Cisco Networking/CCENT/Troubleshooting

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CCENT
  1. Networking Models
  2. Ethernet LANs
  3. IP Addressing
  4. Subnetting
  5. Lab Setup
  6. IOS Basics
  7. Remote Management
  8. Network Services
  9. Static Routing
  10. Dynamic Routing
  11. Switching
  12. VLANs
  13. Security
  14. Access Control Lists
  15. Troubleshooting
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This lesson covers troubleshooting.

Objectives and Skills[edit | edit source]

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[edit | edit source]

  1. Wikipedia: Troubleshooting
  2. Cisco: Troubleshooting Ethernet
  3. Cisco: Troubleshooting Tools

Multimedia[edit | edit source]

  1. YouTube: The Network Troubleshooting Process - CompTIA Network+ N10-005: 1.8
  2. YouTube: Switch and Routing Diagnostics - CompTIA Network+ N10-005: 2.1
  3. YouTube: Troubleshooting Switch Loops - CompTIA Network+ N10-005: 2.5
  4. YouTube: Troubleshooting Network Cabling - CompTIA Network+ N10-005: 2.5
  5. YouTube: Troubleshooting Port Configuration - CompTIA Network+ N10-005: 2.5
  6. YouTube: Troubleshooting VLAN Assignments - CompTIA Network+ N10-005: 2.5
  7. YouTube: Troubleshooting Bad Fiber Modules - CompTIA Network+ N10-005: 2.5
  8. YouTube: Troubleshooting Mismatched MTUs - CompTIA Network+ N10-005: 2.5
  9. YouTube: Troubleshooting Power Failures - CompTIA Network+ N10-005: 2.5
  10. YouTube: Troubleshooting Routing - CompTIA Network+ N10-005: 2.5
  11. YouTube: Troubleshooting Subnet Masks and Gateways - CompTIA Network+ N10-005: 2.5
  12. YouTube: Troubleshooting Duplicate IP Addresses - CompTIA Network+ N10-005: 2.5
  13. YouTube: Troubleshooting DNS - CompTIA Network+ N10-005: 2.5
  14. YouTube: Cisco Troubleshooting Exercise

Examples[edit | edit source]

IP Addressing[edit | edit source]

show interfaces[edit | edit source]

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[edit | edit source]

  1. Review Cisco Networking/CCENT/Remote Management#show ip interface
  2. Review Cisco Networking/CCENT/Remote Management#show ip interface brief
  3. Review Cisco Networking/CCENT/Static Routing#show ip route
  4. Review Cisco Networking/CCENT/Switching#show arp
  5. Review Cisco Networking/CCENT/IOS Basics#show running-config
  6. Review Cisco Networking/CCENT/IOS Basics#show startup-config
  7. Review Cisco Networking/CCENT/Remote Management#ping
  8. Review Cisco Networking/CCENT/Static_Routing#trace / traceroute
  9. Review Cisco Networking/CCENT/Remote Management#telnet

VLANs[edit | edit source]

  1. Review Cisco Networking/CCENT/VLANs#show vlan
  2. Review Cisco Networking/CCENT/VLANs#show interface trunk
  3. Review Cisco Networking/CCENT/VLANs#show interfaces switchport

Access Control Lists[edit | edit source]

  1. Review Cisco Networking/CCENT/Access Control Lists#show access-lists
  2. Review Cisco Networking/CCENT/Access Control Lists#show ip access-lists
  3. Review Cisco Networking/CCENT/Remote Management#show ip interface

Layer 1 Problems[edit | edit source]

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

Activities[edit | edit source]

  1. 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
  2. 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
  3. 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
  4. 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[edit | edit source]

  • 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[edit | edit source]

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[edit | edit source]

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Click on a question to see the answer.
  1. 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.
  2. 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.
  3. A basic principle in troubleshooting is to _____.
    A basic principle in troubleshooting is to start from the simplest and most probable possible problems first.
  4. Serial substitution involves _____.
    Serial substitution involves checking each component in a system one by one, substituting known good components for each potentially suspect one.
  5. Bisection involves _____.
    Bisection involves separating a larger system into two or more subsystems to isolate and identify problems and causes.
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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.
  11. Troubleshoot ACL issues using the _____ commands.
    Troubleshoot ACL issues using the show access-lists, show ip access-lists, and show ip interface commands.
  12. Troubleshoot Layer 1 problems using the _____ commands.
    Troubleshoot Layer 1 problems using the show interfaces and show cdp neighbors commands.

Assessments[edit | edit source]

See Also[edit | edit source]

References[edit | edit source]

Completion status: this resource is considered to be complete.
  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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