What is a broadcast MAC address?

A broadcast MAC address is a special MAC address that means the frame is sent to all devices within a single local network.

Put simply: broadcast = "one → all".

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#What a broadcast MAC address looks like

The broadcast MAC address is always the same one:

FF:FF:FF:FF:FF:FF

• all 48 bits = 1
• there is no other version of a broadcast MAC

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#How broadcast works at the data link layer

1. The device sends a frame with the destination MAC address FF:FF:FF:FF:FF:FF
2. The switch:

• sends the frame out on all ports (except the incoming one)

3. Every device on the network:

• receives the frame
• checks it
• decides whether it needs it or not

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#Why broadcast is needed

Broadcast is used when:

• the sender does not know the recipient's MAC address
• the message needs to be delivered to everyone on the network

Typical examples:

• an ARP request
• service announcements on the network
• some device discovery protocols

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#Limitations of broadcast

Important for an interview:

• broadcast does not pass through routers
• it is limited to a single broadcast domain
• a large amount of broadcast traffic:
  • loads the network
  • reduces performance

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#Comparing MAC address types

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#Short version for an interview

A broadcast MAC address is the MAC address FF:FF:FF:FF:FF:FF, used to send frames to all devices within a single local network.