Unicast, Multicast, and Broadcast Addresses

In Ethernet, broadcast and multicast addresses always describe a group of recipients. But the unicast is used to explain communication where data is sent from one point to another point.

Unicast Address

In case of a unicast address, a packet has sent from a single source to a specific destination. All Ethernet and IP networks support unicast transmission. A unicast MAC address is the unique address uses for sending a  packet from a single transmitting device to a single destination device.

For sending a unicast packet from source to destination, a destination IP address must be in the IP packet header. A destination MAC address must also be present in the Ethernet frame header. The IP address and MAC address combine to deliver data to a specific destination

Multicast Address

A multicast address is a logical identifier for a group of hosts in a computer network that is available to process datagram or frames intended to be multicast for a designated network service. The Data link layer of the OSI model also uses a multicast address.

The multicast MAC address is a special value that begins with 01-00-5E in hexadecimal. The range of multicast MAC addresses is from 01-00-5E-00-00-00 to 01-00-5E-7F-FF-FF for Ethernet and Fiber Distributed Data Interface (FDDI) media access control (MAC) addresses. The remaining portion of the multicast MAC address is created; by converting the lower 23 bits of the IP multicast group address into 6 hexadecimal characters.

The range of IPv4 multicast addresses is 224.0.0.0 to 239.255.255.255. By the help of multicast addresses; a source device can send a packet to a group of devices that belong to a multicast group. These devices assign a multicast group of IP address. The source will also be a unicast address.

The online games also use multicast addresses, where many players connected remotely but playing the same game. Another use of the multicast address is in distance learning through video conferencing, where many students connected to the same class.

Broadcast Address

When a single computer sends messages to many at once, is called a broadcast. The television broadcasting is the most common example of a broadcast. The radio transmission is another example of broadcasting.

In computer networking, a broadcast means that the network sends one copy of a packet to each destination. The broadcast is used very frequently in the networking world. The terms broadcast IP address and broadcast MAC address is common in networking.

A broadcast packet also contains a destination IPv4 address that has all ones (1s) in the host portion (see 172.17.255.255) in IP Packet. This numbering in the address means that all hosts on that local network (broadcast domain) will receive the packet.

Several network protocols, such as ARP and DHCP, use broadcasts. When the IPv4 broadcast packet is encapsulated in the Ethernet frame, the destination MAC address is the broadcast MAC address of FF-FF-FF-FF-FF-FF in hexadecimal which is 48 ones in binary.