VLAN C
ONFIGURATION
13-26
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 (and this feature is enabled on the switch).
2. After successful source and destination lookup, the ingress pr ocess
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.
3. After packet classification through the switching p rocess, 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)