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TOPIC: Need some help on subnetting qn

Need some help on subnetting qn 10 years 4 months ago #14462

Hi guys, im currently kinda lost tryin to calculate subnets and hosts for my network. (its a project btw)

Scenario :

I am given 2 blocks of Class C n/w add.
I am required to cater to 4 classrooms each with 30 hosts each.

In trying to save the address space, i decided to use 3 bits for subnet and 5 bits for the host portion.

That would leave me with 6usable subnets and 30hosts
eg,
192.168.0.32
192.168.0.64
192.168.0.96
192.168.0.128
192.168.0.160

My question is if i had assigned ALL 30hosts on the 192.168.0.32 subnet to the 1st classroom, wouldnt i be short of 1 address for the Gateway to connect to a router?

Secondly, would it be possible to further subnet a subnet with the mask of 255.255.255.252 and use them for gateways for each classroom?

Thanks for your time guys. Lookin forward to your response :)
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subnetting 10 years 4 months ago #14464

  • Arani
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answer to first question : no you are not running out of the gateway address, as the network address of that subnet is the gateway for that subnet. that would be the first address of the subnet.

answer to second question: you can do that by using super - subnetting
Picking pebbles on the shore of the networking ocean
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Re: Need some help on subnetting qn 10 years 4 months ago #14466

hi arani, thanks for ur reply but i am still somewhat confused.

Lets take for example the 192.168.0.32 subnet

I would use all valid host range which is 33-62 in this case for all
computers in Classroom A. Wouldnt i be 1 address short for connecting this network to a router? It would be like :

30 hosts --> switch --> router

Therefore, i would need 30 + 1 ip addresses wouldnt i ? Pls enlighten me. Thank you!!
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IP subnet 10 years 4 months ago #14470

  • Arani
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hi
the first IP address of that very subnet is your network address. if you do remember, there are two addresses that you cannot use for allotment, one of them is the first address of that particular subnet. hence that is the address you use for the network determination. the last address is for a broadcast over that part of the subnet. hence that cannot be your network address.
Picking pebbles on the shore of the networking ocean
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Re: Need some help on subnetting qn 10 years 4 months ago #14475

  • d_jabsd
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hi arani, thanks for ur reply but i am still somewhat confused.

Lets take for example the 192.168.0.32 subnet

I would use all valid host range which is 33-62 in this case for all
computers in Classroom A. Wouldnt i be 1 address short for connecting this network to a router? It would be like :

30 hosts --> switch --> router

Therefore, i would need 30 + 1 ip addresses wouldnt i ? Pls enlighten me. Thank you!!

you are correct. If all 30 addrs are getting assigned to hosts, there would be nothing left for the gateway. In this case, the smallest subnet you could use is /26 for 62 usable addresses. If you only have 4 classrooms of ~ 30 hosts each, you would still have an entire /24 left over.

you could try to get creative and subnet based on class of user- maybe split further into a teacher subnet and student subnet per room. Or use a big teacher subnet, and the student's systems are their own networks in each room.

there are many ways to do it but don't forget to account for class size increases. No one wants to renumber later when it could have been taken into account in the beginning.
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Re: Need some help on subnetting qn 10 years 4 months ago #14477

thanks d_jabsd and arani for your replies. So there is no other way around it other than borrowing more bits from the host portion to cater to just that 1 IP add for the GW? :?
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