What is Broadcast IP?

What Is Broadcast IPIntro

IPv4 addresses come in 4 forms: Unicast, Broadcast, Multicast and Anycast. On the other hand, IPv6 addresses only come in 3 forms: Unicast, Multicast and Anycast. For the purpose of this article, we’ll explain in more detail what is Broadcast and how does it work.

The various forms mentioned above are referring to how data is routed to the destination IP addresses. Each form has a different way of being routed to the destination. Unicast is the most basic. When you send data to a Unicast IP address, it just goes from the sender’s machine to the recipient machine that is using that IP address. We have previously covered Anycast & Multicast and today we’ll focus on Broadcast.

 

Basic concept of Broadcast

When your computer first connects to a Local Area Network (LAN), it does not have an IP address. It has to connect to the Dynamic Host Configuration Protocol (DHCP) server to get an IP address. To do so, your computer has to perform a broadcast to a special Broadcast IP address 255.255.255.255 which essentially means every machine on the LAN will receive your request for an IP address. The DHCP server will then respond with an IP address to be assigned to your machine.

Read more about DHCP

 

Broadcast routing

The Broadcast IP address 255.255.255.255 mentioned above is known as a limited broadcast address because the traffic will never be forwarded by the router to outside of the LAN. If there is a need to send Broadcast data to a specific subnet from outside of that subnet, you will need to perform a broadcast using the direct broadcast address.

To calculate the direct broadcast address, you need to flip the host part of the IP address to all “1”.

Example:

Dot-decimal notation Binary
IP address space 172.16.0.0 10101100.00010000.00000000.00000000
Subnet mask 255.240.0.0 11111111.11110000.00000000.00000000
Network prefix vs. host 172.16.0.0 10101100.00010000.00000000.00000000
Broadcast address 172.31.255.255 10101100.00011111.11111111.11111111

 

 

Benefits of Broadcast

Broadcast allows the machines on a network to auto discover services being offered by various machines on the network. The example mentioned above about DHCP is vital as it reduces the workload of network administrators since they don’t have to manually configure all computers with a static IP address. Using broadcast, computers can also locate any network devices like printers and scanners without knowing their IP addresses. Without Broadcast IP, you will find daily life to be very tedious as everything needs to be manually configured.

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