NETGEAR M4100 Series ProSAFE Manual

350 East Plumeria Drive
San Jose, CA 95134
USA
December 2012
202-11104-01
v1.0
Managed Switch
Hardware Installation Guide
Models:
M4100 Series

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NETGEAR Managed Switch
© 2012 NETGEAR, Inc. All rights reserved.
No part of this publication may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated
into any language in any form or by any means without the written permission of NETGEAR, Inc.
Technical Support
When you register your product at http://www.netgear.com/register, we can provide you with faster expert technical
support and timely notices of product and software upgrades.
NETGEAR, Inc.
350 East Plumeria Drive
San Jose, CA 95134 USA
E-mail: [email protected]
Website: http://www.netgear.com
Phone: 1-888-NETGEAR, for US & Canada only. For other countries, see your Support information card.
Trademarks
NETGEAR, the NETGEAR logo, ProSafe, Smart Wizard, and Auto Uplink are trademarks or registered
trademarks of NETGEAR, Inc. Microsoft, Windows, Windows NT, and Vista are registered trademarks of Microsoft
Corporation. Other brand and product names are registered trademarks or trademarks of their respective holders.
Statement of Conditions
To improve internal design, operational function, and/or reliability, NETGEAR reserves the right to make changes
to the products described in this document without notice. NETGEAR does not assume any liability that may occur
due to the use or application of the product(s) or circuit layout(s) described herein.
Revision History
Publication Part Number Version Publish Date
202-11104-01 v1.0 December 2012

3
Contents
Chapter 1 Introduction
Front Panels and LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Rear Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Safety Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Chapter 2 Hardware Installation
Package Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Protecting Against Electrostatic Discharge. . . . . . . . . . . . . . . . . . . . . . . . . 11
Unpacking the Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Select a Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Install the Switch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Check the Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Connect to Power and Check the LEDs . . . . . . . . . . . . . . . . . . . . . . . . . 16
SFP Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Connecting Equipment to the Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
RJ-45 Ports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Connecting a Console to the Switch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Chapter 3 Troubleshooting
Troubleshooting Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Additional Troubleshooting Suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Appendix A Technical Specifications
Appendix B Default Configuration Settings
Appendix C Notification of Compliance

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1
1. Introduction
The NETGEAR ProSafe® 4100 series managed switches provide state-of-the-art,
high-performance, IEEE-compliant network solutions. They include powerful management
features that you can use to eliminate bottlenecks, boost performance, and increase productivity.
The M4100 Series switches include the following:
M4100-26G
M4100-50G
M4100-26-PoE
M4100-26G-PoE
M4100-50G-PoE+
M4100-50-PoE
M4100-D10-PoE
M4100-D12G
This guide describes hardware installation and basic troubleshooting for these managed
switches.
These switches can be free-standing, wall mounted, or rack-mounted in a wiring closet or an
equipment room. For information about features for each product, see the NETGEAR website at
http://www.netgear.com.
Front Panels and LEDs
The following figures show the front panels of the ProSafe 4100 series managed switches.
The front panel contains LEDs, a Reset button, a USB flash port, RJ45 ports, copper
(RJ45)/fiber (SFP) combo ports, and USB console selection slide switch, amd USB console
port.

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NETGEAR Managed Switch
Figure 1. M4100-26G Front Panel
Figure 2. M4100-50G Front Panel
LEDs
Reset button
SFP Ports
PoE Ports
USB Port
Console Port
Console Selection Switch
NEW ART
Figure 3. M4100-26-POE Front Panel
LEDs
R
eset button
SFP Ports
PoE Ports
USB Port
Console Port
Console Selection Switch
NEW ART
LEDs
Reset button RJ45 and Fiber Ports
USB Port
Console Port
Console Selection Switch
NEW ART

LEDs
Reset button
SFP Ports
PoE Ports
USB Port
Console Port
Console Selection Switch
NEW ART
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NETGEAR Managed Switch
Figure 4. M4100-50-POE Front Panel
Figure 5. M4100-26G-POE Front Panel
Figure 6. M4100-48G-POE+ Front Panel
Figure 7. M4100-D10-POE Front Panel
Figure 8. M4100-D12G Front Panel
Table 1. LED Descriptions
LED Description
Power Solid green: Internal power supply operating normally and supplying power to the
switch
Solid yellow: The system is in boot-up stage
Blinking yellow: Power module is present but has failed
Off: Power is disconnected.
Fan Solid green: The fan is operating normally
Solid yellow: The fan has failed
Off: No fan is detected
RPS Solid Green: RPS connected (Using internal power supply’s power)
Solid Yellow: The internal power supply has failed and the RPS is providing power
to switch.
Blinking Yellow: RPS is present but RPS has failed
Off: RPS Disconnected
Note: only for M4100-26G, -50G, -26-POE, 26G-POE, 50G-POE+, and 50-POE
PD Solid Green: PD port 1 is connected to PSE getting 802.3at specified power
Blinking Green: PD port 1 is connected to PSE getting 802.3af specified power
Off: PD port 1 is not connected to PSE
Note: only for M4100-D12G
Max PoE Solid Yellow: Indicates less than 7W of PoE power is available
Blinking Yellow: Indicates the PoE MAX LED was active in the previous two
minutes
Off: There is at least 7W of PoE power available for another device

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NETGEAR Managed Switch
SPD/Link/ACT
(RJ45 port)
OFF: No link is established on the port
Solid Green: A valid 1000Mbps link is established on the port
Blinking Green: Packets transmission or reception is occurring on the port at
1000Mbps
Solid Yellow: A valid 10/100Mbps link is established on the port
Blinking Yellow: Packets transmission or reception is occurring on the port at
10/100Mbps
Note: If combo port media change to fiber, the Ethernet LED will change to OFF
status
PoE OFF: No PoE powered device (PD) connected
Solid Green:The PoE powered device (PD) is connected and the port is supplying
power successfully
Solid Yellow: Indicates one of the following failures resulted in stopping power to
that port:
- Short circuit on PoE power circuit
- PoE power demand exceeds power available
- PoE current exceeds PD's classification
- Out of proper voltage (44 ~ 57 VDC for af, 50~57 VDC for at)
Link/ACT
(RJ45 port)
OFF: No link is established on the port
Solid Green: A valid link is established on the port
Blinking Green: Packets transmission or reception is occurring on the port
Note: If a combo port media changes to fiber, the copper port LED will change to OFF
status.
SPD (RJ45 port) OFF: No link is established on the port
Solid Green: A valid 1000Mbps link is established on the port
Solid Yellow: A valid 10/100Mbps link is established on the port.
PoE-PD OFF: No PSE is connected or connected but has failed
Solid Green: The PSE is connected and get 30W power from PSE successfully
Solid Yellow: The PSE is connected and get 15.4W power from PSE successfully
Note: only for M4100-D12G
SPD/Link/ACT
(SFP port)
Off: No SFP/SFP+ module link is established on the port
Solid green: A valid 1000Mbps SFP+ module link is established on the port
Blinking green: The port is transmitting or receiving packets at 1000Mbps
Solid yellow: A valid 100Mbps SFP module link is established on the port
Blinking yellow: Packet transmission or reception is occurring on the port at
100Mbps
Note: If combo port media change to Copper, the SFP port LED will change to OFF
status.
Table 1. LED Descriptions (Continued)
LED Description

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NETGEAR Managed Switch
Rear Panels
The rear panels have a DB9 console port, a mini-USB port, and a redundant power supply
connector (only for M4100-26G, -50G, -26-POE, -26G-POE, -50G-POE+, and -50-POE), and
a standard AC power receptacle for the supplied power cord.
Figure 9. M4100-26G, -50G, -26-PoE, -26G-PoE, -50G-PoE+, and -50-PoE Rear Panels
Figure 10. M4100-D10 Poe and M4100-D12G Rear Panels
Safety Instructions
Use the following safety guidelines to ensure your own personal safety and to help protect
your system from potential damage.
To reduce the risk of bodily injury, electrical shock, fire, and damage to the equipment,
observe the following precautions.
• Observe and follow service markings.
- Do not service any product except as explained in your system documentation.
- Opening or removing covers that are marked with the triangular symbol with a
lightning bolt may expose you to electrical shock. Only a trained service
technician should service components inside these compartments.
• If any of the following conditions occur, unplug the product from the electrical outlet and
replace the part or contact your trained service provider:
AC Power
connector
Lock
Console
port Power supply
connector
RPS
Power adapter
connector
Lock
Console
ports
Console
selection
switch

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NETGEAR Managed Switch
- The power cable, extension cable, or plug is damaged.
- An object has fallen into the product.
- The product has been exposed to water.
- The product has been dropped or damaged.
- The product does not operate correctly when you follow the operating instructions.
• Keep your system away from radiators and heat sources. Also, do not block cooling
vents.
• Do not spill food or liquids on your system components, and never operate the product in
a wet environment. If the system gets wet, see the appropriate section in your
troubleshooting guide or contact your trained service provider.
• Do not push any objects into the openings of your system. Doing so can cause fire or
electric shock by shorting out interior components.
• Use the product only with approved equipment.
• Allow the product to cool before removing covers or touching internal components.
• Operate the product only from the type of external power source indicated on the
electrical ratings label. If you are not sure of the type of power source required, consult
your service provider or local power company.
• To help avoid damaging your system, be sure that the voltage selection switch (if
provided) on the power supply is set to match the power available at your location:
- 115 volts (V), 60 hertz (Hz) in most of North and South America and some Far
Eastern countries such as South Korea and Taiwan
- 100 V, 50 Hz in eastern Japan and 100 V, 60 Hz in western Japan
- 230 V, 50 Hz in most of Europe, the Middle East, and the Far East
• Also, be sure that attached devices are electrically rated to operate with the power
available in your location.
• Use only approved power cables. If you have not been provided with a power cable for
your system or for any AC powered option intended for your system, purchase a power
cable that is approved for use in your country. The power cable must be rated for the
product and for the voltage and current marked on the product's electrical ratings label.
The voltage and current rating of the cable should be greater than the ratings marked on
the product.
• To help prevent electric shock, plug the system and peripheral power cables into properly
grounded electrical outlets.
• The peripheral power cables are equipped with three-prong plugs to help ensure proper
grounding. Do not use adapter plugs or remove the grounding prong from a cable. If you
must use an extension cable, use a three-wire cable with properly grounded plugs.
• Observe extension cable and power strip ratings. Make sure that the total ampere rating
of all products plugged into the extension cable or power strip does not exceed 80
percent of the ampere ratings limit for the extension cable or power strip.
• To help protect your system from sudden, transient increases and decreases in electrical
power, use a surge suppressor, line conditioner, or uninterruptible power supply (UPS).

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NETGEAR Managed Switch
• Position system cables and power cables carefully; route cables so that they cannot be
stepped on or tripped over. Be sure that nothing rests on any cables.
• Do not modify power cables or plugs. Consult a licensed electrician or your power
company for site modifications.
• Always follow your local and national wiring rules.

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2
2. Hardware Installation
This chapter explains how to install the hardware for the managed switches.
Package Contents
Each switch is packed and shipped separately. The package contains the following items:
• Managed Stackable Switch with preinstalled software
• Power cord
• Rubber footpads for tabletop installation
• Rubber caps for the SFP sockets
• Rack-mounting kit
• Magnets and wall-mounting kit (M4100-D10-POE and M4100-D12G only)
• USB console cable with one Mini B connector and one type A connector
• Resource CD: The CD either includes these documents or links to access them:
- ProSafe Managed Switch CLI Manual, Version 9.0.2
- NETGEAR Managed Switch Administration Guide
- NETGEAR Managed Switch Installation Guide
- This Hardware Installation Guide
• ProSafe NMS200 Network Management System 30-day trial DVD
Protecting Against Electrostatic Discharge
WARNING!
Static electricity can harm delicate components inside your
system. To prevent static damage, discharge static electricity
from your body before you touch any of the electronic
components, such as the microprocessor. You can do so by
periodically touching an unpainted metal surface on the switch.

Hardware Installation
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NETGEAR Managed Switch
You can also take the following steps to prevent damage from electrostatic discharge (ESD):
1. When unpacking a static-sensitive component from its shipping carton, leave it in the
antistatic package until you are ready to install it. Just before unwrapping the antistatic
package, discharge static electricity from your body.
2. Before moving a sensitive component, place it in an antistatic container or package.
3. Handle all sensitive components in a static-safe area. If possible, use antistatic floor pads,
workbench pads, and an antistatic grounding strap.
Unpacking the Hardware
Check the contents of the boxes to make sure that all items are present before installing the
switch.
1. Place the container on a clean flat surface and cut all straps securing the container.
2. Unpack the hardware from the boxes.
Carefully remove the hardware and place it on a secure and clean surface. See “Select a
Location” on page 2-12.
3. Remove all packing material.
4. Make sure that all items are present. See “Package Contents” on page -11.
Note: If any item is found missing or damaged, contact your local
NETGEAR reseller for replacement.
5. Inspect the products and accessories for damage. Report any damage immediately.
Installation
Install the equipment in the sequence presented in this section:
1. Select a Location. See “Select a Location” on page -12.
2. Install the Switch. See “Install the Switch” on page -13.
3. Check the installation. See “Check the Installation” on page -15.
4. Apply power and check the LEDs. See “Connect to Power and Check the LEDs” on
page -16.
Select a Location
The switch can be mounted in a standard 19-inch (48.26-centimeter) rack, wall-mounted, or
left freestanding (placed on a tabletop).

Hardware Installation
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NETGEAR Managed Switch
The site where you install the switch may greatly affect its performance. Before installing the
switch or switches, make sure that the chosen installation location meets the following site
requirements.
Install the Switch
You can install the switch on a flat surface or in a standard 19-inch rack.
Installing the Switch on a Flat Surface
The switch ships with four self-adhesive rubber footpads. Stick one rubber footpad on
each of the four concave spaces on the bottom of the switch. The rubber footpads
cushion the switch against shock and vibrations.
Installing the Switch in a Rack.
Note: The M4100-D12G and M4100-D12G are not rack mountable.
Table 2. Site Requirements for Switch Location
Requirements
Mounting • Desktop Installations: Provide a flat table or shelf surface.
• Rack-mount Installations: Use a 19-inch (48.3-centimeter) EIA standard
equipment rack that is grounded and physically secure. You need the
rack-mount kit supplied with your switch.
Access Locate the switch in a position that lets you access the front panel RJ-45 ports,
view the front panel LEDs, and access the rear-panel power connector.
Power source Provide a power source within 6 feet (1.8 meters) of the installation location.
Power specifications for the switch are shown in Appendix A. Be sure that the
AC outlet is not controlled by a wall switch, which can accidentally turn off power
to the outlet and the switch.
Environment Install the switch in a site free from strong electromagnetic field generators (such
as motors), vibration, dust, and direct exposure to sunlight.
Temperature The ambient switch operating temperature range is 0º to 50ºC (32º and 122ºF).
Keep the switch away from heat sources such as direct sunlight, warm air
exhausts, hot-air vents, and heaters.
Operating humidity Install the switch in a dry area with a maximum relative humidity of 90%,
noncondensing.
Ventilation Do not restrict airflow by covering or obstructing air inlets on the sides of the
switch. Keep at least 2 inches (5.08 centimeters) free on all sides for cooling. Be
sure that there is adequate airflow in the room or wiring closet where you intend
to install the switch.
Cabling Route the cable to avoid sources of electrical noise such as radio transmitters,
broadcast amplifiers, power lines, and fluorescent lighting fixtures.

Hardware Installation
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NETGEAR Managed Switch
To install the switch in a rack, you will need the 19-inch rack-mount kit supplied with your
switch.
1. Attach the supplied mounting brackets to the side of the switch.
2. Use the provided Phillips head screws to fasten the brackets to the sides of the
switch.
mounting
bracket
Figure 11. Installing the Switch in a Rack
3. Tighten the screws with a No. 1 Phillips screwdriver to secure each bracket.
4. Align the bracket and rack holes. Use two pan-head screws with nylon washers to
fasten each bracket to the rack.
5. Tighten the screws with a No. 2 Phillips screwdriver to secure the switch in the rack.
Installing the Switch on a Wall (M4100-D12G and M4100-D10-PoE Only)
If you install the switch on a wall in the vertical position, be sure to orient the switch with
the grill holes on top (as shown in Figure 8 right). Exhaust air should come out the top of
the switch case.
1. Attach the supplied mounting brackets to the side of the switch.
2. Use four Phillips head screws to fasten each bracket to the sides of the switch
3. Tighten the screws with a No. 1 Phillips screwdriver to secure each bracket.
4. Mark the position of bracket holes on the wall.
5. Drill 4.7mm-diameter and 22.2mm-depth wells at each mark.
6. Hammer caps into the wall.
7. Use two Phillips head screws to fasten each bracket to the wall.

Hardware Installation
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NETGEAR Managed Switch
8. Tighten the screws with a No. 2 Phillips screwdriver to secure the switch in the wall.
Horizontal Vertical
Figure 12. Installing the M4100-D12G and M4100-D10-POE Switches on a Wall Using
Brackets
Figure 13. Installing the M4100-D12G and M4100-D10-POE Switches using Magnets (ART
To Be Supplied)
Check the Installation
Before you apply power, perform the following checks:
1. Inspect the equipment thoroughly.
2. Verify that all cables are installed correctly.
3. Check cable routing to ensure that cables are not damaged and will not create a safety
hazard.
4. Be sure that all equipment is mounted properly and securely.

Hardware Installation
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NETGEAR Managed Switch
Connect to Power and Check the LEDs
The switch does not have an On/Off switch. The only way to apply or remove power is to
connect or disconnect the power cord. Before you connect the power cord, select an AC
outlet that is not controlled by a wall switch (which can turn off power to the switch).
After you select an appropriate outlet, follow these steps to apply AC power.
1. Connect one end of the AC power adapter cable (M4100-DG12 or M4100-D10-PoE) or
the AC power cord to the rear of the switch, and the other end to a grounded 3-pronged
AC outlet.
Note: The M4100-26G, -50G, -26-PoE, -26G-PoE, -50-PoE+ and 50G-PoE
can also obtain power from an RPS. Supported RPS models are the
RPS5412 and RPS4000.
Note: The M4100-D12G can get power from PSE if AC power is not
available. Connect port 1 of the switch to a PSE (Power Sourcing
Equipment) switch. The PSE device should support IEEE802.1at
and IEEE802.1af so that it can provide full power to M4100-D12G
for system operation. If the PSE device used does not support
IEEE802.1at or IEEE802.1af, the M4100-D12G may not operate
correctly.
2. Check the Power LED on the front panel of the switch. The LED should light up in the
following sequence:
• The LED turns yellow as the switch runs a Power-On Self-Test (POST).
• If the switch passes the test, the LED turns green. The switch is working and ready to
pass data.
• If the POST fails, the Power LED blinks yellow.
Note: If the PD LED on the front panel of GSM5212P blinks yellow, port 1
is connected to a IEEE802.1af PoE device. Check the PoE device
specification to make sure it supports IEEE802.1at.
If the Power LED does not light up, check that the power cable is plugged in correctly and
that the power source is good. For help with troubleshooting, see Chapter 3.3,
“Troubleshooting.”

Hardware Installation
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NETGEAR Managed Switch
SFP Modules
SFP modules (sold separately) can be inserted directly into the switch’s ports.
• AGM731F - SFP module with LC connector, compatible with the IEEE 802.3z
1000Base-SX standard.
• AGM732F - SFP module with LC connector, compatible with the IEEE 802.3z
1000Base-LX standard.
• AFM735 - SFP module with LC connector, compatible with the IEEE 802.3u 100Base-FX
standard.
1. insert the module into the switch port.
2. Press firmly to ensure that the module seats into the connector.
Figure 14. Insert the SPF Module into the Switch

Hardware Installation
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NETGEAR Managed Switch
Connecting Equipment to the Switch
You can connect devices, a Gigabit Ethernet module, and/or a console to the switch.
RJ-45 Ports
The switch uses Auto Uplink technology, which enables you to attach devices using either
straight-through or crossover cables. Use a Category 5 (Cat5) unshielded twisted-pair (UTP)
cable terminated with an RJ-45 connector.
Note: Ethernet specifications limit the cable length between the switch and
the attached device to 328 feet (100 meters).
Connecting a Console to the Switch
After you install the switch and apply power, you can connect to it with a terminal or
workstation. You can use the Command Line Interface (CLI) to identify the IP address.
To use a console you need the following items:
• VT100/ANSI terminal, or a Windows PC, Apple Macintosh PC, or UNIX workstation.
• USB console cable (shipped with the product) or a Null-modem cable with 9-pin
connectors on each end.
To connect a console to the switch:
1. Connect the null-modem cable to the console port on the rear of the switch or connect
the USB console cable to the console USB port on the front of the switch.
Console Port
Rear Panel
Front Panel
Console Port
Figure 15. Console Ports
2. Select console port via the console slide switch on the front panel:
a. Select the mini USB (cable included) as console port by pushing the slide switch to
the left. Use the Resource CD to install the USB driver on your PC.
b. Select the DB9 (cable not included) in the back as console port by pushing the slide
switch to the right.

Hardware Installation
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NETGEAR Managed Switch
3. Connect the other end of the cable to a workstation or terminal.
4. If you attached a workstation, start a terminal-emulation program.
• Microsoft Windows users can use HyperTerminal if it comes with the Windows
operating systems. If not, you need to install another 3rd party terminal emulator such
as Tera Term.
• Macintosh users can use ZTerm.
• UNIX users can use a terminal emulator such as TIP.
5. Configure the terminal-emulation program to use the following settings:
• Baud rate: 115,200 bps
• Data bits: 8
• Parity: none
• Stop bit: 1
• Flow control: none
After you connect a console to the switch, you will need to configure it. The following
documents are provided for this purpose:
• Quick Installation Guide: Explains basic setup and configuration (provided as both a print
document and in PDF format on the Resource CD).
• ProSafe Managed Switch CLI Manual, Version 9.0.2: Gives detailed examples of how to
use the CLI.
• NETGEAR Managed Switch Administration Guide: Describes configuration tasks.

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3
3. Troubleshooting
Troubleshooting Chart
The following table lists symptoms, causes, and solutions of possible problems.
Table 3. Troubleshooting Chart
Problem Cause Solution
Power LED is off. No power is received Check the power cord connections for the switch
at the switch and the connected device.
Make sure that all cables used are correct and
comply with Ethernet specifications.
Link LED is off or intermittent. Port connection is not
working.
• Check the crimp on the connectors. Make sure
the plug is fully inserted and locked into the
port at both the switch and the connecting
device.
• Make sure that all cables used are correct
and comply with Ethernet specifications. See
Appendix A.
• Check for a defective adapter card, cable, or
port by testing it in an alternate environment
where all products are functioning.
Slow file transfer or there is
performance degradation.
Half- or full-duplex setting on
the switch and the connected
device are not the same.
• Make sure that the attached device is set to
auto negotiate.
• Check the system message log.
A segment or device is not
recognized as part of the
network.
One or more devices are not
properly connected, or cabling
does not meet Ethernet
guidelines.
Verify that the cabling is correct. Be sure that all
connectors are securely positioned in the
required ports. Equipment may have been
accidentally disconnected.
ACT LED flashes
continuously on all connected
ports and the network is
disabled.
A network loop (redundant
path) has been created.
Break the loop by ensuring that there is only one
path from any networked device to any other
networked device.