Completely illustrate "Broadcast", a special move to all opponents

In the IoT era when everything leads to a network, IT engineers have an essential basic knowledge about network.Therefore, in this special feature, Nikkei Network's past article was re -edited.We will explain the basic network technology in an easy -to -understand manner in all 12 times.

　When computers communicate with each other in the IP network, add the destination and source address to the data.Specifically, write the destination and source IP address to the header of the IP packet, and the destination and the send source MAC address to the header of the Mac frame.Thus, IP network communication requires four addresses.

　However, there are communications that can be exchanged without these four addresses.For example, this is a communication when a DHCP server is dynamically assigned network information.

　The newly launched computer does not know the DHCP server IP address or MAC address until the interaction with the DHCP server begins.Not only that, I don't even know my IP address.In such a case, "broadcast" is used.This time, I will cover the broadcast.

1回のデータ送信ですべてのホストに届ける

　Broadcast is to send data to all hosts in one network.

　One network refers to a set of hosts with the same network in IP addresses.The scope of physically separated by the router is applicable.

　When a computer receives network information from a DHCP server, broad cast to the network (own network) where the computer itself is connected.This allows you to interact with the DHCP server.

　The ARP, which I mentioned earlier, also uses a broadcast.ARP examines the MAC address of the destination that sends the data at the request of the IP processing program.At this time, use the broadcast to contact the host of the entire network for the MAC address.

　On the other hand, normal communication in which computers exchange data one -on -one is called "unicast".

　The major difference between broadcast and unicast is that in addition to whether the data is specified in the data and the address of each sender, there are differences between the IP packet and the number of IP packets received.

　For example, when sending the same data to all hosts in the network with a unicast, the transmitting computer duplicates the data as the number of hosts and sends the data to each host.On the other hand, the broadcast will receive data to all hosts if the computer sends out one data.

　For this reason, the amount of data flows to the network is smaller.In addition, the load on the transmitting side is lower because the data is not copied on the computer.

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