Unicast, Multicast, and Broadcast Addresses
In Ethernet, broadcast and multicast addresses always describe a group of recipients. However, the unicast explains communication where data is sent from one point to another.
Unicast Address
In the case of a unicast address, a packet has been 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 used to send a packet from a single transmitting device to a single destination device.
A destination IP address must be in the IP packet header to send a unicast packet from source to destination. A destination MAC address must also be present in the Ethernet frame header. The IP and MAC addresses 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 datagrams or frames intended for multicasting 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. With 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 addresses. The source will also be a unicast address.
Online games also use multicast addresses, where many players connect remotely but play the same game. Another use of the multicast address is in distance learning through video conferencing, where many students connect to the same class.
Broadcast Address
When a single computer sends messages to many at once, it is called a broadcast. Television broadcasting is the most common example of a broadcast. Radio transmission is another example of broadcasting.
In computer networking, a broadcast means the network sends one copy of a packet to each destination. The terms broadcast IP address and broadcast MAC address are common in networking.
A broadcast packet also contains a destination IPv4 address with all (1s) in the host portion (see 172.17.255.255) in the 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.
Address Resolution Protocol (ARP) - Networkustad
June 4, 2019 @ 8:12 pm
[…] (ARP) for determining the destination MAC address. Although the destination MAC address can be a unicast, broadcast, or multicast address, the source MAC address must always be unicast. Every device with an IP address on a network also […]