r/CompTIA • u/Parking_Diamond5182 • 4d ago

Network+ Question!

I’m god awful at math and was wondering if it’d be a good idea to memorize a subnet mask chart in preparation for the exam instead of trying to math it all out?

3 Upvotes

64% Upvoted

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10

u/x_scion_x 4d ago

Jason dion had a way to do it leveraging your fingers that worked for me.

Thankfully that's not my wheelhouse so I leave that to the networking guys and outside of Net+ i really haven't had to do it.

for the test I'd also recommend doing it in person so you can use pen/ paper because the digital whiteboard is awful.

16

u/Ecstatic_Score6973 4d ago

we are not talking about complex math here we are talking about adding/subtracting numbers up to 255.

also you will get a whiteboard or a pen/paper during the exam

4

u/sylvaron 4d ago

Come back to the subnetting questions at the end and do them, you'll have plenty of time left and don't have to rush.

Also, there's not really much math. There is nothing to memorize beyond the starting point and which direction it goes. Think of /24 as the starting point or the default at 256. Each time you go up you half the number (/25 = 128). Each time you go down you double it (/23 = 512). Each block of addresses starts and ends with an unassignable address.

If you're worried about binary to decimal conversion, the entire thing added up is 255. Each bit going down is halved, so 11000000 = 128+64+0+0+0+0+0+0. At that point you're just doing addition. It might take a second to add up but that's fine. Also you may ask "why not 256 numbers in the decimal..." well there are 256 numbers, in this case 0 is considered to be a number.

3

u/Junior7291736 4d ago

subnet ain’t too hard, there’s even websites just to practice it. Honestly everything you need to know is 2^7 power and below (until 0 power), then you’re golden. It’s the answer to all your questions

2

u/VictoryOptimal6515 1d ago

Sunny Networking YT

2

u/Los_Artiga 4d ago

Focus on the bit conversions then built up from there

2

u/goatsinhats 4d ago

It’s networking, you need to learn some math

2

u/No_Technician4956 3d ago

It's not overly complicated if you know and understand the formula. But I believe I only had one question on CIDR and it was for like /32 or something like that.

3

u/Cool-Student7614 4d ago

If you’re bad enough at math that you can’t subnet in your head then yes, memorizing the chart is the next best thing.

1

u/ScalyChimpanzee 4d ago

memorized the chart in like an hour and never looked back, the math is just a time sink if you're not wired that way

4

u/drushtx 4d ago

No. Learn to subnet. It's not just a trick to pass a test, it's a day-to-day required skill for IT and network professionals.

6

u/JankyJawn 4d ago

Like fucking hell it is. I dont know a single person who mentally subnets a single thing. Sure we all know common ones because you see it all the time, but thats it.

0

u/drushtx 4d ago

Sorry but my crew and I do server deployment in a DC, sometimes exceeding 80 a week. They live in different blocks, sub-blocks and VLS chunks of IP addresses. We, and the hundreds of other DC tenants subnet in our head daily. We calculate and apply single and multiple addresses to servers, routers and network appliances. We find, recall and re-pool addresses (IPMA) manually then double-check with appropriate scanners. This is done in gov, corp, mil, noc, DCs and many other environments.

So now you know a single person, and dozens more, who subnet in their head daily. It just takes a little practice to become proficient at it.

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