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Chapter 17 — Ethernet Switching

A complete networking lesson based on the course chapter menu.

20 topicsPractical examplesTroubleshooting checksReview Q&A
Estimated reading time0% read

Chapter 17: Ethernet Switching

This chapter follows the topics shown in the Networking chapter menu. Work through each section in order, then use the review questions to check recall and troubleshooting reasoning.

17.1 Switch Operation

Switch Operation is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Switch Operation in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Switch Operation without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.2 MAC Address Table

MAC Address Table is a Layer 2 concept involving Ethernet hardware addressing or switch forwarding state. Switches learn source MAC addresses and use destination MAC information to choose whether to forward, flood, or filter frames.

Example: place MAC Address Table in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain MAC Address Table without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.3 MAC Learning

MAC Learning is a Layer 2 concept involving Ethernet hardware addressing or switch forwarding state. Switches learn source MAC addresses and use destination MAC information to choose whether to forward, flood, or filter frames.

Example: place MAC Learning in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain MAC Learning without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.4 Frame Forwarding

Frame Forwarding is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Frame Forwarding in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Frame Forwarding without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.5 Frame Flooding

Frame Flooding is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Frame Flooding in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Frame Flooding without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.6 Unknown Unicast

Unknown Unicast is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Unknown Unicast in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Unknown Unicast without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.7 Broadcast Forwarding

Broadcast Forwarding concerns traffic delivered to every member of a Layer 2 or IP broadcast scope. Broadcast behavior matters because excessive or unintended broadcasts can consume shared capacity and reveal segmentation problems.

Example: place Broadcast Forwarding in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Broadcast Forwarding without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.8 MAC Aging

MAC Aging is a Layer 2 concept involving Ethernet hardware addressing or switch forwarding state. Switches learn source MAC addresses and use destination MAC information to choose whether to forward, flood, or filter frames.

Example: place MAC Aging in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain MAC Aging without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.9 Access Ports

Access Ports is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Access Ports in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Access Ports without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.10 Switch Port Status

Switch Port Status is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Switch Port Status in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Switch Port Status without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.11 Port Speed

Port Speed is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Port Speed in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Port Speed without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.12 Duplex

Duplex is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Duplex in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Duplex without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.13 Auto-Negotiation

Auto-Negotiation is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Auto-Negotiation in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Auto-Negotiation without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.14 Interface Counters

Interface Counters is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Interface Counters in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Interface Counters without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.15 CRC Errors

CRC Errors is a troubleshooting condition. The useful approach is to confirm symptoms, determine scope, identify the relevant layer, compare actual values with the intended design, test one theory at a time, and verify service after the fix.

Example: place CRC Errors in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Confirm the symptom and determine whether the problem affects one host, one segment, one site, or many sites.
  • Compare actual configuration and measurements with the intended design, baseline, or documentation.
  • Change one variable at a time, verify the result, and document both the cause and the final fix.
Practice: Practice: explain CRC Errors without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.16 Runts

Runts is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Runts in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Runts without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.17 Giants

Giants is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Giants in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Giants without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.18 Port Errors

Port Errors is a troubleshooting condition. The useful approach is to confirm symptoms, determine scope, identify the relevant layer, compare actual values with the intended design, test one theory at a time, and verify service after the fix.

Example: place Port Errors in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Confirm the symptom and determine whether the problem affects one host, one segment, one site, or many sites.
  • Compare actual configuration and measurements with the intended design, baseline, or documentation.
  • Change one variable at a time, verify the result, and document both the cause and the final fix.
Practice: Practice: explain Port Errors without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.19 Interface Flapping

Ping is a basic reachability and round-trip-time test. A failed ping does not always prove the destination is down because policy may block ICMP.

Example: ping the local loopback, local interface, default gateway, remote IP, and finally a hostname. The first failed step helps narrow the fault domain, but remember that ICMP filtering can produce false negatives.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.

Command or data example

ping 192.0.2.1
Practice: Practice: explain Interface Flapping without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

17.20 Switching Troubleshooting

Switching Troubleshooting is a troubleshooting condition. The useful approach is to confirm symptoms, determine scope, identify the relevant layer, compare actual values with the intended design, test one theory at a time, and verify service after the fix.

Example: place Switching Troubleshooting in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Confirm the symptom and determine whether the problem affects one host, one segment, one site, or many sites.
  • Compare actual configuration and measurements with the intended design, baseline, or documentation.
  • Change one variable at a time, verify the result, and document both the cause and the final fix.
Practice: Practice: explain Switching Troubleshooting without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

Chapter 17 Review Questions

1. What should you remember about Switch Operation?

Answer: Switch Operation is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

2. What should you remember about MAC Learning?

Answer: MAC Learning is a Layer 2 concept involving Ethernet hardware addressing or switch forwarding state. Switches learn source MAC addresses and use destination MAC information to choose whether to forward, flood, or filter frames.

3. What should you remember about Frame Flooding?

Answer: Frame Flooding is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

4. What should you remember about Broadcast Forwarding?

Answer: Broadcast Forwarding concerns traffic delivered to every member of a Layer 2 or IP broadcast scope. Broadcast behavior matters because excessive or unintended broadcasts can consume shared capacity and reveal segmentation problems.

5. What should you remember about Access Ports?

Answer: Access Ports is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

6. What should you remember about Duplex?

Answer: Duplex is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

7. What should you remember about Interface Counters?

Answer: Interface Counters is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

8. What should you remember about Runts?

Answer: Runts is one of the core topics in Ethernet Switching. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

9. What should you remember about Port Errors?

Answer: Port Errors is a troubleshooting condition. The useful approach is to confirm symptoms, determine scope, identify the relevant layer, compare actual values with the intended design, test one theory at a time, and verify service after the fix.

10. What should you remember about Switching Troubleshooting?

Answer: Switching Troubleshooting is a troubleshooting condition. The useful approach is to confirm symptoms, determine scope, identify the relevant layer, compare actual values with the intended design, test one theory at a time, and verify service after the fix.