subnetting

[jonk34567]

question is attached below ? what is the answer ?

[Joseph W. Doherty]

I don't see an attachment.

[jonk34567]

image is attached now 

[Julio E. Moisa · Accepted solution]

Hi

The answer is 496

Why, The main subnet is 172.16.128.0/23 so you will make subnetting per 8 new subnets, so you will use the following formula:

2^n >= 8 ; where "n" is the bits used to subnetting.

2^3 >= 8

8 >= 8

So How many bits you have to subnetting

32 - CIDR = available bits to subnetting

32 - 23 = 9

So you have 9 bits to make subnetting.

Now you have used 3 (from "n") the current and new subnet mask are:

Current: 255.255.254.0

New: 255.255.255.192

Why? Binary:

Current : 11111111.11111111.11111110.00000000   (9 zeros)

New:      11111111.11111111.11111111.11000000    (using the new 3 bits "n")

Now the block will be:

256 - modified octet

256 - 192 = 64 ; so the block will be increasing 64 by 64 at the fourth octet.

172.16.128.0/26

172.16.128.64/26

172.16.128.128/26

172.16.128.192/26

172.16.129.0/26

172.16.129.64/26

172.16.129.128/26

172.16.128.192/26

The host per network are 64 (64 - 2 (network and broadcast))

Now the total is: 62 x 8 = 496

Hope it is useful

:-)

[Joseph W. Doherty]

496
A /23 supports 8 /26s, each /26 supports 62 hosts IPs, so 8 * 62 = 496.
Or a /23 is 512 IPs. 8 subnets will use 2 IPs (network prefix and broadcast), i.e. 16, so 512 - 16 = 496.