Unicast, Multicast, and Broadcast Addresses Definition & Examples

Unicast, Multicast, and Broadcast Address.

There will be many moments in your networking career where you will need to send data to either one device, or a cluster of devices, or every device. Understanding Unicast, Multicast, and Broadcasting is important as it details the measure in which we want to transmit data to a destination.

The three types of Ethernet addresses:

• Unicast Address – A unicast frame will be sent to a specific device, not to a group of devices on the LAN. One-to-one. An example of this is a person in a room talking to another person in the room.
• Multicast Address –  A frame sent to a multicast address is forwarded to a group of LAN devices. One-to-Many. A good way to picture this is a person talking to one group of people in the presence of many groups in a room.
• Broadcast Address – Frames sent to a broadcast address are sent to all LAN devices. One device sending data to a Broadcast address will send frames to ALL devices. One-to-All. A good way to picture this is a person in a room talking to everyone in that room. 

The MAC Address used for layer 2 broadcast (broadcast MAC address) is ff:ff:ff:ff:ff:ff.

The broadcast address is FFFF.FFFF.FFFF.  The switch would flood broadcast frames out all ports except the one on which they were sent.

The least-significant bit of the first octet of the destination address in multicast frames is set to 1. This allows a network switch to tell the difference between unicast and multicast addresses. One example of an Ethernet multicast address is 01:00:0C:CC:CC:CC, which is a CDP address (Cisco Discovery Protocol).

Unicast, Multicast, and Broadcast Address, further explained.

What is the difference between unicast, multicast, and broadcast?

• As mentioned above, there are three ways to send packets over a network: unicast, multicast, and broadcast.
• Unicast contact requires a single sender and a single receiver. Since the packet is only sent to one destination at a time, this is a form of point-to-point transmission.
• Multicast is a method of sending packets to a group of addresses, which is characterized by a “group address.” Packets are sent from a single sender to multiple receivers in this situation. Since the same data packet may be sent to several nodes by sending just one copy of the data, both the sender’s and the network’s load are minimized.
• Broadcasting entails sending packets to all nodes on a network at the same time. This form of transmission is used to create contact with another host as well as for DHCP-style IP address assignment methods. In the first example, it is needed because your packets must know the correct MAC address in order to communicate with a computer on your local network. Assume you have the IP address (for example, obtained by querying a DNS server) but have not yet determined the node’s MAC address.

If you broadcast a packet requesting the identity of the node with that specific IP address, any machine on the network will receive the message, but only the machine with that IP address will reply.