Chapter 5
| VLAN Configuration
IEEE 802.1Q Tunneling
– 178 –
Figure 81: QinQ Operational Concept
Layer 2 Flow for Packets Coming into a Tunnel Access Port
A QinQ tunnel port may receive either tagged or untagged packets. No matter how
many tags the incoming packet has, it is treated as tagged packet.
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. An SPVLAN tag is added to all outbound packets on the SPVLAN interface, no
matter how many tags they already have. The switch 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), unless otherwise
defined as described under “Creating CVLAN to SPVLAN Mapping Entries” on
page 182. The priority of the inner tag is copied to the outer tag if it is a tagged
or priority tagged packet.
2. After successful source and destination lookup, the ingress process 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 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.
Tunnel Uplink Ports
Double-Tagged Packets
Outer Tag - Service Provider VID
Inner Tag - Customer VID
QinQ Tunneling
Service Provider
(edge switch A)
Customer A
(VLANs 1-10)
Customer B
(VLANs 1-50)
Customer A
(VLANs 1-10)
Customer B
(VLANs 1-50)
Service Provider
(edge switch B)
VLAN 10
Tunnel PortAccess
Tunnel Port
VLAN 20
Access
VLAN 10
Tunnel PortAccess
Tunnel Port
VLAN 20
Access
To Next Page
Loading...
Need help?
General