Multicast Service on a Termination Sub-interface
With wide applications of multicast services on the Internet, when double-tagged multicast packets are sent from the user side to a sub-interface for QinQ VLAN tag termination sub-interface, the sub-interface needs to support the Internet Group Management Protocol (IGMP). In this manner, the UPE can maintain outbound interface information of the multicast packets based on the created multicast forwarding table, and the hosts can communicate with the multicast source.
On the network shown in Figure 1, when the DSLAM forwards double-tagged multicast packets to the UPE, the UPE processes the packets as follows based on double-tag contents:
When the double-tagged packets carrying an outer S-VLAN tag and an inner C-VLAN tag are transmitted to the UPE to access the Virtual Switching Instances (VSIs), the UPE terminates the double tags and binds the packets to the multicast VSIs through Pseudo Wires (PWs). Then, the PE-AGG terminates PWs and adds multicast VLAN tags to the packets. Finally, the packets are transmitted to the multicast source. For example, IPTV packets with S-VLAN 3 and C-VLANs ranging from 1 to 1000 are terminated on the UPE and then access a PW. The PE-AGG terminates the PW and adds multicast VLAN 8 to the packets. IGMP snooping sets up forwarding entries based on the interface number, S-VLAN tag, and C-VLAN tag and supports multicast packets with different C-VLAN tags. Each PW then forwards the multicast packets based on their S-VLAN IDs and C-VLAN IDs.
When the double-tagged packets carrying an outer C-VLAN tag and an inner S-VLAN tag are transmitted to the UPE, the UPE enabled with VLAN swapping swaps the outer C-VLAN tag and inner S-VLAN tag. If multicast packets access Layer 2 VLANs, the packets are processed in mode 1; if multicast packets access VSIs, the packets are processed in mode 2.
Generally, VLANs are divided into the following types:
C-VLAN: customer VLAN
S-VLAN: service VLAN
Single-tagged packets: The sub-interface for Dot1q VLAN tag termination needs to have IGMP and IGMP snooping configured.
Double-tagged packets: The sub-interface for QinQ VLAN tag termination needs to have IGMP and IGMP snooping configured.