# Subnet question

#### Networknoobie83

##### New member
Sorry if it doesnt make sense , i am new to this ,
so I have been given Netowrk IDs and subnets amounts and i need to find the subnet mask and the number of hosts per subnet. If anyone can help me or give me some sort of Formula please i need a specific formula for this kind of question and heres an example: 148.25.0.0 with 37 subnets = what's the subnet mask and how to find it , also how to figure out how many hosts per subnet there are?

#### Otis

##### Senior Member
…i need a specific formula for this …
148.25.0.0 with 37 subnets … what's the subnet mask and how to find it , also …
how many hosts per subnet …
Hi noobie. I don't think there are specific formulas for those tasks. They each seem to require an algorithm. Are you interested in using the binary method, for finding subnet masks? If so, you could google keywords like subnetting using binary method, to find tutorials and examples that show the steps. Some of those sites explain how to determine the number of hosts per subnet, also.

#### Networknoobie83

##### New member
Hi noobie. I don't think there are specific formulas for those tasks. They each seem to require an algorithm. Are you interested in using the binary method, for finding subnet masks? If so, you could google keywords like subnetting using binary method, to find tutorials and examples that show the steps. Some of those sites explain how to determine the number of hosts per subnet, also.

Please sir I do not understand anything at all they say in these websites , can you explain to me how it works I don't get it how do I figure out the subnet mask from the given ID and amount of subnets ( 37 ) how do I use this information to figure out what the subnet mask is I am so sad this is going to be my exam friday and i cant understand it at all please help!

#### Networknoobie83

##### New member
how to get to the conclusion.... its the part i dont get .. "
Calculating the Subnet Mask by Number of Subnets. Given a network ID and the required number of subnets, determine the subnet mask and the number of hosts per subnet:
• Network ID 148.25.0.0 with 37 subnets. Subnet mask is 255.255.252.0 with 1 022 hosts per subnet.
"

#### Otis

##### Senior Member
… I do not understand anything [at those] websites … my exam [is] friday and i cant understand it at all …
I'm sorry, but I cannot replace your instruction. Can you post an example from your course, so we can see their method?

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#### Networknoobie83

##### New member
I'm sorry, but I cannot replace your instruction. Can you post an example from your course, so we can see their method?

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That was an example from my course .. example Network ID 209.206.202.0 with 60 subnets and the answer is 255.255.255.252 with 2 hosts ! .. No clue how it got to that conclusion im trying to figure it out.. but I simply dont understand how you would end up to that conclusion with the information that is given......
• Network ID 148.25.0.0 with 37 subnets. Subnet mask is 255.255.252.0 with 1 022 hosts per subnet.
• Network ID 198.63.24.0 with 2 subnets. Subnet mask is 255.255.255.192 with 62 hosts per subnet.
• Network ID 110.0.0.0 with 1000 subnets. Subnet mask is 255.255.192.0 with 16 382 hosts per subnet.
• Network ID 175.23.0.0 with 550 subnets. Subnet mask is 255.255.255.192 with 62 hosts per subnet.
• Network ID 209.206.202.0 with 60 subnets. Subnet mask is 255.255.255.252 with 2 hosts per subnet.
• Network ID 98.25.0.0 with 737 subnets. Subnet mask is 255.255.192.0 with 16 382 hosts per subnet.
• Network ID 222.125.60.0 with 38 subnets. Subnet mask is 255.255.255.252 with 2 hosts per subnet.
• Network ID 223.21.25.0 with 14 subnets. Subnet mask is 255.255.255.240 with 14 hosts per subnet.
• Network ID 154.25.0.0 with 30 subnets. Subnet mask is 255.255.248.0 with 2 046 hosts per subnet.
• Network ID 63.0.0.0 with 131000 subnets. Subnet mask is 255.255.255.128 with 126 hosts per subnet.
the only thing i notice is that the lower the amount of subnet the lower the amount of hosts is... and the higher and close to being 255.255 the last couple of bits get.

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#### Otis

##### Senior Member
That was an example from my course …
I wasn't asking for an example answer. I meant a fully-worked example, showing their steps and calculations. Did the course show you any method?

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#### Networknoobie83

##### New member
I wasn't asking for an example answer. I meant a fully-worked example, showing their steps and calculations. Did the course show you any method?

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no im alone to study this no one taught me anything otherwise i wouldnt be here asking for help , hey do u know how to find the subnet mask linked to any given IP ? how do i do that

#### Otis

##### Senior Member
… no one taught me anything …
I think it's strange for a course to test students on material not covered. That doesn't sound nice at all.

… hey do u know how to find the subnet mask linked to any given IP ?
I don't have a working knowledge. I would need to study the steps provided at a few of those tutorial sites.

If you have specific questions about a step or the math presented at those sites (eg: using binary), then feel free to ask. (In general, I'm not motivated to duplicate classroom material here -- especially when such lessons already exist at multiple locations on the Internet.)

Please ensure that you've seen the forum guidelines, also (i.e., the Read Before Posting notice). Thanks.

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#### pka

##### Elite Member
I think it's strange for a course to test students on material not covered. That doesn't sound nice at all.
I don't have a working knowledge. I would need to study the steps provided at a few of those tutorial sites.
If you have specific questions about a step or the math presented at those sites (eg: using binary), then feel free to ask. (In general, I'm not motivated to duplicate classroom material here -- especially when such lessons already exist at multiple locations on the Internet.)
@Otis, don't worry about this question. I my previous life I supervised ten PhDs in computer science. I sent this question to four of them who I know taught net-working courses, All four replied that none of them understood the question. That was my own reaction upon first reading this question. It is a unique question dedicated to a particular course.

#### Networknoobie83

##### New member
Alright I understood lets say we have
148.25.0.0 which is a classs B address /16 by default that require 37 subnets which means 37 is 6 bit additional over the default value which means that 16 becomes infact a 22 and therefor 22 bits will be reserved for hosting and the result will be a 22 bit mask which becomes then 255.255.252.0 and provides 1022 hosts per subnet.
Another example is 198.63.24.0 which is a class C and it requires 2 subnets, andwe know 2 subnets can be host by 2 bits so we add 2 bits to the default class C CIDR which is 24 so 24+2 =26 and we have our subnet for the address which is the 26 bit subnet mask 255.255.255.192 .
(sorry for bad explanation i study in french )
So yeah another example

110.0.0.0 which is a class B ( 8 by default CIDR so -> 110.0.0.0/8 but we need 1000 subnets whcih means the value closest and higher than 1000 is 1022 which is 10 bits that we are going to add to the default of 8 which makes then 18 bit subnetmask which happens to be 255.255.192.0 with 16382 hosts

Thanks for everyone involved in helping

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#### Networknoobie83

##### New member
I actually didn't explain it too well 10 bits will be used for hosting is what i meant to type in the first part ! =) I will be back with more questions shortly have many upcoming exams thanks for the help ppls!