Multicast Features | 609As the upper five bits of an IP Multicast address are dropped in the translation, 32 different multicastgroup IDs all map to the same Ethernet address. For example, 224.0.0.5 is a well known IP address forOSPF that maps to the multicast MAC address 01:00:5e:00:00:05. However, 225.0.0.5, 226.0.0.5, etc.,map to the same multicast MAC address. The Layer 2 FIB alone cannot differentiate multicast controltraffic 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 onesbelow.• The FTOS implementation of MTRACE is in accordance with IETF draft draft-fenner-traceroute-ipm.• Multicast is not supported on secondary IP addresses.• Egress L3 ACL is not applied to multicast data traffic if multicast routing is enabled.First Packet Forwarding for Lossless MulticastBeginning with FTOS version 7.8.1.0 for the E-Series TeraScale, version 8.2.1.0 for E-Series ExaScale,and version 8.3.1.0 on all other FTOS platforms, all initial multicast packets are forwarded to receivers toachieve lossless multicast.In previous versions, when the Dell Force10 system is an RP, all initial packets are dropped until PIMcreates an (S,G) entry. When the system is an RP and a Source DR, these initial packet drops represent aloss of native data, and when the system is an RP only, the initial packets drops represent a loss of registerpackets.Both scenarios might be unacceptable depending on the multicast application. Beginning with the FTOSversions above, when the Dell Force10 system is the RP, and has receivers for a group G, it forwards allinitial multicast packets for the group based on the (*,G) entry rather than discarding them until the (S,G)entry is created, making Dell Force10 systems suitable for applications sensitive to multicast packet loss.Protocol Ethernet AddressOSPF 01:00:5e:00:00:05 01:00:5e:00:00:06RIP 01:00:5e:00:00:09NTP 01:00:5e:00:01:01VRRP 01:00:5e:00:00:12PIM-SM 01:00:5e:00:00:0dNote: When a source begins sending traffic, the Source DR forwards the initial packets to the RP asencapsulated registered packets. These packets are forwarded via the soft path at a maximum rate of 70packets/second. Incoming packets beyond this rate are dropped.
