IP Subnetting and Supernetting

jskfan
jskfan used Ask the Experts™
on
In the case I have 192.168.25.0/24 and   the request is about adding 10 subnets ,will the new mask be :
192.168.25.0/28 or ?

Thanks
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Mohammed KhawajaManager - Infrastructure:  Information Technology
Commented:
That is correct.  You will have 16 subnets with each subnet accomodating 14 hosts.
Russ SuterSenior Software Developer
Commented:
Here's a handy resource for figuring that sort of thing out. I use it all the time because I'm far too lazy to do binary math in my head.

http://www.subnet-calculator.com/
Distinguished Expert 2018
Commented:
You will have 16 subnets with each subnet accomodating 14 hosts.
Ain't necessarily so, that depends on user's needs - it is just said 10 subnets.
You should ask number of hosts per subnet since there can be a lot of combinations.
:)
For example : you can also have 8 networks with 14 clients, and 2 networks with 30 clients. Or any other valid combination.
192.168.25.0/28
192.168.25.16/28
192.168.25.32/28
192.168.25.48/28
192.168.25.64/28
192.168.25.80/28
192.168.25.96/28
192.168.25.112/28
192.168.25.128/26
192.168.25.192/26

If you don't get more specific information go with /28 mask for all 10 subnets.
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Author

Commented:
Predrag Jovic

I thought with 10 subnets, you can get 254 hosts by subnet .
Correct ?
Mohammed KhawajaManager - Infrastructure:  Information Technology
Commented:
This is a C class address where each C class is 254 hosts.  When you divide this to smaller subnets, obviously each subnet will have less hosts.  Now if you were using a B class address then you would start with 65534 hosts and then sub-divide that to additional networks.  If you broke this down to 16 subnets then you would end up with each subnet having 4094 hosts.  As an example, 172.16.0.0/16 = 4094 hosts, 172.116.0.0/20 would give following:

172.16.0.0
172.16.16.0
172.16.32.0
172.16.48.0
172.16.64.0
...
172.16.240.0
Distinguished Expert 2018
Commented:
You can have 254 host per network, but not if you create subnets from 192.168.25.0/24 network, you can't divide it and still have 254 hosts per subnet.
You can create 192.168.26.0/24 - 192.168.34.0/24 networks and have 10 subnets, but...
Be careful where network start and where networks end.
I like create networks that can easily be summarized.

If you want you can use any private range.
I always prefer A or B class networks for bussines.
If networks need to have 254 hosts per subnet, I guess I would go with some range like (depending on  already existing networks)
172.16.0.0/24
172.16.1.0/24
.
172.16.9.0/24

As Mohammed already wrote summary would be 172.16.0.0/20 (he had typing by mistake 172.116. :) )
and it would cover 172.16.0.0 - 172.16.15.0 networks

Author

Commented:
I do not us subnetting often
where I get confused is where to add the bits when it come to subnetting and supernetting

ex: 192.168.0.0/24 ...if the request says add 20 subnets , then the closest is 2^5, which means you add 5 bits from the left
it will become 192.168.0.0/29 =192.168.0.0 255.255.255.248

I guess supernetting (reducing subnets in order to add more hosts) is not very common

Author

Commented:
I will come back to this at later time

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