Subnetting question.

IP of 156.233.42.56 with a subnet mask of 7 bits. How many hosts and subnets are possible assuming
that subnet 0 is not used?

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echo_time_cat

I believe this was the same question below.

https://in.answers.yahoo.com/question/index?qid=20120513042701AA5ABdz

satishtech

I am confused.
subnet mask of 7 bits is /25 am I correct ?
In that case , since it is class we get 2^9 subnets and 2^7-2 hosts per subnet.
which is 512 subnets and 126 hosts per subnet.

I think 7 bits ON it is /23
and we get 2^7 = 128 Subnets
Off bits or zero bits are 9 , hence 2^9 = 512 - 2 = 510 hosts per subnet.

The magic number in the third octet will be 2.

128 64 32 16 8 4 2 1
2 is in the 7th position.

In relation to 42 in the third octet above we

156.233.42.0 ---- Network number
156.233.42.1

First Host (Hosts .1 to .255)
156.233.43.254 --Last Host (Hosst .1 to .254)
156.233.43.255---Broadcast Address

Kindly correct me.

Alceo

satishtech wrote: »

I am confused.
subnet mask of 7 bits is /25 am I correct ?

I think subnet mask is intended as the additional bits stealed from the host part and added to the network mask of the class B address:
16 bit Class B + 7 bit subnet mask -> /23

Number of subnets 2^7 -1= 127 ( we can't use subnet 156.233.0.0)

satishtech

7 bits on is a /23 mask , since it is a class B address.

ccie14023

Goodness gracious, when is the training material going to drop classful addressing? This is not 1995. With the exception of Class D, address classes really are not relevant any more. I suspect it is just to torture newbies that they continue to include this nonsense.

Jasiono

Isn't it easier to think of it classful at first? Makes for faster solving.

networker050184

I think it's just confusing to learn this whole classful way and then have to forget it and never think about it again the rest of your career. Most people I see having trouble with it is because they are stuck in a classful way of thinking. Just learn the binary and it's the same regardless.

satishtech

Should one be prepared the classful way for ccent
or the classless way ?

If classless I would presume /7 would mean the first 7 bits in the first octet are on that is one.

could anyone subnet the above example the classless way ?