Transcript Troubleshooting

Chp. 9: Troubleshooting
CCNA Discovery 2
Version 4.1
Contents
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9.1: Troubleshooting approaches
9.2: Troubleshooting Layer 1 and 2
9.3: Troubleshooting Layer 3 IP Addressing
9.4: Troubleshooting Layer 3 Routing
9.5: Troubleshooting Layer 4 & Upper Layers
Troubleshooting by Layers
• One of the most important abilities for a
network professional to develop is the ability
to efficiently troubleshoot network problems
• Knowing and Understanding the OSI Layers
can help you Troubleshoot Networks
▫ Logical networking models separate network
functionality into modular layers.
▫ Each layer of the OSI or TCP/IP model has
specific functions and protocols.
Layered Models
Network Applications
File format, compression and
encryption
Manages communication sessions
between applications
Manages end-to-end message
delivery, TCP provides reliability
IP addressing , Routing of packets
between networks
Frames, MAC Addressing, Media
Access Control
Transmission of Bits over Media,
Signaling, Encoding
Upper Layer Errors
• The upper layers (5-7) of the OSI model deal
with specific application functionality and are
generally implemented only in software.
• Problems in the Upper Layers (5 to 7) are
frequently be caused by software configuration
errors on clients and servers
Layer 3 and 4 Errors
• The lower layers (1-4) of the OSI model handle
data-transport issues.
• Layers 3 and 4 are generally implemented only
in software.
• Problems in layers 3 and 4 are frequently
caused by:
1. Software configuration errors on Clients
2. Router configuration errors
3. Firewall configuration errors
• Layer 3 Problems are commonly caused by:
1. IP addressing and routing errors
Layer 1 and 2 Errors
• Layer 1 and Layer 2 are implemented in both
hardware and software.
• The Physical Layer is closest to the physical
network medium, such as the network cabling,
and is responsible for actually placing
information on the medium.
• Most problems in Layer 1 and Layer 2 are
caused by:
1. Hardware problems
2. Hardware incompatibilities
Technologies by Layer
• It is important to understand where different
Networking Technologies fit into the OSI Layers
so you will know where to begin Troubleshooting
Layer 1
•Media
•Hubs
•Signals
•NICs
Layer 2
•NICs
•MAC Address
•Frames
•Switches
Layer 3
•Routers
•IP Addresses
•Packets
Layer 4
•TCP
•UDP
•Segments
•Port Numbers
•Sockets
Upper Layers
•Applications
•Telnet
•FTP
•HTTP
•DNS
•DHCP
•SMTP
•SNMP
Troubleshooting Approaches
• There are 3 main troubleshooting
approaches when using network models:
1. Top-down
2. Bottom-up
3. Divide-and-conquer
• Using one of these troubleshooting methods, a
troubleshooter can verify all functionality at
each layer until the problem is located and
isolated.
Top-down
• The Top-down approach starts with the
Application Layer and works down.
• It looks at the problem from the point of view of
the user and the application.
• Is it just one application that is not functioning,
or do all applications fail?
• For example:
▫ Can the user access various web pages on the
Internet, but not email?
▫ Do other workstations have similar issues?
• Suitable for simpler problems or those where an
application error is suspected
Bottom-up
• The Bottom-up approach starts with the Physical
Layer and works up.
• The Physical Layer is concerned with hardware
and wire connections.
▫ Are cables securely connected?
▫ If the equipment has indicator lights, are those
lights on or off?
• Suitable for more complex problems
• Slow, but solid method
Divide-and-Conquer
• The Divide-and-Conquer begins at one of the
middle layers and works up or down from there.
• For example:
a) The troubleshooter begins at the Network Layer
by verifying IP configuration information
b) Next, they may work up or down the layers:
 The functionality of the NIC is checked
OR
 Port Number Assignments are checked
• Suitable for more complex problems and when
the problem has less precise symptoms
Troubleshooting Approaches
Problem: A customer reports that they are unable to view web pages
from a web server located at the ISP
A.
Bottom-Up Approach
1. The technician checks the cable connections between the web
server and switch
2. The technician checks the lights on the NIC in the web server
B. Top-Down Approach:
1. The technician calls the customer to find out which apps are
affected
2. The technician verifies that the DNS server has the correct DNS
entry and is resolving the name
C. Divide-and-Conquer Approach:
1. The technician pings the server and then pings the customer’s
switch
2. The technician checks the firewall configuration
Troubleshooting Tools
• It is very difficult to troubleshoot any type of
network connectivity issue without a network
diagram that depicts the IP addresses, IP routes,
and devices, such as firewalls and switches.
• Logical and physical topologies are
extremely useful in troubleshooting.
Physical Network Topology
• A physical network topology shows the physical
layout of the devices connected to the network.
▫ Knowing how devices are physically connected is
necessary for troubleshooting problems at the Physical
Layer, such as cabling or hardware problems.
• Physical network topologies typically include:
▫ Device types
▫ Models and manufacturers of devices
▫ Locations
▫ Operating system versions
▫ Cable types and identifiers
▫ Cabling endpoints
Physical Topology Diagram
Logical Network Topology
• A logical network topology shows how data is
transferred on the network.
▫ Symbols are used to represent network elements such
as routers, servers, hubs, hosts, and security devices.
• Logical network topologies typically include:
▫ Device identifiers
▫ IP addresses and subnet masks
▫ Interface identifiers
▫ Routing protocols
▫ Static and default routes
▫ Data-link protocols
▫ WAN technologies
Logical Topology Diagram
Troubleshooting tools
• In addition to network diagrams, other tools
may be needed to effectively troubleshoot
network performance issues and failures.
▫ Documentation and baseline tools
 To create network diagrams and document hardware
▫ Management system tools
 To monitor network performance
▫ Knowledge bases
 Network device vendor knowledge bases are an
indispensable sources of information.
▫ Protocol analyzers
 Decodes the protocol layers in a recorded frame and
presents the information in an easy-to-use format.
Troubleshooting Hardware Tools
Sometimes failures in the lower layers of the OSI model
must be identified with hardware troubleshooting
tools:
▫ Cable testers
 Handheld devices designed for testing data communication
cabling for broken wires, crossed-over wiring, shorted
connections, and improperly paired connections
▫ Digital multimeters
 Test instruments that measure electrical values of voltage,
current, and resistance.
▫ Portable network analyzers
 For testing network traffic utilization
9.2: Layer 1 and 2 Issues
• The Physical and the Data Link Layers encompass
both hardware and software functions.
• All network communications rely on the technologies at
Layers 1 and 2 in order to function
• A network technician must be able to quickly isolate and
correct problems occurring at these layers
• To effectively troubleshoot Layer 1 and Layer 2
problems, technicians must be familiar with:
▫ Cabling standards
▫ Encapsulation
▫ Framing
Layer 1 Issues
• Layer 1 problems can result in loss of connectivity or degraded
network performance
• Symptoms of Layer 1 Issues:
1. Loss of connectivity
2. Network congestion
3. High collision count
4. Console error messages
• Causes of Layer 1 Issues :
1. Bad, Improperly terminated or too long cables
2. Wrong cable type
3. Electrical or wireless Interference
See Troubleshooting chart
Troubleshoot Layer 1 Issues
• Most layer 1 issues are caused by Hardware
problems and incompatibilities
• To Troubleshoot Layer 1 Issues:
1.
2.
3.
4.
Visually Inspect Cables
Check Hardware Configurations
Use Show Interfaces to check Interface statistics
Monitor Network Performance
Layer 2 Issues
• Symptoms of Layer 2 Issues:
1. Excessive Broadcasts
2. Intermittent Loss of connectivity
3. Excessive Collisions on an Interface
4. Console Error Messages
• Causes of Layer 2 Issues:
1. Misconfigured Network cards
2. Faulty NIC drivers
3. Encapsulation errors on WAN links
4. Overly large Broadcast Domains
Troubleshoot Layer 2 Issues
• Network analyzers can diagnose Layer 2 issues
• To Troubleshoot Layer 2 Issues:
1. Check NIC drivers and configuration
2. Use Show Interfaces to check encapsulation
3. Monitor Network Performance with Network
analzyers
Router Bootup
• To troubleshoot device hardware failures and boot errors,
you must understand the Router Boot Process:
1. Perform the POST and load the bootstrap program.
▫
▫
▫
tests the router hardware
After POST, the bootstrap program is loaded
The Bootstrap program is loaded from ROm
2. Locate and load the Cisco IOS software
▫
IOS is located from: flash memory (default), a TFTP server, or router
Boots into ROMmon Mode and loaded into RAM
▫
The IOS locates the hardware and software components and lists
the results on the console terminal
3. Locate and load the startup configuration file or enter
setup mode
▫
▫
Config file is loaded from: NVRAM, a TFTP server, or the router
enters into setup mode
This starts routing processes and supplies addresses to interfaces
Router Bootup Process
Layer 1 & 2 Bootup Errors
1. POST failure
▫ If POST fails, turn off the power, unplug the device, remove all interface
modules., then reboot
2. Corrupt flash image
▫ Some devices can load a boothelper image from ROM memory with limited
capabilities. If no boothelper, the device will boot into ROMmon mode
3. Corrupt or missing configuration file
▫ Use either a TFTP server to restore a backup file or manually re-configure the
device
4. Configuration-Register Setting error
▫
▫
An incorrect configuration register setting tells the router the wrong location
to look for the Cisco IOS image
From ROMmon mode, you can change the config-register setting back
5. Memory error
▫ If there is not enough memory to load the image, you can usually boot into
ROMmon mode with Ctrl-Break and load an older one
6. Module error
▫ Faulty or improperly seated interface modules may not be recognized during
the POST and Cisco IOS load. Remove them and reboot
Configuration Register
• The configuration register setting on a router
tells it where to look for the IOS file to boot from
• The normal, default config-register setting is:
0x2102
▫ This indicates a normal Flash boot and tells the router
to use the default boot sequence:
• Flash, TFTP Server, ROMmon mode
▫ If the config-register is set to something other than
0x2102, this will cause the router to look somewhere
other than FLASH memory for the IOS file, and it will
usually not boot properly
Viewing the Config-Register
• Once a router is booted, the ONLY command
that can be used to view the config-register is
show version
▫ Router# show version
ROMmon Mode
• If a router fails to boot a valid IOS file, it will boot up in
ROM monitor (ROMmon) mode
• ROMmon software is a simple command set stored in
read only memory (ROM)
• It can be used to troubleshoot boot errors and recover
the router when the IOS is not present
• Troubleshooting in ROMmon mode:
1. Look in flash memory for a valid IOS image

rommon 1> dir flash:
2. Once an IOS image is found, boot the image
manually

rommon 1> boot flash:<IOS filename>
Troubleshooting Boot Errors
• In order to troubleshoot Router bootup errors:
1. Observe console messages during the boot
sequence
2. Use the show commands to verify operational
status
When boot problems cause a network outage, use
substitution to replace the device with a
known good device to restore services to end
users
Troubleshoot Boot Errors
• Show version
▫ displays the version of the operating system and whether all
interface hardware is recognized.
• Show flash
▫ displays the contents of the Flash memory, including the
Cisco IOS image file. It also displays the amount of Flash
memory currently being used and the amount of memory
available.
• Show ip interfaces brief
▫ shows the operational status of the device interfaces and IP
addresses assigned.
• Show running-configuration and show startupconfiguration
▫ verify whether all the configuration commands were
recognized during boot
Layer 1 & 2 Router Interface Errors
• Router Interface errors are often the first
symptom of Layer 1 and Layer 2 cabling or
connectivity errors
• Causes of Layer 1 Interface errors:
1. Cable Errors
2. Physical Interface Errors
3. Hardware Errors
• Causes of Layer 2 Interface Errors:
1.
2.
3.
4.
Encapsulation Error
Clock Rate Error
Misconfigured IP Address
Interface not Enabled
Interface Issues
Layer 1 Issues
The interface cannot detect any signal on
the line – due to a bad cable, no cable,
interface error, or failed CSU/DSU on a
serial interface
The Interface is disabled due to hardware
errors
Layer 2 Issues
There is an encapsulation error, a missing
clock rate, misconfigured IP Address or
the interface is not receiving keepalives
The Interface has not been enabled with
the no shutdown command
Layer 1 & 2 Interface Media Errors
• 4 different types of Layer 1 and 2 Media Errors
that can exist on a router interface
▫
▫
▫
▫
Excessive noise
Excessive collisions
Excessive runts
Late collisions
Excessive Noise
• The Interface shows many CRC errors but not many
collisions
• Usually indicates a media or cable error
• Common causes are electrical interference, loose or
damaged connections, or incorrect cabling type
Excessive Collisions
• Can only occur on half-duplex or shared-media
Ethernet connections (when hubs in use)
• Can be caused by Damaged cables
Excessive Runts
• Run Frames are usually caused by
Malfunctioning NICs
• Can also be caused by Damaged Cables
Late Collisions
• A properly designed and configured network
should never have late collisions.
• The most common cause is excessive cable
lengths
• Can also be caused by Duplex mismatches
Troubleshoot Interface Errors
• To troubleshoot Interface Errors:
1. Use show interfaces to look at the interface
statistics
2. Use show ip interface brief to check the
status of interfaces
Show ip interfaces brief
Layer 2: LAN Connectivity Errors
LAN troubleshooting usually centers around switches,
because the majority of LAN users connect to the
network via switch ports.
• Causes of LAN Connectivity Errors:
1.
2.
3.
4.
Port hardware failures
Cable errors
Ports not Enabled
Duplex and/or Speed Mismatch
LAN Connectivity Troubleshooting
Switch Troubleshooting:
1. Observe port LEDs to verify port functionality
▫
Red or orange indicates an error
2. Verify cable connections
3. Verify configuration to ensure ports are enabled
▫
Switch# show run
▫
Switch# show interfaces
4. Verify duplex settings on ports
▫
Switch# show interface port status
Layer 2: WAN Connectivity Errors
Typically, WAN connectivity relies on equipment and media that is
owned and managed by a telecommunications service provider
(TSP)
2 Most Common WAN Connectivity Issues on
Routers:
1. Clock rate errors
2. Mismatched Encapsulation or Timing
Troubleshooting WAN connectivity issues:
1. Verify functionality of WAN Interfaces with show
interfaces serial
1. Router# show interfaces serial
You should also know the type of modem or CSU/DSU
being used
9.3: Layer 3 Issues
• Layer 3 Issues are largely due to poorly
designed and configured IP addressing schemes
▫ At Layer 3, each packet must be identified with the
source and destination addresses of the two end
systems.
▫ A device must be configured with an IP address to
exchange messages using TCP/IP
• To troubleshoot Layer 3 problems, you must be
able to:
▫ Determine the range of host addresses that belong
to each individual IP network or subnet
Subnetting Example
• The Network 192.168.1.0 /24 needs to be subnetted to
create 6 usable Subnets
▫ Class:
C
▫ Default Subnet Mask:
255.255.255.0
▫ # of Bits to borrow :
3
 Total Subnets Created:
8
 2X
(x = bits borrowed)
 Usable Subnets Created:
6
2X-2
(x = bits borrowed)
 Total Host Addresses per Subnet:
32
 2y
(y = host bits left over)
 Usable Host Addresses per Subnet:
30
2y-2
(y = host bits left over)
Subnetting Example
Not Usable
Not Usable
IP Addressing Scheme
Network Address
Not Usable = Network Address
Not Usable=Broadcast Address
Subnet Practice
Given the Network Address and Subnet Mask, Define:
1. The Range of Host Addresses
2. The Broadcast Address
3. The Next Network Address
10
255
244
255
30
255
252= 11111100
Place value of last bit borrowed = 4
Subnets Increase by a value of 4:
10
244
10
244
10
244
30
30
30
10
244
228
252
30
Go to Section: 9.3.1.3 in Discovery 2 to Practice this Activity
Layer 3 IP Design Issues
• Common Layer 3 Problems caused by Poor
Address Design and Planning
1. Overlapping subnets
 When the address range of two separate subnets includes some
of the same host or broadcast addresses
 The Router IOS does not allow you to configure overlapping
subnets on multiple interfaces of the same device
 However, it will allow you to configure overlapping subnets on
different devices, which will cause problems
2. Misconfigured subnet masks

On Hosts and routers
3. Insufficient addresses available through DHCP
 If the subnetting design does not allow for enough available
host addresses, then the DHCP server will not be able to assign
them
Overlapping Subnets
Overlapping Subnets
Misconfigured Subnet Mask
Misconfigured Subnet Mask
Insufficient addresses available
• If the IP subnetting scheme does not allow for
enough host addresses in each subnet, some
hosts will be unable to receive an IP address
from the DHCP server.
▫ When a host can not receive an address from a
DHCP server, it automatically assigns itself an
address on the 169.254.0.0 network.
▫ A duplicate IP address Error can also occur on a host
▫ Use the show ip dhcp binding command from the
command prompt to check whether the DHCP server has
available addresses
Determine # of Hosts Available
62
Go to Section: 9.3.3.2 in Discovery 2 to
Practice this Activity
9.4: Layer 3 Routing issues
• Common Symptoms of Layer 3 Routing
Errors:
1. Network failures
2. Poor network performance
• Routing problems are usually the result of :
1. Static (manual) route entry errors
2. Routing protocol configuration errors
3. Routing Protocol operation errors
▫ They can also be caused by failures at the lower layers
of the OSI model
Interpreting the Routing Table
• When there is a change in the network status, routes can
be lost, or an incorrect route can be installed into the
routing table.
• The primary tool to use when troubleshooting Layer 3
routing problems is examining the Routing Table
▫ Router: Show ip route
• The routing table consists of route entries from the
following sources:
▫ Directly connected networks
▫ Static routes
▫ Dynamic routing protocols
• Any time a routing problem is suspected, use the show ip route
command to ensure that all the expected routes are installed in the
routing table.
Examining Routing Tables
Connected Routes
• Connected Route Problems
▫ Directly connected routes are automatically installed
in the routing table when an IP address is configured
on an interface, and the interface is enabled using the
no shutdown command.
• Causes of Connected Route Problems
1. An Interface has an invalid IP Address
2. An Interface is not enabled
• Troubleshooting Connected Routes
1. Use the show interfaces or show ip interface
brief command to verify that the Interface is UP and
has a valid IP address
Static and Default Routes
•
Static and Default Route Problems
▫ Static and default routes must use either an exit interface on the
router or the IP address of the next hop router.
• Causes of Problems
▫ When a static or default route does not appear in the routing
table, the problem is most likely a configuration error.
1. If the next hop address is not in the correct IP address range of
a directly connected network, then the route will not be vaild
• Troubleshooting Static and Default Routes
1.
Verify that the configuration statements are correct with the
show run command
2. Verify that the exit interfaces used by the routes are in an up/up
state with the show ip interfaces brief command
Dynamic Routes
• Dynamic Route Problems
▫ Dynamic Routes are learned from other routers through the use
of routing protocols
▫ In order for dynamic routes to be correct, the routing protocol
must be operating properly
• Causes of Dynamic Route Problems
▫ A missing route could be caused by a misconfiguration on one or
more of the routers on the path to the destination.
1. Missing Network Statements in the Routing Protocol
configuration of another router can cause dynamic routes to not
be advertised properly
• Troubleshooting Dynamic Routes
1.
Use show ip protocols to check the configuration of routing
protocols
2. Use show run to check the routing protocol configuration
3. Use show ip interfaces brief to view interface status
4. Use the debug ip rip command to verify routing updates
Layer 3 RIP Issues
• Issues related specifically to RIP:
1. RIP Version mismatch between routers
2. Incorrect or missing network statements
RIP Network Statement
• When configuring RIP, the network statement
does two things:
1. It enables the routing protocol to send and
receive updates on all the local interfaces that
belong to that network.
2. It includes that network in its routing updates to
its neighboring routers.
• A missing or incorrect network statement results
in inaccurate routing updates and can prevent
an interface from sending or receiving routing
updates.
RIP Configuration
Troubleshooting RIP issues
Tools for troubleshooting dynamic routing issues:
1. Use TCP/IP utilities to test connectivity
▫ Ping to test connectivity
▫ Traceroute to test connectivity
▫ Telnet to verify connectivity and make
configuration changes.
2. Use Debug commands to view updates
▫ Debug ip rip – to view RIP updated in real-time
3. Use Show commands to verify configuration & routes
Show run –view version and network statements
Show ip protocols – view rip configuration
Show ip interfaces – view interface status
Show ip route – view routes
Show interfaces – view interface status
Debug ip rip
9.5: Troubleshooting Layer 4 Issues
• Layer 4 is responsible for transporting data
packets and specifies the port number used to
reach specific applications.
• Layer 4 network problems can arise at the edge
of the network where security technologies are
examining and modifying the traffic.
• Many problems at Layer 4 are caused by
misconfigured firewalls, which might deny
traffic based on port numbers, even though this
traffic should be forwarded.
Layer 4 Issues
• Symptoms of Layer 4 problems:
1. Security problems
2. Intermittent network problems
3. Trouble using some services
• Causes of Layer 4 Problems
1. Firewall misconfiguration

Example: ftp active connections blocked
2. Incorrect port assignments for applications
Well Known Port Numbers
21
Upper Layer Issues
• Most of the upper layer protocols provide user services that are
typically used for network management, file transfer, distributed file
services, terminal emulation, and email.
▫ It can be difficult to isolate problems to the upper layers,
especially if the client configuration does not reveal any obvious
problems.
• Symptoms of Upper Layer issues:
1. Slow application performance
2. Application error messages
3. Unable to access application services or web
services
• Common Causes of Upper layer issues:
1. Software configuration errors on clients and
servers
Troubleshoot upper layer issues
• In order to determine if an issue exists with the upper
layers, you must RULE OUT basic connectivity
issues first
• Use the "divide and conquer" method – start at layer 3
1.
2.
3.
4.
5.
Ping default gateway
Verify end to end connectivity – ping destination
Verify router configuration
Verify nat configuration
Verify firewall filtering
• If connectivity is not the issue, but the end device is still
not operating as expected, the problem has been isolated
to the upper layers.
Divide and Conquer Approach – Rule out
Connectivity Issues
Upper Layer Issues
• Upper layer problems prevent services from being
provided to application programs.
• A problem at the upper layers can result in unreachable
or unusable resources, even when the lower layers are
functional.
• Upper layer issues can exist even with full network
connectivity
• Problems with upper layer functions usually affect just a
few applications, perhaps even only one
Causes of Upper Layer Issues
•
Most upper layer network problems are caused by
Misconfigured client applications
1. If more than one application is affected, a DNS server
issue may be the problem
▫ Use the nslookup command from the command line to verify
DNS functioning on a client
2. A mismatch between the way a client encrypts or
compresses the data and the way the server
interprets it can cause applications to not function or to
function poorly.
▫ When a problem occurs on a single host or workstation, it
may be a problem with the way the information is being
interpreted in the host software.
DHCP issues
• When a host can not obtain an IP address, or
assigns itself an IP Address in the 169.254.0.0
network, that is an indication of a DHCP error
• DHCP Issues are usually caused by:
1. Physical connectivity issue with the host or
DHCP server
2. DHCP Server misconfiguration
3. IP Address conflicts between 2 hosts
DHCP troubleshooting
• DHCP troubleshooting:
1. Use the ipconfig /all command
2. Check the physical connectivity of devices
3. Verify that the DHCP server is correctly
configured and has available IP addresses to
lease
4. Check for any address conflicts

Use the show ip dhcp conflict command
5. Test to ensure that the issue is actually with
DHCP

Assign a static IP address to the host and ping the
DHCP server
NAT issues
• Usually the first indication that there is a NAT problem is that users
cannot reach sites located on the Internet.
• NAT issues:
▫ Incorrectly designated inside & outside interfaces
 The inside interface connects to the local network, which uses private
IP address space
 The outside interface connects to the public network, usually the ISP
▫ NAT Pool misconfiguration
 The IP address pool and static NAT translation entries must use IP
addresses that are on the same local IP network as the outside
interface
▫ No route to the Internet for translated addresses
 If external users must be able to reach specific servers on the internal network,
be sure that static NAT translations are configured.
NAT Configuration
NAT Troubleshooting
1. Verify NAT operation:
▫
Router# show ip nat translations
2. Clear NAT translations:
▫
Router# clear ip nat translation *
3. Verify that there is a route to the Internet for
the translated addresses
▫
Router# traceroute …..
Troubleshooting Tools
1. Telnet is an excellent tool to use when
troubleshooting upper layer issues
▫ Use Telnet to access networking devices remotely
▫ The ability to reach devices using Telnet indicates
that the lower layer connectivity exists between
the devices.
▫ However, Telnet is an insecure protocol
2. SSH is a more secure method for remote
device access.
Troubleshooting Chart
Layer
Symptoms
Layer 1:
Physical
•
•
•
•
Loss of connectivity
Network congestion
High collision count
Console error messages
•Cable Errors
•Interference
•Router Boot Errors
•Interface Hardware errors
Layer 2: Data
Link
•
•
•
•
•
•
•
Excessive Broadcasts
Loss of connectivity
Console Error Message
Excessive noise
Excessive collisions
Excessive runts
Late collisions
•
•
•
•
•
Layer 3:
Network
Layer 4:
Transport
Upper Layers
Causes
Misconfigured NIC
Faulty NIC drivers
Large Broadcast Domains
Encapsulation errors
Clock Rate errors
Troubleshooting