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TOPIC: Broadcast and Multicast basic concepts

Broadcast and Multicast basic concepts 11 years 5 months ago #8162

  • thorpe
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I have been reading the section on firewall.cx Data Transmissions and I am having an issues with a basic concept.

The page on broadcasts states:
A Broadcast means that the network delivers one copy of a packet to each destination. On bus technologies like Ethernet, broadcast delivery can be accomplished with a single packet transmission.

Does this mean if I had 50 machines in my broadcast domain that

A) the sender would send 50 packets

or

B) the sender would send 1 packet and the 50 machines would copy the packets when it arrives and then send on the original packet.

Further to if I had a multicast group in my 50 machines with only 2 machines taking part in the multicast group would

A) the sender send 2 packets of data

or

B) the sender would send 1 packet and the 2 machines would copy the packet and send on the original

thanks
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Re: Broadcast and Multicast basic concepts 11 years 5 months ago #8169

  • sahirh
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B)

and

B)
Sahir Hidayatullah.
Firewall.cx Staff - Associate Editor & Security Advisor
tftfotw.blogspot.com
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Bcast 11 years 5 months ago #8181

  • TheBishop
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Sahir's right. Every packet sent onto an Ethernet segment is seen by all the stations. However every station ignores it except the one whose MAC address matches the destination MAC address in the packet. This is unicast. With broadcast, the packet is given a special MAC address (all the FF's) which tells every station to accept and process it regardless. So there's just one packet sent but everyone pays attention. Analogy - Go into a crowded shop and call "Fred" and only Fred will turn round. But yell "Fire" and everyone will pay attention. Multicast is similar except it's the multicast group rather than all the stations that pay attention to the packet.
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