3. After packet classification through the switching proce ss, the pa cket is wr itten to
memory with one tag (an outer tag) or with two tags (both an outer tag and inner
tag).
4. The switch sends the packet to the proper egress port.
5. 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 packets will have two tags.
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 lo okups. I f both lo okups are
successful, the ingress process writes the packet to memory. Then the egress
process transmits the packet. Packets entering a QinQ uplink port are processe d 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 co nfigured o n a per port bas is, 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 upli nk port is not the
member of the outer VLAN of the incoming packets, the packet will be dropp ed
when ingress filtering is enabled. If ingress filtering is not enabled, the pac ke t 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 lookups, the pac ket is do uble tagged.
The switch uses the TPID of 0x8100 to indic ate tha t an incoming packet is
double-tagged. If the outer tag of an incoming double-tagged packet is eq ual to
the port TPID and the inner tag is 0x8100, it is treate d as a doubl e-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-ta gged pac ket.
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 memor y for proc essing 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.
11-14
VLAN Configuration
11