Hello! Well, for several days I have been browsing the Internet and trying to figure out how to calculate the number of possible subnets. I have the following examples of masks: 255.255.255.0/24 255.255.255.224/27 255.255.0.0/16 255.0.0.0/8 I will calculate the number of possible hosts e.g. for...

Hello! Welcome.. // I will calculate the number of possible hosts e.g. for the mask / 24 - 2 ^ 8 = 256 - 2 = 254 // for only hosts yes, but more correctly 256 -3 = 253 network address, broadcast, Gateway. The number of possible IP addresses in a given subnet is calculated as follows: I. to the expected number of H hosts; add the number 3 (because there must be three additional addresses per subnet, broadcast and gateway address); as a result you got the number A; needed IP addresses. II. if the number A; is a power of two (i.e., it is 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, ...) then go to the next step; if it is not, replace the number A with the nearest number which is a power of two (but upwards), e.g. if A = 13, then we change it to A = 16 II. obtained number A; is the number of possible IP addresses in the given subnet, that is, how many IP addresses can be used in the given subnet (the maximum number of hosts is less than 3 than this number). The network mask and address depend on the obtained number of possible IP addresses Greetings.

Thanks for the answer. However, this I can do, I mean how to calculate the number of possible subnets in the given examples.

There are no specified address pools, so it is impossible to determine the maximum number of subnets. What you entered is a subnet mask. The smallest mask is / 30 So if you have, for example, addresses 192.168.0.0/24 and you want to divide it into the max, you will do 64 subnets with mask / 30 For PPPoE, the mask can be as high as / 32

Ok, from this pool I can make max 64 subnets, but how did you calculate it? As I understand on one example, I should be able to do another.

Here you have a link to a cool LAN calculator that helped me understand it: Link and here based on your example: and broken down into the maximum mask from 24 to 30

Calculating Number of Possible Subnets for Masks: /24, /27, /16, /8 - IP Addressing

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#1 14568742 28 Mar 2015 16:19

Arek15111 Arek15111

Level 16

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Post #1
14568742 28 Mar 2015 16:19

Hello!

Well, for several days I have been browsing the Internet and trying to figure out how to calculate the number of possible subnets.
I have the following examples of masks:
255.255.255.0/24
255.255.255.224/27
255.255.0.0/16
255.0.0.0/8

I will calculate the number of possible hosts e.g. for the mask / 24 - 2 ^ 8 = 256 - 2 = 254

But I can't figure out how to calculate the number of possible subnets.
I know you borrow bits, but I don't understand the principle that you can borrow so much here and so much here.
Could somebody help me understand this?
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#2 14568930 28 Mar 2015 17:20

Felix76 Felix76

Level 12

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Post #2
14568930 28 Mar 2015 17:20

[quote = "Arek15111"] Hello!
Welcome..
//
I will calculate the number of possible hosts e.g. for the mask / 24 - 2 ^ 8 = 256 - 2 = 254
//
for only hosts yes, but more correctly 256 -3 = 253
network address, broadcast, Gateway.

The number of possible IP addresses in a given subnet is calculated as follows:
I. to the expected number of H hosts; add the number 3 (because there must be three additional addresses per subnet, broadcast and gateway address); as a result you got the number A; needed IP addresses.

II. if the number A; is a power of two (i.e., it is 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, ...) then go to the next step; if it is not, replace the number "A" with the nearest number which is a power of two (but upwards), e.g. if A = 13, then we change it to A = 16

II. obtained number A; is the number of possible IP addresses in the given subnet, that is, how many IP addresses can be used in the given subnet (the maximum number of hosts is less than 3 than this number).

The network mask and address depend on the obtained number of possible IP addresses

Greetings.
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#3 14568992 28 Mar 2015 17:39

Arek15111 Arek15111

Level 16

» | Topic author Helpful post? (0)

Post #3
14568992 28 Mar 2015 17:39

Thanks for the answer.
However, this I can do, I mean how to calculate the number of possible subnets in the given examples.
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#4 14570230 29 Mar 2015 01:31

smario11 smario11

Level 31

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Post #4
14570230 29 Mar 2015 01:31

There are no specified address pools, so it is impossible to determine the maximum number of subnets.
What you entered is a subnet mask.
The smallest mask is / 30

So if you have, for example, addresses 192.168.0.0/24 and you want to divide it into the max, you will do 64 subnets with mask / 30
For PPPoE, the mask can be as high as / 32
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#5 14570318 29 Mar 2015 07:57

Arek15111 Arek15111

Level 16

» | Topic author Helpful post? (0)

Post #5
14570318 29 Mar 2015 07:57

smario11 wrote:
So if you have, for example, addresses 192.168.0.0/24 and you want to divide it into the max, you will do 64 subnets with mask / 30

Ok, from this pool I can make max 64 subnets, but how did you calculate it?
As I understand on one example, I should be able to do another.
#6 14570370 29 Mar 2015 09:13

zuczek1987 zuczek1987

Level 23

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Post #6
14570370 29 Mar 2015 09:13

Here you have a link to a cool LAN calculator that helped me understand it: Link

and here based on your example:

Quote:

decimal binary
IP address 192.168.1.1 11000000.10101000.00000001 .00000001 private network RFC1918
mask 255.255.255.0 = 24 11111111.11111111.11111111 .00000000
network address 192.168.1.0/24 11000000.10101000.00000001 .00000000 old class C
broadcast address 192.168.1.255 11000000.10101000.00000001 .11111111
254 network hosts
host min 192.168.1.1 11000000.10101000.00000001 .00000001
host max 192.168.1.254 11000000.10101000.00000001 .11111110

and broken down into the maximum mask from 24 to 30

Quote:
The smallest network including these addresses is: 192.168.1.0 with mask / 24
It can be divided into the following subnets:
number of subnets: 1
usage: 99.22% (254 IP)
number of effective subnets: 1
usage: 99.22% (254 IP)
number of hosts to use on each subnet: 254
list of subnets:
192.168.1.0/24
number of subnets: 2
usage: 98.44% (252 IP)
number of effective subnets: 0
Usage: 0.00% (0 IP)
number of hosts to use for each subnet: 126
list of subnets:
192.168.1.0/25 192.168.1.128/25
number of subnets: 4
usage: 96.88% (248 IP)
number of effective subnets: 2
usage: 48.44% (124 IP)
number of hosts to use on each subnet: 62
list of subnets:
192.168.1.0/26 192.168.1.64/26 192.168.1.128/26 192.168.1.192/26
number of subnets: 8
usage: 93.75% (240 IP)
number of effective subnets: 6
usage: 70.31% (180 IP)
number of hosts to use on each subnet: 30
list of subnets:
192.168.1.0/27 192.168.1.32/27 192.168.1.64/27 192.168.1.96/27 192.168.1.128/27 192.168.1.160/27 192.168.1.192/27 192.168.1.224/27
number of subnets: 16
usage: 87.50% (224 IP)
number of effective subnets: 14
usage: 76.56% (196 IP)
number of hosts to use on each subnet: 14
list of subnets:
192.168.1.0/28 192.168.1.16/28 192.168.1.32/28 192.168.1.48/28 192.168.1.64/28 192.168.1.80/28 192.168.1.96/28 192.168.1.112/28 192.168.1.128/28 192.168.1.144/28 192.168.1.160/28 192.168.1.176/28 192.168.1.192/28 192.168.1.208/28 192.168.1.224/28 192.168.1.240/28
number of subnets: 32
usage: 75.00% (192 IP)
number of effective subnets: 30
usage: 70.31% (180 IP)
number of hosts to use on each subnet: 6
list of subnets:
192.168.1.0/29 192.168.1.8/29 192.168.1.16/29 192.168.1.24/29 192.168.1.32/29 192.168.1.40/29 192.168.1.48/29 192.168.1.56/29 192.168.1.64/29 192.168.1.72/29 192.168.1.80/29 192.168.1.88/29 192.168.1.96/29 192.168.1.104/29 192.168.1.112/29 192.168.1.120/29 192.168.1.128/29 192.168.1.136/29 192.168.1.144/29 192.168.1.152/29 192.168.1.160/29 192.168.1.168/29 192.168.1.176/29 192.168.1.184/29 192.168.1.192/29 192.168.1.200/29 192.168.1.208/29 192.168.1.216/29 192.168.1.224/29 192.168.1.232/29 192.168.1.240/29 192.168.1.248/29
number of subnets: 64
Usage: 50.00% (128 IP)
number of effective subnets: 62
usage: 48.44% (124 IP)
number of hosts to use on each of the subnets: 2
list of subnets:
192.168.1.0/30 192.168.1.4/30 192.168.1.8/30 192.168.1.12/30 192.168.1.16/30 192.168.1.20/30 192.168.1.24/30 192.168.1.28/30 192.168.1.32/30 192.168.1.36/30 192.168.1.40/30 192.168.1.44/30 192.168.1.48/30 192.168.1.52/30 192.168.1.56/30 192.168.1.60/30 192.168.1.64/30 192.168.1.68/30 192.168.1.72/30 192.168.1.76/30 192.168.1.80/30 192.168.1.84/30 192.168.1.88/30 192.168.1.92/30 192.168.1.96/30 192.168.1.100/30 192.168.1.104/30 192.168.1.108/30 192.168.1.112/30 192.168.1.116/30 192.168.1.120/30 192.168.1.124/30 192.168.1.128/30 192.168.1.132/30 192.168.1.136/30 192.168.1.140/30 192.168.1.144/30 192.168.1.148/30 192.168.1.152/30 192.168.1.156/30 192.168.1.160/30 192.168.1.164/30 192.168.1.168/30 192.168.1.172/30 192.168.1.176/30 192.168.1.180/30 192.168.1.184/30 192.168.1.188/30 192.168.1.192/30 192.168.1.196/30 192.168.1.200/30 192.168.1.204/30 192.168.1.208/30 192.168.1.212/30 192.168.1.216/30 192.168.1.220/30 192.168.1.224/30 192.168.1.228/30 192.168.1.232/30 192.168.1.236/30 192.168. 1.240 / 30 192.168.1.244/30 192.168.1.248/30 192.168.1.252/30
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