SMC Networks SMC8126L2 Management Manual page 178

3
Configuring the Switch
using a VLAN-in-VLAN hierarchy, preserving the customer's original tagged packets,
and adding SPVLAN tags to each frame (also called double tagging).
A port configured to support QinQ tunneling must be set to tunnel port mode. The
Service Provider VLAN (SPVLAN) ID for the specific customer must be assigned to
the QinQ tunnel access port on the edge switch where the customer traffic enters
the service provider's network. Each customer requires a separate SPVLAN, but this
VLAN supports all of the customer's internal VLANs. The QinQ tunnel uplink port
that passes traffic from the edge switch into the service provider's metro network
must also be added to this SPVLAN. The uplink port can be added to multiple
SPVLANs to carry inbound traffic for different customers onto the service provider's
network.
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.
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. New SPVLAN tags are added to all incoming packets, no matter how many tags
they already have. The ingress process constructs and inserts the outer tag
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