Broadcast

What is Broadcast ?

Broadcast is a method used on IP (and other) Networks to distribute a data block on the network to every connected device. Of course, a device may want to not process the block, it may have no application listening to the port the block is sent to, or it may be switched off - but generally, broadcasts are received by all hosts on the network

How does Broadcast differ from Multicast ?

Multicast is a "group specific" broadcast. Using special Addresses, a Multicast is *not* received by all host on the network, but only by those who are explicitely asking for it. Details in the Multicast article on this wiki.

What is the Broadcast address ?

To address a block to a device on the network, it either needs to be sent to the IP Address of the device, or sent as broadcast. For the broadcast, a specific IP Address is used, which is determined by setting all "host" bits in the IP address to "1", and using the same "network" part. For details on this, please check IP Address on this wiki. To determine the correct broadcast address, the correct netmask is crucial. With a wrong netmask, the calculated broadcast address will not match the network and is either sent as a direct block to one host or eventually considered to be on another network (and ignored by all hosts). Here is an example of how a broadcast address is determined: 192.168.001.010 - IP Address of the sender 255.255.255.000 - Netmask 000.000.000.255 - all host bits to one 192.168.001.255 - calculated correct broadcast address

=== Can I send a Broadcast to another network ? Generally, NO - a Broadcast is a function on a local network. Routers will generally not forward the broadcasts. Depending on the system configuration and routers used, there may be ONE special exception: the "global" broadcast address, which will be addressing all IP networks on the same lan. It is also used for applications such as getting an IP address by DHCP (when the network is not yet known). The global broadcast address is 255.255.255.255 However, do NOT expect a router to forward global broadcasts unless it is capable and configured to do so !

How can I send a block to a group of remote devices, then ?

Well ... Barix devices eventually (depending on firmware version and type) provide a "rebroadcasting" feature. IP Blocks sent to the device (for example, from a remote source), may be rebroadcasted on the local LAN by the network. This is exstreamely helpful to address many devices concurrently in a remote network without multiplying the packets to all destinations and clogging the links.

Back to FAQ