LevelOne GTL-2691 - Manual (Page 216)

C HAPTER 6 | VLAN Configuration
IEEE 802.1Q Tunneling
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When a double-tagged packet enters another trunk port in an intermediate
or core switch in the service provider’s network, the outer tag is stripped
for packet processing. When the packet exits another trunk port on the
same core switch, the same SPVLAN tag is again added to the packet.
When a packet enters the trunk port on the service provider’s egress
switch, the outer tag is again stripped for packet processing. However, the
SPVLAN tag is not added when it is sent out the tunnel access port on the
edge switch into the customer’s network. The packet is sent as a normal
IEEE 802.1Q-tagged frame, preserving the original VLAN numbers used in
the customer’s network.
Figure 78: QinQ Operational Concept
Layer 2 Flow for Packets Coming into a Tunnel Access Port
A QinQ tunnel port may receive either tagged or untagged packets. No
matter how many tags the incoming packet has, it is treated as tagged
packet.
The ingress process does source and destination lookups. If both lookups
are successful, the ingress process writes the packet to memory. Then the
egress process transmits the packet. Packets entering a QinQ tunnel port
are processed in the following manner:
1. An SPVLAN tag is added to all outbound packets on the SPVLAN
interface, no matter how many tags they already have. The switch
constructs and inserts the outer tag (SPVLAN) into the packet based on
the default VLAN ID and Tag Protocol Identifier (TPID, that is, the
ether-type of the tag), unless otherwise defined as described under
"Creating CVLAN to SPVLAN Mapping Entries" on page 220 . The priority
of the inner tag is copied to the outer tag if it is a tagged or priority
tagged packet.
2. After successful source and destination lookup, the ingress process
sends the packet to the switching process with two tags. If the
incoming packet is untagged, the outer tag is an SPVLAN tag, and the
inner tag is a dummy tag (8100 0000). If the incoming packet is
tagged, the outer tag is an SPVLAN tag, and the inner tag is a CVLAN
tag.
Tunnel Uplink Ports
Double-Tagged Packets
Outer Tag - Service Provider VID
Inner Tag - Customer VID
QinQ Tunneling
Service Provider
(edge switch A)
Customer A
(VLANs 1-10)
Customer B
(VLANs 1-50)
Customer A
(VLANs 1-10)
Customer B
(VLANs 1-50)
Service Provider
(edge switch B)
VLAN 10
Tunnel
Port Access
Tunnel Port
VLAN 20
Access
VLAN 10
Tunnel Port Access
Tunnel Port
VLAN 20
Access