Aaron
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Registered: 9th Aug 04
Location: Cottingham, East Riding
User status: Offline
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I've working in IT for a fair while, but the logic behind subnetting is something i've always struggled with (and mental arithmetic in general)
I've decided to pull my finger out with this and try to get the process hard-wired in my brain due to an exam i'm studying to pass.
Anyway, could someone in the know take a look at the workings in the following link and see if you agree it's accuracy?
Cheers
http://imageshack.com/a/img822/6992/qfv5.jpg
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Kyle T
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Registered: 11th Sep 04
Location: Selby, North Yorkshire
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EVERYONE has a different way of doing it. Writing out a quick "sheet" like your picture really helped me, though mine was more of a grid to show the patterns of each CIDR notation, once familiar with it I could work out pretty much any question about subnetting within 5 or 6 seconds.
Wonder if I've got one lying around somewhere from when I did CCNA, I even drew my sheet out on the whiteboard when taking my exam - helped loads.
Your scenario looks good to me.
Lotus Elise 111R
Impreza WRX STi
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pow
Premium Member
Registered: 11th Sep 06
Location: Hazlemere, Buckinghamshire
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Looks good to me. I do very similar to you, using the binary to work everything out. Never found a grid helped me. The more you use it the more you just start to know it.
Unless you were really struggling for space (like a couple of schools I've worked win that have assigned class A ranges), you'd pretty much always use a /24 mask in a class A range for subnetting in the real world. Certainly all I've ever come across or implemented myself.
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Aaron
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Registered: 9th Aug 04
Location: Cottingham, East Riding
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I think i've got my head around class B now. I've been over-complicating it due to the additional octet..but i think i'm there now.
http://imageshack.com/a/img716/8603/9rw1.png
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pow
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Registered: 11th Sep 06
Location: Hazlemere, Buckinghamshire
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Put the Network Addresses in there (192.168.1.0/24 for example) to help it flow as well 
Network number, Network Address, Usable IPs, Broadcase Address
[Edited on 15-02-2014 by pow]
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Aaron
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Registered: 9th Aug 04
Location: Cottingham, East Riding
User status: Offline
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Indeed
Class A to come, but i think I should be ok.
I feel as though i'm re-lighting parts of my brain to do the "simple" binary calculations. Then there's the "to the power of" calculations to work out how many networks or hosts are required.
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pow
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Registered: 11th Sep 06
Location: Hazlemere, Buckinghamshire
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Class A is a piece of piss. Like I said, in the real world you use 10.1.x.x with a mask of 255.255.255.0 to give you 256 networks with 254 usable addresses on the whole unless you are doing something BIG
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pow
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Registered: 11th Sep 06
Location: Hazlemere, Buckinghamshire
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...and then if you need a bigger subnet just change the mask ofcourse
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Aaron
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Registered: 9th Aug 04
Location: Cottingham, East Riding
User status: Offline
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quote:
Originally posted by pow
Class A is a piece of piss. Like I said, in the real world you use 10.1.x.x with a mask of 255.255.255.0 to give you 256 networks with 254 usable addresses on the whole unless you are doing something BIG
Yeah we use class A addresses for the networks which we support, however, because some of these schools have over 2000 devices, the subnets have to be altered to accommodate this
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pow
Premium Member
Registered: 11th Sep 06
Location: Hazlemere, Buckinghamshire
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Yeah standard, my last place had a guest subnet with a 255.255.0.0 mask lol
[Edited on 15-02-2014 by pow]
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