CANOGA PERKINS 9175 Configuration Guide - Manual (Page 67)

CanogaOS Configuration Guide
10-2
Figure 10-1: 802.1q Topology
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 service-provider network on an 802.1Q
trunk port.