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# Subnetting for Dummies

Banned Posts: 36 ■■□□□□□□□□
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!!!!

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Member Posts: 842
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?
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Banned Posts: 278
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

192.168.1.127

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
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Member Posts: 897
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