available hosts per subnet

Ok guys i just started the ccna study about 2 weeks ago so dont know much yet... My question is, whats the fastest way to calculate hosts availability on a /whatever subnet... i went to an interview and they asked me how many host are availabe in a /30 subnet... i knew hot to calculate this with pen and paper LAST WEEK (already forgot have not had a chance to open the book since). i know some people have thier ways of calculating this in their head fast and i need help on this.

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Comments

markzab

gaby_978 wrote:

Ok guys i just started the ccna study about 2 weeks ago so dont know much yet... My question is, whats the fastest way to calculate hosts availability on a /whatever subnet... i went to an interview and they asked me how many host are availabe in a /30 subnet... i knew hot to calculate this with pen and paper LAST WEEK (already forgot have not had a chance to open the book since). i know some people have thier ways of calculating this in their head fast and i need help on this.

If I were you I wouldn't look for a quick fix in regards to subnetting. Some people will argue this but it may just be the single most important thing you learn while studying for your CCNA. Open the book and read your chapter on subnetting over and over and over again until you have it mastered. Also, the FAQ has a ton of great threads to help you learn different ways to subnet.

But to answer your question...

/30 = 252

256 - 252 = 4 - 2 = 2

2 hosts per subnet.

BeaverC32

I have to say I agree with Markzab....master subnetting now, and you'll remember it for life (like riding a bike). I personally found that once I understood how and why it works, you will be able to subnet faster than Quick Draw McGraw (if he ever subnetted).

gaby_978

thank you guys.. i am actually reading it over again today and the more i readit the clearer it gets..

markzab

Don't forget the read the FAQ section on subnetting. The explanations in there are invaluable(sp?).

Noe84

I usually put inside my head, it's the remaining bits that is the host portion, if you convert decimal to binary and compare an IP address or network address to it's subnet mask, using the Boleean AND (1x0=0, 1x1=1) the 0 is the host portion 2^remaining bits -2.

Armand

markzab wrote: »

Don't forget the read the FAQ section on subnetting. The explanations in there are invaluable(sp?).

I'm new to the forum...been looking for the FAQ..can someone please point me to it? Thanks.

blackninja

Armand wrote: »

I'm new to the forum...been looking for the FAQ..can someone please point me to it? Thanks.

That'll be the section marked **CCNA FAQ** - Please read before posting.

http://www.techexams.net/forums/ccna-ccent/6434-ccna-faq-please-read-before-posting.html

Armand

blackninja wrote: »

That'll be the section marked **CCNA FAQ** - Please read before posting.

http://www.techexams.net/forums/ccna-ccent/6434-ccna-faq-please-read-before-posting.html

Thank you!

Kaminsky

Also search this forum for "subnetting" for extra hints and tips. This is a common topic in this forum so you will get all sorts of very usefull information.