H3C Technologies H3C S10500 Series Switches - Manual (Page 176)

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the same time, forwards it through U-PW to NPE 1, which replicates the packet and sends a copy to each
peer CE.
2. H-VPLS with QinQ access
Figure 41 H-VPLS with QinQ access
As shown in Figure 41 , MTU is a standard bridging device and QinQ is enabled on its interfaces
connected with CEs.
Data forwarding in H-VPLS with QinQ access is as follows:
• Upon receiving a packet from a CE, MTU labels the packet with a VLAN tag as the multiplex
distinguishing flag, and transparently sends the packet to PE 1 through the QinQ tunnel.
• When receiving the packet, PE 1 determines which VSI the packet belongs to by the VLAN tag and,
based on the destination MAC address of the packet, tags the packet with the multiplex
distinguishing flag (MPLS label) for the PW. Then, it forwards the packet.
• Upon receiving the packet from the PW, PE 1 determines to which VSI the packet belongs by the
multiplex distinguishing flag (MPLS label) and, based on the destination MAC address of the packet,
labels the packet with the VLAN tag. Then, it forwards the packet through the QinQ tunnel to MTU,
which in turn forwards the packet to the CE.
For packets to be exchanged between CE 1 and CE 2, MTU can forward them directly without PE 1
because it holds the bridging function by itself. For the first data packet with an unknown destination
MAC address or a broadcast packet, MTU broadcasts the packet to CE 2 through the bridging function
and, at the same time, forwards it through the QinQ tunnel to PE 1, which replicates the packet and sends
a copy to each peer CE.
3. PW switchover
The network design with a single PW between a UPE and an NPE has a distinct drawback: once the PW
experiences a failure, all VPNs connected to the aggregate device will lose connectivity. The H-VPLS with
LSP access provides redundant links for PW backup. Normally, only the primary PW link is used. When
the main link fails, the backup link will take over the VPN services.