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Broadcast - an explanation

Data transmission to all addresses or functions.Network interface cards are usually programmed to listen for three types of messages. They are messages sent to their specific address, messages broadcast to all NICs, and messages that qualify as a multicast for the specific card. There are three types of addressing:
  • Unicast - A transmission to a single interface card.
  • Multicast - A transmission to a group of interface cards on the network.
  • Broadcast - A transmission to all interface cards on the network. RFC 919 and 922 describe IP broadcast datagrams.
  • Limited Broadcast - Sent to all NICs on the some network segment as the source NIC. It is represented with the 255.255.255.255 TCP/IP address. This broadcast is not forwarded by routers so will only appear on one network segment.
  • Direct broadcast - Sent to all hosts on a network. Routers may be configured to forward directed broadcasts on large networks. For network 192.168.0.0, the broadcast is 192.168.255.255.
The types of broadcasting uses on TCP/IP:
  • ARP on IP
  • DHCP on IP
  • Routing table updates. Broadcasts sent by routers with routing table updates to other routers.
The ethernet broadcast address in hexadecimal is FF:FF:FF:FF:FF:FF. There are several types of IP broadcasting:
  • The IP limited broadcast address is 255.255.255.255. This broadcast is not forwarded by a router.
  • A broadcast directed to a network has a form of x.255.255.255 where x is the address of a Class A network. This broadcast may be forwarded depending on the router program.
  • A broadcast sent to all subnetworks. If the broadcast is 10.1.255.255 on network 10.1.0.0 and the network is subnetted with multiple networks 10.1.x.0, then the broadcast is a broadcast to all subnetworks.
  • A broadcast sent to a subnet in the form 10.1.1.255 is a subnet broadcast if the subnet mask is 255.255.255.0.