On the S-component side, frames received on a virtual link are tagged with the S-VID
indicated, and each frame is emitted untagged. The net effect of these VID transformations
is that
?– Customer 1s C-VLANs 1, 2, and 40 are encapsulated (double-tagged) in S-VLAN 10.
?– Customer 1s C-VLAN 18 is translated (single-tagged) into S-VLAN 11.
?– A frame tagged with any other C-VID received from customer 1 is discarded.
?– Customer 2s odd-numbered C-VLANs are encapsulated in S-VLAN 20.
?– Customer 2s even-numbered C-VLANs are encapsulated in S-VLAN 21.
It appears that placing a full VLAN bridge on every physical port of a provider
edge bridge can be a very complex and expensive task. Fortunately, two key limitations
on the way C-components can be used reduce its complexity to a simple VID
translation table:
?– A C-component can have only one physical link on the customer side, no matter
how many virtual links it has.
?– No C-VID can be enabled on more than one of the virtual ports to the S-component.
Therefore, a C-component never has to bridge from one virtual link to another and
never has to replicate multicast frames; every frame passes directly across the
C-component between a single virtual link and the single physical link.
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