CCNA1 6 Addressing the Network - IPv4(13)

CCNA1 第六章

In all of these examples, it is the last octet. While this is common, the prefix can also divide any of the octets.

To get started understanding this process of determining the address assignments, let's break some examples down into binary.

See the figure for an example of the address assignment for the 172.16.20.0 /25 network.

In the first box, we see the representation of the network address. With a 25 bit prefix, the last 7 bits are host bits. To represent the network address, all of these host bits are '0'. This makes the last octet of the address 0. This makes the network address 172.16.20.0 /25.

In the second box, we see the calculation of the lowest host address. This is always one greater than the network address. In this case, the last of the seven host bits becomes a '1'. With the lowest bit of host address set to a 1, the lowest host address is 172.16.20.1.

The third box shows the calculation of the broadcast address of the network. Therefore, all seven host bits used in this network are all '1s'. From the calculation, we get 127 in the last octet. This gives us a broadcast address of 172.16.20.127.

The fourth box presents the calculation of the highest host address. The highest host address for a network is always one less than the broadcast. This means the lowest host bit is a '0' and all other host bits as '1s'. As seen, this makes the highest host address in this network

172.16.20.126.

Although for this example we expanded all of the octets, we only need to examine the content of the divided octet.

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