available hosts per subnet

gaby_978gaby_978 Member Posts: 222
in CCNA & CCENT
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 you spend too much time thinking about a thing,
you'll never get it done"
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  • markzabmarkzab Member Posts: 619
    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.
    "You, me, or nobody is gonna hit as hard as life. But it ain't how hard you hit; it's about how hard you can get hit, and keep moving forward. How much you can take, and keep moving forward. That's how winning is done!" - Rocky
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  • BeaverC32BeaverC32 Member Posts: 670 ■■■□□□□□□□
    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).

    quick.jpg
    MCSE 2003, MCSA 2003, LPIC-1, MCP, MCTS: Vista Config, MCTS: SQL Server 2005, CCNA, A+, Network+, Server+, Security+, Linux+, BSCS (Information Systems)
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  • gaby_978gaby_978 Member Posts: 222
    thank you guys.. i am actually reading it over again today and the more i readit the clearer it gets..
    ‎"If you spend too much time thinking about a thing,
    you'll never get it done"
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  • markzabmarkzab Member Posts: 619
    Don't forget the read the FAQ section on subnetting. The explanations in there are invaluable(sp?).
    "You, me, or nobody is gonna hit as hard as life. But it ain't how hard you hit; it's about how hard you can get hit, and keep moving forward. How much you can take, and keep moving forward. That's how winning is done!" - Rocky
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  • Noe84Noe84 Member Posts: 60 ■■□□□□□□□□
    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.
    On to MCSA 2003.
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  • ArmandArmand Member Posts: 2 ■□□□□□□□□□
    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.
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  • blackninjablackninja Member Posts: 385
    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
    Currently studying:
    CCIE R&S - using INE workbooks & videos

    Currently reading:
    Everything. Twice ;)
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  • ArmandArmand Member Posts: 2 ■□□□□□□□□□
    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!
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  • KaminskyKaminsky Member Posts: 1,235
    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.
    Kam.
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