When I try the sh mac address-table int gi 1/0/19 command:

sh mac address-table int gi 1/0/19
          Mac Address Table

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
  20    38ed.1855.ed28    DYNAMIC     Gi1/0/19
  30    38ed.1855.ed28    DYNAMIC     Gi1/0/19
Total Mac Addresses for this criterion: 2

I connected an IP phone on VLAN 30 and a PC on VLAN 20. The switch is a Cisco 2960 48-port, IOS version 15.0(2a)EX5.

1 Answer 1


Your Cisco VoIP phone is also a switch which negotiates a trunk link with the switch to which it connects. It shows up on both VLANs because it is on both VLANs. This is normal behavior.

This is the reason you need to be careful when configuring port security on your switch. You would probably need to allow three connections, two for the phone, and one for the PC connected to the phone.

  • If am using port security as vlan voice then i need 3 connections ? eg: switchport port-security mac-address xxxx.xxxx.xxxx vlan voice
    – Tech
    Apr 17, 2016 at 4:17
  • Port security is MAC addresses per port, not VLAN, while MAC addresses are per VLAN (layer-2 domain). If you use port security, you will need to allow three MAC addresses: two for the phone (one on each VLAN) and one for the PC connected to the phone. You don't need to specify the MAC addresses, although you can, but that doesn't scale; just specify the number of MAC addresses allowed.
    – Ron Maupin
    Apr 17, 2016 at 13:37

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