Subnetting

sdy74

Hi guys,


I was wondering if anyone can assist me as how I can solve this question on subnetting?


Q) Which two address can be assigned to a host with a subnet mask of 255.2555.254.0?




A) 113.10.4.0
186.54.3.0
c) 175.33.3.255
D) 17.35.36.0

Cheers.....

MAC_Addy

We're not doing your homework for you. I suggest you use the search button - there are plenty of threads on subnetting.

http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html

FloOz

none of the above.

255.2555.254.0 is not a valid subnet mask :P

On a serious note though, there are plenty of great threads on the forum that will teach you how to subnet easily.

TehToG

This is great practice too

MAC_Addy

TehToG wrote: »

This is great practice too

+1 for this, too. I used this website a ton when studying for the ICND1 exam. I still use it quite often to make sure my subnetting skills are top-notch.

NetworkVeteran

OP, lots of great tips and advice in this thread for you.

showbo

Not that I want to just give you the answer, but I am studying for ICND1 which I take in 1 week. So B is the only answer that I see can work. Please correct me if I am wrong guys

A is a subnet ID with valid hosts being 113.10.4.1 - 113.10.5.254
C is a broadcast address for subnet 175.33.2.0 - 175.33.3.255 with valid hosts being 175.33.2.1 - 175.33.3.254
D is a subnet ID with valid hosts 17.35.36.1 - 17.35.37.254

Michael2

Showbo, you didn't even need to do all that work. It should be painfully obvious that A and D can not be answers because the mask is referring to a class B network. A and D are class A addresses. Nevertheless, you did arrive at the correct answer. It seems that B is the only correct choice. While C is in the correct class, it is a broadcast address, meaning the last address in the range, and therefore cannot be assigned to a host.

mgates67

Michael2 wrote: »

Showbo, you didn't even need to do all that work. It should be painfully obvious that A and D can not be answers because the mask is referring to a class B network. A and D are class A addresses. Nevertheless, you did arrive at the correct answer. It seems that B is the only correct choice. While C is in the correct class, it is a broadcast address, meaning the last address in the range, and therefore cannot be assigned to a host.

Granted I'm not a subnetting expert, but I'm not sure how the class of the IP comes into play here. A mask of 255.255.254.0 can be used to subnet a Class A address.

NetworkVeteran

Michael2 wrote:

It should be painfully obvious that A and D can not be answers because the mask is referring to a class B network.

mgates67 wrote: »

A mask of 255.255.254.0 can be used to subnet a Class A address.

Correct! 255.255.254.0 doesn't refer to a class B network.

255.255.254.0 is usable on class A networks!

Granted I'm not a subnetting expert, but I'm not sure how the class of the IP comes into play here.

Well, you can't "subnet" a class C (/24) with a /23... subnet masks aren't used on class D networks... and class E isn't usable. (But that's a stretch! None of these addresses are from the class C, D or E range and they don't invoke classful addressing in the question.)

Michael2

Wow! The question says that the host has a subnet mask of 255.255.254.0, which means that the increment is is the third octet. This makes it a class B subnet mask. I just can't figure out when a mask of 255.255.0.0 could be used to subnet a class A network.

NetworkVeteran

Michael2 wrote: »

Wow! The question says that the host has a subnet mask of 255.255.254.0, which means that the increment is is the third octet. This makes it a class B subnet mask.

Michael, sorry mate, that's hogwash. If subnetting's important to you, I'd advise you to review a bit. Look in your book for phrases like "a class <x> subnet mask."

I just can't figure out when a mask of 255.255.0.0 could be used to subnet a class A network.

Well, most people don't want a flat address space of 16,000,000+ hosts, so they're going to subnet a /8. 255.255.0.0 isn't an uncommon place to begin. It's administratively easy to understand without any calculation. "I'm assigning you x.y.0.0/16" With VLSM, it's possible for a sub-administrator to subnet further, say x.y.z.0/24.

blatini

I'm about a month away from taking the exam so I just want to post what I think the answer is to get some feedback if I'm right or not.

A and D should be the correct answers. The subnets would build in increments of two for the third octet.

Also I guess this would be a good place to bring up something I've been wondering. For questions similar to this and when they ask what a subnet range would be with no comment on subnet zero or broadcast subnet, do you assume the zero subnet can be used? Most of my practice has not let me use them, in particular the questions on subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online

Thanks!

phatrik

blatini wrote: »

I'm about a month away from taking the exam so I just want to post what I think the answer is to get some feedback if I'm right or not.

A and D should be the correct answers. The subnets would build in increments of two for the third octet.

Both A and D are subnets therefore aren't assignable IPs.

blatini wrote: »

Also I guess this would be a good place to bring up something I've been wondering. For questions similar to this and when they ask what a subnet range would be with no comment on subnet zero or broadcast subnet, do you assume the zero subnet can be used? Most of my practice has not let me use them, in particular the questions on subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online

Thanks!

If the question on the exam doesn't specify, assume subnet zero can be used.

blatini

If subnet zero could be used wouldn't that make A and D viable options? Unless the answer is none of them...

atorven

blatini, I think you getting confused, none of those answers are in subnet zero, for the given subnet mask the subnet zero range that could be assigned to hosts would be x.x.0.1 to x.x.1.254, (it's always the first subnet after subnetting). Take a look at show bo's post about the answers.

blatini

Thanks for the clarification... I had thought subnet zero meant the subnet number of each subnet... oops lol

mgates67

NetworkVeteran wrote: »

Well, you can't "subnet" a class C (/24) with a /23

Technically you can, at least on a private network. We use 192.168.0.0/11 on our corporate network.

NetworkVeteran

Well, you can't "subnet" a class C (/24) with a /23

mgates67 wrote: »

Technically you can, at least on a private network. We use 192.168.0.0/11 on our corporate network.

192.168.0.0/16 "is a set of 256 contiguous class C network numbers" per the RFCs. Your 11-bit block would technically be an aggregate of those class Cs.