Types and Ranges of IPv4 "cast" Packets

In IPv4 there are several types of "cast" packets you will hear about.  Each of these works within an assigned space and has specific functions.

Broadcast Packets

• Reserved IP of 255.255.255.255
• All "broadcast traffic" of the local network are sent on this IP and considered broadcast packets.

Multicast Packets

• Sent on Class D address space in the range of:  224.x.x.x to 239.x.x.x
• Use less "network resources" than Broadcast packets because only devices programmed to listen and use types of packets will pickup this traffic (ie. Cisco CDP)

Unicast Packets

• Use standard addressable class A, B, C space.
• Packets sent directly to a specific device on the network.

Directed Broadcast

• Will use the Layer 3 broadcast address of the local subnet to broadcast to on the LAN.
• The local broadcast address is always the last address of the subnet. 
• On network 192.168.1.0/24 the directed broadcast or local broadcast address is 192.168.1.255
• On network 10.10.0.0/16 the directed broadcast or local broadcast address is 10.10.255.255
• On network 172.16.14.0/23 the directed broadcast address is 172.16.15.255

Important things to remember:

A Layer 2 switch is obligated to flood all broadcast, multicast, and unknown unicast packets out all interfaces except the interface the packet came in on until it learns port-to-mac association.

Cisco switches by default do not learn mac addresses from multicast packets, you can enable this functionality as a network admin.

Layer 3 devices filter broadcasts.

Another way to look at this is switches create one broadcast domain (255.255.255.255) and multiple collision domains (see different article for definition).  Routers separate broadcast domains.  The concept might seem simple, but it is a very important lesson.