SMC Networks SMC TigerAccess SMC7824M/FSW - Manual (Page 278)

VLAN C
ONFIGURATION
12-20
3. After packet classification through the switching process, the packet is
written 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 an 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.