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Local vs Directed Broadcasts

Within this short article, we will look at the difference between local and directed broadcasts.

Local Broadcast

A local (link-local) broadcast (255.255.255.255) is performed within the broadcast domain. It is only local and never forwarded.

Directed Broadcast

A directed broadcast, on the other hand, is the broadcast address for the subnet such as, in the case of the network 192.168.1.0/24 - 192.168.1.255. When a host sends a directed broadcast it is routed until it reaches the router that has the locally connected network. The router then converts the directed broadcast (192.168.1.255) into a local broadcast of 255.255.255.255 out to the locally attached network/broadcast domain.

Therefore we can say,

"The local broadcast address is never converted to the directed broadcast address, however, the directed is converted to the local broadcast address."

Due to the security implications of this, i.e providing a vector for DoS amplification attacks it is typically disabled by default.

 

About the Author

RDonato

R Donato

Rick Donato is the Founder and Chief Editor of Fir3net.com. He currently works as an SDN/NFV Solutions Architect and has a keen interest in automation and the cloud.

You can find Rick on Twitter @f3lix001