Reference Guide

Figure 93. Multicast with ECMP
Implementation Information
Because protocol control traffic in FTOS is redirected using the MAC address, and multicast control traffic and multicast
data traffic might map to the same MAC address, FTOS 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.
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 .
556