HP HSR6800 Configuration Manual page 207

Figure 54 MAC learning and flooding on PEs
•
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.
•
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.
•
Full mesh—PEs are logically fully meshed (so are PWs). Each PE must create for each VPLS
forwarding instance a tree to all the other PEs of the instance.
•
Split horizon forwarding—Each PE must support horizontal split to avoid loops. A PE cannot
forward packets through PWs of the same VSI, because all the PEs of a VSI are directly
connected. Packets from PWs on the public network side cannot be forwarded to other PWs.
They can only be forwarded to the private network side.
199