VPLS packet walkthrough

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 (shown in the following figure) in an H-VPLS configuration. This section does not describe the processing on the PE routers, but only on 7210 SAS routers:

Figure: VPLS service architecture

1. 7210-A (shown in the following figure)

   1. Service packets arriving at 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

      

   2. 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.

   3. 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 Customer Location A).

   4. If the destination MAC address has already been learned by 7210, an existing entry in the FIB table identifies the far-end PE-Router and the service VC-label (inner label) to be used before sending the packet to PE-Router-A.

   5. The 7210 SAS chooses a transport LSP to send the customer packets to PE-Router-A. The customer packet is sent on this LSP when the IEEE 802.1Q tag is stripped and the service VC-label (inner label) and the transport label (outer label) are added to the packet. For an Unknown MAC Address (Figure: Network port egress packet format and flooding ).

   6. If the destination MAC address has not been learned, 7210 floods the packet to spoke-SDPs that are participating in the service.

      Figure: Network port egress packet format and flooding Customer Location A

      
      Figure: Network port egress packet format and flooding

      

2. Core Router Switching

   All the core routers ('P' routers in IETF nomenclature) between PE-Router-A and PE-Router-B and PE-Router-C are Label Switch Routers (LSRs) that switch the packet based on the transport (outer) label of the packet until the packet arrives at far-end PE-Router. All core routers are unaware that this traffic is associated with a VPLS service.

3. 7210-C (Figure: Access port ingress packet format and lookup)

   1. 7210-C associates the packet with the VPLS instance based on the VC label in the received packet after the stripping of the tunnel label.

   2. 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 spoke-SDP on which the packet was received.

   3. 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).

   4. If the destination MAC address has been learned by an existing entry in the FIB table identifies the local access port and the IEEE 802.1Q tag to be added before sending the packet to customer Location-C. The egress Q tag may be different from the ingress Q tag.

   5. If the destination MAC address has not been learned, 7210 floods the packet to all the access SAPs that are participating in the service.