CANOGA PERKINS CanogaOS Configuration Guide - Manual (Page 80)

CanogaOS Configuration Guide
Proprietary & Confidential Canoga Perkins Metro Ethernet Switches Page 80 of 350
When the packet enters the trunk port of the service-provider egress switch, the outer tag is again
stripped as the packet is processed internally on the switch. However, the metro tag is not added
when it is sent out the tunnel port on the edge switch into the customer network, and the packet is
sent as a normal 802.1Q-tagged frame to preserve the original VLAN numbers in the customer
network.
In above figure, Customer A was assigned VLAN 30, and Customer B was assigned VLAN 40.
Packets
entering the edge-switch tunnel ports with 802.1Q tags are double-tagged when they enter the
service-provider network, with the outer tag containing VLAN ID 30 or 40, appropriately, and
the inner tag containing the original VLAN number, for example, VLAN 100. Even if both
Customers A and B have VLAN 100 in their networks, the traffic remains segregated within the
service-provider network because the outer tag is different. With 802.1Q tunneling, each
customer controls its own VLAN numbering space, which is independent of the VLAN
numbering space used by other customers and the VLAN numbering space used by the
service-provider network.
At the outbound tunnel port, the original VLAN numbers on the customer’s network are
recovered. It is possible to have multiple levels of tunneling and tagging, but the switch supports
only one level in this release.
If the traffic coming from a customer network is not tagged (native VLAN frames), these packets
are bridged or routed as if they were normal packets. All packets entering the service-provider
network through a tunnel port on an edge switch are treated as untagged packets, whether they
are untagged or already tagged with 802.1Q headers. The packets are encapsulated with the
metro tag VLAN ID (set to the access VLAN of the tunnel port) when they are sent through the