MAC of IP phone in two vlans

Unanswered Question
Sep 6th, 2010
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do you have any idea about why I see the MAC address of an IP phone in both access vlan and voice vlan? vlan 11 is my access vlan, and vlan 2222 is my voice vlan.

TNSWACCS01A1#sh mac address-table interface fa1/0/12
          Mac Address Table

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
  11    0024.8154.2aca    DYNAMIC     Fa1/0/12
  11    9caf.caff.5a8c    DYNAMIC     Fa1/0/12
2222    9caf.caff.5a8c    DYNAMIC     Fa1/0/12
Total Mac Addresses for this criterion: 3

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ADAM CRISP Mon, 09/06/2010 - 03:41
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The switch port is a trunking port, and if it's a Cisco phone, it learns which vlan to tag voice frames with from CDP.

Presuumably the CDP frames are present on the native vlan, which in your case is vlan 11, so the phone is present on this vlan.

Other brand phones - such as Avaya use a different mechanism for discovering the voice vlan, eg via dhcp in the native vlan and using a dhcp option to learn the voice vlan....


Wassim Aouadi Mon, 09/06/2010 - 04:56
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Here, vlan 11 is my access vlan not the native one. Let me show you the configuration:

interface FastEthernet1/0/12
switchport access vlan 11
switchport mode access
switchport voice vlan 2222
priority-queue out
mls qos trust cos
spanning-tree portfast
spanning-tree bpduguard enable

ADAM CRISP Mon, 09/06/2010 - 05:23
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yes, so CDP frames will leave your switch untagged in vlan 11

and untagged frames from your phone will be in vlan 11.



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