Multicast FeaturesThe 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 PoliciesEnabling IP MulticastBefore enabling any multicast protocols, you must enable IP multicast routing.• Enable multicast routing.CONFIGURATION modeip multicast-routingImplementation InformationBecause protocol control traffic is redirected using the MAC address, and multicast control traffic andmulticast data traffic might map to the same MAC address, the system might forward data traffic with certainMAC 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 allmap 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 cannotdifferentiate multicast control traffic multicast data traffic with the same address, so if you use IP address225.0.0.5 for data traffic, both the multicast data and OSPF control traffic match the same entry and areforwarded to the CPU. Therefore, do not use well-known protocol multicast addresses for data transmission,such as the following.33Multicast Features 719
