Configuring the Switch

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3
Layer 2 Flow for Packets Coming into a Tunnel Uplink Port
An uplink port receives one of the following packets:
• Untagged
• One tag (CVLAN or SPVLAN)
• Double tag (CVLAN + SPVLAN)
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 uplink port are processed in
the following manner:
1. If incoming packets are untagged, the PVID VLAN native tag is added.
2. If the ether-type of an incoming packet (single or double tagged) is not equal to
the TPID of the uplink port, the VLAN tag is determined to be a Customer VLAN
(CVLAN) tag. The uplink port’s PVID VLAN native tag is added to the packet.
This outer tag is used for learning and switching packets within the service
provider’s network. The TPID must be configured on a per port basis, and the
verification cannot be disabled.
3. If the ether-type of an incoming packet (single or double tagged) is equal to the
TPID of the uplink port, no new VLAN tag is added. If the uplink port is not the
member of the outer VLAN of the incoming packets, the packet will be dropped
when ingress filtering is enabled. If ingress filtering is not enabled, the packet will
still be forwarded. If the VLAN is not listed in the VLAN table, the packet will be
dropped.
4. After successful source and destination lookup, the packet is double tagged. The
switch uses the TPID of 0x8100 to indicate that an incoming packet is
double-tagged. If the outer tag of an incoming double-tagged packet is equal to
the port TPID and the inner tag is 0x8100, it is treated as a double-tagged
packet. If a single-tagged packet has 0x8100 as its TPID, and port TPID is not
0x8100, a new VLAN tag is added and it is also treated as double-tagged packet.
5. If the destination address lookup fails, the packet is sent to all member ports of
the outer tag's VLAN.
6. After packet classification, the packet is written to memory for processing as a
single-tagged or double-tagged packet.
7. The switch sends the packet to the proper egress port.
8. If the egress port is an untagged member of the SPVLAN, the outer tag will be
stripped. If it is a tagged member, the outgoing packet will have two tags.
Configuration Limitations for QinQ
• The native VLAN of uplink ports should not be used as the SPVLAN. If the SPVLAN
is the uplink port's native VLAN, the uplink port must be an untagged member of
the SPVLAN. Then the outer SPVLAN tag will be stripped when the packets are
sent out. Another reason is that it causes non-customer packets to be forwarded
to the SPVLAN.