Solved Net+ Study Help - Subnetting
-
I got this question on a practice test, and I was hoping someone might be able to help me in figuring out why the right answer is the right answer:
A Company is configuring an internal network with routed subnets based on the following class B address range:
172.30.8.0/21
The company wants to set up the following subnets:
Network A - 600 hosts
Network B - 100 hosts
Network C - 56 hosts
Network D - 40 hostsThe company wants to keep the unused addresses in each subnet to a minimum.
Which network address ranges should the company use?
A:
Network A: 172.30.8.0/22
Network B: 172.30.12.0/25
Network
172.30.12.128/26
Network
172.30.12.192/26B:
Network A: 172.30.8.0/22
Network B: 172.30.10.0/25
Network 172.30.10.128/26
Network 172.30.10.192/26
Network A: 172.30.8.0/23
Network B: 172.30.10.0/25
Network 172.30.10.128/26
Network 172.30.10.192/26
Network A: 172.30.8.0/22
Network B: 172.30.12.0/25
Network 172.30.12.128/26
Network 172.30.12.192/27I've ruled out C on account of /23 only supplying 512 (510 host) addresses (Required 600).
I've ruled out D on account of /27 only supplying 32 (30 host) addresses (Required 40).
Because I'm obviously missing something, I feel like either A or B could be the correct answer, but the practice test claims that B is wrong because "Network B, C, and D all overlap with Network A." and I don't understand that.
I would love some insight.
-
In answer B, Network A starts at 172.30.8.0 and ends at 172.30.11.255. The other three networks suggested are in a space that is already taken by that range.
-
@ndc Thanks. I figured with only 256 possible addresses, the addresses spill over into the 3rd octet. If that's what's going on here, what's a good way to calculate this in the future?
1024 ÷ 256 = 4? Being that 8,9,10,11 are the 4 taken up?
-
@mr-jones said in Net+ Study Help - Subnetting:
@ndc Thanks. I figured with only 256 possible addresses, the addresses spill over into the 3rd octet. If that's what's going on here, what's a good way to calculate this in the future?
1024 ÷ 256 = 4? Being that 8,9,10,11 are the 4 taken up?
That looks to be a decent approach! TBH I cheated and used a subnet calculator to look up the final address quickly. I haven't done that stuff by hand in rather a long time so I don't have any amazing suggestions for alternatives.
-
@mr-jones said in Net+ Study Help - Subnetting:
A Company is configuring an internal network with routed subnets based on the following class B address range:
172.30.8.0/21LOL, there aren't even Class Bs for decades, and when there were, they were never a /21. Who wrote this question and got something so basic wrong?
-
@scottalanmiller They need to start revising these questions. I mean if they want to get it as close as possible to real life scenarios. Just a thought.
-
@scottalanmiller said in Net+ Study Help - Subnetting:
@mr-jones said in Net+ Study Help - Subnetting:
A Company is configuring an internal network with routed subnets based on the following class B address range:
172.30.8.0/21LOL, there aren't even Class Bs for decades, and when there were, they were never a /21. Who wrote this question and got something so basic wrong?
yeah that was the first thing I was wondering.... /21 and calling it a class B.. /sigh.
-
@dashrender said in Net+ Study Help - Subnetting:
@scottalanmiller said in Net+ Study Help - Subnetting:
@mr-jones said in Net+ Study Help - Subnetting:
A Company is configuring an internal network with routed subnets based on the following class B address range:
172.30.8.0/21LOL, there aren't even Class Bs for decades, and when there were, they were never a /21. Who wrote this question and got something so basic wrong?
yeah that was the first thing I was wondering.... /21 and calling it a class B.. /sigh.
Even if it was a /16, the Class B bit would be wrong. Better, but still wrong.
-
@itivan80 said in Net+ Study Help - Subnetting:
@scottalanmiller They need to start revising these questions. I mean if they want to get it as close as possible to real life scenarios. Just a thought.
That, too. Like this is not a skill anyone would ever need. Ever.
-
@scottalanmiller said in Net+ Study Help - Subnetting:
@itivan80 said in Net+ Study Help - Subnetting:
@scottalanmiller They need to start revising these questions. I mean if they want to get it as close as possible to real life scenarios. Just a thought.
That, too. Like this is not a skill anyone would ever need. Ever.
Especially considering the hundreds of free online calculators. The ones that can do this in their head are network guys from 90s, and the only reason they can do it in their head is because they've worked with it back when there was a lack of technology like VLANs.
-
@irj said in Net+ Study Help - Subnetting:
@scottalanmiller said in Net+ Study Help - Subnetting:
@itivan80 said in Net+ Study Help - Subnetting:
@scottalanmiller They need to start revising these questions. I mean if they want to get it as close as possible to real life scenarios. Just a thought.
That, too. Like this is not a skill anyone would ever need. Ever.
Especially considering the hundreds of free online calculators. The ones that can do this in their head are network guys from 90s, and the only reason they can do it in their head is because they've worked with it back when there was a lack of technology like VLANs.
Good point. That's so true. Even if you are "good" at this, never ever ever should you try to do it manually. There is zero value to taking that risk.
-
@scottalanmiller said in Net+ Study Help - Subnetting:
@irj said in Net+ Study Help - Subnetting:
@scottalanmiller said in Net+ Study Help - Subnetting:
@itivan80 said in Net+ Study Help - Subnetting:
@scottalanmiller They need to start revising these questions. I mean if they want to get it as close as possible to real life scenarios. Just a thought.
That, too. Like this is not a skill anyone would ever need. Ever.
Especially considering the hundreds of free online calculators. The ones that can do this in their head are network guys from 90s, and the only reason they can do it in their head is because they've worked with it back when there was a lack of technology like VLANs.
Good point. That's so true. Even if you are "good" at this, never ever ever should you try to do it manually. There is zero value to taking that risk.
Yeah, excellent point. I've thought the same. I mean, I get it, they want you to try and get your brain to really understand it but in any real world situation, always use a subnet calculator and double-check it a few times, lol.
-
@dave247 said in Net+ Study Help - Subnetting:
@scottalanmiller said in Net+ Study Help - Subnetting:
@irj said in Net+ Study Help - Subnetting:
@scottalanmiller said in Net+ Study Help - Subnetting:
@itivan80 said in Net+ Study Help - Subnetting:
@scottalanmiller They need to start revising these questions. I mean if they want to get it as close as possible to real life scenarios. Just a thought.
That, too. Like this is not a skill anyone would ever need. Ever.
Especially considering the hundreds of free online calculators. The ones that can do this in their head are network guys from 90s, and the only reason they can do it in their head is because they've worked with it back when there was a lack of technology like VLANs.
Good point. That's so true. Even if you are "good" at this, never ever ever should you try to do it manually. There is zero value to taking that risk.
Yeah, excellent point. I've thought the same. I mean, I get it, they want you to try and get your brain to really understand it but in any real world situation, always use a subnet calculator and double-check it a few times, lol.
I think you have the right of it. If you UNDERSTAND it, you can do it manually, sure, but would you really want to? Do a few problems by hand and check your answers with an online tool to make sure you got the idea and and then, never do it manually again, lol.
I can do 15 digit addition, subtraction, multiplication, and division... but I'd rather just punch it into my calculator and get my answer, lol.
-
Hmm, I changed my mind. It's not that easy if your not very comfortable with binary stuff and know the powers of two table.
These questions where pretty basic to be honest. You should be able to them in your head, just as you should be able to do 16+8 or whatever.The only difference between this and math in fourth grade is that you need to know some "binary".Even easier is if you know the powers of two table.
2^0=1
2^1=2
2^2=4
2^3=8
2^4=16
2^5=32
etc...
2^8=256
2^9=512
2^10=1024
2^11=2048
etc...
2^15=32768If a subnet is /21 you do 32-21=11. That subnet has 2^11=2048 addresses total.
-
This post is deleted! -
@dave247 said in Net+ Study Help - Subnetting:
@pete-s said in Net+ Study Help - Subnetting:
These questions where pretty basic to be honest. You should be able to them in your head, just as you should be able to do 16+8 or whatever.
The only difference between this and math in fourth grade is that you need to know some "binary".
Even easier is if you know the powers of two table.
2^0=1
2^1=2
2^2=4
2^3=8
2^4=16
2^5=32
etc...
2^8=256
2^9=512
2^10=1024
2^11=2048
etc...
2^15=32768If a subnet is /21 you do 32-21=11. That subnet has 2^11=2048 addresses total.
I can't do 2^11 (or others) in my head. That's the challenge. Its relatively basic, yes, but most our brains grew up on base 10 not base 2, so its not actually simple.
You have a point. It is a table you could potentially learn by heart just like multiplication. But not if this application is the one and only thing you'll use it for.
But you could also just extrapolate from /24 being 256. That means /23 is 512 and /25 is 128 etc etc.
I'm probably biased since I've known these by heart since I was a kid learning to program.
-
@pete-s said in Net+ Study Help - Subnetting:
@dave247 said in Net+ Study Help - Subnetting:
@pete-s said in Net+ Study Help - Subnetting:
These questions where pretty basic to be honest. You should be able to them in your head, just as you should be able to do 16+8 or whatever.
The only difference between this and math in fourth grade is that you need to know some "binary".
Even easier is if you know the powers of two table.
2^0=1
2^1=2
2^2=4
2^3=8
2^4=16
2^5=32
etc...
2^8=256
2^9=512
2^10=1024
2^11=2048
etc...
2^15=32768If a subnet is /21 you do 32-21=11. That subnet has 2^11=2048 addresses total.
I can't do 2^11 (or others) in my head. That's the challenge. Its relatively basic, yes, but most our brains grew up on base 10 not base 2, so its not actually simple.
You have a point. It is a table you could potentially learn by heart just like multiplication. But not if this application is the one and only thing you'll use it for.
But you could also just extrapolate from /24 being 256. That means /23 is 512 and /25 is 128 etc etc.
I'm probably biased since I've known these since I was a kid learning to program.
Actually when I'm writing it down it doesn't look as simple as when I think about it in my mind. I think I'll have to change my mind and agree that it's not easy - unless you're very comfortable with the binary stuff.
-
All that just goes back to whoever said it above - it's stupid to test about it today, unless you're at an engineering level...
-
@pete-s said in Net+ Study Help - Subnetting:
@dave247 said in Net+ Study Help - Subnetting:
@pete-s said in Net+ Study Help - Subnetting:
These questions where pretty basic to be honest. You should be able to them in your head, just as you should be able to do 16+8 or whatever.
The only difference between this and math in fourth grade is that you need to know some "binary".
Even easier is if you know the powers of two table.
2^0=1
2^1=2
2^2=4
2^3=8
2^4=16
2^5=32
etc...
2^8=256
2^9=512
2^10=1024
2^11=2048
etc...
2^15=32768If a subnet is /21 you do 32-21=11. That subnet has 2^11=2048 addresses total.
I can't do 2^11 (or others) in my head. That's the challenge. Its relatively basic, yes, but most our brains grew up on base 10 not base 2, so its not actually simple.
You have a point. It is a table you could potentially learn by heart just like multiplication. But not if this application is the one and only thing you'll use it for.
But you could also just extrapolate from /24 being 256. That means /23 is 512 and /25 is 128 etc etc.
I'm probably biased since I've known these by heart since I was a kid learning to program.
The only ones I know offhand are /24=256 and /29=4. The only reason I know the /29 is because so many ISPs use that for static IP addressing.
-
@travisdh1 said in Net+ Study Help - Subnetting:
/29=4. The only reason I know the /29 is because so many ISPs use that for static IP addressing.
umm 8 with 5 usable the way it is passed through the ISP gear.
