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Networking Fundamentals · Intermediate

Multicast MAC Address

A MAC address with the least significant bit of the first byte set to 1, used to deliver frames to a group of interfaces.

Definition

IPv4 multicast maps to 01:00:5e followed by the low 23 bits of the group address, and IPv6 multicast maps to 33:33 followed by the low 32 bits. Switches flood multicast unless IGMP or MLD snooping limits it.

Example

IPv4 group 224.0.0.5 maps to MAC 01:00:5e:00:00:05.

Exam tip

Odd first byte (01, 33 is odd) = group address; even = unicast.

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