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Dell Configuration Guide for the S4048–ON System 9.14.2.5

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Implementation Information

Because protocol control traffic in the Dell EMC 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 EMC 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:
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 Dell EMC Networking OS implementation of MTRACE is in accordance with IETF draft draft-fenner-traceroute-ipm.
  • Multicast is not supported on secondary IP addresses.
  • If you enable multicast routing, egress Layer 3 ACL is not applied to multicast data traffic.
  • Multicast traffic can be forwarded to a maximum of 15 VLANs with the same outgoing interface.

Dell EMC Networking OS does not support multicast routing in the following VLT scenarios:

  • In a VLT enabled PIM router, multicast routing is not supported when there are multiple PIM spanned paths to reach source or RP. The workaround is to configure only one PIM spanned path to reach any PIM router in the aggregation or spine.
  • If a source is connected to a non-spanned interface of the VLT peer nodes and the RP is reachable on a spanned interface from both the VLT nodes, there is a possibility to receive duplicate traffic on the source. To avoid this, you should configure the source to be reachable on a spanned interface.

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