Subnetting Confusion
I was ok with subnetting untill I read this post on internet.
#-Link-Snipped-#
Here they have tried to subnet a IP 192.168.1.0/24
I have pasted that part below if you dont want to search for it.
"We will try and subnet 192.168.1.0 /24 to sooth this network which allows a total number of 254 hosts I recommend you get familiar with this table below. I never leave home without it!
Lets start with HQ with 50 hosts, using the table above:
We are borrowing 2 bits with value of 64. This is the closest we can get for 50 hosts.
HQ - 192.168.1.0 /26 Network address
HQ = 192.168.1.1 Gateway address
192.168.1.2, First usable address
192.168.1.62- Last usable address. Total address space -192.168.1.2 to 192.168.1.62
192.168.1.63 will be the broadcast address (remember to reserve the first and last address for the Network and Broadcast)
HQ Network Mask 255.255.255.192 - we got the 192 by adding the bit value from the left to the value we borrowed = 128+64=192
HQ address will look like this 192.168.1.0 /26"
Now its clear that he asked us to memorize a table. No problem with that.
Now he said "
Lets start with HQ with 50 hosts, using the table above:
We are borrowing 2 bits with value of 64. This is the closest we can get for 50 hosts.
"
My question :-
1) We are borrowing 2 bits ? WHY ???
I know according to his table its correct. But Dont we have to use the formula 2^n -2 = No: of Hosts ? By using this we get totally different number.
I know he is trying to calculate for 50 hosts and not subnets. Is the above table hold good in case if we are calculating the no: of subnets ?
I mean to ask can we use the same table to calculate the number subnets required ?
Lets consider we want to divide 199.131.20.0/24 in to 5 subnets.
So the formula 2^3 holds good. so we need to borrow 3 bits.
How do we infer the above statement using the given table above ?
#-Link-Snipped-#
Here they have tried to subnet a IP 192.168.1.0/24
I have pasted that part below if you dont want to search for it.
"We will try and subnet 192.168.1.0 /24 to sooth this network which allows a total number of 254 hosts I recommend you get familiar with this table below. I never leave home without it!
Bit Value
128
64
32
16
8
4
2
1
Bits Borrowed
1
2
3
4
5
6
7
8
Subnet mask
128
192
224
240
248
252
254
255
Subnet Prefix /CIDR
/25
/26
/27
/28
/29
/30
Lets start with HQ with 50 hosts, using the table above:
We are borrowing 2 bits with value of 64. This is the closest we can get for 50 hosts.
HQ - 192.168.1.0 /26 Network address
HQ = 192.168.1.1 Gateway address
192.168.1.2, First usable address
192.168.1.62- Last usable address. Total address space -192.168.1.2 to 192.168.1.62
192.168.1.63 will be the broadcast address (remember to reserve the first and last address for the Network and Broadcast)
HQ Network Mask 255.255.255.192 - we got the 192 by adding the bit value from the left to the value we borrowed = 128+64=192
HQ address will look like this 192.168.1.0 /26"
Now its clear that he asked us to memorize a table. No problem with that.
Now he said "
Lets start with HQ with 50 hosts, using the table above:
We are borrowing 2 bits with value of 64. This is the closest we can get for 50 hosts.
"
My question :-
1) We are borrowing 2 bits ? WHY ???
I know according to his table its correct. But Dont we have to use the formula 2^n -2 = No: of Hosts ? By using this we get totally different number.
I know he is trying to calculate for 50 hosts and not subnets. Is the above table hold good in case if we are calculating the no: of subnets ?
I mean to ask can we use the same table to calculate the number subnets required ?
Lets consider we want to divide 199.131.20.0/24 in to 5 subnets.
So the formula 2^3 holds good. so we need to borrow 3 bits.
How do we infer the above statement using the given table above ?
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