Dell S4048T, Configuration Manual

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Multicast Features
NOTE: Multicast routing is supported on secondary IP addresses; it is not supported on IPv6.
NOTE: Multicast routing is supported across default and non-default virtual routing and forwarding (VRFs).
The Dell Networking operating system (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
• Multicast Policies
Enabling IP Multicast
Before enabling any multicast protocols, you must enable IP multicast routing. To enable multicast routing,
use the following command.
• Enable multicast routing.
CONFIGURATION mode
ip multicast-routing
Implementation Information
Because protocol control traffic in the Dell Networking OS is redirected using the MAC address, and multicast
control traffic and multicast data traffic might map to the same MAC address, the 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
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 and 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:
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