SMC Networks SMC TigerAccess SMC7824M/FSW - Manual (Page 276)

VLAN C
ONFIGURATION
12-18
IDs. QinQ tunneling expands VLAN space by 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 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 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 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.