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Net Bits


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#1
starjax

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I'm having some problems wrapping my head around this thing called Net Bits and CIDR (subnet mask) notation.
If someone could help me understand it, I would be greatly appreciated.

165.218.92.0/24 really equates to 165.218.92.0-165.218.92.255
/24 = 0-255

/22 = 1024 What would be the equivilant ip notation?
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#2
dsenette

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to understand that you've got to break each octet into binary...they call them an octed because each section of the netmask (or ip) is represented by an 8 digit binary number (i think that's a byte?)...so you've got a 4 byte subnet...or a 32 bit subnet (since there are 8 bits in a byte and 4 bytes in a subnet mask)....so the /24 denotes how many bits of the subnet denote the network id...leaving the rest as the node id

so if your ip were 192.168.202.44/24 then the first 24 bits (which would be the first 3 full blocks) would be the network id and the last 1 is the node id

so your /22 would be the first 22 bits of the ip address...so lets say your ip was 192.168.0.1 then in binary that would be 11000000.10101000.00000000.00000001 so...you count over 22 bits from the left to 11000000.10101000.000000 (notice that's 6 bits into the 3rd octet)...the simple translation here is that anything that's going to be a subnet mask in a binary IP has to be all 1s...so you make that into 11111111.11111111.11111100.00000000 to be the full subnet mask when you do your binary conversions on all them onesies you get 255.255.252.0 which would be a 22 bit subnet and you could have 4 class c subnets with 1024 hosts per subnet....this is the most confusing thing i've ever had to type...and i hate you for it

the easy answer is to get a subnet calculator

http://en.wikipedia....-Domain_Routing
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#3
starjax

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that was almost the most confusing thing I've had to ready and I hate you back for it.


actually I found this: http://xtronics.com/...subnetmasks.htm

I think I understand some of it. What I don't get is the relation ship between a defined ip range. say 192.168.1.0 through 192.168.1.255 compared to the subnet mask.


or rather perhaps I don't undstand subnet masking itself.... no wait that isn't it.... God I love google define: feature.



165.218.98.0 through 165.218.98.128 gives the notation of
165.218.0 /25
which in turn makes the subnet mask of 255.255.255.128

verified with http://www.subnet-ca...or.com/cidr.php


god it makes sense now.
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#4
dsenette

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yeah....CORNFUSTIGATION!! the key to understanding how to do this stuff without a calculator is to understand how to translate ip's and subnet masks into dotted binary numbers... it get;s REALLY REALLY funky
...i was gonna explain some more..but i confused myself :whistling:
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#5
starjax

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I don't care about the binary part. Just the relationship between ip address range and subnet mask. That and be able to translate between standard notation and cidr.

context:
we just consolidated one site from 2 buildings to one. Number if ip ranges were eleminated. Also we are taking the voip phones and moving them from a single ip range (/220 to 4 ip ranges (/24). This gives the phone network greater redunance.

I get the cidr notation, but my software requires standard notation for input (security scanning). My report program is in cidr. I wasn't the one who set it up orgiginally, but I get to maintain it. It was driving me nutz.

mucho gracias.
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#6
dsenette

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I don't care about the binary part. Just the relationship between ip address range and subnet mask. That and be able to translate between standard notation and cidr.

hehehe that's the problem...the relationship between the IP address and the subnet mask and the formation there of is all based on the IP notation....for the desription of what you need (heck for any network needs) a subnet calculator is the way to go...the last time i had to do this crap manually....was in school
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#7
Dryfter

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When I went and took my CCNA test. I hated Cisco for that. I got like 3 or 4 question about that stuff. I understood it but it was a nightmare. I probably should start studing again and go take it.
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#8
diabillic

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And then you learn about supernetting..
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#9
dsenette

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i'll kill you cilix...i'll kill you dead!!!!
*dsenette 's brain explodes
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#10
starjax

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I love what this guys has to say about supernetting http://www.firewall....tting-chart.php


:whistling:
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#11
peterm

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Starjax
I don't know if I like you or hate you for that link to supernet

Cheers
Peterm
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#12
diabillic

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Haha, its fairly easy once you start using it. I know when i first learned about subnetting and how difficult it looked whereas its actually quite simple to figure out. Supernetting isnt all that much different, just a few more things involved when determining network and ip ranges.
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