Using the IEEE 802.1Q tunneling feature, service providers can use a single VLAN to support
customers who have multiple VLANs. Customer VLAN IDs are preserved, and traffic from
different customers is segregated within the service-provider network, even when they appear
to be in the same VLAN. Using IEEE 802.1Q tunneling expands VLAN space by using a
VLAN-in-VLAN hierarchy and retagging the tagged packets. A port configured to support IEEE
802.1Q tunneling is called a tunnel port. When you configure tunneling, you assign a tunnel
port to a VLAN ID that is dedicated to tunneling. Each customer requires a separate service-
provider VLAN ID, but that VLAN ID supports all of the customer’s VLANs.
Customer traffic tagged in the normal way with appropriate VLAN IDs comes from an IEEE
802.1Q trunk port on the customer device and into a tunnel port on the service-provider edge
switch. The link between the customer device and the edge switch is asymmetric because
one end is configured as an IEEE 802.1Q trunk port, and the other end is configured as a
tunnel port. You assign the tunnel port interface to an access VLAN ID that is unique to each
customer.
Example : PortX configuration
Trunk-VLAN = 10, 11, 12
Access-VLAN = 20
Mode = Access
PortX is an Access Port
PortX’s VID is ignored
PortX’s PVID is 20
PortX sends Untagged packets (PortX takes away VLAN tag if the
PVID is 20)
PortX receives Untagged packets only
Trunk-VLAN = 10,11,12
Access-VLAN = 20
Mode = Trunk
PortX is a Trunk Port
PortX’s VID is 10,11 and 12
PortX’s PVID is ignored
PortX sends and receives Tagged packets VID 10,11 and 12
Trunk-VLAN = 10,11,12
Access-VLAN = 20
Mode = Trunk-native
PortX is a Trunk-native Port
PortX’s VID is 10,11 and 12
PortX’s PVID is 20
PortX sends and receives Tagged packets VID 10,11 and 12
PortX receives Untagged packets and add PVID 20
Trunk-VLAN = 10,11,12
Access-VLAN = 20
Mode = Dot1q-tunnel
PortX is a Dot1q-tunnel Port
PortX’s VID is ignored.
PortX’s PVID is 20
PortX sends Untagged or Tagged packets VID 20
PortX receives Untagged and Tagged packets and add PVID
20(outer tag)
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