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Phone showing in both data and voice vlans

I think this one should be simple for someone, but I am stumped...

In my customer's network, the IP phones show up in the mac address table under both the data and the voice vlans. Any suggestions? It doesn't appear to be causing any problems.

Router# sho run int fa0/33

interface FastEthernet0/33

description *** end-user data/voice port ***

switchport access vlan 100

switchport mode access

switchport voice vlan 200

no logging event link-status

srr-queue bandwidth share 1 35 40 25

priority-queue out

mls qos vlan-based

no snmp trap link-status

spanning-tree portfast


Router# sho mac-address-table | incl Fa0/33

100 0024.810f.5fdf DYNAMIC Fa0/33

100 0024.c4bf.2a09 DYNAMIC Fa0/33

200 0024.c4bf.2a09 DYNAMIC Fa0/33

As you can see, the phone shows up in the mac-address-table for each vlan. The other vlan 100 device is the pc plugged into the phone.

Any suggestions?




Re: Phone showing in both data and voice vlans

Hi John,

I checked some of my switches and this is normal behavior.

It is likely CDP which is not on the voice VLAN and keeps activity on the native vlan in the mac address table. There may be other traffic, but I would say this is the most likely.


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