Multicast Address

Multicast addresses are specially designated IP and MAC addresses that are reserved for sending packets to multiple hosts
- They are not forwarded by routers between subnets

802.3 Frames are Layer 2, not Layer 3, so Multicast IP addresses must be mapped to MAC addresses
The reserved range is 01-00-5E-00-00-00 through 01-00-5E-7F-FF-FF
- The first 24 bits are always 01-00-5E, and the 25th bit is always 0, so the 7th octet can only ever equal 0-7
  - Prefix binary: 00000001.00000000.01011110.0
- The remaining 23 bits are derived from the last 23 bits of the IPv4 multicast address
Example: 224.1.2.3
- In binary, with the last 23 bits highlighted
  - 11100000.00000001.00000010.00000011
- Combine the MAC prefix and the IP suffix
  - 00000001.00000000.01011110.00000001.00000010.00000011
  - 01-00-5E-01-02-03
Example: 224.134.36.64
- In binary, with the last 23 bits highlighted
  - 11100000.10000110.00100100.01000000
- Combine the MAC prefix and the IP suffix
  - 0000-0001-0000-0000-0101-1110-0000-0110-0010-0100-0100-0000
  - 01-00-5E-06-24-40

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