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CCNA lab 4 of 46

How a switch learns MAC addresses and floods frames

Watch two switches build their MAC address tables, catch flooded broadcasts and unknown unicasts with a packet capture, tune aging and pin a printer with a static entry.

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It needs Lite: its 6 nodes are set to 6 vCPU and 5,632 MB in total. That fits the free demo too.

In your workspace: Shared, then CCNA 200-301 guided labs, then 04 - How a switch learns MAC addresses and floods frames

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Level
Beginner
Time
About 45 minutes
Nodes need
6 vCPU, 5,632 MB
Smallest plan
Lite

The scenario

Lakeside Library has two switches on one floor: S1 by the front desk and S2 in the study area, joined by one cable. Every device is in VLAN 1 and the subnet 10.4.1.0/24. A label printer (H1, a small Linux box) is about to be installed on S2.

The IT volunteer wants to understand what the switches actually do with frames before anyone starts adding VLANs. You'll watch the MAC address tables fill up, prove flooding with a packet capture on the printer, change the aging timer and pin the printer to its port.

DevicePortAddressNotes
PC1S1 Gi0/110.4.1.11/24front desk
PC2S1 Gi0/210.4.1.12/24catalogue terminal
PC3S2 Gi0/110.4.1.13/24study area
H1S2 Gi0/210.4.1.14/24, MAC 02:00:00:00:04:44 (you set both)label printer
S1 Gi0/0S2 Gi0/0–inter-switch link

Topology: PC1, PC2 — S1 Gi0/1, Gi0/2 · S1 Gi0/0 — S2 Gi0/0 · PC3, H1 — S2 Gi0/1, Gi0/2.

What you’ll practise

  • Read and clear the MAC address table and explain each column
  • Predict which port learns which MAC address across two switches
  • Prove broadcast and unknown-unicast flooding with a packet capture
  • Change the aging time and explain why entries expire
  • Add a static MAC entry and explain the forward, filter and flood decisions

The tasks

  1. Look at an empty MAC address table
  2. Watch the tables fill up
  3. Catch flooding in the act
  4. Change the aging time
  5. Install the label printer and pin it to its port
  6. Summarise what the switch decides

The Lab Tasks pane has the scenario, these tasks, the checks to run, hints and the full solution.

Topology and devices

The network as it opens in EVE-NG, drawn from the lab’s own canvas, and the image each node runs.

Topology of How a switch learns MAC addresses and floods frames6 nodes, 5 links. Every link is listed as text below the diagram.S1S2PC1PC2PC3H1Gi0/1eth0Gi0/2eth0Gi0/1eth0Gi0/2eth0Gi0/0Gi0/0
6 nodes, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • S1 Gi0/0 to S2 Gi0/0
  • S1 Gi0/1 to PC1 eth0
  • S1 Gi0/2 to PC2 eth0
  • S2 Gi0/1 to PC3 eth0
  • S2 Gi0/2 to H1 eth0
Nodes in How a switch learns MAC addresses and floods frames, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
S1Cisco IOSvL2viosl2-adventerprisek9-m.ssa.high_iron_202009291 vCPU, 1,024 MB
S2Cisco IOSvL2viosl2-adventerprisek9-m.ssa.high_iron_202009291 vCPU, 1,024 MB
PC1VPCS hostBuilt in to EVE-NGCounted as 1 vCPU, 1,024 MB
PC2VPCS hostBuilt in to EVE-NGCounted as 1 vCPU, 1,024 MB
PC3VPCS hostBuilt in to EVE-NGCounted as 1 vCPU, 1,024 MB
H1Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB

How to open this lab

  1. Sign in to your workspace at lab.cloudlabbox.com.

  2. In File Manager, open Shared, then the folder CCNA 200-301 guided labs.

  3. Open 04 - How a switch learns MAC addresses and floods frames and start its nodes, then open Lab Tasks for the scenario and the steps.

The lab is read-only. You can start the nodes and configure the devices, but changes to the topology can’t be saved. To change it, rebuild it in your own folder.

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CloudLabBox is independent of Cisco. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.