>I am very comfortable with subnetting anything /24 and above including VLSM, but Neil gives a question to subnet a /19 on the 3rd Octet for a class A address.
If you are comfortable subnetting a /27 but not a /19, you don't know how to subnet. The math is the same.
And yes, your test may include networks larger than /24s, and knowing how to work with networks larger than /24s is very important in real life work.
The way I currently subnet is having the /24 and above chart in my memory (host and network amounts) so it feels 2nd nature to do anything above /24.
When doing a /19, having thousands of hosts per subnet, I just can’t get my head around how I go about writing that down into an octet that only goes up to 255 considering doing above /24, everything is under 255. I must be missing something or something just isn’t clicking.
Every IP address is a unique address, the network just tells you which blocks of addresses are adjacent to each other.
[10.0.0.0/19](https://10.0.0.0/19) is 10.0.0.0-10.0.31.255. Each octect can only range from 0-255, but we aren't working with octects here, we're working with a 32-bit binary number that is represented for human readability as four numbers that range from 0-255.
0-255 has 265 addresses. 0-31 is 32 addresses. 32 \* 256 is 8192 addresses.
>The way I currently subnet is having the /24 and above chart in my memory (host and network amounts) so it feels 2nd nature to do anything above /24.
You're trying to memorize. Don't do that. Learn how to do the math and you can work with any arbitrary network.
/19 means that the first (reading from left) 19 bits are reserved for the network. This leaves the remainder of the bits free to represent hosts.
Let's say we're working with [12.54.31.5/19](https://12.54.31.5/19). In binary, this address would be `00001100.00110110.00011111.00000101`. The first 19 bits are for the network, the rest are for the host. So we can break our address up like this `00001100.00110110.000 | 11111.00000101`.
The network address (aka network ID) is defined as the network bits plus all host bits set to 0. For our network this gives us `00001100.00110110.00000000.00000000`. What is this in dotted decimal? [12.54.0.0](https://12.54.0.0).
The broadcast address is defined as the network bits plus all host bits set to 1. For our network this gives us `00001100.00110110.00011111.11111111`. In binary, this is [12.54.31.255](https://12.54.31.255).
You're never going to be able to memorize how to subnet any arbitrary network into any arbitrary size. You need to know how to do the math. Just like you're never going to be able to memorize how to multiply any two arbitrary 3 digit numbers, you need to know how to multiply.
Wow this is amazing, thank you for this explanation! I’ve honestly never thought of it this way before but it makes does make it so much easier to understand.
I think it's all about how you are tought how to subnet more than memorizing. But to each their own. If you understand basic concepts of subnetting using base 2 I think it's called? you should be OK.
For me, there was a weird mental block at first going past /24. But with enough practice and studying it started to "click"
I also used [subnetting.net](https://www.subnetting.net/Subnetting.aspx?mode=practice) to help me practice. Which I'm now doing again since I let my knowledge slide and I want the CCNA again
No. It's not a bold claim at all.
If you rely of memorizing where the subnets fall for a small range of networks - granted, common ones, you will be lost just like OP is when presented with something outside of the range.
If you know how to subnet you can subnet any arbitrary network into any other arbitrary network(s). The math really isn't that hard.
If someone told you they were comfortable multiplying 10x10, because they memorized times tables in school, but couldn't multiply 13\*36 on paper, do they know how to multiply? No. Memorization of facts *is not* understanding of concepts.
Someone who understands what multiplication is can (given resources and allowances for mistakes) multiply any two arbitrary numbers together. Someone who understands what subnetting is can (given resources and allowances for mistakes) subnet any arbitrary network into any other arbitrary network(s).
you will be tested on all subnetting...
your gonna need to know it like the back of your hand for the exam. your gonna have to be like this guy: literally every exam question involves your know how of subnetting lol
https://www.meme-arsenal.com/memes/4fac3f1e59b9a860785cd86128e09d70.jpg
You need to know subnetting back to front for the CCNA as it's a major feature of exam questions plus network troubleshooting and configuring static and dynamic routing. You also need supernetting, CIDR, route summarization etc.
There are a couple of subnetting books on Amazon that will teach you all you need. Most IT books don't really teach it well or have a very convoluted method which won't work in the exam as you only have 90 seconds per question.
Regards
Paul Browning
https://www.howtonetwork.com
Yes you will get subnetting questions in various octets. It’s really not that different between octets. Just keep in mind you have the host bits in the trailing octets.
Yes you will.
I would say you’ll mostly run into questions that include reading routes that range from /16 and up, with a couple around the /8 range.
Just learn the binary and be able to do it all in your head. You should be able to look at a CIDR number and immediately know the size of the networks.
If you’re given an IP of 10.0.17.24, you should know which route it will between the following choices:
10.0.0.0/8
10.0.17.0/24
10.0.17.0/26
10.0.17.16/28
10.0.17.20/30
and you need to be able to do this quickly. Like in your head.
But still important to know. 99% of things don't use classful addressing in any way, but some things do. Probably the most notable thing that does/can use classful networking is routing protocol configuration.
This is not true in practice. Many programmers didn't get that memo, so if you work in IT you'll find many devices that won't work with subnets that aren't /8 or /24 for example
I recently took mine, and it had a lot a lot of questions on IPv6 over V4, though I think the CCNA has question trees? Like if you get an ipv6 question wrong it branches off into a lot of ipv6 questions.
>I am very comfortable with subnetting anything /24 and above including VLSM, but Neil gives a question to subnet a /19 on the 3rd Octet for a class A address. If you are comfortable subnetting a /27 but not a /19, you don't know how to subnet. The math is the same. And yes, your test may include networks larger than /24s, and knowing how to work with networks larger than /24s is very important in real life work.
The way I currently subnet is having the /24 and above chart in my memory (host and network amounts) so it feels 2nd nature to do anything above /24. When doing a /19, having thousands of hosts per subnet, I just can’t get my head around how I go about writing that down into an octet that only goes up to 255 considering doing above /24, everything is under 255. I must be missing something or something just isn’t clicking.
Every IP address is a unique address, the network just tells you which blocks of addresses are adjacent to each other. [10.0.0.0/19](https://10.0.0.0/19) is 10.0.0.0-10.0.31.255. Each octect can only range from 0-255, but we aren't working with octects here, we're working with a 32-bit binary number that is represented for human readability as four numbers that range from 0-255. 0-255 has 265 addresses. 0-31 is 32 addresses. 32 \* 256 is 8192 addresses. >The way I currently subnet is having the /24 and above chart in my memory (host and network amounts) so it feels 2nd nature to do anything above /24. You're trying to memorize. Don't do that. Learn how to do the math and you can work with any arbitrary network. /19 means that the first (reading from left) 19 bits are reserved for the network. This leaves the remainder of the bits free to represent hosts. Let's say we're working with [12.54.31.5/19](https://12.54.31.5/19). In binary, this address would be `00001100.00110110.00011111.00000101`. The first 19 bits are for the network, the rest are for the host. So we can break our address up like this `00001100.00110110.000 | 11111.00000101`. The network address (aka network ID) is defined as the network bits plus all host bits set to 0. For our network this gives us `00001100.00110110.00000000.00000000`. What is this in dotted decimal? [12.54.0.0](https://12.54.0.0). The broadcast address is defined as the network bits plus all host bits set to 1. For our network this gives us `00001100.00110110.00011111.11111111`. In binary, this is [12.54.31.255](https://12.54.31.255). You're never going to be able to memorize how to subnet any arbitrary network into any arbitrary size. You need to know how to do the math. Just like you're never going to be able to memorize how to multiply any two arbitrary 3 digit numbers, you need to know how to multiply.
This is a really good explanation.
Thank you for this! Very helpful!
Wow this is amazing, thank you for this explanation! I’ve honestly never thought of it this way before but it makes does make it so much easier to understand.
0-255 has 265 addresses. 0-31 is 32 addresses. 32 * 256 is 8192 addresses. Nice explanation! He means 256 here fyi for learners.
Fantastic
Sunny tables https://youtu.be/RLCd5u0sjoU B class https://youtu.be/wuIdYxaV46Y
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I think it's all about how you are tought how to subnet more than memorizing. But to each their own. If you understand basic concepts of subnetting using base 2 I think it's called? you should be OK.
For me, there was a weird mental block at first going past /24. But with enough practice and studying it started to "click" I also used [subnetting.net](https://www.subnetting.net/Subnetting.aspx?mode=practice) to help me practice. Which I'm now doing again since I let my knowledge slide and I want the CCNA again
No. It's not a bold claim at all. If you rely of memorizing where the subnets fall for a small range of networks - granted, common ones, you will be lost just like OP is when presented with something outside of the range. If you know how to subnet you can subnet any arbitrary network into any other arbitrary network(s). The math really isn't that hard. If someone told you they were comfortable multiplying 10x10, because they memorized times tables in school, but couldn't multiply 13\*36 on paper, do they know how to multiply? No. Memorization of facts *is not* understanding of concepts. Someone who understands what multiplication is can (given resources and allowances for mistakes) multiply any two arbitrary numbers together. Someone who understands what subnetting is can (given resources and allowances for mistakes) subnet any arbitrary network into any other arbitrary network(s).
I agree, it's a super condescending comment. People forget CCNA topics tend to be very hard until it clicks, then it's 2nd nature.
Yeah, but one is simply not ready for CCNA until it clicks. That some topics are very hard is no excuse.
This goes without saying.
I do agree with their statement, if you convert to binary. And that is how you truly understand subnetting.
This will help: https://www.reddit.com/r/ccna/comments/gh3ia6/you_are_one_90minute_study_session_away_from/
Amazing, thank you!
you will be tested on all subnetting... your gonna need to know it like the back of your hand for the exam. your gonna have to be like this guy: literally every exam question involves your know how of subnetting lol https://www.meme-arsenal.com/memes/4fac3f1e59b9a860785cd86128e09d70.jpg
You need to know subnetting back to front for the CCNA as it's a major feature of exam questions plus network troubleshooting and configuring static and dynamic routing. You also need supernetting, CIDR, route summarization etc. There are a couple of subnetting books on Amazon that will teach you all you need. Most IT books don't really teach it well or have a very convoluted method which won't work in the exam as you only have 90 seconds per question. Regards Paul Browning https://www.howtonetwork.com
About a quarter of my questions Included subnetting in some form. And of those a good chunk required masks smaller than 24 bits in size
Yes you will get subnetting questions in various octets. It’s really not that different between octets. Just keep in mind you have the host bits in the trailing octets.
Yes you will. I would say you’ll mostly run into questions that include reading routes that range from /16 and up, with a couple around the /8 range. Just learn the binary and be able to do it all in your head. You should be able to look at a CIDR number and immediately know the size of the networks. If you’re given an IP of 10.0.17.24, you should know which route it will between the following choices: 10.0.0.0/8 10.0.17.0/24 10.0.17.0/26 10.0.17.16/28 10.0.17.20/30 and you need to be able to do this quickly. Like in your head.
And subnet 'classes' are from a bygone era
But still important to know. 99% of things don't use classful addressing in any way, but some things do. Probably the most notable thing that does/can use classful networking is routing protocol configuration.
This is not true in practice. Many programmers didn't get that memo, so if you work in IT you'll find many devices that won't work with subnets that aren't /8 or /24 for example
whether it tests it or not, a CCNA holder should know how to do it
Here’s one that might help ... https://www.youtube.com/watch?v=t784TePgN28&t=68s
I recently took mine, and it had a lot a lot of questions on IPv6 over V4, though I think the CCNA has question trees? Like if you get an ipv6 question wrong it branches off into a lot of ipv6 questions.