Cisco Networking/CCENT/Troubleshooting

This lesson covers troubleshooting.

Objectives and Skills

Objectives and skills for the troubleshooting portion of Cisco CCENT certification include:^[1]

Troubleshoot and correct common problems associated with IP addressing and host configurations
Troubleshoot and resolve VLAN problems
- Identify that VLANs are configured
- Verify port membership is correct
- Correct IP address is configured
Troubleshoot and resolve trunking problems on Cisco switches
- Verify correct trunk states
- Verify correct encapsulation is configured
- Correct VLANs are allowed
Troubleshoot and resolve ACL issues
- Verify statistics
- Verify permitted networks
- Verify direction
  - Interface
Troubleshoot and resolve Layer 1 problems
- Framing
- CRC
- Runts
- Giants
- Dropped Packets
- Late Collisions
- Input/Output errors

Readings

Multimedia

Examples

IP Addressing

show interfaces

To display statistics for all interfaces configured on the router or access server, use the show interfaces command in privileged EXEC mode.^[2]

show interfaces

Review

VLANs

Access Control Lists

Layer 1 Problems

Review #show interfaces
Review Cisco Networking/CCENT/Static Routing#show cdp neighbors

Activities

Troubleshoot and correct common problems associated with IP addressing and host configurations.
1. Add two routers to a new GNS3 project and start the devices.
2. Set the router global, password, interface, line, and remote management configurations to various matching and mismatched configurations.
3. Practice verifying and troubleshooting the configurations using the following commands.
  - show interfaces
  - show ip interface
  - show ip interface brief
  - show ip route
  - show arp
  - show running-config
  - show startup-config
  - ping
  - trace / traceroute
  - telnet
  - ssh
Troubleshoot and resolve VLAN and trunking problems.
1. Add a router, an EtherSwitch router and four VPCS PCs to a new GNS3 project and start the devices.
2. Set the VLANs, port membership, encapsulation, trunking, and IP addressing to various matching and mismatched configurations.
3. Practice verifying and troubleshooting the configurations using the following commands.
  - show vlan
  - show interface trunk
  - show interfaces switchport
Troubleshoot and resolve ACL issues.
1. Add three routers and two VPCS PCs to a new GNS3 project and start the devices.
2. Configure IP addressing and static or dynamic routing to connect all devices.
3. Test the configuration using the following commands from the routers and the PCs. Test all router and PC addresses. All tests should be successful.
  - ping
  - trace
4. Configure standard and extended ACLs to various matching and mismatched configurations.
5. Practice verifying and troubleshooting the configurations using the following commands.
  - show access-lists
  - show ip access-lists
  - show ip interface
Troubleshoot and resolve Layer 1 problems.
1. Add two routers to a new GNS3 project and start the devices.
2. Set the link between the devices to various matching and mismatched configurations.
3. Practice verifying and troubleshooting Layer 1 problems using the following commands.
  - shutdown
  - no shutdown
  - show interfaces
  - show cdp neighbors

Lesson Summary

Troubleshooting is a logical, systematic search for the source of a problem so that it can be solved, and so the product or process can be made operational again.^[3]
Troubleshooting requires identification of the malfunction(s) or symptoms within a system. Then, experience is commonly used to generate possible causes of the symptoms. Determining the most likely cause is a process of elimination - eliminating potential causes of a problem. Finally, troubleshooting requires confirmation that the solution restores the product or process to its working state.^[4]
A basic principle in troubleshooting is to start from the simplest and most probable possible problems first.^[5]
Serial substitution involves checking each component in a system one by one, substituting known good components for each potentially suspect one.^[6]
Bisection involves separating a larger system into two or more subsystems to isolate and identify problems and causes.^[7]
One of the core principles of troubleshooting is that reproducible problems can be reliably isolated and resolved.^[8]
Intermittent problems are often the result of components that are thermally sensitive, because the resistance of a circuit varies with the temperature of the conductors in it.^[9]
Troubleshooters must always consider the possibility that there is more than one fault causing a given system failure.^[10]
Troubleshoot common problems associated with IP addressing and host configurations using the show interfaces, show ip interface, show ip interface brief, show ip route, show arp, show running-config, show startup-config, ping, trace / traceroute, telnet, and ssh commands.
Troubleshoot VLAN and trunking problems using the show vlan, show interface trunk, and show interfaces switchport commands.
Troubleshoot ACL issues using the show access-lists, show ip access-lists, and show ip interface commands.
Troubleshoot Layer 1 problems using the show interfaces and show cdp neighbors commands.

Key Terms

CRC (cyclic redundancy check): An error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data.^[11]
duplex mismatch: A condition where two connected devices operate in different duplex modes, that is, one operates in half duplex while the other one operates in full duplex.^[12]
error disabled (err-disabled): A error situation detected on a port, resulting in the software shutting down that port.^[13]
giant: An Ethernet frame that is longer than the IEEE standard 1,518 bytes.^[14]
late collision: A collision that occurs more than 64 octets into the frame.^[15]
runt: An Ethernet frame that is less than the IEEE 802.3's minimum length of 64 octets.^[16]
up and up: Refers to the two interface states of line status and protocol status both being enabled.^[17]

Review Questions

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Troubleshooting is _____.

Troubleshooting is a logical, systematic search for the source of a problem so that it can be solved, and so the product or process can be made operational again.
Troubleshooting requires _____.

Troubleshooting requires identification of the malfunction(s) or symptoms within a system. Then, experience is commonly used to generate possible causes of the symptoms. Determining the most likely cause is a process of elimination - eliminating potential causes of a problem. Finally, troubleshooting requires confirmation that the solution restores the product or process to its working state.
A basic principle in troubleshooting is to _____.

A basic principle in troubleshooting is to start from the simplest and most probable possible problems first.
Serial substitution involves _____.

Serial substitution involves checking each component in a system one by one, substituting known good components for each potentially suspect one.
Bisection involves _____.

Bisection involves separating a larger system into two or more subsystems to isolate and identify problems and causes.
One of the core principles of troubleshooting is that _____.

One of the core principles of troubleshooting is that reproducible problems can be reliably isolated and resolved.
Intermittent problems are often the result of _____.

Intermittent problems are often the result of components that are thermally sensitive, because the resistance of a circuit varies with the temperature of the conductors in it.
Troubleshooters must always consider the possibility that _____.

Troubleshooters must always consider the possibility that there is more than one fault causing a given system failure.
Troubleshoot common problems associated with IP addressing and host configurations using the _____ commands.

Troubleshoot common problems associated with IP addressing and host configurations using the show interfaces, show ip interface, show ip interface brief, show ip route, show arp, show running-config, show startup-config, ping, trace / traceroute, telnet, andssh commands.
Troubleshoot VLAN and trunking problems using the _____ commands.

Troubleshoot VLAN and trunking problems using the show vlan, show interface trunk, and show interfaces switchport commands.
Troubleshoot ACL issues using the _____ commands.

Troubleshoot ACL issues using the show access-lists, show ip access-lists, and show ip interface commands.
Troubleshoot Layer 1 problems using the _____ commands.

Troubleshoot Layer 1 problems using the show interfaces and show cdp neighbors commands.

Assessments

Flashcards: Quizlet: CCENT - Troubleshooting
Quiz: Quizlet: CCENT - Troubleshooting

References

← Access Control Lists

Cisco Networking/CCENT

[1] Cisco: ICND1 Exam Topics

[2] Cisco: IOS Interface Command Reference

[3] Wikipedia: Troubleshooting

[4] Wikipedia: Troubleshooting

[5] Wikipedia: Troubleshooting

[6] Wikipedia: Troubleshooting

[7] Wikipedia: Troubleshooting

[8] Wikipedia: Troubleshooting

[9] Wikipedia: Troubleshooting

[10] Wikipedia: Troubleshooting

[11] Wikipedia: Cyclic redundancy check

[12] Wikipedia: Duplex mismatch

[13] Cisco: Errdisable Port State Recovery on the Cisco IOS Platforms

[14] Wikipedia: Jumbo frame

[15] Wikipedia: Carrier sense multiple access with collision detection

[16] Wikipedia: Ethernet frame

[17] Odom, W. (2013). CCENT/CCNA ICND1 100-101 Official Cert Guide. Cisco. ISBN 9781587143854

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