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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
(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. 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.
11-13
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.
Custome
r
A
(VLANs 1-10)
VLAN 10
Tunnel Access Port
Tunnel Access Port
VLAN 20
Customer B
(VLANs 1-50)
Custome
r
A
(VLANs 1-10)
VLAN 10
Tunnel Access Port
Tunnel Access Port
VLAN 20
Customer B
(VLANs 1-50)
QinQ
T
unneling
Service Provider
(edge switch B)
Tunnel Uplink Ports
Double-Tagged Packets
Outer Tag - Service Provider VID
Inner Tag - Customer VID
Service Provide
r
(edge switch A)
Configuring IEEE 802.1Q Tunneling
11