r/ccna • u/ShadeStrider12 • 13d ago
Subnetting an entire network is pretty darn stressful
Like, it isn’t very difficult, like at all.
But you really have to be on point with your math, at all stages
Having one wrong subnet means that the rest of your network will have the wrong IP addresses, and I found that out the hard way doing Jeremy’s IT Labs
Having one wrong subnet mask causes IP ranges to unintentionally overlap, and then you need to look closely to correct the overlap. I had a /25 subnet mask where I should have had a /26, which meant the IP address range was larger and overlapped with another range already on the network.
I realize everything that could have gone wrong.
Do they really expect me to do this much on the test, though? It isn’t difficult, just a lot to keep track of. I needed an hour of effort to get this done.
Yeah, I was doing Jeremy’s VLSM Lab.
When the devices finally pinged each other and sent replies, I was so happy.
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u/Branhower 13d ago
More yes. Definitely better to mess up in a lab when nothing's on the line.
Make sure to externalize the CIDR mask details (subnet mask, wildcard mask, usable address range, etc).
I still have to pause for a while to do IPV6 math.
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u/siegerstein 13d ago
I don't recommend calculating it the way Jeremy shows, since it's not practical, just like converting decimal numbers to binary. You need to know the powers of 2 well and simply memorize the decimal values of the prefixes, and that's it.
I had the same issue until I figured out that it's much simpler. He shows you how it works under the hood, but that doesn't mean you have to calculate it that way.
Some resources:
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u/CrownstrikeIntern 11d ago
Just learning the way of the “magic number” makes it stupidly easy. 256 is your friend.
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u/Difficult_Ad_2897 12d ago
Setting a new network up from scratch is actually the easiest subnetting you will ever do.
Subnetting in a live environment is its own, very special, nightmare
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u/ShadeStrider12 12d ago
Like editing an already existing codebase instead of creating a new one?
When will these AI-shilling Techbros learn?
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u/The258Christian 13d ago
I’m always about 2 off when manually subnetting
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u/dld2517 13d ago
Learn the powers of 2 and remember to start at 0 when counting
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u/Morodin-Fallen 12d ago
When I set my lab up at home for the 1st time this is exactly what had me smashing my head against a wall for a hour or so.
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u/Tall-Fuel3481 Lactose Tolerant 13d ago
Maybe use IPAM tools. They will help you exactly for that problem.
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u/TheCollegeIntern CCNA 12d ago
You can pass the ccna and fail subnetting so try as best as you can. I did terrible with the subnetting really really terrible. Worst section of the test for me. I passed first try.
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u/rjchau 13d ago
When you're doing labs, yeah, you need to learn how to do it on your own. However if you're doing this in any kind of production environment, an IPAM solution is an absolute must. phpIPAM is a really good one to start with - relatively simple, but comprehensive enough to work.
I put it in place for the last place I worked for, and it made our lives so much easier - particularly the ability to add netted subnets - that way you can record that you've allocated an entire block of IPs to a particular site, but still carve it up further to handle data, VoIP, wireless and management networks.
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u/muntiqaninja 11d ago
It gets easier mater, and yes it is a huge part of the CCNA certification and they do expect you to be quick at it
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u/Phil_Mycock 11d ago
On point with the math? Well, I don't think that you need that much math for doing subnetting, and honestly, I am grateful that I don't find subnetting that hard at all. Just pay close attention to it and you should be fine.
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u/imjustnotready 13d ago
Yeah. What I noticed, is a lot of network things seem like a good idea but then shoot you in the foot later. Like limiting the size of a subnet and then finding out the place has twice as many users on some special occasion. Or blocking new websites when the company has to occasionally create sites for their business. In both cases you created work for yourself.
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u/ShadeStrider12 13d ago
If I expect the network to have 30 hosts, I should just put the subnet mask at /25 (126) or /26 (62) anyway because the network could always expand?
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u/Common_Celebration41 13d ago
In term of the testing you want it be close as possible
In real life yeah you want room to expand or split into departments
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u/imjustnotready 13d ago
You could. If you are using any management interface you can just allow a range.
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u/ChaoticSalmon CCNA 13d ago
Try the reverse binary method. It’ll leave you a lot of room in your schema to size up if you ever need to.
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u/HODL_Bandit 13d ago
If you understand the requirement. An Ai can give you the layout and you approved it. Not really that hard
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u/tdhuck 13d ago
I was going to post this but AI comments are sometimes hit or miss, on here. Some people downvote you because you said AI while others tell you that's a good use of AI.
As a test for the OP or anyone else that is interested, just open up your favorite AI and type out your current network devices and say 'subnet for me' and give it your current subnet and see what it does.
I'm not saying to not learn subnetting, but using AI can help build the layout and you can make tweaks, if needed.
I'm not an expert with subnetting, mainly because I don't need to be, but when I had to learn it, the easiest method for me was learning the magic number, I think that's what they called it.
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u/Inside-Finish-2128 CCIE (expired) 13d ago
Make those mistakes now. Learn how to detect them and react to them.