# One weird subnetting question....

Posts: 3Member ■□□□□□□□□□
Can someone help me out with this doozy...

An admin has decided to use the private address 172.20.0.0 for the internal network. If the maximum # of hosts on a subnet is 62 what is the subnet?
[post edited by webmaster]

Man, this one is killing me!

Copying question from other sites, **** or books and posting them in our forums is not allowed. So I edited your post. The subnet mask is 255.255.255.192. This info should enable you to rule out the 2 incorrect answers.
• Posts: 18Member ■□□□□□□□□□
dear friend here is some details about how to solve this Question

u said hat the network IDis 172.20.0.0
and u want the maximum no. of hosts in subnet to be 62

it is ok
look
the 172.20.0.0 is a class B adders and the default subnet should
be 255.255.0.0
my traditional way to solve such of this Q. I loo at the no.. of hosts and I see if it is in the range of 2-254 if it is ok so I put my mind on the class C subnetting cuse in this case u will determine a custom subnet mask

so if u analyzed the last octet of the class the 0 from the 255.255.255.0

SNm (last octet)
SNM
No. of SNID
#of hosts
1000 0000
128
2-2=0
126 ( this is invalid)
1100 0000
192
4-2=2
64-2=62
1110 0000
224
8-2=6
32-2=30
1111 0000
240
16-2=14
16-2=14
and so on

so as u see from this table that we will need the 192 Custom subnet
so the sn.u want will be 255.255.255.192

sorry people for my poor english
and my regards to webmaster
• Posts: 18Member ■□□□□□□□□□
dear friend I looked at the question
but this q. will need u to full design the network and u should have a spacific program to design it u know but it is a good Q. I'll try to solve it on a piece of papper
• Posts: 1Member ■□□□□□□□□□
If its a 172.20.0.0 address, isnt that class B? If thats so, the default subnet mask is 255.255.0.0. With the 62 host question, I thought the subnet mask would therefore be:

255.255.192.0

not

255.255.255.192 [As this would use 11 bits for subnetting on a class B subnet].

Please can you clarify for me?

• Posts: 1Member ■□□□□□□□□□
255.255.255.192 does not use 11 bits, it is using 10. Anyway thats not the point.

The question requires you to have 62 hosts.

If you use 255.255.192.0 then you will end up with 16384 -2(network and broadcast) = 16382 hosts on 2 subnets (11000000). Thats fair enough as you have managed to get more than 62 hosts but what they want is you to only have 62 hosts per subnet.

So, if you use 255.255.255.192 you are leaving 6 bits for you hosts (2 to the power of 6 = 64 - 2 gives you 62 hosts) and you have 10bits for your network giving you 1024 subnets.

Hope that makes sense
• Posts: 22Member ■□□□□□□□□□
choinga, check ur pm i need some help with a problem im having.

thanks
There are 10 kinds of people in the world, those that understand binary and those that don't.