Hi every body!
According to my book vlans1 through 1005 are automatically created and set aside for special uses.
When we use the command switchport voice vlan dot1p, It will cause voice traffic to use vlan 0
But the question is vlan 0 is not created by default on switches but yet the command assume this vlan 0 is created by default.
Any suggestion ?
thanks a lot!
Just to add a small note to Guiseppe's post
The IP phones understand 802.lq, we all agree on that.
The IP phone's access port is thus capable of sending and receiving tagged or untagged frames (from PC). It need not be in access mode or trunk to be capable of simply relaying frames back and forth (switch to pc or pc to switch).
My understanding is the same as Giuseppe's, ie. you must have a vlan ID but because you want to just use the tag for 802.1p markings you use a "dummy" vlan as such.
I have to admit though that the documentation is a little confusing. From the 3750 configuration guide about the dot1p option -
dot1p-Configure the phone to use IEEE 802.1p priority tagging for voice traffic and to use the default native VLAN (VLAN 0) to carry all traffic. By default, the Cisco IP Phone forwards the voice traffic with an IEEE 802.1p priority of 5.
Not sure what it means by native vlan 0 as i always though the default native vlan is 1 unless it is different for an IP Phone ?
the automatically created Vlans should be only the following:
1 : ethernet default vlans
1002-1005 : legacy Vlans for token ring switching and FDDI switching cannot be used.
Sometimes this can create some issue on trunks to modules like WISM (not VOIP related)
a vlan-id of 0 is just a placeholder to send an 802.1Q 4 bytes header and the meaningful three bits of CoS = 802.1p that is inside it.
That's all vlan 0 does not exist and you cannot create it
In my understanding an 802.1p marking cannot be sent alone but only as the CoS field of an 802.1Q vlan tag so the vlan-id 0 can just mean this field is unused
Happy New Year
Hope to help