H3C Technologies H3C S10500 Series Switches - Manual (Page 173)

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This refers to learning source MAC addresses from Layer 2 packets originated by CEs. This occurs on the
corresponding VSI interfaces.
Figure 39 shows the procedure of MAC address learning and flooding on PEs.
Figure 39 MAC learning and flooding on PEs
2. MAC address reclaim
Dynamic address learning must support refreshing and relearning. The VPLS draft defines a dynamic
address learning method that uses the address reclaim message, which carries MAC TLV. Upon receiving
such a message, a device removes MAC addresses or relearns them according to the specified
parameters in the TLV. If NULL is specified, the device removes all MAC addresses of the VSI, except for
those learned from the PW that received the address reclaim message.
The address reclaim message is very useful when the network topology changes and you must remove
the learned MAC addresses quickly. There are two types of address reclaim messages: those with MAC
address lists and those without MAC address lists.
After a backup link becomes active and a message with the instruction of relearning MAC entries arrives,
a PE updates the corresponding MAC entries in the FIB table of the VPLS instance and sends the message
to other PEs that are directly connected through LDP sessions. If the message contains a null MAC
address TLV list, these PEs remove all MAC addresses from the specified VSI, except for those learned
from the PW that sent the message.
3. MAC address aging
Remote MAC addresses learned by a PE that are related to VC labels but no longer in use must be aged
out by an aging mechanism. The aging mechanism used here is the aging timer corresponding to the
MAC address. When receiving a packet whose source MAC address has an aging timer started, the PE
resets the aging timer.
VPLS loop avoidance
To avoid loops in a VPLS network, full mesh and split horizon forwarding are used instead of STP at the
private network side.