cisco phones & VLAN

Hey guys,

I'm having a hard time conceptualizing this.

Cisco IP phones have a small internal switch that places an 802.1q tag on voice traffic and marks the Class of Service
(CoS) bits in the tag. Data traffic is sent untagged over the native VLAN. The switch port does not actually become a
trunk and still can be configured as an access port. It is considered a multi-VLAN access port.

Ok so here's my issue:

1) If the data is sent over the native VLAN, what if the native VLAN is not used? What if the host PC/data is on VLAN 10?

2) What the heck is a multi-VLAN access port? I thought access ports could only carry ONE vlan?

3) If the switchport is not actually becoming a trunk, then how is the 802.1Q going to work?

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Comments

azaghul

1) If the data is sent over the native VLAN, what if the native VLAN is not used? What if the host PC/data is on VLAN 10?

Not an expert here, but my understanding is that the access vlan carries the native/untagged traffic. So in this case vlan 10 would provide this function.

switchport mode access
switchport access vlan xx

2) What the heck is a multi-VLAN access port? I thought access ports could only carry ONE vlan?
3) If the switchport is not actually becoming a trunk, then how is the 802.1Q going to work?

A multi-vlan access port is one configured for both data and voice traffic on separate vlans. It sort of "fakes" the port into believing its a "mini-trunk" with the access vlan carrying the untagged traffic, and the voice vlan carrying the tagged dot1q traffic.

switchport mode access
switchport access vlan xx
switchport voice vlan yy

chmorin

notgoing2fail wrote: »

Hey guys,

I'm having a hard time conceptualizing this.

Cisco IP phones have a small internal switch that places an 802.1q tag on voice traffic and marks the Class of Service
(CoS) bits in the tag. Data traffic is sent untagged over the native VLAN. The switch port does not actually become a
trunk and still can be configured as an access port. It is considered a multi-VLAN access port.

Ok so here's my issue:

1) If the data is sent over the native VLAN, what if the native VLAN is not used? What if the host PC/data is on VLAN 10?

2) What the heck is a multi-VLAN access port? I thought access ports could only carry ONE vlan?

3) If the switchport is not actually becoming a trunk, then how is the 802.1Q going to work?

I agree with the individual above me.

I think that it uses the native vlan between the computer and the phone and switch, however the packets from the computer are not tagged and the packets from the phone are. This way when it hits the switchport the switch is able to tell the difference between the two and send them on their specified vlan path. Once the packets hit the switchport the native thing is gone, and they can be sent on their way. Before this, they use the native vlan.

I THINK that is how it works. I am open to correction.

Fatbunny

I think the "native" reference is slightly confusing here, I do believe its trying to say the vlan native to the port, not native to the actual switch. That is, untagged traffic will be assigned to the access vlan assigned to that port.

AFAIK the switchport will always read the tag in the tagged traffic. It will discard/ignore tags that are not applicable to the port. The "switchport voice vlan xx" allows xx tagged traffic to be allowed and assigned to the xx vlan. Not a trunk but just one additional (voice) vlan allowed. It used to be listed as an auxiliary vlan I believe but now its referenced a voice vlan.