Subnetting question, why was the problem worked the way it was?

Still working...

Here is another one that has stumped me from subnettingquestions.com

Question: How many subnets and hosts per subnet can you get from the network 10.0.0.0/20?

Answer: 4096 subnets and 4094 hosts

If converting over to binary, this is the result:

00001010.00000000.00000000.00000000

11111111.11111111.11110000.00000000

I orginally took all of the 1 values and tried to use that to get the number of subnets, but that number is way to high.

Once I got the answer, they only used the 1 values from the 2nd and 3rd octect.

I'm confused on not using any of the values from the 1st octect and not sure.

thanks

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Comments

bud08

http://www.techexams.net/forums/ccna-ccent/60468-explain-me-subnetting-question.html

Ltat42a

Remember, the network 10.0.0.0 is a Class A network (default mask is 255.0.0.0). So.... a /20 gives you an extra 12 bits for subnetting, 12 bits for hosts. 2(12) = 4096 (subnets); 2(12)-2 = 4094 (hosts).

SharkDiver

Ltat4a is completely correct.
The fact that is is a class A network is the third variable.
If they had asked the same question of a 172.16.0.0/20 network, you would get a different number of subnets, but the same number of hosts.

j-man

I've said it in the subnetting made easy thread but Always figure out what class network you're dealing with.

Class A: first 8 bits are network
Class B: first 16 bits are network
Class C: first 24 are network

Anything above 224.... you know the rest.