Web Management Guide-R03

Chapter 5 | 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). This outer tag is used
for learning and switching packets across the metropolitan network. 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 PortAccess
Tunnel Port
VLAN 20
Access
VLAN 10
Tunnel PortAccess
Tunnel Port
VLAN 20
Access