Network Basics: What is Multicast Networking and How Does It Work?

Multicast networking is group communication based on the simple concept that data transmission can be achieved by a server, and it will be received by a group of destination receivers simultaneously. 

Multicast must be the physical layer of point-to-multipoint communication, which allows all hosts to receive packets on a particular address forming a multicast group.

Having a multifaceted internet connection is crucial in this technological age. Multicast networking assures you that no matter how many users participated in and use the service, there is no problem when sending information over IP networks.

But what is multicast networking and how does it work for communication? Let's first get the basics.

What is Multicast Networking?

Multicast is similar to broadcast because both of them use the UDP protocol. The difference between them is that a node must first join the group before receiving the multicast message. Design a group (multicast group) must be composed of a class D IP and a port. The Class D IP range is between 224.0.0.0 ~ 239.255.255.255, of which 224.0.0.0 is a reserved IP and should not be used. 

In IPv6 networks, there’s no such thing as multicast used for everything that broadcast was previously used for, including a host of standard network infrastructure things like neighbor discovery, router discovery, address allocation, and so on.

Multicast possesses many fundamental attributes that determine its usage, which proves the fact that a server only needs to transmit each packet once reaching all recipients immediately, beneficial in situations where numerous receivers can require the same data. The network handles the replication and distribution of packets, which allows for seamless scalability to accommodate exceedingly large numbers of receivers. 

However, given that multicast is unidirectional, any responses necessitate the use of a distinct protocol causing overutilization. Moreover, any dropped packets must either be inconsequential or recovery mechanisms for lost data to be established separately. 

Why multicast is the key to a communication system?

As we’ve mentioned, multicast group IP addresses appear to be regular addresses, but they have a distinct characteristic as they belong to a special range. Any packet addressed to one of these IPs is automatically classified as multicast and is delivered based on the multicast forwarding tables in the router.

If there is no recipient for this multicast group or if multicast is not configured, the packet is either dropped. It is necessary to note that certain multicast addresses and their ranges are reserved for specific purposes and should not be used for other intents.

The common application is the provision of real-time stock market data. In this scenario, all market participants must receive the same information simultaneously, ensuring a fair market. Multicast emerges as an optimal method for distributing this data. However, a potential challenge lies in the loss of packets, as they contain vital data regarding prices and transactions. To address this concern, supplementary systems are employed alongside multicast, allowing market participants to recover any lost data through standard TCP unicast protocols.

Another application of distributed data streams is seen in the seamless delivery of content to a large number of users involved in modern IP-based cable TV networks, where users' set-top boxes subscribe to a multicast data stream that represents a specific program or channel. The network then efficiently forwards this data stream to each device.

How to create a multicast application on your network?

If you are planning to develop a multicast application on your local network, there are three approaches you can consider. The first method of addressing local environments and labs is through the use of the organization's local scope within administratively scoped ranges. These addresses work similarly to private IP address ranges as they can be utilized within individual networks.

However, network administrators have the responsibility of ensuring that these addresses do not extend beyond the local network. GLOP addressing offers an alternative approach, where it is not an acronym, and is described in RFC 3180. This method leverages a registered BGP ASN to establish a multicast address range. Another way to achieve multicasting is by utilizing permanently assigned addresses within the ranges 224.0.2.0-224.0.255.0 and 224.1.0.0-224.1.255.255.

Conclusion:

This article discusses everything about multicast. However, we’re not aware of any internet services that provide multicast forwarding capabilities. So caution must be exercised to prevent potential misuse, as multicast traffic can be easily abused to cause denial of service (DoS) attacks or unnecessary packet replication leading to increased network congestion and packet loss.