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Broadcast

With reference to Ethernet, a broadcast is defined as a packet that will be sent to all hosts in the broadcast domain (the area between routers/switches).

A broadcast is addressed to a MAC of FF:FF:FF:FF:FF:FF, (equivalent to a subnet mask of 255.255.255.255)

A broadcast domain is only able to be segregated by OSI layer 3 devices (routers). In effect, if a host is on the same network/subnet it will receive any broadcast sent on that network. However, the boundary between layer 2 and 3 is blurred by VLAN Switches - which also separate broadcast domains.

Broadcast!
Diagram 1: In this situation, server has sent a broadcast to the network. Each workstation receives a copy.

Related to Broadcast, Multicast is simply a broadcast where the data packet is not sent back to the source port. Where a hub broadcasts, a switch multicasts. For example, OSPF Designated routers multicast link state advertisements to all other OSPF routers in the area using the multicast address of 224.0.0.5.


On the other hand, a unicast is simply transfer from one source to a single destination.



It appears from my quick readings that we have:
* Ethernet broadcast 
* Limited broadcast
* Directed broadcast

It may be worth expanding each of these into their own subsection, especially as we are dealing with multiple subnets in our network.

This External linkpdf appears to be a reasonable overview.

I've made a couple of changes to your original, revert them if need be.


Version 3 (current) modified Tue, 03 Jul 2007 23:11:54 +1000 by gummAY
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