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ONFIGURING
IEEE 802.1Q T
UNNELING
12-19
Layer 2 Flow for Packets Coming into a Tunnel 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.
Double Tagged Packets
Outer Tag - Service Provider VID
Inner Tag - Customer VID
QinQ Tunneling
Service Provider
(edge routerA)
CustomerA
(VLANs 1-10)
Customer B
(VLANs 1-50)
CustomerA
(VLANs 1-10)
Customer B
(VLANs 1-50)
Service Provider
(edge router B)
VLAN 10
Tunnel Port
Tunnel Port
VLAN 20
VLAN 10
Tunnel Port
Tunnel Port
VLAN 20