A trunk on Cisco switch has to tag a frame with vlan id before transmitting it. However, frames originating in native vlan are not tagged. Receiving trunk port understands that the untagged frames should go to native vlan on its switch.
Native vlans are sometimes called as default vlans. On Cisco switches there is no vlan 0. Vlans range is from 1-4094. Default vlan on Cisco switches are vlan 1.
Cisco's Catalyst 3750 Metro Switch
command reference says that a Cisco's IP phone has a value of 0 for default native vlan. I think, we can configure ANY value for native vlan. By default Cisco's IP Phone carries voice traffice with 802.1p priority tag value of 5.
For IP Edge Routers such as Redback/Ericsson's
SmartEdge 1200, a vlan 0 cannot be configured. Vlan id start from 1.
The
documentation for Juniper's E-Series Edge Routers[such as
ERX 1440] says that the default vlan for untagged frame is vlan 0.
That's another source of vlan 0 packets.
Labels: Cisco 3750, Cisco switches, ERX 1440, Juniper E-Series, SmartEdge, Vlan 0
