3. I-component C learns the {source MAC address, S-VLAN} pair in the received
frame, along with the port on which it was received, in the standard fashion of
VLAN bridges.
Figure 13.10 802.1ah backbone bridge architecture
S-cloud 2
S-cloud 1A
S-cloud 3
S-cloud 1B
B-tag +
I-tag
I-tag only S-tagged
frames
Backbone edge
bridge R
Backbone edge
bridge P
Backbone edge
bridge Q
B-component X
(Backbone core
bridge, or
provider bridge)
B-component Y
(Backbone core
bridge, or
provider bridge)
B-component P
B-component Q
B-component R
C-S
C-T
I-
component
A
I-
component
B
I-
component
C
I-
component
D
I-
component
E
I-
component
F
398 Chapter 13
4. Supposing I-component C does not know the destination MAC address of the
frame, it floods the frame to the other I-components by encapsulating it in a MACin-
MAC frame in the format shown in Figure 13.9d. It removes the S-tag, translating
it to an I-tag using a configured translation table. The outer source address of
the resultant frame is the MAC address of I-component C. The outer destination
address is either
?– The broadcast MAC address.
?– A multicast MAC address recognized by at least all of the I-components that
carry this particular EVC.
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