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TOPIC: Subnetting

Subnetting 15 years 1 month ago #2536

Hey guys, I dont wanna try sound too stupid here but I have just finished a subnetting assignment for college where I had to subnet a given class A, B and C IP address.

Anyhow I am just a litlte confused about something. here is my Class C IP and its default mask.

Now I subnetted it borrowing 3 bits leaving me with

Now after I have worked out all my usuable subnets and hosts (6/30) I will end up with something for example....

196.200.32.x - 196.200.192.x

**now here is where i am confused!**

so for my first subnet it would have an IP address of say


I know the first looks correct since we are only working with the fourth octet on a Class C, but on class A and B masks the subnet value is included in its address? but not with a class does this work?

I dunno if I'm being confusing here or stupid, but I just dont get it :-)
Love your Optical Drive :-)

Re: Subnetting 15 years 1 month ago #2540

hi...okay heres what i think it is...

with the address subnetted....with a subnet mask of will result in

since the last octet is 224,
the last octet has been u use 256-224=32
so ur subnets are of size 32....

and the subnets are of 0, 32, 64,96.......1st subnet is 0..
2nd subnet is 32

2^n - 2= number of hosts
n being number of host bits
hence in this case 2^5-2=30 hosts

2^n - 2= number of subnets
n being the bits borrowed from the host
hence in this case since 3 bits are borrowed from the host
2^3-2=6 subnets

hence the subnets are
1st subnet:
with 10.0 being the network id and 10.31 being the broadcast address

2nd subnet
10.63 being the broadcast address....

and so on...hope this helps...
oh if its class b...then u have borrowed not 3 bits from host but
8+3 bits from host...since class c is NNHH
N=network, H=host....3rd octet being all ones...
so u have subnetted 3rd n 4th oct in this case....
am i right guys?

Re: Subnetting 15 years 1 month ago #2554

Hey and thanks for your prompt responce.

and to me everything in which you have said there looks pretty fine, you confirmed also the question I was asking about the subnet address since "2nd subnet
" in that since you did not include the actual subnet address within it.

Incase I am a little confusing what I am actually asking is (it was late last night when I asked so i wasnt being very clear :)) is why are the subnet addresses VISIBLE in our class A and B network addresses but INVISIBLE on our class C address?

Thanks - Gav
Love your Optical Drive :-)

Subnetting 15 years 1 month ago #2764

  • mew
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First you might want to distinguish between classful and classless. Because indebluez is confusing rules between the two. in classful subnetting you cannot use subnet zero (0). In classless you can in which case 2^n-2 no longer applies.

Otherwise I'm not sure what you mean by visible and invisible. If your talking about the fact that you can borrow eight bits at a time and number your subnets in the borrowed octets it should be obvious why this is not possible with class C as you cannot borrow the entire octet.

Re: Subnetting 15 years 6 days ago #3040

  • zeo
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Hi people,

I'm new in networking so I might ask some silly questions. Sorry for that.


when I'm applying a subnet mask on a class C network and I put subnet mask, does it mean that I haven't subnetted the network? Because 0 is 00000000 and and I haven't borrowed and bits for subnet?


If I have three departments in the company and I want to subnet the class C network, which is the best model to use? To borrow first three 1s?

mew, could you elaborate a bit more about classful and classless?

Thanks a lot

Re: Subnetting 15 years 6 days ago #3041

hi zeo! wow u are from bosnia! thats soo cool:)
hmmm heres what i noe...

classful includes RIP V1 and IGRP...these must have same subnet mask...
of /24 bits on each different interface....they dont change....

classess are OSPF, EIGRP, RIP V2...these can have different subnet masks...on each different interface...

i did not noe we cannot use subent 0 for classful subnettin..
is this true guys?

when u apply a subnet mask of /24...the class C has not been subnetted,,,as class C is N.N.N.H....
if u want to have 3 subnets then use this...

2^n -2=3
hence the network bits to be borrowed from the host is...n=3,
number of host bits are denoted by 0 hence in the last octet should have 5 zeros.
and (2^5)-2= will be the number of hosts in each subnet.

am i right pple?
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