Subnetting for Dummies

MeastMeast Posts: 36Banned ■■□□□□□□□□
Hey Guys,

I can't believe this but I'm having the hardest time grasping subnetting, and I know once I get this down everything will come naturally.

Whats the foundation on learning how to subnet, especially doing it in your head, I'm great math, any ideas would be greatly appreciated!!!!

Comments

  • MonkerzMonkerz Posts: 842Member
    What are you having troubles with? Seeing a netmask and trying to figure out how many hosts and subnets you get? Having a CIDR and trying to figure out hosts and subnets?
  • abefromanabefroman Posts: 278Banned
    Meast wrote: »
    Hey Guys,

    I can't believe this but I'm having the hardest time grasping subnetting, and I know once I get this down everything will come naturally.

    Whats the foundation on learning how to subnet, especially doing it in your head, I'm great math, any ideas would be greatly appreciated!!!!

    Remember the commond numbers:
    Ie:
    /24 is a cblock 256 ips and the subnet mask is 255.255.255.0
    /25 is half of a /24 or 128 ips so the subnet is 255.255.255.128
    /26 is half of a /25 or 64 so the subnet is 255.255.255.192 (128+64=192)

    So if you have a /26 and it says something like is this a valid host address:
    192.168.1.64
    no, thats a network address

    192.168.1.127
    no thats a broadcast address

    192.168.1.193
    yes, valid hosts for that subnet are 192.168.1.193-254 (62 ips)

    /23 is 2 /24's or 512 and the subnet mask is 255.255.254.0
    /22 is 4 /24's or 2 /23's or 1024 ips and hte subnet mask is 255.255.252.0

    Also like for a /22 to find the 3rd octet its 4 cblocks - 256 = 252

    /32 is 1 ip
    /31 is 2 ips
    /30 is 4 ips
    etc.

    Before the test you probably want to right down /16 - /32, what the subnet mask is for those, and how many ips there.

    HTH
    Next certs:
    CCNA 99.9999999999999999999999999999999% Ready

    There are /31 types of people in this world, those who understand subnetting, and those who don't
  • miller811miller811 Posts: 897Member
    Meast wrote: »
    Hey Guys,

    I can't believe this but I'm having the hardest time grasping subnetting, and I know once I get this down everything will come naturally.

    Whats the foundation on learning how to subnet, especially doing it in your head, I'm great math, any ideas would be greatly appreciated!!!!

    here is a great place to start

    http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html
    I don't claim to be an expert, but I sure would like to become one someday.

    Quest for 11K pages read in 2011
    Page Count total to date - 1283
  • captobviouscaptobvious Posts: 648Member
    miller811 wrote: »
    +1

    Made subnetting click in my head!
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