is available online (in PDF and HTML formats) and on
paper, is designed to be used online. For the online version,
cross-references to other sections are indicated with links in blue,
underlined text, which you can click. You can print any pages as
needed.
Table 1 provides guidelines for navigating through this document.
What to Expect
from This Guide
Table 1 Guidelines for Finding Specific Information in This Guide
If you are looking for See
An introduction to network troubleshooting,
information about troubleshooting tools, and
guidelines for getting ready for management
Part I: Before Troubleshooting
(page 17)
Note: This part is recommended
reading for users who are new to
network management.
Specific troubleshooting scenarios that will help
you solve real network problems
Part II: Network Connectivity
Problems and Solutions (page
65)
Part III: Network Performance
Problems and Solutions (page
83)
Useful background information to help you with
troubleshooting tasks
Part IV: Reference (page 131)
This guide demonstrates how to troubleshoot problems on your
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
troubleshooting, see:
n The Transcend Management Software Installation Guide (for help
with installation and startup problems)
n 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
14. Conventions 13
applied using Transcend management software. For additional
information, see the resources listed in Information Resources (page
143).
Conventions Table 2, Table 3, and Table 4 list conventions that are used throughout
this guide.
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
injury
Table 3 Troubleshooting Icons
Icon Type Points out
Troubleshooting
procedure
Where a troubleshooting procedure begins
Troubleshooting
tip
Tips and other useful information for performing a
troubleshooting task or working with a Transcend
management software tool
15. 14 ABOUT THIS GUIDE
Table 4 Text Conventions
Convention Description
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.
Example:
Enable RIPIP by using the following syntax:
SETDefault !<port> -RIPIP CONTrol = Listen
In this example, you must supply a port number for
<port>.
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
command:
SETDefault !0 -IP NETaddr = 0.0.0.0
Screen displays This typeface represents information as it appears on the
screen.
The words “enter”
and “type”
When you see the word “enter” in this guide, you must
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:
n Referred to by their labels, such as “the Return key” or
“the Escape key”
n 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:
Press [Ctrl]+[Alt]+[Del].
Menu commands
and buttons
Menu commands or button names appear in italics.
Example:
From the Help menu, select Contents.
Words in italicized
type
Italics emphasize a point or denote new terms at the place
where they are defined in the text.
Words in boldface
type
Bold text denotes key features.
16. Related Documentation 15
Related
Documentation
This guide is complemented by other 3Com documents and
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:
n Transcend Management Software Installation Guide
(A paper version is also shipped with the product.)
n Transcend Management Software Getting Started Guide
(A paper version is also shipped with the product.)
n Transcend Management Software Transcend Central User Guide
n Transcend Management Software Status View User Guide
n Transcend Management Software LANsentry Manager User Guide
n Transcend Management Software ATMvLAN Manager User Guide
n 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:
n The Help menu in any application by selecting Help Topics (in the
Help Topics window, you can view the Contents and Index)
n A Help button in windows and dialog boxes
n Your 3Com/Transcnd/Help directory (or the directory that you have
set for your Transcend software installation)
18. I BEFORE TROUBLESHOOTING
Network Troubleshooting Overview (page 19)
Your Network Troubleshooting Toolbox (page 31)
Steps to Actively Managing Your Network (page 43)
19.
20. NETWORK TROUBLESHOOTING
OVERVIEW
These sections introduce you to the concepts and practice of network
troubleshooting:
n Introduction to Network Troubleshooting (page 19)
n Network Troubleshooting Framework (page 21)
n Troubleshooting Strategy (page 23)
Introduction to
Network
Troubleshooting
Network troubleshooting means recognizing and diagnosing
networking problems with the goal of keeping your network running
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
Problems
Connectivity problems occur when end stations cannot communicate
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:
n Loss of connectivity — Immediately correct any connectivity
breaks. When users cannot access areas of your network, your
organization’s effectiveness is impaired.
n 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.
n Timeout problems — Timeouts cause loss of connectivity, but are
often associated with poor network performance.
21. 20 NETWORK TROUBLESHOOTING OVERVIEW
About Performance
Problems
Your network has performance problems when it is not operating as
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
and Performance
Problems
When troubleshooting your network, you employ tools and knowledge
already at your disposal. With an in-depth understanding of your
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:
n Baseline your network’s normal status so that you can use it as a
basis for comparison when troubleshooting
n Precisely monitor network events
n Be immediately notified of critical problems on your network, such
as a device losing connectivity
n Establish alert thresholds that warn you of potential problems so
that you can correct problems before they affect your network
n Resolve problems by disabling ports or reconfiguring devices
See Your Network Troubleshooting Toolbox (page 31) for details about
each troubleshooting tool.
22. Network Troubleshooting Framework 21
Network
Troubleshooting
Framework
The International Standards Organization (ISO) Open Systems
Interconnect (OSI) reference model is the foundation of all network
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
Presentation
Remote Monitoring (RMON)
and RMON2 data
Session
Transport
n LANsentry Manager (page 33)
n Traffix Manager (page 34)
(for more detail)
Network Routing information n Status Watch (page 32)
n LANsentry® Manager
(for more detail)
n Traffic Manager
(for more detail)
Data Link Traffic counts and other packet
breakdowns
n Status Watch
n LANsentry Manager
(for more detail)
Physical Error counts n Status Watch
23. 22 NETWORK TROUBLESHOOTING OVERVIEW
SNMP
managers Console
SNMP
manager, agent,
proxy agent
Telnet,
rlogin, FTP
TCP UDP
IP
Troubleshooting
Tools
LLC
MAC
PHY
LLC
MAC
PHY
LLC
MAC
PHY
PMD
Figure 1 OSI Reference Model and Network Troubleshooting
For information about network troubleshooting tools, see Your Network
Troubleshooting Toolbox (page 31).
Application
Layer 7
Presentation
Layer 6
Session
Layer 5
Transport
Network
Layer 3
Analyzers
Probes
Traffix Manager
LANsentry Manager
Probes
LANsentry Manager
Status Watch
Examples:
Examples:
Examples:
IPX
Data link
Layer 2
Physical
Layer 1
Ethernet
Token
Ring
FDDI
Layer 4
Status
Watch
Cable
testing
tools
24. Troubleshooting Strategy 23
Troubleshooting
Strategy
How do you know when you are having a network problem? The
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:
n Is the change expected or unusual?
n Has this event ever occurred before?
n Does the change involve a device or network path for which you
already have a backup solution in place?
n Does the change interfere with vital network operations?
n 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
problem.
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:
n Recognizing Symptoms (page 24)
n Understanding the Problem (page 25)
n Identifying and Testing the Cause of the Problem (page 26)
n Solving the Problem (page 29)
25. 24 NETWORK TROUBLESHOOTING OVERVIEW
Recognizing
Symptoms
The first step to resolving any problem is to identify and interpret the
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.
User Comments
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
usually does.”
“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:
n The application displays red (Warning) icons.
n 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
than normal.
n You receive an e-mail message from your network management
station that the threshold for broadcast and multicast packets has
been exceeded.
These signs usually provide additional information about the problem,
allowing you to focus on the right area.
26. Troubleshooting Strategy 25
Analyzing Symptoms
When confronted with a symptom, ask yourself these types of
questions to narrow the location of the problem and to get more data
for analysis:
n To what degree is the network not acting normally (for example,
does it now take one minute to perform a task that normally takes
five seconds)?
n On what subnetwork is the user located?
n Is the user trying to reach a server, end station, or printer on the
same subnetwork or on a different subnetwork?
n Are many users complaining that the network is operating slowly or
that a specific network application is operating slowly?
n Are many users reporting network logon failures?
n 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
freeze.
Understanding the
Problem
Networks are designed to move packets of data from a transmitting
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:
n The physical connection breaks (that is, a cable is unplugged or
broken).
n 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.
27. 26 NETWORK TROUBLESHOOTING OVERVIEW
When trying to determine why a network device is not working
properly, check first for:
n 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
established?
n 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?
n 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
Testing the Cause of
the Problem
After you develop a possible theory about what is causing the problem,
you must test your theory. The test must conclusively prove or disprove
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
in progress.
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
to check.
28. Troubleshooting Strategy 27
Sample Problem Analysis
This section illustrates the analysis phase of a typical troubleshooting
incident.
On your network, a user reports that she cannot access her mail server.
You need to establish two areas of information:
n What you know — In this case, the workstation cannot
communicate with the server.
n What you do not know and need to test —
n 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.
n 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.
n If other workstations cannot communicate with the server, can
they communicate with other network devices? Again, test the
connectivity.
The analysis process follows these steps:
1 Can the workstation communicate with any other device on the
subnetwork?
n If no, then go to test 2.
n If yes, determine if it is only the server that is unreachable.
n If only the server cannot be reached, this suggests a server
problem. Confirm by doing test 2.
n 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?
n If no, then most likely it is a server problem. Go to test 3.
n 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?
n If no, then the problem is likely a network problem.
n If yes, the problem is likely a server problem.
29. 28 NETWORK TROUBLESHOOTING OVERVIEW
When you determine whether the problem is with the server,
subnetwork, or workstation, you can further analyze the problem, as
follows:
n For a problem with the server, examine whether the server is
running, if it is properly connected to the network, and if it is
configured appropriately.
n For a problem with the subnetwork, examine any device on the
path between the users and the server.
n 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:
n 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
segment.
n 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.
n A single port probe to insert in the network if you are having a
problem where you do not have management capability.
n Console cables for each type of connector, labeled and stored in a
secure place.
30. 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:
n Upgrading software or hardware (for example, upgrading to a new
version of agent software or installing Gigabit Ethernet devices)
n Balancing your network load by analyzing:
n What users communicate with which servers
n What the user traffic levels are in different segments of your
network
Based on these findings, you can decide how to redistribute
network traffic.
n Adding segments to your LAN (for example, adding a new switch
where utilization is continually high)
n 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:
n Spare hardware equipment (such as modules and power supplies),
especially for your critical devices
n 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.
32. YOUR NETWORK
TROUBLESHOOTING TOOLBOX
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:
n Transcend Applications (page 31)
n Network Management Platforms (page 35)
n 3Com SmartAgent Embedded Software (page 36)
n Other Commonly Used Tools (page 38)
Transcend
Applications
Transcend® management software is optimized for managing 3Com
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:
n Transcend Central (page 32)
n Status View (page 32)
n LANsentry Manager (page 33)
n Traffix Manager (page 34)
n Device View (page 35)
This guide primarily focuses on using these applications to troubleshoot
your network.
33. 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
browser.
Using Transcend Central for troubleshooting, you can:
n Display an inventory of device, module, and port information.
n 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.
n Launch Transcend applications, including some of your primary
Transcend troubleshooting tools:
n Status View (page 32), which includes Status Watch and MAC
Watch (from the native version) and Web Reporter (from the Java
version)
n LANsentry Manager (page 33)
n 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)
data.
Check the Status View help to see which 3Com devices are supported
by each Status View application.
Status Watch
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.
34. Transcend Applications 33
MAC Watch
MAC Watch is an address collection and discovery application that:
n Polls managed devices for all MAC addresses
n Polls managed devices and routers for IP addresses to perform
MAC-to-IP address translation
n Allows you to disable troublesome ports
Web Reporter
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:
n Monitor current performance of network segments
n See trends over time
n Spot signs of current problems
n Configure alarms to monitor for specific events
n 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
(page 140).
35. 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:
n Monitors all the stations seen by the RMON2–compliant probes
deployed on your network
n Captures and stores RMON and RMON2 data for your network’s
protocols and applications
n Displays traffic between stations in user-defined views of the
network
n Graphs current or historical data on the devices selected
n Delivers reports for user-specified stations and time periods as
postscript to your printer or as HTML to your web server
n Launches LANsentry Manager tools for in-depth analysis of a station
or a conversation between stations
You can use Traffix Manager to:
n Know your network — Understand overall flow patterns and
interactions between systems and see how your network is really
being used at the application level
n 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).
36. 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
alarms.
Device View manages only 3Com devices.
See the Device View help for which 3Com devices are supported by
Device View.
You can also use Transcend Upgrade Manager, which is one of the
Network Admin Tools applications, to perform bulk software upgrades
on devices.
Network
Management
Platforms
As part of your troubleshooting toolbox, your network management
platform is the first place that you go to view the overall health of your
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
tools.
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
troubleshooting.
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.
37. 36 YOUR NETWORK TROUBLESHOOTING TOOLBOX
You can use NNM to monitor network performance and to diagnose
network performance and connectivity problems. You can:
n 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.
n Quickly determine the connectivity status of a device by noting the
color of its map symbol. Red usually means a device disconnection.
n 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.
n 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
exceeded.
n 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
software.
3Com SmartAgent
Embedded
Software
Traditional SNMP management places the burden of collecting network
management information on the management station. In this
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).
38. 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
traffic.
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
able to:
n Perform broadcast throttling to minimize the flow of broadcast
traffic on your network
n Monitor the ratio of good to bad frames
n Switch a resilient link pair to the standby path if the primary path
corrupts frames
n Report if traffic on vital segments drops below minimum usage
levels
n Disable a port for five seconds to clear problems, and then
automatically reconnect it
To configure these advanced SmartAgent software features, see your
device documentation.
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
important information.
39. 38 YOUR NETWORK TROUBLESHOOTING TOOLBOX
Other Commonly
Used Tools
These commonly used tools can also help you troubleshoot your
network:
n 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.
n Network monitoring devices, such as Analyzers (page 41) and Probes
(page 41).
n Tools, such as Cable Testers (page 42), for working on physical
problems.
Many of the tools discussed in this section are only useful in TCP/IP
networks.
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
devices:
n A successful response tells you that a valid network path exists
between your station and the remote host and that the remote host
is active.
n Slower response times than normal can tell you that the path is
congested or obstructed.
n 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
responder.
40. Other Commonly Used Tools 39
Strategies for Using Ping
Follow these strategies for using Ping:
n 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.
n Ping by IP address when:
n 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.
n 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.
n Ping by hostname when you want to identify DNS server problems.
n To troubleshoot problems involving large packet sizes, Ping the
remote host repeatedly, increasing the packet size each time.
n 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.
n To determine a route taken to a destination, use the trace route
function (tracert) on Windows 95 and Windows NT.
n 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.
n 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.
41. 40 YOUR NETWORK TROUBLESHOOTING TOOLBOX
Tips on Interpreting Ping Messages
Use the following Ping failure messages to troubleshoot problems:
n No reply from <destination> — Shows that the destination routes
are available but that there is a problem with the destination itself.
n <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.
n 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
local terminal.
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
remote system.
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.
42. Other Commonly Used Tools 41
FTP provides flexibility and security for file transfer by:
n Accepting many file formats, such as ASCII and binary
n Using data compression
n Providing Read and Write access so that you can display, create, and
delete files and directories
n 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
traffic.
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
again.
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).
43. 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.
44. STEPS TO ACTIVELY MANAGING
YOUR NETWORK
These sections describe the steps you can take to effectively
troubleshoot your network when the need arises:
n Designing Your Network for Troubleshooting (page 43)
n Preparing Devices for Management (page 53)
n Configuring Transcend Software (page 54)
n Knowing Your Network (page 58)
Designing Your
Network for
Troubleshooting
Designing your network for troubleshooting facilitates your access to
key devices on your network when your network is experiencing
connectivity or performance problems. Having adequate management
access depends on these design criteria:
n Position of the management station so that it can gather the
greatest amount of network data through SNMP polling
n Position of probes for distributed management of critical networks
n 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:
n Positioning Your SNMP Management Station (page 44)
n Using Probes (page 45)
n Monitoring Business-critical Networks (page 47)
n Using Telnet, Serial Line, and Modem Connections (page 49)
n Using Communications Servers (page 50)
n Setting Up Redundant Management (page 51)
n Other Tips on Network Design (page 52)
45. 44 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Positioning Your
SNMP Management
Station
In a typical LAN, it is best to locate your Windows NT or UNIX
management station directly off the backbone where it can conduct
SNMP polling and manage network devices. The backbone is usually
the optimum location for the management station because:
n The backbone is not subject to the failures of individual
subnetworked routers or switches.
n In a partial network outage, the information collected by a
backbone management station is probably more accurate than a
station in a routed subnet.
n 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.
n 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.
Management
workstation
x
FDDI card or
network device
Figure 2 SNMP Management at the Backbone
FDDI Backbone
x x x
x x x x x x x x x
x = Network devices that you want to poll
46. 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:
n Very heavy data traffic or a break in the network can make it
difficult or impossible for the management station to poll a device.
n Traffic added to the network by SNMP polling may contribute to
networking problems.
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.
47. 46 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Probe
FDDI card or
network device
FDDI Backbone
Management
workstation
x
x
FDDI card or x
network device
x x x
x x x x x x
x = Network devices that you want to poll
x
Probe
x
x x x
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.
48. Designing Your Network for Troubleshooting 47
Monitoring
Business-critical
Networks
On business-critical networks, you need to increase your level of
management by dedicating probes to the essential areas of your
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:
n FDDI Backbone Monitoring (page 48)
n Internet WAN Link Monitoring (page 48)
n Switch Management Monitoring (page 48)
FDDI Backbone
Management
workstation
x
SuperStack II
Enterprise Monitor
x x
x
x x x x x x
x = Network devices that you want to poll
SuperStack® II
WAN Monitor 700
Figure 4 Probes Monitoring a Business-critical Network
SuperStack II
Enterprise Monitor
with FDDI module
Direct connection to the
management workstation
WAN = Possible probe attachment to a switch’s
roving analysis port
Inline monitoring
on Fast Ethernet
49. 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
protocols.
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
conversation level.
50. 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,
Serial Line, and
Modem Connections
To minimize your dependency on SNMP management, set up a way to
reach the console of your key networking devices. Through the console,
you can often view Ethernet, FDDI, ATM, and token ring statistics, view
routing and bridging tables, and check and modify device
configurations.
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:
n 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
(in-band).
n 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.
n Modem — Remote, out-of-band access using a modem connection.
Figure 5 shows management of a device through the serial line and
modem ports.
51. 50 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Management
workstation
Modem
Modem
Modem port
Serial line port
Management
workstation
Wiring closet
Network
switch
Attached LAN
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
Communications
Servers
While out-of-band management keeps you in contact with a particular
device during a network problem, it does not inform you about all the
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.
52. Designing Your Network for Troubleshooting 51
Management
workstation
Figure 6 Out-of-band Management with a Communications Server
For optimal benefit, provide two management connections to the
comm server:
n 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.
n 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
Redundant
Management
To add redundancy to your management strategy so that a
management station can always access the backbone, set up a “buddy
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.
Wiring closet
Serial line port
Attached LAN
Serial line port
Communications server
(“Comm” server)
Wiring closet
Network
switch
Network
switch
53. 52 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Other Tips on
Network Design
This section provides some additional tips for designing your network
for troubleshooting.
Management Station Configuration
n 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.
n 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
communication.
n 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.
n 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.
n Regularly back up the management station.
More Tips
n Provide remote access through a modem to the management
station so that you can keep track of your network’s activity
remotely.
n 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.
n 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.
54. Preparing Devices for Management 53
Preparing Devices
for Management
Before Transcend management software (or any other management
software) can work with the devices on your network, make sure that
the devices are configured appropriately for management
communication.
If you have a problem establishing a management connection, see
Manager-to-Agent Communication (page 67) for more information
about solving this problem.
Configuring
Management
Parameters
Before attempting to manage the supported devices with Transcend
applications, check these prerequisites for each device:
n The device must have an IP hostname and IP address. When you are
managing modular devices, use the IP address of the device’s
management module, if one is present.
n The device and your network management platform must use the
same SNMP read (get) and write (set) community strings. See
Security (page 135) for more information about community strings.
Configuring Traps SNMP trap reporting means that management agents send unsolicited
messages to management stations, relaying events that have occurred
at the device, such as a system reboot. Traps include an object
identification (OID) that passes integer values or strings that are
decoded by the management software.
Configure each device to send the SNMP traps that are required by the
network management applications to the management station. You can
set SNMP traps using the device’s console program or Device View
(page 35), a Transcend application.
For more information about traps, see Trap Reporting (page 134).
55. 54 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Configuring
Transcend Software
Configure your Transcend management software to monitor your
network most effectively, identify when thresholds are exceeded, and
alert you to problems or potential problems.
Monitoring Devices For Transcend management software to monitor your devices:
n Use your platform’s autodiscovery feature to detect all manageable
devices on your network and to create a network map. Transcend
applications use this data for their operation. For Transcend
applications to recognize 3Com devices from the platform, the
device icons must be 3Com device icons.
n Add 3Com devices to an inventory database using Transcend Central
(page 32). You can import devices from your platform’s database.
The Transcend Central database defines the devices to be managed
by many of the Transcend applications and allows you to group
devices for easier management and faster troubleshooting.
n Create logical and physical groups of the devices in your database
using Transcend Central.
Setting Thresholds
and Alarms
Thresholds are the upper and lower limits that you set for the network
conditions and events that you are monitoring with network
management software. When these limits are exceeded, the
management software reports that a threshold has been exceeded
(usually by icons changing color). Alarms add to this reporting
functionality by allowing you to configure an action to be taken (such
as disabling ports or sending e-mail) if the threshold is exceeded.
Alarms are powerful tools that, when configured correctly, can be used
to prevent inconvenient or even catastrophic network failures. The main
advantage of alarms is that you can specify at exactly which point an
action should take place, and you can tailor them to suit the normal
operating conditions of your network.
The first time you are using the Transcend applications, you should use
the default thresholds to see how they apply to your network. After
assessing your network’s normal behavior, you can adjust the thresholds
and alarms to make them more useful for your particular network. See
Identifying Your Network’s Normal Behavior (page 62) for more
information.
56. Configuring Transcend Software 55
Setting Thresholds in Status Watch
You can set a rising threshold and a falling threshold for most
Status Watch (page 32) tools. The rising threshold triggers a status
severity change when the threshold is exceeded. The falling threshold
causes a status severity change when the excessive activity or abnormal
condition has returned to normal.
For example, your Ethernet network may normally accommodate 50
percent utilization. If it exceeds 60 percent for an extended time, your
network slows considerably. You want to know when and for how long
you network exceeds the threshold of 60 percent.
Status Watch also allows you to set status severity levels for events in
the FDDI Status and the System Status tools. You can set the severity
level setting for the conditions and events. For some conditions and
events, you can specify severity level settings for the individual values of
the variables.
For more information about setting thresholds in Status Watch, see the
Status View User Guide and Status Watch help.
Setting Thresholds and Alarms in LANsentry Manager
Much of network management involves monitoring for specific network
events. LANsentry Manager (page 33) lets you specify these events in
advance and then lets you know as soon as they occur. This process is
known as setting alarms.
Consider the following examples of alarms:
n Example A: The router on your network, which is capable of
forwarding data at 3,000 packets per second (pps), appears to have
problems forwarding at the top of its specification. You configure an
alarm to tell you as soon as the traffic approaches this rate.
n Example B: Your network is running at 1,400 pps. Typically, a Cyclic
Redundancy Check (CRC) rate of more than 1 percent of network
traffic is considered excessive. You configure an alarm to tell you as
soon as the CRC rate climbs above the threshold of 14 pps.
Over time, you build up a library of alarms tailored to your own
network.
57. 56 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Refining Alarm Settings
You can refine your alarms for more exact monitoring by setting the
hysteresis zone and defining Start and Stop events.
Hysteresis zone For more control over the conditions that trigger an alarm, you can also
specify a hysteresis zone around the specified value. The hysteresis zone
ensures that alarms are not triggered due to small fluctuations around
the threshold value. The hysteresis zone is the area where a value has
fallen below the upper threshold (also called the rising threshold) but
has not yet reached a lower threshold (also called the falling threshold).
After a rising threshold generates an alarm, the value must fall below
the falling threshold before another alarm is generated. For alarms set
on falling thresholds, the rule is reversed. An example of this alarm
mechanism is shown in Figure 5-7.
Hysteresis zone
Figure 5-7 Alarm Triggering Mechanism
58. Configuring Transcend Software 57
Stop and Start
events
As well as using alarms on their own, in LANsentry Manager, you can
use them as Start or Stop events when capturing packets with the
Capture application. In Example A, you could start capturing all packets
transmitted by the router whenever the traffic rate rose above 2,800
packets per second and then stop capturing when it dropped below
this level. By combining alarms and the Capture application, you have
powerful troubleshooting capabilities.
For more information about setting alarms with LANsentry Manager,
see the LANsentry Manager User Guide and help.
Setting Alarms Based on a Baseline
When you have determined the baselines of your network’s normal
activity with Traffix Manager (page 34) and LANsentry Manager, you
can use the Alarms View in LANsentry Manager to set alarms that
trigger when network activity deviates from the baseline. See Baselining
Your Network (page 62) for more information.
When determining the baseline for setting utilization alarms, use either
of these approaches:
n Set alarms for any peaks in network utilization — Pick a
baseline value that covers most of your network traffic, ignoring any
obvious one-time-only peaks. For example, as users log on at the
start of the day, you would to see a large peak in network
utilization. The alarm is triggered whenever such peaks occur.
n Set alarms for exceptional peaks in network utilization — Pick
a baseline value that covers the highest possible peak seen when
service was still provided. The alarm is triggered at levels higher than
this peak, alerting you to the most serious utilization on your
network.
When you choose the baseline for error alarms, pick the lowest
possible baseline so that the alarm is triggered by any peaks.
Other Tips for Setting Thresholds and Alarms
For SNMP traps to be effective, their thresholds must be high enough
so that they do not generate false alarms. On the other hand, high
thresholds also mean that small amounts of errors can escape
detection.
59. 58 STEPS TO ACTIVELY MANAGING YOUR NETWORK
A very small error rate that regularly occurs (such as four per minute)
can cause major problems with protocols with large retry delays. For
example, some MAC-level errors corrupt packets so that a switch does
not forward them.
Knowing Your
Network
You can better troubleshoot the problems on your network by:
n Knowing Your Network’s Configuration (page 58)
n Identifying Your Network’s Normal Behavior (page 62)
Knowing Your
Network’s
Configuration
Part of understanding how your network normally looks is in knowing
its physical and logical configuration. You should know which devices
are on your network, how the devices are configured, which devices
are attached to the backbone, and which devices connect your network
to the outside world (WAN). To keep track of your network’s
configuration, gather the following information:
n Site Network Map (page 58)
n Logical Connections (page 60)
n Device Configuration Information (page 60)
n Other Important Data About Your Network (page 61)
This data, when kept up to date, is extremely helpful for locating
information when you experience network or device problems.
Site Network Map
A network map helps you to:
n Know exactly where each device is physically located
n Easily identify the users and applications that are affected by a
problem
n Systematically check each part of your network for problems
You can create a network map using any drawing or flow chart
application. Store your network map online. In addition, make sure that
you always have a current version on paper in case you cannot access
the online version. Figure 8 shows a simple example of a network map
consisting of 3Com devices.
60. Knowing Your Network 59
CoreBuilder 5000
with SwitchModules
Macintosh workstations
SuperStack II
WAN Monitor 700
SuperStack II
Switch 3000 FX
Server farm
Web server
Figure 8 Example of a Site Network Map
Consider including the following information on your network map:
n Location of important devices and workgroups (by floor, building, or
area)
n Location of the network backbone, data center, and wiring closets,
as appropriate for your network
n Location of your network management stations
n Location and type of remote connections
n IP subnetwork addresses for all managed switches and hubs
n Other subnetwork addresses, such as Novell IPX and AppleTalk, if
appropriate for your network
NETBuilder II®
8-slot
AccessBuilder®
5000 7-slot
CS/2500
Servers
Windows NT workstations
Printers
Network
management
station
with FDDI card
Floor 1
SuperStack® II
Switch 2200
CoreBuilderTM 2500
Internet Modems
ISDN
Ethernet
Windows 95
workstations
Printers
FDDI
IP: 138.6.12.xxx
Floor 2
Floor 1
Ethernet
SuperStack II
Hub 100 TX
UNIX workstations
CoreBuilder 2500
Ethernet
Fast
Ethernet
FDDI
IP: 138.6.13.xxx
FDDI Backbone
IP: 138.6.1.xxx
Data center
Fast Ethernet
Fast Ethernet
FDDI
Mail server
NetWare servers
NETBuilder II
8-slot
SuperStack II
Enterprise Monitor
with FDDI module
UNIX workstations
61. 60 STEPS TO ACTIVELY MANAGING YOUR NETWORK
n Type of media (by actual name, such as 10BASE-T, or by grouping,
such as Ethernet), which can be shown with callouts, colors, line
weights, or line styles
n Virtual workgroups, which can be shown with colors or shaded
areas
n Redundant links, which can be shown with gray or dashed lines
n Types of network applications used in different areas of your
network
n Types of end stations connected to the switches and hubs
Complete data about end station connections is usually too detailed for
the network map. Instead, maintain tables that detail which end
stations are connected to which devices, along with the MAC addresses
of each end station. Use tools like MAC Watch (page 33) to generate
the MAC address information.
Logical Connections
With the advent of virtual LANs (VLANs), you need to know how your
devices are connected logically as well as physically. For example, if you
have connected two devices through the same physical switch, you can
assume that they can communicate with each other. However, the
devices could be in separate VLANs that restrict their communication.
Knowing the setup of your VLANs can help you to quickly narrow the
scope of a problem to a VLAN instead of to a network connection.
The Transcend application ATMvLAN Manager allows you to view the
logical makeup of your network. Depending on the complexity of your
network and VLAN configurations, you can use colors to show the
VLANs graphically on your network map.
Device Configuration Information
Maintain online and paper copies of device configuration information.
Make sure that all online data is stored with your site’s regular data
backup. If your site does not have a backup system, you should copy
the information onto a backup disc (CD, Zip disk, and the like) and
store it offsite.
The Transcend Network Admin Tools includes applications that allow
you to save device configurations.
62. Knowing Your Network 61
Follow these guidelines for saving configuration information:
n Because the easiest way to recover a device’s configuration is to use
FTP or TFTP, save the configuration settings of each device that
supports this method of uploading.
n For other devices, Telnet in and save the session (which contains
configuration details) to a file. If you cannot print the configuration
of a device, then create a quick “rebuild” guide that explains the
quickest way to configure the device from a fresh install.
n For devices that store information to diskette, store this data as part
of your site’s regular backup.
n For routers and other important devices with text configuration files,
store this data online in a revision control system. Keep the most
recent version on paper. Keep previous versions.
n For PCs, keep a recovery disk for each type of PC. For any device
that you use as a server, store all startup scripts and copies of
registries.
Other Important Data About Your Network
For a complete picture of your network, have the following information
available:
n All passwords — Store passwords in a safe place. Keep previous
passwords in case you restore a device to a previous software
version and need to use the old password that was valid for that
version.
n Device inventory — The inventory allows you to see the device
type, IP address, ports, MAC addresses, and attached devices at a
glance. Software tools, such as Transcend Central (page 32), can
help you keep track of the 3Com devices on your network. Using
Transcend Central, you can group devices by type and location and
have this information on hand for troubleshooting.
n MAC address-to-port number list — If your hubs or switches are
not managed, you must keep a list of the MAC addresses that
correlate to the ports on your hubs and switches. Generate and
keep a paper copy of this list, which is crucial for deciphering
captured packets, using MAC Watch (page 33).
63. 62 STEPS TO ACTIVELY MANAGING YOUR NETWORK
Do not rely on getting an up-to-date list of MAC addresses from MAC
Watch because the network may be down, which prevents SNMP
polling. If the network is down, an exported copy of MAC Watch’s data
is invaluable (online or on paper).
n Log book — Document your interactions, no matter how trivial,
with each device that is critical to your network’s operation (that is,
routers, remote access devices, security servers). For example,
document that you noticed a fan making noise one morning (which
is probably not a problem). Your note may help you to identify why
a device is over temperature a week later (because the fan stopped
working).
n Change control — Maintain a change control system for all critical
systems. Permanently store change control records.
n Contact details — Store, online and on paper, the details of all
support contracts, support numbers, engineer details, and telephone
and fax numbers.
To be ready to remotely access your network, store the network maps,
contact details, and important network addresses at the homes of
those who support the network.
Identifying Your
Network’s Normal
Behavior
By monitoring your network over a long period, you begin to
understand its normal behavior. You begin to see a pattern in the
traffic flow, such as which servers are typically accessed, when peak
usage times occur, and so on. If you are familiar with your network
when it is fully operational, you will be more effective at
troubleshooting problems that arise.
Baselining Your Network
You can use a baseline analysis, an important indicator of overall
network health, to identify problems. A baseline can serve as a useful
reference of network traffic during normal operation, which you can
then compare to captured network traffic while troubleshooting
network problems. A baseline analysis speeds the process of isolating
network problems.
By running tests on a healthy network, you compile “normal” data to
compare against the results you get when your network is in trouble.
For example, Ping (page 38) each node to discover how long it typically
takes you to receive a response from devices on your network.
64. Knowing Your Network 63
Applications such as Status Watch (page 32), LANsentry Manager (page
33), and Traffix Manager (page 34) allow you to collect days and weeks
of data and set a baseline for comparison. Through the reporting
mechanisms in the following list, you can continuously assess the data
from your network and ensure that its performance is optimal:
n Web Reporter (page 33) generates daily or weekly reports from data
collected by Status Watch.
n Traffix Manager generates weekly reports from collected data and
calculates the baselines for you. Set up Utilization History and Error
History reports with data resolution set to Weekly.
n LANsentry Manager History View generates daily utilization graphs,
sampled every 30 minutes, for each day over one week. Use these
graphs to calculate your network baselines manually.
Identifying Background Noise
Know your network’s background noise so that you can recognize
“real” data flow. For example, one evening after everyone is gone, no
backups are running, and most nodes are on, analyze the traffic on
your network using the Traffix Manager (page 34) application. The
traffic you see is mostly broadcast and multicast packets. Any errors
you see are the result of very faulty devices (trace). This traffic is the
background noise of your network — traffic that occurs for little value.
If background noise is high, redesign your network.
66. II
NETWORK CONNECTIVITY
PROBLEMS AND SOLUTIONS
Manager-to-Agent Communication (page 67)
FDDI Connectivity (page 73)
67.
68. MANAGER-TO-AGENT
COMMUNICATION
Use these sections to identify and correct problems with
communication between the management station and network devices:
n Manager-to-Agent Communication Overview (page 67)
n Checking Management Configurations (page 68)
See Manager-to-Agent Communication Reference (page 69) for
additional conceptual and problem analysis detail.
Manager-to-Agent
Communication
Overview
If your management workstation cannot communicate with devices on
the network, check your management configurations for the devices
and your management station configurations.
For more information about SNMP, see SNMP Operation (page 133).
Understanding
the Problem
If your management station or the devices you are managing are
incorrectly configured for management, then the management station,
which includes your Transcend applications, cannot perform
autodiscovery, polling, or SNMP Get and Set requests on the device.
If you have not configured port connections (including a possible
out-of-band serial or modem connection) and created an administration
password for access to the management agent, then do so before
continuing.
Identifying
the Problem
Check your management configurations for any device that your
management station cannot reach. Also check your management
station setup. If you can reach a device but are not receiving traps, first
check the trap configurations (the trap destination address and the
traps configured to send). See Configuring Traps (page 53) for more
information.
69. 68 MANAGER-TO-AGENT COMMUNICATION
Solving the Problem Either modify device configurations so that they are the same as your
management stations or modify the management station to match the
configurations of your devices.
Checking
Management
Configurations
Check the following management configurations:
n IP Address (page 69)
n Gateway Address (page 69)
n Subnetwork Mask (page 69)
n SNMP Community Strings (page 69)
n SNMP Traps (page 72)
How these parameters are configured can vary by device. For more
information, see the user guide provided with each device.
Follow these steps:
1 Ping the device.
If the device is accessible by Ping, then its IP address is valid and you
may have a problem with the SNMP setup. Go to step 5.
If the device is not accessible by Ping, then there is a problem with
either the path or the IP address.
2 To test the IP address, Telnet into the device using an out-of-band
connection.
If Telnet works, then your IP address is working.
3 If Telnet does not work, connect to the device’s console using a serial
line connection and check your device’s IP address setting.
If your management station is on a separate subnetwork, make sure
that the gateway address and subnetwork mask are set correctly.
4 Using a management application, perform an SNMP Get and an SNMP
Set (that is, try to poll the device or change a configuration using
management software).
5 If you cannot reach the device using SNMP, access the device’s console
and make sure that your SNMP community strings and traps are set
correctly.
You can access the console using Telnet, a serial connection, or a web
management interface.
70. Manager-to-Agent Communication Reference 69
Manager-to-Agent
Communication
Reference
This section explains terms relevant to management configurations and
provides additional conceptual and problem analysis detail.
IP Address Devices use IP addresses to communicate (that is, to talk to the
management station and to perform routing tasks). Assign a unique IP
address to each device in your network. Choose each IP address from
the range of addresses assigned to your organization.
Gateway Address The default gateway IP address identifies the gateway (for example, a
router) that receives and forwards those packets whose addresses are
unknown to the local network. The agent uses the default gateway
address when sending alert packets to the management workstation on
a network other than the local network. Assign the gateway address
on each device.
Subnetwork Mask The subnetwork mask is a 32-bit number in the same format and
representation as IP addresses. The subnetwork mask determines which
bits in the IP address are interpreted as the network number, which as
the subnetwork number, and which as the host number. Each IP
address bit that corresponds to a 1 in the subnetwork mask is in the
network/subnetwork part of the address. This group of numbers is also
called the Network ID. Each IP address bit that corresponds to a 0 is in
the host part of the IP address.
The subnetwork mask is specific to each type of Internet class. The
subnetwork mask must match the subnetwork mask that you used
when you configured your TCP/IP software.
SNMP Community
Strings
An SNMP community string is a text string that acts as a password. It is
used to authenticate messages sent between the management station
(the SNMP manager) and the device (the SNMP agent). The community
string is included in every packet transmitted between the SNMP
manager and the SNMP agent.
71. 70 MANAGER-TO-AGENT COMMUNICATION
After receiving an SNMP request, the SNMP agent compares the
community string in the request to the community strings that are
configured for the agent. The requests are valid under these
circumstances:
n Only SNMP Get and Get-next requests are valid if the community
string in the request matches the read-only community.
n SNMP Get, Get-next, and Set requests are valid if the community
string in the request matches the agent’s read-write community.
For more information about SNMP requests and community strings, see
SNMP Operation (page 133).
A device is difficult or impossible to manage if:
n The device is not using the correct community strings.
n Your management station uses community strings that do not
match those of the devices it manages
If community strings do not match, either modify the community string
at the device so it is the string expected by the management station, or
modify the management station so that it uses the device’s community
strings.
Table 6 lists the default community strings for some common 3Com
devices. Modify these default strings when you install a new device.
You can use Device View (page 35) to change community strings of
most 3Com devices.
Community string settings are case-sensitive for all devices.
72. Manager-to-Agent Communication Reference 71
Table 6 Default Security Settings for Common 3Com Devices
Device
Read-Only
Community
Read-Write
Community
AccessBuilder® 7000 BRI Card and PRI Card public private
CoreBuilder™ 2500 public private
CoreBuilder™ 3500 public private
CoreBuilder™ 5000 public private
CoreBuilder™ 6000 public private
CoreBuilder™ 7000 public private
NETBuilder® public *
NETBuilder II® public *
OfficeConnect® products monitor security
OfficeConnect® Remote 511, 521, and 531 public private
Online™ hubs public *
SuperStack® II Desktop Switch public security
SuperStack® II Hub TR Network Management
public private
Module
SuperStack® II Enterprise Monitor public admin
SuperStack® II PS Hub monitor security
SuperStack® II Switch 1000 public security
SuperStack® II Switch 2000 TR public private
SuperStack® II Switch 2200 public private
SuperStack® II Switch 3000 (all variations) public security
SuperStack® II Token Ring Monitor public admin
SuperStack® II WAN 700 Monitor public admin
Transcend® Enterprise Monitor 540 public admin
Transcend® Enterprise Monitor 542 public admin
Transcend® Enterprise Monitor 570 public admin
* By default, no setting exists or is needed for initial access on this device.
Although community strings are SNMP’s way to secure management
communication, these strings appear in the SNMP packet header
unencrypted and are visible if the packet data is analyzed. For this
reason, change community string settings frequently to improve
management security.
73. 72 MANAGER-TO-AGENT COMMUNICATION
SNMP Traps If your platform or management applications do not report events for
some devices, then SNMP trap reporting may not be configured
correctly for those devices.
If you find that traps are overwhelming your management workstation,
you can filter out (disable) some common traps so that the
management station does not receive them. Most devices allow you to
select which traps to send to a management station IP address.
You can use Device View (page 35) to change the trap reporting
configuration of most 3Com devices.
See Trap Reporting (page 134) for more information.
74. FDDI CONNECTIVITY
Use these sections to identify and correct connectivity errors on an FDDI
ring:
n FDDI Connectivity Overview (page 73)
n Monitoring FDDI Connections (page 77)
See FDDI Connectivity Reference (page 79) for additional conceptual
and problem analysis detail.
FDDI Connectivity
Overview
FDDI, a self-healing technology, automatically corrects ring faults to
maintain connectivity throughout most of the network. However, you
should monitor your FDDI connections for wrapped rings and other
problems with ring connectivity.
Understanding
the Problem
As shown in Figure 9, in a thru FDDI LAN, no stations on the trunk ring
have a Configuration State (SMTConfigurationState) of Wrap or
Isolated. However, users complaining about network performance may
have lost connectivity to other stations on the network because the
FDDI network is wrapped or segmented.
thru
thru thru
thru
Figure 9 Thru Ring
