Quick subnet question.

Fernling306

I just started messing with subnetting today, I am learning it through the CBT nuggets video as of right now. he provides some practice subnetting questions and my work is not matching up to the instructors work.

"200.1.1.0, break into networks of 40 hosts each" is the practice question.

MY WORK-

40 networks= 00101000 Which is 6 bits.

Class C IP mask- 255.255.255.0- 11111111.11111111.11111111.00000000 /24

Add the 6 bits to the mask which would start at the 4th octet making it 11111100 right? If so that would be 252. So now I would have 255.255.255.252 /30 with increments of 4 since that is the lowest network bit.
If someone can tell me what I am doing wrong I would greatly appreciate it.
P.S. I've only been studying CCENT for a few days now.

My problem is that the instructor Jeremy(sp?) shows this as the answer: As you can see our mask and increment is not matching, which I am sure he is right.

40 hosts = 00101000 (6 bits) Subnet Mask = 255.255.255.192 Increment = 64
Ranges: 200.1.1.0 – 200.1.1.63 200.1.1.64 – 200.1.1.127 200.1.1.128 – 200.1.1.191 200.1.1.192 – 200.1.1.255

Excellent1

Fernling306 wrote: »

Add the 6 bits to the mask which would start at the 4th octet making it 11111100 right?

That's where you're going wrong. The host portion of the address requires 6 bits, which are the last 6 bits of the octect, meaning the last octect, instead of being 11111100 is 11000000. The 0's represent the host portion of the address. Those 6 0's are what's being looked at. Your answer, 11111100 only leaves 2 bits for hosts, which leaves 2 available addresses for hosts (subtracting 2 for the subnet/broadcast addresses).

Check out the subnetting made easy thread on this forum. Read through it and practice some and you'll have it down in no time.