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Subnetting on 255.255.255.128 /25 network address: 172.16.0.0?

The fourth octet is confusing me a bit. What are the valid hosts and how to find them in such cases?

  • Total 1 Answer
  • 11142
author
Rajan Arora
,
CCNA Routing and Switching

Network 172.16.0.0

Subnet Mask : /25 = 255.255.255.128 (   by default its 255.255.0.0 means change has been done in 1st and 2nd octet ) 

                                             |      |

                                     11111111   10000000

so find block size for both of them 

Block Size = 2nd octet ( 256-255 = 1 ) , 1st Octet ( 256-128 = 128 )

Number of subnets = 2^9 = 512

Number of Valid ips in every subnet = 2^7-2 = 128-2 = 126

Now lets see subnets :

1)  172.16.0.0 /25   2)  172.16.0.128/25                 -  -   Subnet-Id's

             |                              |

     172.16.0.127/25    172.16.0.255/25                 -  -  Broadcast - Id's

3) 172.16.1.0 /25     4) 172.16.1.128 /25

            |                               |                  

     172.16.1.127 /25    172.16.1.255 /25

.

.

.

511) 172.16.255.0 /25  512) 172.16.255.128 /25

                  |                                  |

       172.16.255.127            172.16.255.255 /25

 

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