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| 7.2 |  | Examining Multicast in a Multilayer Switched Network |
| 7.2.4 |  | Layer 2 multicast addressing |

When assigning a Layer 3 multicast address, a Layer 2 address is automatically generated from the IP address. To calculate the Layer 2 address, the host copies the last 23 bits of the IP address into the last 24 bits of the MAC address. The high-order bit is set to 0.

The first 3 bytes (24 bits) of the multicast MAC address are 0x01-00-5E. This is a reserved value that indicates a multicast application.

Consider an example: The IP address 224.1.10.10, assigned by an administrator, has a low 23-bit value of 1.10.10. In hexadecimal format, this is 0x01-0A-0A. The MAC address takes the last 23 of the 24 bits and places them into the MAC field. The complete MAC address in this case is 01-00-5E-01-0A-0A.

Figure illustrates another example. In this case, the IP address 224.10.8.5 translates to a MAC address of 01.00.5e.0a.08.05.

| Interactive Media Activity Drag and Drop: Multicast Addressing After completing this activity, the students will be able to understand multicast addressing.