Help: subnetting

[darwinsanchez6774]

Good day,

Can u help me subnet 172.16.0.0/16 for me to have 256 networks.

What subnetworks will I have?

[Dennis Mink]

how many IP addresses do you need in each subnet?

if you were to do 172.16.1.0/24-172.16.255.0/24 you have 255

if you do 172.16.1.0/25-172.16.255.0/25 you have even more

please rate if useful

[chrihussey]

Actually 172.16.1.0/24 - 172.16.255.0/24 will give you 256 subnets. (0 to 255 = 256)

(Dennis should still get the credit)

[Dennis Mink]

Yeah, uuuh OK, true , oops  ;-)

[darwinsanchez6774]

Hi...i see your point and thankyou. But i am wondering, Iam actually following a method of subnetting and all of the time I get the right answers through it until i encountered this problem.

It goes like this.

Given: 172.16.0.0/16

Requirement: split the given IP address to make 256 subnets.

Step 1: convert the required target subnet into binary

So: 256 is 100000000 in binary

And it takes 9 bits to get to it

Step 2: reserve the number of bits in the given IP

So: 172.16.11111111.10000000/25

Step 3: find the increment

So: 128

From the last octet:

1=128

0=64

0=32

0=16

0=8

0=4

0=2

0=1

Step 4: determine the subnets through incrementing the subnets by the "increment"

So: 1st subnet..172.16.0.0/25

       2nd subnet...172.16.0.128/25

       3rd subnet...172.168.1.0/25

      4th subnet...172.168.1.128/25

       5th subnet...172.168.2.0/25

And so on....

I realized...i will get more that 256 subnets if ifollowed my process....so where did igo wrong?

[chrihussey · Accepted solution]

You are making a fundamental mistake in that to get 256 subnets in binary you only need 8 bits.

128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255, but what you are missing is the zero subnet which is 00000000. which gives you the 256.

So to get 256 subnets for 172.16.0.0 /16 the first would be:

172.16.0.0 /24 (Third octect being 00000000)

The next would be 172.16.1.0 /24 (Third octect being 00000001)

172.16.2.0 /24 (Third octect being 00000010)

172.16.3.0 /24 (Third octect being 00000011)

Up to 255 with 172.16.255.0 /24 (Third octect being 11111111)

So in binary 00000000 to 11111111 is 256 subnets.

[darwinsanchez6774]

So for this particular scenario....i should make an excemption and always remember that 0 is included in the count....thankyou very much