Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 719

33 Multicast Features The Dell Networking OS supports the following multicast protocols: • PIM Sparse-Mode (PIM-SM) • Internet Group Management Protocol (IGMP) • Multicast Source Discovery Protocol (MSDP) Topics: • Enabling IP Multicast • Implementation Information • First Packet Forwarding for Lossless Multicast • Multicast Policies Enabling IP Multicast Before enabling any multicast protocols, you must enable IP multicast routing. • Enable multicast routing. CONFIGURATION mode ip multicast-routing Implementation Information Because protocol control traffic is redirected using the MAC address, and multicast control traffic and multicast data traffic might map to the same MAC address, the system might forward data traffic with certain MAC addresses to the CPU in addition to control traffic. As the upper5 bits of an IP Multicast address are dropped in the translation, 32 different multicast group IDs all map to the same Ethernet address. For example, 224.0.0.5 is a known IP address for open shortest path first (OSPF) that maps to the multicast MAC address 01:00:5e:00:00:05. However, 225.0.0.5, 226.0.0.5, and so on, map to the same multicast MAC address. The Layer 2 forwarding information base (FIB) alone cannot differentiate multicast control traffic multicast data traffic with the same address, so if you use IP address 225.0.0.5 for data traffic, both the multicast data and OSPF control traffic match the same entry and are forwarded to the CPU. Therefore, do not use well-known protocol multicast addresses for data transmission, such as the following. Multicast Features 719