In this video we’ll pick apart Broadcasts – specifically the difference between a Local Broadcast and a Directed Broadcast (which is sometimes referred to as a Targeted Broadcast).
This is the "short version" of this video. In the longer video, we’ll run through the same demonstration, but I’ll also show you the packet captures of what is so you can see exactly what is happening on the wire.
0:00 - Start
0:11 - Topology
0:21 - Official Definition of a Broadcast message
0:49 - Layer 2 Broadcast vs Layer 3 Broadcast
1:24 - Local Broadcast
2:16 - Demonstration: ping 255.255.255.255
3:14 - Directed Broadcast - speaking to all hosts in the LOCAL subnet
3:54 - Demonstration: pinging the Broadcast IP of a Local Network
4:32 - Directed Broadcast - speaking to all hosts in a FOREIGN subnet
5:23 - Demonstration: pinging the Broadcast IP of a Foreign Network
6:20 - Summary
6:44 - Directed Broadcasts are a Security Risk
The Local Broadcast IP is always 255.255.255.255. Regardless of what your Subnet IP addresses are, you can always use the specially reserved IP address of 255.255.255.255 to send a packet to everyone on the local IP subnet.
The Directed Broadcast (also called Targeted Broadcast) is the last IP address in each Subnet (also known simply as "the broadcast IP"). You can use the Directed Broadcast to speak to every host in your own local Subnet…. OR, you can send a packet to a Broadcast IP in another subnet to speak to every host in a Foreign network.
To calculate your Broadcast IP, you’ll have to do a little Subnetting. This video series will teach you everything you need to know about Subnetting:
If you are studying for your CCNA, you’ll want to check out the compendium of free CCNA study resources from Practical Networking .net: