# Cannot figure out how many sub & hosts for 10.0.0.0/20

Posts: 199Member ■■■□□□□□□□
@#\$@!! Ok I'm a little frustrated here lol..with this subnetting question.

How many subnets and host can you get out of 10.0.0.0/20 ?

I'm using the 2^N and (2^N)-2 formula.

2^N, N being the # of bits turned on, hence,
IIII IIII.IIII IIII.IIII 0000.0000 0000
so that would be 4 bits?

• Posts: 897Member
I don't claim to be an expert, but I sure would like to become one someday.

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Class A is /8 by default, so you would have 12 bits, not 4.
• Posts: 429Member
4096 subnets with 4094 usable hosts in each subnet.

What is the default mask for the network?

/8 or 255.0.0.0 or 11111111.0000000.0000000.0000000

/20 or 255.255.240.0 or 11111111. 11111111.11110000.00000000

Looking at the above mask, we borrowed 12 bits for subnetting and have 12 bits left over for hosts.

Now apply your formulas, 2^12 = 4096, (2^12)-2 = 4094

@#\$@!! Ok I'm a little frustrated here lol..with this subnetting question.

How many subnets and host can you get out of 10.0.0.0/20 ?

I'm using the 2^N and (2^N)-2 formula.

2^N, N being the # of bits turned on, hence,
IIII IIII.IIII IIII.IIII 0000.0000 0000
so that would be 4 bits?
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TRANSFERRED/COMPLETED: AGC1,BBC1,LAE1,QBT1,LUT1,QLC1,QMC1,QLT1,IWC1,INC1,INT1,BVC1,CLC1,MGC1, CWV1 BNC1, LIT1,LWC1,QAT1,WFV1,EST1,EGC1,EGT1,IWT1,MKC1,MKT1,RWT1,FNT1,FNC1, BDC1,TPV1 REQUIRED:
• Posts: 1,235Member
SurferDude .... this is where you kick yourself and slap your forehead ..... and welcome to the club
Kam.
• Posts: 128Member
I wrote a white paper on IP addressing I think it makes it pretty easy. I use it on my students at ITT Tech and they get it pretty fast. It may help on some of it. I am currently doing one on VLSM that may be more applicable. I have it on my linkedin site just go in and download it

Good luck
Bill

Go EVERTON

• Posts: 953Member
@#\$@!! Ok I'm a little frustrated here lol..with this subnetting question.

How many subnets and host can you get out of 10.0.0.0/20 ?

I'm using the 2^N and (2^N)-2 formula.

2^N, N being the # of bits turned on, hence,
IIII IIII.IIII IIII.IIII 0000.0000 0000
so that would be 4 bits?

SurferdudeHB,

What class is that network address?
• Posts: 199Member ■■■□□□□□□□
SurferdudeHB,

What class is that network address?

Class A
• Posts: 199Member ■■■□□□□□□□
Kaminsky wrote: »
SurferDude .... this is where you kick yourself and slap your forehead ..... and welcome to the club

Thanks I'm doing this daily lol..
• Posts: 953Member
Class A

SurferdudeHB,

• Posts: 933Member
Subnetting Quiz #1

Subnetting Quiz #2 (CIDR)

These are pretty helpful to help you practice and really get things down. You can also check out subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online, it is pretty good as well. Good luck and may the force be with you!
• Posts: 199Member ■■■□□□□□□□
surferdudehb,

255.0.0.0
• Posts: 199Member ■■■□□□□□□□
Subnetting Quiz #1

Subnetting Quiz #2 (CIDR)

These are pretty helpful to help you practice and really get things down. You can also check out subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online, it is pretty good as well. Good luck and may the force be with you!

Thx Bill!
• Posts: 953Member
255.0.0.0

What is the difference in bits from 255.0.0.0 to /20?
• Posts: 73Member ■■□□□□□□□□
Interesting exercise for me to see if I could do it in my head just from the title of the post.

2^12 subnets, 2^4 -2 hosts.

PS. All the materials I have seen indicate not subtracting 2 from the number of subnets unless the question gives some sort of hint that the zero subnet is not allowed or some such.
• Posts: 128Member
Tech I think you are asking what the mask represented by the /20 is versus 255.0.0.0

If that is it the /20 would mean the first 20 bits of the mask are 1's which would come out as

The 255.0.0.0 would be a /8
Go EVERTON

• Posts: 199Member ■■■□□□□□□□
What is the difference in bits from 255.0.0.0 to /20?

255.0.0.0 = 1111 1111.0000 0000.0000 0000.0000 0000

/20 = 1111 1111.1111 1111.1111 0000.0000 0000

so the difference in bits is 12
• Posts: 953Member
255.0.0.0 = 1111 1111.0000 0000.0000 0000.0000 0000

/20 = 1111 1111.1111 1111.1111 0000.0000 0000

so the difference in bits is 12

SurferdudeHB,

Including subnet zero, how many subnets can you have with 12 bits?
• Posts: 199Member ■■■□□□□□□□
SurferdudeHB,

Including subnet zero, how many subnets can you have with 12 bits?

That would be 2^N N being the number of turned on bits. So 4096 # of subnets.
• Posts: 933Member

2^12 = 4096 subnets. Which leaves 12 host bits 2^12 - 2 = 4094 (since the network and broadcast addresses are reserved.)

Just remember if IP subnet-zero is in use, you can use the reserved subnets (subnet zero)

2^n

If there is NO IP SUBNET-ZERO

You would use 2^n-2
• Posts: 953Member
That would be 2^N N being the number of turned on bits. So 4096 # of subnets.

Since the subnet mask is /20, how many bits are left in the IP address for hosts?
• Posts: 199Member ■■■□□□□□□□
Since the subnet mask is /20, how many bits are left in the IP address for hosts?

12 bits
• Posts: 953Member
12 bits

SurferdudeHB,

How many hosts can you have using 12 bits?
• Posts: 2Member ■□□□□□□□□□
we have 12 bits for networks and 12 bits for hosts
12^2=4096 networks
12^2-2=4094 hosts
p.s
ip subnet-zero is default for cisco router
• Posts: 199Member ■■■□□□□□□□
4094 hosts.
• Posts: 953Member
4094 hosts.

SurferdudeHB,

Looks like NOW you CAN figure out how many sub & hosts for 10.0.0.0/20.
• Posts: 199Member ■■■□□□□□□□
SurferdudeHB,

Looks like NOW you CAN figure out how many sub & hosts for 10.0.0.0/20.

Thank you Tech-airman!