Microsens MS453490M Management Guide - Manual (Page 170)

C HAPTER 6 | VLAN Configuration
IEEE 802.1Q Tunneling
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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 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 lookups, 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.