Broadcast address
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In computer networking, a broadcast address is an IP address that allows information to be sent to all machines on a given subnet rather than a specific machine. The exact notation can vary by operating system, but the standard is laid out in RFC 919.
Generally, the broadcast address is found by taking the bit complement of the subnet mask and then OR-ing it bitwise with the IP address.
Example: to broadcast a packet to an entire class B subnet using a private IP address space, the broadcast address would be 172.16.255.255.
This can be found from the subnet mask (255.255.0.0) and the IP address (eg. 172.16.48.196) - the complement of the subnet mask is 0.0.255.255, and 172.16.48.196 | 0.0.255.255 = 172.16.255.255.
A special type of IP address is the limited broadcast address 255.255.255.255. A broadcast involves delivering a message from one sender to many recipients. This broadcast is 'limited' in that it does not reach every node on the Internet, only nodes on the LAN.
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[edit] Other protocols
[edit] IPX
The Novell IPX protocol allows broadcast as well. When the network address is specified as FFFFFFFF, the packet is to be sent to all the networks available. When the target node address is specified as FFFFFFFFFFFF, the packet is intended to be received by all the computers in the network.
[edit] Ethernet layer
Broadcast is possible also on the underlying data link layer. Ethernet frames can be addressed to every computer on a given LAN segment if they are addressed to MAC address FF:FF:FF:FF:FF:FF. Ethernet frames that contain IP broadcast packages are usually sent to this address. ARP typically uses segment-wide broadcast for its queries.
