164
• PW signaling—The PW signaling protocol is the fundament of VPLS. It is used for creating and
maintaining PWs and automatically discovering VSI peer PEs. Two PW signaling protocols are
available: LDP and BGP.
Figure 38 VPLS network diagram
MAC address learning and flooding
VPLS provides reachability by MAC address learning. Each PE maintains a MAC address table.
• Source MAC address learning
MAC address learning includes the following parts:
{ Remote MAC address learning associated with PWs
A PW consists of two unidirectional VC LSPs. A PW is up only when both of the VC LSPs are
up. When the inbound VC LSP learns a new MAC address, the PW must map the MAC
address to the outbound VC LSP.
{ Local MAC address learning of interfaces directly connected to users
This refers to learning source MAC addresses from Layer 2 packets originated by CEs. This
occurs on the corresponding VSI interfaces.
Figure 39 sho
ws the procedure of MAC address learning and flooding on PEs.
CE 3
VPN 1
Site 2
VPN 2
CE 4
PE 1
PE 2
P
AC
PWSignaling
PW
Site 3
Site 1
VPN 1
VPN 2
CE 1
CE 2
MPLS backbone
Forwarder
Tunnel
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