This section provides an example of VPLS processing of a customer packet sent across the network from site-A, which is connected to PE-Router-A through a 7210 SAS to site-C, which is connected through 7210 SAS to PE-Router-C (Figure: VPLS service architecture) in an H-VPLS configuration. This section does not describe the processing on the PE routers but only on 7210 SAS routers:
7210-A (shown in the following figure)
Service packets arriving at 7210-A are associated with a VPLS service instance based on the combination of the physical port and the IEEE 802.1Q tag (VLAN-ID) in the packet.
Figure: Access port ingress packet format and lookup
7210-A learns the source MAC address in the packet and creates an entry in the FIB table that associates the MAC address to the service access point (SAP) on which it was received.
The destination MAC address in the packet is looked up in the FIB table for the VPLS instance. There are two possibilities: either the destination MAC address has already been learned (known MAC address) or the destination MAC address is not yet learned (unknown MAC address).
For a Known MAC Address (Figure: Network port egress packet format and flooding ):
If the destination MAC address has already been learned by 7210, an existing entry in the FIB table identifies destination uplink QinQ SAP to be used for sending the packet toward the PE-Router-A.
The customer packet is sent on this uplink SAP when the IEEE 802.1Q tag is stripped and the uplink SAP tag is added to the packet.
For an Unknown MAC Address (shown in the following figure):
If the destination MAC address has not been learned, 7210 will flood the packet to all the uplink SAP spoke-SDPs that are participating in the service.
Figure: Network port egress packet format and flooding
Core Router Switching
The PE router will encapsulate this packet in the appropriate MPLS header and transport it across the core network to the remote 7210-C.
7210-C (Figure: Access port ingress packet format and lookup)
7210-C associates the packet with the VPLS instance based on the VLAN tags in the received packet.
7210-C learns the source MAC address in the packet and creates an entry in the FIB table that associates the MAC address to the access-uplink port on which the packet was received.
The destination MAC address in the packet is looked up in the FIB table for the VPLS instance. Again, there are two possibilities: either the destination MAC address has already been learned (known MAC address) or the destination MAC address has not been learned on the access side of 7210-C (unknown MAC address).
If the destination MAC address has been learned by 7210-C, an existing entry in the FIB table identifies the local access port and the IEEE 802.1Q tag (if any) to be added before sending the packet to customer Location-C. The egress Q tag may be different from the ingress Q tag.
If the destination MAC address has not been learned, 7210 floods the packet to all the access SAPs that are participating in the service.