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Layer 2Privileged EXEC

show mac address-table dynamic

Displays the dynamically learned MAC address table entries on a switch, used to verify which devices are learned on which ports and VLANs.

Syntax·Privileged EXEC
show mac address-table dynamic

When to Use This Command

  • Verify that a specific host's MAC address has been learned on the correct switch port and VLAN.
  • Troubleshoot connectivity issues by checking if MAC addresses are appearing on expected interfaces.
  • Identify unauthorized devices connected to the network by reviewing unknown MAC addresses.
  • Monitor MAC table aging and ensure entries are being refreshed properly.

Command Examples

Basic dynamic MAC address table display

show mac address-table dynamic
          Mac Address Table
-------------------------------------------
Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
   1    0050.7966.6800    DYNAMIC     Gi0/1
  10    0011.2233.4455    DYNAMIC     Gi0/2
  10    00a0.c9b1.d2e3    DYNAMIC     Gi0/3
  20    0c75.bd0a.1234    DYNAMIC     Gi0/4
Total Mac Addresses for this criterion: 4

Vlan: VLAN ID where the MAC was learned. Mac Address: MAC address in dotted-hex format. Type: Always DYNAMIC for this command. Ports: Switch port where the MAC was learned. Total count shows number of dynamic entries.

Filter by VLAN

show mac address-table dynamic vlan 10
          Mac Address Table
-------------------------------------------
Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
  10    0011.2233.4455    DYNAMIC     Gi0/2
  10    00a0.c9b1.d2e3    DYNAMIC     Gi0/3
Total Mac Addresses for this criterion: 2

Filters output to only show dynamic MAC addresses learned in VLAN 10. Useful for isolating traffic in a specific VLAN.

Understanding the Output

The output displays a table with columns: Vlan (VLAN ID), Mac Address (48-bit MAC in dotted hex), Type (always DYNAMIC for this command), and Ports (interface where MAC was learned). Each row represents a dynamically learned MAC-to-port mapping. A healthy network shows expected MACs on correct ports. Unexpected MACs may indicate loops, misconfigurations, or rogue devices. Missing expected MACs could point to connectivity issues or VLAN mismatches. The total count helps verify the number of learned hosts.

CCNA Exam Tips

1.

CCNA exam tip: Remember that 'show mac address-table dynamic' only shows entries learned via incoming frames, not static or secure MACs.

2.

CCNA exam tip: Know that dynamic MAC entries age out by default after 300 seconds (configurable with 'mac address-table aging-time').

3.

CCNA exam tip: Be able to identify which port a given MAC is on; exam may ask you to trace a frame's path based on MAC table.

4.

CCNA exam tip: Understand that the MAC address table is used for Layer 2 forwarding decisions; a missing entry can cause flooding.

Common Mistakes

Mistake 1: Confusing dynamic entries with static or secure entries; use 'show mac address-table' to see all types.

Mistake 2: Forgetting that the MAC table is per-VLAN; a MAC learned in one VLAN won't appear in another.

Mistake 3: Assuming the output shows all MACs; it only shows dynamic entries unless you specify otherwise.

Related Commands

show mac address-table

Displays the MAC address table (also known as CAM table) on a switch, showing which MAC addresses are learned on which VLAN and port, used to verify Layer 2 forwarding and detect issues like MAC flooding or incorrect port assignments.

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