The broadcast address can be used to send data packets in IP networks to all par­ti­cipants of a local network. The in­di­vidu­al addresses of each party in the network do not have to be known for this to work. If necessary, the broadcast address can be cal­cu­lated quite easily.

Cheap domain names – buy yours now
  • Free website pro­tec­tion with SSL Wildcard included
  • Free private re­gis­tra­tion for greater privacy
  • Free Domain Connect for easy DNS setup

What’s behind the broadcast address?

Each network or subnet has a reserved broadcast address that can be used by all par­ti­cipants of the network to send a broadcast. Broad­casts allow in­form­a­tion and services to be trans­mit­ted to all devices and com­pon­ents of the network without the need to know their in­di­vidu­al IP addresses. Among other things, routers in a local area network use the broadcast IP to send HELLO packets to all endpoints, switches, and other routers to maintain in­ter­re­la­tion­ships on the network and discover neigh­bour­ing devices.

Defin­i­tion

Broadcast: a mul­ti­point con­nec­tion in IP networks that auto­mat­ic­ally reaches all nodes in the network without knowing the recipient addresses. For this purpose, a fixed reserved broadcast address exists in each network or subnet.

How is the broadcast address cal­cu­lated?

Each IP address consists of 4 decimal numbers — so-called octets — separated by dots. An octet contains 8 bits, which is why every IPv4 address is auto­mat­ic­ally a 32-bit address. Each octet can represent a number between 0 and 255. The broadcast address is always iden­ti­fied in the final part of the host part of an address (starts in the third or fourth octet): If all host bits are set to the binary value ‘1’, this is the broadcast address.

Note

If all host bits are set to the value ‘0’, this is the subnet address.

The following example is intended to clarify the com­pos­i­tion of the in­di­vidu­al com­pon­ents of an IP address, including the cal­cu­la­tion of the broadcast address:

192.128.64.7/24

192.128.64.7 is the IP address in this case, while the suffix ‘/24’ indicates the subnet mask 255.255.255.0.

Image: Schematic representation of the IPv4 address 192.128.64.7/24
The example of the IPv4 address 192.128.64.7/24 shows the host and network part of an address.

In each network, a broadcast IP is assigned only once. It is always the last IP address of the subnet. The broadcast address — where all host bits are set to ‘1’ as already mentioned — is therefore: 192.128.64.255 in this example.

1pZNjRZLNqI.jpg To display this video, third-party cookies are required. You can access and change your cookie settings here.

How to find out the broadcast IP

You want to find out the broadcast address of your network? For this, common operating systems with native command line ap­plic­a­tions and the network program ipconfig (Windows) or ‘ifconfig’ or ‘ip’ (Linux, macOS) provide the ap­pro­pri­ate tool set.

In Windows, for example, proceed as follows:

  1. Start the command prompt by using the key com­bin­a­tion [Windows] + [R] and execute the command ‘cmd’.
  2. Enter the CMD command ‘ipconfig /all’ into the command line tool to get an overview of all important key data of your local network.
Image: Windows 11 prompt: Output for ‘ipconfig /all’wk1003mikeShut­ter­stock
Windows 11 prompt: Output for ‘ipconfig /all’.

Among other things, the prompt presents you with your device’s IP address and subnet mask. You can derive the broadcast IP from this in­form­a­tion. In our example where the IP address is 192.168.2.34 and the subnet mask is 255.255.255.0, the broadcast address is 192.168.2.255.

How exactly you find out the broadcast address in Linux and macOS depends on the available network tool of the re­spect­ive dis­tri­bu­tion or version. In Ubuntu 20.04, for example, you can proceed as follows:

  1. Open the ‘Show ap­plic­a­tions’ menu.
  2. Search for ‘Terminal’ and start the ap­plic­a­tion by double-clicking on it.
  3. Enter the command ‘ifconfig’.
Image: Ubuntu 20.04: Output for the command ‘ifconfig’
Ubuntu 20.04: Output for the command ‘ifconfig’

Right in the second line, Ubuntu presents three values after executing the command:

  • inet: the Internet address of your device (here: 172.18.166.193)
  • netmask: the subnet mask of the local network (here: 255.255.250.0)
  • broadcast: the broadcast address of the local network (here: 172.18.175.255)
Go to Main Menu