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 tagg ed pack et.
The ingress process does source and destination lookups. If both look ups are
successful, the ingress process writes the packet to memory. Then the egress
process transmits the packet. Packets entering a QinQ tunnel port are process ed in
the following manner:
1. New SPVLAN tags are added to all incoming pa ckets, n o ma tter ho w man y ta gs
they already have. The ingress process constructs and inser ts th e outer ta g
(SPVLAN) into the packet based on the default VLAN ID and Tag Protocol
Identifier (TPID, that is, the ether-type of the tag). Th is outer tag i s used for
learning and switching packets. The priority of the inn er tag is co pied t o the oute r
tag if it is a tagged or priori ty tagge d packe t.
2. After successful source and destination lookup, the ingress pro cess sends the
packet to the switching process with two tags. If the inco ming 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.
11-13
When a double-tagged packet enters another trunk port in an inter mediate o r core
switch in the service provider’s network, the outer tag is strip ped for pa cket
processing. When the packet exits another trunk port on the same core switch, the
same SPVLAN tag is again added to the packet.
When a packet enters the trunk port on the serv ice provi der ’s egress switch, the
outer tag is again stripped for packet processing. However, the SPVLAN tag is n ot
added when it is sent out the tunnel access port on the edge switch i nto the
customer’s network. The packet is sent as a normal IEEE 802.1Q-tagged frame,
preserving the original VLAN numbers used in the customer’s network.
Custome
r
A
(VLANs 1-10)
VLAN 10
Tunnel Access Port
Tunnel Access Port
VLAN 20
Customer B
(VLANs 1-50)
Custome
r
A
(VLANs 1-10)
VLAN 10
Tunnel Access Port
Tunnel Access Port
VLAN 20
Customer B
(VLANs 1-50)
QinQ
T
unneling
Service Provider
(edge switch B)
Tunnel Uplink Ports
Double-Tagged Packets
Outer Tag - Service Provider VID
Inner Tag - Customer VID
ServiceProvide
r
(edge switch A)
Configuring IEEE 802.1Q Tunneling
11