Net+ 3.4 Lesson

Do be aware that restarting a switch, router, or server can be very disruptive to the rest of the network. Identify how to mitigate potential impacts and seek authorization for your plan before proceeding. Also, remember that a restart will apply the startup configuration. Any unsaved changes in the running configuration will be discarded. 

ALERT

When you are troubleshooting a suspected layer 1 or layer 2 problem, check the LED status indicators on the NIC at one end and the switch/router port at the other. You will need the vendor documentation to interpret the LEDs.

ALERT

Multiple Choice

On a switch, a SOLID GREEN LIGHT on a port means what?

• The port is experiencing a fault.
• The port is inactive and disconnected.
• The port is active and connected.
• The port is in a power-saving mode.

Multiple Choice

On a switch port, what does a FLICKERING GREEN light mean?

• The port is powered off.
• It means there is network activity on the port.
• The port is in a fault state.
• The port is configured for VLAN tagging.

Multiple Choice

On a switch port, if there is NO LIGHT, what does that mean?

• The switch port is functioning normally.
• There is a power outage affecting the switch.
• The switch port is configured for a different VLAN.
• There is no physical connection or link established.

Multiple Choice

A SOLID AMBER light on a port of a switch means what?

• The port is not connected at all.
• The port is transmitting data successfully.
• The port is malfunctioning and needs repair.
• The port is connected but not transmitting data.

Multiple Choice

A BLINKING AMBER light indicates what on a switch port?

• A problem with the connection or link failure.
• A solid amber light indicates power supply issues.
• A blinking red light indicates data transfer activity.
• A stable green light indicates a successful connection.

This command is your go-to for viewing the device's overall current setup. It pulls up the comprehensive settings and configurations that are applied and functioning at the moment.

show config

When you're preparing for future operations or maintenance windows, this command is critical. It displays the configuration that has been saved and will be automatically applied the next time the device restarts. This is essential for verifying changes intended for future application.

show startup-config

Use this command to see the configuration actively being used by the device in real-time. It's particularly useful for troubleshooting or verifying that recent changes have taken effect without needing a restart.

show running-config

This command offers a deep dive into each network interface on the device. It covers a variety of details including status (up/down), protocol status, speed, and packet statistics. This is helpful for diagnosing connectivity issues or for regular network health checks.

show interface

Multiple Choice

This command shows the device current configuration

• show config

• show startup-config

• show running-config

• show interface

Multiple Choice

This command shows the configuration the device will use upon the next restart

• show config

• show startup-config

• show running-config

• show interface

Multiple Choice

This command shows the active configuration currently used by the device

• show config

• show startup-config

• show running-config

• show interface

Multiple Choice

This command shows detailed information about the devices network interfaces

• show config

• show startup-config

• show running-config

• show interface

Down/Down
This indicates the port is currently inoperable and unable to transmit or receive data.

• This could be due to a physical cable issue, disabled interface configuration, or a hardware problem on the switch or connected device.

Command Status

Administratively down/down
The port is intentionally disabled by the administrator, likely through configuration settings.

• It remains inoperable even if a cable is connected.

Command Status

Down/error disabled
The port has encountered an error and has been automatically disabled by the switch for protection.

• This might be due to excessive link errors or detected hardware issues on the port.

Command Status

Up/down (suspended)
The port is currently up and able to transmit/receive data, but it has experienced prior issues and is in a suspended state.

• This could be a temporary condition or might require further investigation depending on the switch model and specific details.

Command Status

Multiple Choice

port is currently inactive on both layer 1 and 2

• down/down

• administratively down/down

• down/error disabled

• up/down (suspended)

Multiple Choice

interface/port has been manually disabled by an admin using the shutdown command

• down/down

• administratively down/down

• down/error disabled

• up/down (suspended)

Multiple Choice

due to a network error or violation, the interface has been automatically disabled

• down/down

• administratively down/down

• down/error disabled

• up/down (suspended)

Multiple Choice

physical layer is up, as is, it is physically connected, but layer 2 is inactive due to settings

• down/down

• administratively down/down

• down/error disabled

• up/down (suspended)

An interface might change rapidly or "flap" between up and down states, making the problem harder to observe and diagnose.

Interface counters record the number of events over time. This allows you to diagnose issues with an interface that is up but that is unreliable or performing poorly.

Interface Error Counters

Link State:
This counter indicates the number of times the physical link between the switch port and the connected device has transitioned from up to down or vice versa.

• Frequent link state changes suggest potential cabling issues, device instability, or errors on the connected device.

Key Error Counters

Resets
This counter reflects the number of times the switch has reset a specific port.

• This can be triggered by various factors, including excessive errors, duplex mismatch, or negotiation issues with the connected device. High reset counts could indicate a faulty cable or hardware problem.

Key Error Counters

Discards/Drops
This counter represents the number of packets the switch has discarded or dropped due to errors.

• Reasons for discards/drops can be diverse, such as buffer overflow, invalid packets, or errors detected during transmission. An abnormally high discard/drop rate warrants investigation.

Key Error Counters

By analyzing these error counters in conjunction with the basic port status, network administrators can gain deeper insights into potential network connectivity problems.

Utilizing Error Counters

• A high Link State change count suggests verifying cable integrity and ensuring secure connections.

• Frequent port resets might indicate a faulty cable, duplex mismatch, or hardware issues on the switch or connected device.

• Abnormally high Discards/Drops could point towards switch buffer overload, invalid packet formats, or errors on the connected device.

Troubleshooting Strats

Multiple Choice

To become a good troubleshooter of network switches, sometimes you have to analyze THIS aspect of the SHOW INTERFACE STATUS command

• key error counters

• port status

• link lights

Multiple Choice

This counter indicates the number of times the physical link between the switch port and the connected device has transitioned from up to down or vice versa.

• link state

• resets

• discard/drops

Multiple Choice

This counter reflects the number of times the switch has reset a specific port.

• link state

• resets

• discard/drops

Multiple Choice

This counter represents the number of packets the switch has discarded or dropped due to errors.

• link state

• resets

• discard/drops

• Description: These errors occur when the calculated checksum of a received frame doesn't match the checksum transmitted with the frame.

• Possible Causes: Noise, electromagnetic interference, or malfunctioning equipment on the network path can corrupt data during transmission, leading to CRC errors.

• Troubleshooting Tips: Verify cable integrity, check for loose connections, and rule out potential sources of interference. Consider replacing malfunctioning devices if necessary.

Cyclic Redundancy Check

• Description: These errors indicate receiving frames that are smaller than the minimum allowable frame size.

• Possible Causes: Collisions during transmission or damaged network hardware can cause incomplete frames, resulting in runt errors.

• Troubleshooting Tips: Investigate potential causes of collisions, such as excessive network traffic or misconfigured devices. Check for damaged cables or faulty network adapters on connected devices.

Runt Frame Errors

• Description: These errors occur when received frames exceed the maximum permitted size on the network.

• Possible Causes: Misconfiguration of network devices or malfunctioning equipment can lead to giant frames being sent.

• Troubleshooting Tips: Verify switch and device configuration settings for correct frame size. Consider replacing malfunctioning equipment identified as the source of giant frames.

Giant Frame Errors

• Again, you can verify the amount of errors using the "show interface status" command

Key Counters

Multiple Choice

These errors occur when the calculated checksum of a received frame doesn't match the checksum transmitted with the frame.

• Cyclic Redundancy Check

• Runt Frame Errors

• Giant Frame Errors

Multiple Choice

These errors indicate receiving frames that are smaller than the minimum allowable frame size.

• Cyclic Redundancy Check

• Runt Frame Errors

• Giant Frame Errors

Multiple Choice

These errors occur when received frames exceed the maximum permitted size on the network.

• Cyclic Redundancy Check

• Runt Frame Errors

• Giant Frame Errors

• Description:  A network loop occurs when a single frame of data is endlessly replicated within a network segment due to redundant pathways. This can quickly consume network resources and bring communication to a halt.

  Causes:

  • Redundant connections: Incorrectly configured redundant links between switches can create loops.

  • End-device side: Certain device configurations or bridging features can also introduce loops on the end-device side.

Network Loop

• Solutions:

  • Proper redundant connection configuration: Ensure redundant links are configured correctly to avoid creating loops (e.g., using Spanning-Tree Protocol – STP).

  • Implement Spanning-Tree Protocol (STP): STP is a standard protocol that helps prevent loops by electing a single path for data flow while keeping redundant links available for failover.

  • Educate users: Educate users on potential loop-causing configurations, such as enabling bridging functions on devices that shouldn't act as bridges.

Network Loop

• Description:  A broadcast storm occurs when a broadcast frame (like a DHCP request) is endlessly replicated and flooded throughout the network, consuming bandwidth and degrading performance.

  Causes:

  • DHCP issues: Malfunctioning DHCP servers or misconfigured clients can continuously broadcast DHCP requests, triggering a storm.

  • Very large broadcast domains: Large, unsegmented networks can exacerbate broadcast storms as the broadcast traffic reaches a wider range of devices.

Broadcast Storm

• Solutions:

  • Monitor DHCP traffic: Monitoring DHCP activity can help identify malfunctioning servers or rogue clients causing excessive broadcasts.

  • Segment the network: Segmenting the network into smaller broadcast domains using techniques like VLANs can limit the impact of broadcast storms, preventing them from flooding the entire network.

Broadcast Storm

• Network loops and broadcast storms can have severe consequences, causing network outages and hindering communication.

• Understanding their causes and implementing preventive measures is crucial for maintaining network stability and performance.

Additional Points

Multiple Choice

occurs when a single frame of data is endlessly replicated within a network segment due to redundant pathways

• Network loop

• Broadcast storm

Multiple Choice

occurs when a broadcast frame (like a DHCP request) is endlessly replicated and flooded throughout the network, consuming bandwidth and degrading performance

• Network loop

• Broadcast storm

Multiple Choice

Implement Spanning-Tree Protocol would fix which problem?

• Network loop

• Broadcast storm

Multiple Choice

Monitoring DHCP traffic would solve which problem?

• Network loop

• Broadcast storm

Multiple Choice

Segmenting the network would solve which problem?

• Network loop

• Broadcast storm

Multiple Choice

Ensuring proper redundant connections would solve what problem?

• Network loop

• Broadcast storm

Cabling Considerations

• Cat 5e or Better: While Cat 5e cables meet the minimum PoE standard, consider using Cat 6A for futureproofing and potentially better performance over longer distances.

• Conductor Thickness: Opt for cables with thicker conductors (23 AWG gauge) compared to thinner ones (24 AWG). Thicker conductors offer less resistance, leading to lower power loss over longer cable runs.

• Shielded Cabling: Shielded cabling can be beneficial, especially in environments with electromagnetic interference (EMI). Shielding helps disperse heat more efficiently, further enhancing performance.

PoE issues - Cabling

Standard Compatibility

• Negotiation is Key: PoE devices and switches need to negotiate the correct PoE mode (e.g., 802.3af Alternative A, 802.3at Type B, or Four-Pair PoE) to ensure proper power delivery.

• Legacy Device Challenges: Devices that only support the first PoE standard (802.3af with a 15.4W maximum) might not function correctly with newer PoE switches that offer higher power options. Consider upgrading older devices or using PoE injectors to supplement power delivery if necessary.

PoE issues - Compatibility

Power Budget Management

• Limited Switch Capacity: PoE switches have a limited overall power budget (typically ranging from 300W to 400W). This budget is shared across all PoE-powered devices connected to the switch.

• Monitoring Power Levels: Utilize the "show power inline" command (or equivalent depending on the switch model) to monitor power levels delivered to connected devices. This helps identify potential power limitations or overloading scenarios.

• Strategic Power Distribution: Plan your PoE device deployment strategically to ensure the total power draw doesn't exceed the switch's budget. Prioritize devices with higher power requirements (e.g., PTZ cameras) and consider using PoE injectors for specific devices if needed.

PoE issues - Power Budget

Multiple Choice

To ensure future proofing of PoE, what cabling is recommended?

• Fiber optic cabling
• Category 3 (Cat 3) cabling
• Category 5e (Cat 5e) cabling
• Category 6 (Cat 6) cabling

Multiple Choice

The minimum cabling used for PoE is what?

• Category 6 (Cat 6) cable
• Category 5 (Cat 5) cable
• Category 3 (Cat 3) cable
• Fiber optic cable

Multiple Choice

What does it mean to NEGOTIATE PoE?

• To negotiate PoE means to establish the power requirements and capabilities between a powered device and a power sourcing equipment.
• To negotiate PoE means to set the data transfer rates between devices.
• To negotiate PoE refers to the physical installation of power cables.
• To negotiate PoE involves determining the color coding of power wires.

Multiple Choice

When planning to deploy PoE devices, what is one consideration to keep in mind when purchasing a switch?

• Total power budget of the switch.
• Color and design of the switch casing.
• Brand reputation of the switch manufacturer.
• Number of Ethernet ports on the switch.

Poll

End of Lesson Poll

• I can troubleshoot switches!

• I'll need to review again!

• I AM COOKED!

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