Dell Force10 S4820T S4820T Configuration Guide - Page 677

As the upper five 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 well known IP address for OSPF 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 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 ones below. Protocol Ethernet Address OSPF 01:00:5e:00:00:05 01:00:5e:00:00:06 RIP 01:00:5e:00:00:09 NTP 01:00:5e:00:01:01 VRRP 01:00:5e:00:00:12 PIM-SM 01:00:5e:00:00:0d • 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 Multicast Beginning 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 to achieve lossless multicast. In previous versions, when the Dell Force10 system is an RP, all initial packets are dropped until PIM creates an (S,G) entry. When the system is an RP and a Source DR, these initial packet drops represent a loss of native data, and when the system is an RP only, the initial packets drops represent a loss of register packets. Both scenarios might be unacceptable depending on the multicast application. Beginning with the FTOS versions above, when the Dell Force10 system is the RP, and has receivers for a group G, it forwards all initial 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. Note: When a source begins sending traffic, the Source DR forwards the initial packets to the RP as encapsulated registered packets. These packets are forwarded via the soft path at a maximum rate of 70 packets/second. Incoming packets beyond this rate are dropped. Multicast Features | 677