Reference Guide

624 | Multicast Features
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In Figure 33-1, the receiver joins three groups. The last-hop DR initially has two equal-cost routes to the
RP with no streams, so it non-deterministically selects Route 1 for the Group 1 IGMP Join message. Route
1 then has one stream associated with it, so the last-hop DR sends the Group 2 Join by Route 2. It then
non-deterministically selects Route 2 for the Group 3 Join since both routes already have one multicast
stream.
Figure 33-1. Multicast with ECMP
Implementation Information
Multicast is supported on secondary IP addresses on the S5000 switch.
• Because protocol control traffic in Dell Networking OS is redirected using the MAC address, and
multicast control traffic and multicast data traffic might map to the same MAC address, Dell
Networking OS might forward data traffic with certain MAC addresses to the CPU in addition to
control traffic.
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.
TenGig A
IGMP Group Table
Group Address Interface
Group 1 TenGigabitEthernet A
Group 2 TenGigabitEthernet A
Group 3 TenGigabitEthernet A
TenGig X
TenGig Y
TenGig B
Source Receiver
RP
IGMP Group Table
Group Address Interface
Group 1 TenGigabitEthernet Y
Group 2 TenGigabitEthernet X
Group 3 TenGigabitEthernet X
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TenGig Z
TenGig W
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