How Many Subnets and Hosts Per

Nytrocide

I've been studying with SubnettingQuestions.com lately (and getting most of them right! ), but I seem to have trouble whenever I'm thrown a question like this...

How many subnets and hosts per subnet can you get from the network 172.30.0.0/23?

...with a CIDR of /23 that would make the network increment in 2s, right? From there how would I determine the number of hosts per? Wouldn't there have to be a network/broadcast for each, leaving none if it goes up by 2?

Thank you for any replies and sorry for the dumb question! =/

FloOz

11111111.11111111.11111110.00000000 = /23
It is a class B address so the first 16 bits are reserved for the network address. So you have to focus on what remains.

11111111.11111111.11111110.00000000

With the 1's that remain -> 2^7 = 128 subnets
With the 0's that remain -> 2^9-2 = 510 Hosts per subnet

Nytrocide

Thank you so much Flo0z! So simple...

What are you using to study? Apparently I've been using some crappy stuff...

FloOz

Jeremy Ciora's CBT Nuggets His subnetting style cleared everything up for me. Its so simple now.

Nytrocide

Awesome...grabbing that now then, thanks again!

dpjackal89

I watched the CBT nugget videos and they are awesome for subnetting. I liked it so much that I was going to skip the subnetting chapter in the Todd Lammle book but I read it anyway. Todd Lammle's subnetting explanation to my surprise was even better in my opinion. They are both great though.

FloOz

Yah I did the same except for Odom's book. I skipped his subnetting chapters to not confuse myself.

Nytrocide

One more quick question if you have time. I got the hosts correct on this one, but the total subnets way off.

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

Wouldn't that make it...

11111111.11111111.11110000.00000000 = /20

With the 1's that remain -> 2^4 = 16 subnets
With the 0's that remain -> 2^12-2 = 4,094 hosts per

...or should I be including some 0's as ones as well? (I can't wait to get home and get those Nugget videos!)

FloOz

Thats a Class A address so only the first 8 bits are reserved

11111111.11111111.11110000.00000000

2^12 =4096 subnets
2^12-2=4094 hosts per subnet

Nytrocide

Blah...I gotta get my address classes down as well. >_< Thanks!

FloOz

If you set aside just one day to learn how to subnet you will be golden. I practice 2-5 problems a day when I am bored to stay on my A game lol

JeanM

FloOz wrote: »

Jeremy Ciora's CBT Nuggets His subnetting style cleared everything up for me. Its so simple now.

Agreed! Chris Bryant's subnetting videos are good too!

mohamedshajid

this is great things to know but i'm always recommend to go with Todd Lammle because he's solving the subnetting in easy method perhaps it's dependent on the people how they concentrate on it.