critique my subnetting level

I can do 25 questions on that subnettingquestions site in 5-6 minutes with no paper and 95+% accuracy with the odd one wrong because of lost focus. I don't have any peers to measure against yet as I'm self-study until I start the networking academy program at the local college. Think I'm ready to rock the exam?

Find more posts tagged with

Free for TechExams community: Cybersecurity salary guide

Compare cert salaries and plan your next career move

Button

Comments

chmorin

How long does it take you to VLSM some subnet into like, 6 different address spaces? I practiced with someone giving me six random numbers between like 1 and 1024 or some stuff and subnetted up a Class A or B address. My average was 45 seconds to a minute or so of rush subnetting. With practice and memorization you could probably be much faster than me...

I'm not nearly as fast anymore... if you don't do it often you lose it like me haha.

PS: I used paper...

wbosher

Depends on what exam your taking. If your doing CCNA, then I hear you have to be really quick. If you doing the two exam route, then do don't have to be quite as fast.

headshot

chmorin wrote: »

How long does it take you to VLSM some subnet into like, 6 different address spaces? I practiced with someone giving me six random numbers between like 1 and 1024 or some stuff and subnetted up a Class A or B address. My average was 45 seconds to a minute or so of rush subnetting. With practice and memorization you could probably be much faster than me...

I'm not nearly as fast anymore... if you don't do it often you lose it like me haha.

PS: I used paper...

45 to a minute seems pretty fast to me especially if calculating host ranges that span into different octets. I haven't done much VLSM at this stage but certainly understand the concept. Paper seems necessary to prevent host range overlapping but would be pretty epic to be able to do it in your head I would think.

headshot

wbosher wrote: »

Depends on what exam your taking. If your doing CCNA, then I hear you have to be really quick. If you doing the two exam route, then do don't have to be quite as fast.

How fast is "really quick"? I definitely intend to take CCENT first, CCNA seems like quite a bit of material.

chmorin

headshot wrote: »

How fast is "really quick"? I definitely intend to take CCENT first, CCNA seems like quite a bit of material.

The amount of subnetting covered in the ICND1 exam is much larger than compared to the ICND2 exam. So be sharp on your subnetting.

I'd say "really quick" is probably your speed. If you can master VLSM like I described, you will have no problems.

wbosher

headshot wrote: »

How fast is "really quick"? I definitely intend to take CCENT first, CCNA seems like quite a bit of material.

With CCENT if you can do most calculations in under a minute you may be fine, although you should try to get it down to 30 seconds or so.

You don't need to worry about VLSM in ICND1, but it can't hurt to know it.

chmorin

wbosher wrote: »

You don't need to worry about VLSM in ICND1, but it can't hurt to know it.

Thats true, but if you can do it you will not have any problems with subneting on the exam.

higherho

I do not mean to hi jack this thread but I am having some subneting trouble (that or its just to late in the night for me).

I was asked the following question:

Question: Which subnet does host 172.25.26.192 255.255.252.0 belong to?

Answer: 172.25.24.0

Now when I first looked at this I quickly noticed that it was a /22 subnet mask which told me me I have 10 bits to work with which is 1022 hosts. However, I am just stuck on how to make this processes faster when it comes to finding out what subnet does this host belong to type of questions.

Any tips?

wbosher

Have you had a look at Jeremy's CBT Nuggets? I found his method of subnetting a easiest to deal with, after a little practice.

If you convert the third octet into binary, the 252 means an icrement of 4, in the third octet.

128 64 32 16 8 4 2 1
1 1 1 1 1 1 0 0

This would give you the range of 172.25.24.0 - 172.25.27.255.

Subnet: 172.25.24.0
Broadcast: 172.25.27.255
Valid host range: 172.25.24.1 - 172.25.27.254

If you're wonder how to arrive at 24, just count up from 0 in 4s until you arrive at the network your looking for.

higherho

wbosher wrote: »

Have you had a look at Jeremy's CBT Nuggets? I found his method of subnetting a easiest to deal with, after a little practice.

If you convert the third octet into binary, the 252 means an icrement of 4, in the third octet.

128 64 32 16 8 4 2 1
1 1 1 1 1 1 0 0

This would give you the range of 172.25.24.0 - 172.25.27.255.

Subnet: 172.25.24.0
Broadcast: 172.25.27.255
Valid host range: 172.25.24.1 - 172.25.27.254

I will check out CBT nuggets too. Thanks for the link.

I understood that I had a CIDR block of 4 if I took the 252 from the third octet and subtracted it with 255 leaving me with the last two bits in that octet. So I simply took that 3 and relize that I have three subnets from .24 to .27?

Thank you for the quick reply.

wbosher

higherho wrote: »

I will check out CBT nuggets too. Thanks for the link.

I understood that I had a CIDR block of 3 if I took the 252 from the third octet and subtracted it with 255 leaving me with the last two bits in that octet. So I simply took that 3 and relize that I have three subnets from .24 to .27?

Thank you for the quick reply.

First up, it's a block of four, not three - 24, 25, 26 and 27.

Once you know the increment (or block) size, you count from zero in multiples of your block size until you hit the target range. In this case your target address is 172.25.26.192, which fits nicely within this range.

johnwest43

You are ready to go , if you can subnet a network in under a minute.

higherho

wbosher wrote: »

First up, it's a block of four, not three - 24, 25, 26 and 27.

Once you know the increment (or block) size, you count from zero in multiples of your block size until you hit the target range. In this case your target address is 172.25.26.192, which fits nicely within this range.

Whoops, I just took notice to that typo my bad hehe. Thanks for the help. I was thinking about the block size and it seems as long as I know the block size I should be able to answer a majority of these questions quickly.

chmorin

Or do binary ANDing. In which you convert the mask and the address to binary and AND them.

172.25.26.192 255.255.252.0

The significant octet in this case is the third, since 172.25 anded by 255 and 255 is still going to be 172.25. 26 anded by 252 however:
11111100
00011010
00011000

00011000 = 24, so that is the mathmatic way to find the subnet. Good to know.