Seven-Second Subnetting - N10-008 CompTIA Network+ : 1.4
Summary
TLDRThis video script introduces a 'seven-second subnetting' shortcut for quick subnet calculations, ideal for certification exams. It emphasizes creating reference tables for fast lookup of subnet masks and CIDR notations, avoiding complex math. The method involves converting IP addresses and masks to decimal, determining network and broadcast addresses, and calculating usable IP ranges. It also suggests practicing creating charts for exam readiness and using personal markers for clarity.
Takeaways
- π’ The 'seven-second subnetting' is a shortcut method for quick subnetting during exams, minimizing complex math.
- π It relies on pre-made charts for subnetting values, making calculations faster and more accessible.
- π» The method is especially useful for online exams where a digital whiteboard is provided for note-taking.
- π It's beneficial to practice creating and using these charts to become proficient before an exam.
- ποΈ Having a chart ready is crucial for the seven-second subnetting method to work effectively.
- π The script suggests creating a chart summarizing CIDR-block notations for each octet of an IP address.
- π The process involves converting IP addresses and subnet masks to decimal values for easier calculation.
- π The method also includes calculating network and broadcast addresses, as well as usable IP address ranges.
- β±οΈ With practice, subnetting calculations can be performed quickly, often in seven seconds or less.
- π It's recommended to bring your own dry erase marker to exams for easier chart writing and reading.
- π€ The method may be overkill for exams with few subnetting questions but can be advantageous for more complex exams.
Q & A
What is the 'seven-second subnetting' process mentioned in the script?
-The 'seven-second subnetting' process is a shortcut method for quickly performing subnetting calculations, typically used during certification exams. It involves creating reference tables to avoid complex mathematics and allows for fast subnetting by referring to predefined values within those tables.
Why is the 'seven-second subnetting' method designed primarily for exams?
-The method is designed for exams because it allows candidates to subnet very quickly without getting bogged down in complex mathematical calculations, which can be confusing under exam conditions.
What are the challenges of using the 'seven-second subnetting' process?
-One of the main challenges is that it requires having reference charts readily available. Additionally, if taking an exam online, one must be able to create and use these charts digitally, which might be more difficult than writing them out on a physical whiteboard.
How does the 'seven-second subnetting' process handle different subnet masks?
-The process takes into account that different subnet masks follow the same format and uses charts to convert CIDR-block notation to decimal notation quickly. It also helps to determine the number of networks and addresses per subnet associated with each mask.
What is the significance of the subnet mask 255.255.255.0 in the 'seven-second subnetting' method?
-A subnet mask of 255.255.255.0 indicates a single subnet with a range of IP addresses from 0 to 255. Borrowing bits from this subnet allows for the creation of more subnets, each with a smaller range of host addresses.
Can you explain the concept of borrowing bits in subnetting as described in the script?
-Borrowing bits in subnetting refers to the process of using bits from the host portion of an IP address for network addressing. This increases the number of available subnets but reduces the number of host addresses in each subnet.
How does the script suggest converting IP addresses and subnet masks to decimal values?
-The script suggests using a chart that summarizes CIDR-block notations and their corresponding decimal values to quickly convert IP addresses and subnet masks to decimal values.
What is the role of the network and subnet boundary chart in the 'seven-second subnetting' process?
-The network and subnet boundary chart is crucial for determining the network and broadcast addresses without performing complex math. It provides predefined boundaries for different subnet sizes, simplifying the subnetting process.
Why is it beneficial to write out all network address subnet boundaries when using the 'seven-second subnetting' method?
-Writing out all network address subnet boundaries is beneficial because it provides a visual reference that makes it easier to quickly identify network and broadcast addresses, especially when dealing with smaller subnet sizes where mental calculations become more challenging.
How does the 'seven-second subnetting' method handle different IP address ranges such as /24, /26, and /20?
-The method uses a chart to quickly identify the decimal equivalent of the subnet mask and then determines the network and broadcast addresses based on whether the mask bit is a 255 (bring down the address) or a 0 (bring down a 0). For other values, it refers to the chart to find the appropriate address range.
What tips does the script provide for using the 'seven-second subnetting' method during an exam?
-The script suggests practicing creating the reference charts before the exam, possibly bringing your own dry erase marker to exams for easier writing, and finding a method that works best for you, whether it's seven-second subnetting, the magic number method, or a combination of both.
Outlines
π’ Seven-Second Subnetting Method
This paragraph introduces a quick subnetting method designed for certification exams, which minimizes the need for complex math. It emphasizes creating reference tables to facilitate rapid subnetting. The method involves converting IP addresses and subnet masks to decimal values, determining network and broadcast addresses, and calculating usable IP addresses. The speaker also discusses the challenges of using this method, such as the need for a prepared chart, and offers tips for adapting the method to one's preferences.
π Converting and Calculating Subnet Details
The paragraph demonstrates how to apply the seven-second subnetting method to calculate subnet details for a given IP address and various subnet masks. It explains the process of converting CIDR notation to decimal values, identifying network and broadcast addresses, and determining the first and last usable IP addresses. The example uses an IP address of 165.245.12.88 with different subnet masks (/24 and /26) to illustrate the method's efficiency and accuracy.
π Key to Seven-Second Subnetting: Understanding Subnet Mask and Host Range
This section delves deeper into the seven-second subnetting process, focusing on determining the network address based on the subnet mask and host range. It uses the same IP address with different subnet masks (/20) to show how changes in the mask affect the network, broadcast, and usable IP addresses. The importance of understanding where an IP address fits within a given range of addresses per subnet is highlighted as crucial for quick subnetting.
ποΈ Practical Tips for Subnetting During Exams
The final paragraph offers practical advice for using the seven-second subnetting method during exams. It suggests practicing creating the necessary charts and familiarizing oneself with the method to speed up the subnetting process. The speaker also shares personal experiences with bringing a preferred dry erase marker to exams for easier chart writing and reading. The paragraph concludes by encouraging individuals to find the subnetting method that works best for them, whether it's seven-second subnetting, the magic number method, or a hybrid approach.
Mindmap
Keywords
π‘Subnetting
π‘Magic Number Method
π‘CIDR Block Notation
π‘Subnet Mask
π‘Decimal Value
π‘Network Address
π‘Broadcast Address
π‘Usable IP Address
π‘Seven-Second Subnetting
π‘Digital Whiteboard
π‘Certification Exam
Highlights
Introduction to 'seven-second subnetting' as a quick exam technique.
Advantage of 'seven-second subnetting' over traditional methods.
Explanation of creating tables for subnetting references.
Comparison between 'seven-second subnetting' and 'magic number method'.
Challenges of using 'seven-second subnetting' in an online exam environment.
Importance of having a chart ready for the 'seven-second subnetting' process.
How borrowing bits affects subnetting and host ranges.
Use of CIDR-block notations for subnetting.
Avoiding math confusion during exams with pre-calculated values.
The necessity of a subnet boundary chart for 'seven-second subnetting'.
Conversion of IP address and subnet mask to decimal values.
Determining network and subnet addresses using the 'seven-second subnetting' method.
Calculating broadcast address and usable IP addresses quickly.
Example calculation for an IP address with a /24 subnet mask.
Example calculation for an IP address with a /26 subnet mask.
Example calculation for an IP address with a /20 subnet mask.
Example calculation for an IP address with a /11 subnet mask.
Example calculation for an IP address with a /17 subnet mask.
Practical tips for using 'seven-second subnetting' during an exam.
Suggestion to practice creating charts for exam preparation.
Personal experience with bringing a dry erase marker to the exam.
Recommendation to find a subnetting process that works best for the individual.
Transcripts
In previous videos, we performed subnetting manually,
we've used a magic number method as a shortcut,
and I wanted to give you the shortcut that I use when
I take a certification exam.
I call this my "seven-second subnetting" process.
This shortcut is designed for exams.
You're able to subnet very quickly,
and you don't have to perform a lot of mathematics
to confuse things while you're trying
to perform these calculations.
In fact, there's almost no math involved,
other than adding 1 and subtracting 1.
The first thing you would have to do is to create the tables.
And then once the tables are created, all of the subnetting
refers back to values within those tables.
You'll probably want to look at the magic number
method and the seven-second subnetting method
to see which one fits best for you.
And what you'll find is, as we go
through this seven-second subnetting video,
it seems that a lot of the process
is duplicated from the magic number method.
That's because there is really no other way
to perform subnetting other than the processes
that you see in both of these shortcuts.
But there are ways to customize it for the way
that you like to be able to subnet,
so feel free to grab from either or both of these methods,
and find a way to subnet that works best for you.
One of the challenges when using the seven-second subnetting
process is that it expects you to have a chart ready to go.
If you're sitting in a testing center,
they commonly give you a whiteboard
and a dry erase marker, which makes it a little bit easier
to create the chart.
But if you're taking your test online,
you still have a digital whiteboard
that you can type on.
So you may want to try typing these charts out manually, just
to see how well you can create and use them
if everything is online.
The seven-second subnetting process takes into account
that all of these different subnets follow the same format.
For example, a subnet mask of 255.255.255.0
gives us a single subnet.
But if we borrow a bit, we can have two subnets,
because our subnet mask would be 255.255.255.128,
and those two subnets would have host ranges between 0 and 127
and 128 to 255.
If we continue borrowing bits from the subnet,
we can separate it even further into four separate subnets.
Or in the case of 255.255.255.224,
we have eight separate subnets that we've
created all from that original subnet mask.
And obviously, the range for that particular subnet
is between 0 and 31, which is compared to the original range
of 0 to 255.
Knowing that these relationships are in place,
we can create some charts that can help us
with the subnetting process.
I like to use a chart that summarizes
all of the CIDR-block notations for the first octet,
the second octet, the third and the fourth.
And if you looked at our previous video
on the magic number method, then this chart
looks pretty familiar.
We then want to be able to calculate how many networks
would be on a network that had that subnet mask,
and how many addresses per subnet
that would be associated with.
We might also want to add the conversion to decimal
from that CIDR-block notation for each
of these individual masks depending on which
octet it happens to be in.
For example, if the octet is a /25,
we know in the fourth octet that our subnet mask value will be
128.
You can see with this chart created,
you can perform very fast calculations between CIDR-block
notation and decimal notation, and you also
have predefined numbers of networks and addresses
per network that you can also use during the subnetting
process.
I'm also exceptionally bad at multiplying and dividing
when I'm in an exam situation.
So in order to avoid any problems with the math,
I tend to write out all of the network
address subnet boundaries, especially between 32 and 4.
I can usually remember the 128's and the 64's, and usually 32,
but when you get to 16, 8, and 4 devices per subnet,
becomes difficult to exactly know
where the boundaries are for those particular host ranges.
This is the identical subnet boundary chart
that we created for the magic number method.
But for the seven-second subnetting method
it's almost required, especially if you
don't want to perform any math.
The seven-second subnetting process
begins with converting the IP address and subnet
mask to a decimal value, which is especially important if they
give you a CIDR-block notation, and of course we've
already created a chart that does that very, very quickly.
That chart also tells us the range
of IP addresses for each individual subnet as well.
Once we've done the conversion, we
can determine the network and subnet addresses--
that second chart shows us the different boundaries--
and then we can calculate our broadcast address,
and our first and last usable IP address.
You'll find as we step through this that this process goes
very quickly.
And by using the seven-second subnetting,
you actually can perform a subnet
and calculate all of these values in seven seconds
or less.
Let's calculate the subnet address, broadcast address,
first usable host, and last usable host for this address--
165.245.12.88/24.
We note that the /24 is relatively easy to do
in our head, but it makes for a good example to start
the seven-second subnetting tutorial.
Let's first convert the address and the subnet mask to decimal.
Obviously, the IP address is already in decimal,
but we need to convert that /24, so we'll go to our chart that
shows the /24 is our third octet,
and that is a decimal value of 255.
So we'll bring down the 165.245.12.88 by adding 255s
to the left of the value that we've created with the /24,
we'll add the /24 value of 255, and anything after that will be
a 0.
And you probably already knew that the subnet mask of a /24
is 255.255.255.0, but you can see how the chart that we have
really narrows down where the masks are for the /24
in the third octet, and how that decimal value is converted.
Now let's calculate the network or subnet address.
If our mask is 255, we're going to bring down the IP address.
So 255 and 255 and 255 are our first three octets,
so we're going to bring down all three of those addresses,
meaning that the first three octets of your network address
are 165.245.12.
If the subnet mask is a 0, we would bring down the 0.
So you can see here our subnet mask
in the fourth octet was 0, meaning
that our network address is a value of 165.245.12.0.
Now let's calculate the broadcast address.
If our subnet mask is 255, we're going
to bring down the address.
If the subnet mask is a 0, we're going
to bring down and use a 255.
This means that our broadcast address in this example
is 165.245.12.255.
Now the process for determining our first usable IP
address and last usable IP address
is simply adding 1 to the network address
and subtracting 1 from the broadcast address.
This means we'll calculate our first IP by referencing
that network address 165.245.12.1,
because we added 1 to our network address.
The last usable IP address is based on the broadcast address.
So we'll use 165.245.12, and then
we subtract 1 to make that 254.
Now we have all of the values we need for this particular subnet
of 165.245.12.88/24.
Let's use exactly the same IP address,
but this time, let's change our subnet mask.
Let's perform exactly the same process with 165.245.12.88/26.
The first thing we want to do is convert the IP address and mask
to decimal.
We'll look at that /26, we'll find that in our chart.
It's in our fourth octet, and we can see
that it correlates to a 192.
So in our fourth octet, we bring down the 1 and all of the other
octets for the subnet mask are 255,
meaning that a /26 converts to 255.255.255.192.
You'll also see, on that line with the /26 and the conversion
to the 192, that the number of networks is 4 and the number
of addresses is 64.
So 64 is our address range for the subnet.
So we're going to look at that single line of 64
to determine where this particular network happens
to be.
We're going to do that by looking at our IP
address of 165.24.12.88.
We know that 88 is associated with that 192.
We find the 88 is in this range between 64
and what is 127, or 1 minus the number
of the next particular range.
So that means that the value that we're looking for
or the subnet that we're interested in
is this subnet right here of 64 devices.
Let's now calculate the network address.
If our subnet mask is a 255, we're
going to bring down the address.
If our mask is a 0, we're going to bring down a 0.
And in this case, none of those octets happen to be 0.
And we have in that fourth octet a number that is not 255 or 0,
it's 192.
So we need to look at our chart and see that the 192 has
64 addresses per subnet.
We need to look at that 88 and see
where it is in that block of 64, and it
happens to be in that second block that also
starts with the value of 64.
So we bring down that 64 value, making our network address
165.245.12.64.
This multistep process of determining
what the subnet mask is, how many hosts happen
to be in that particular range, and where that range sits
in this chart is the key to the seven-second subnetting
process.
If you can perform that process very quickly,
everything else happens almost automatically.
Let's calculate the broadcast address.
We perform almost exactly the same process
as our network address.
If the mask is 255, we bring down the address.
If the mask is 0, we use a 255.
And in this case, the mask was not 0, it's 192.
So we go back to our chart we know that 192, we
have 64 addresses in that subnet,
we find where the 88 happens to be,
and then we look all the way down our chart
to determine what the next starting value is
in the next set of addresses.
And in this case, it's 128, so we subtract 1
from that to give us the broadcast address, which
is 165.245.12.127.
At this point, we have everything
we need to determine our first usable IP address
and our last usable IP address.
We add 1 to the network address to give us the first usable
IP, which is 165.245.12.65, and we subtract 1
from the broadcast address, giving us our last IP
address of 165.245.12.126.
Let's do another example, using exactly the same IP address,
but we're going to change the subnet mask to a /20.
The first thing we need to do is convert our IP address
and our subnet mask to decimal.
The IP address is already in decimal,
so we'll simply bring that down.
But then we have our /20.
So we want to come down to our /20 in our chart.
We can see that it's in the third octet,
and we know that the decimal version of that is 240.
So that means that our mask will be 255.255.240--
because it is in the third octet--
.0.
Now we can perform the calculation
for the network address.
We're going to, of course, highlight that line that has
the /20.
We know that that /20 has 16 addresses in a single subnet.
So we're going to also highlight the line that shows
all of the 16 host values.
Let's now calculate that network address.
If the mask is 255, we're going to bring down the IP address.
So our first two octets are 255.
If the mask is 0, we're going to bring down the 0.
And then for any other number, we refer to the chart.
We know that this subnet has 16 IP addresses in a subnet.
We know that we started with the value of 12, which
means it's in this very first range between 0 and 15.
Since it's in that first value of 0,
we would now bring that 0 down to identify the network
address, meaning the network address for this IP
is 165.245.0.0.
Now let's calculate the broadcast address.
If the subnet mask is 255, then we bring down the address.
If the mask is 0, we would bring down a 255,
and then we refer to our chart.
We know that we are with 16 addresses in the subnet,
and we would use the last address
in this range, which is a 15, meaning that our broadcast
address is 165.245.15.255.
And now the easy part, where we calculate
the first IP and the last IP based on the network address
and broadcast address, meaning that our first IP
is 165.245.0.1, and our last IP address is 165.245.15.254.
You can see that making simple changes to the subnet mask
changes the network address, broadcast address,
and the usable IP addresses for each of these subnets,
but you're able to use both of these charts
to determine any combination of these,
regardless of what subnet mask might be provided.
Let's change up our IP addresses and perform the same process
again.
In this case, we'll use 18.172.200.77/11.
We'll convert that IP address and subnet mask to decimal,
and we may want to look at our chart and see that a /11 is
in the second subnet, and we can see that it converts to a 224,
meaning that our subnet mask is 255.224.0.0.
Since we know that we're using that /11 or 224 in decimal,
we can highlight that line showing that there are 32
addresses per subnet, and we can highlight the 32 address range
in our lower chart.
Now let's determine what the network address is.
If the subnet mask is 255, we'll bring down our network number,
and if the mask is 0, we'll bring down the 0.
In the second octet, where it's neither 255 nor 0--
we have the value 224.
We know that this is the 32 addresses per subnet.
We have highlighted our 32-address range.
So let's take that value of 172 and see where
it fits in that entire range.
And you can see that it's the range between 160 and 191.
So since we're starting with 160,
this is our network address.
We'll add the 160, meaning that our network address is
18.160.0.0.
Now we'll calculate the broadcast address.
If the mask is 255, we'll bring down the address.
If the mask is 0, we will bring down the value of 255.
And again we'll refer to our chart, where we
have that second subnet of 32.
We also have in this range, starting with 160,
we know that it goes all the way up
to 191 because the next range starts with a 192.
So our broadcast address is 18.191.255.255.
And now we add 1 for the network address.
We can do that by adding 18.160.0.1.
And we subtract 1 from the last IP from the broadcast address,
making the last IP 18.191.255.254.
Let's do another one just for fun.
We'll do the same IP address of 18.172.200.77/17.
We will take our IP address, and then we'll
convert our subnet mask to decimal.
We'll look at that /17.
We can see that the /17 is in the third octet,
and it converts to a 128, so our subnet mask is 255.255.128.0.
We'll highlight that on the screen
so you can see that that 128 range has 128 addresses per IP
subnet, and we'll highlight that 128 range here
on the top of our chart.
Let's now calculate the network address.
If the mask is 255, we're going to bring down the IP address.
And if the mask is 0, we're going to bring down 0.
If it's any other value, then we're
going to have a look at the IP address, which is 200,
and we're going to see where that
fits in our particular range.
We can see that it's on a subnet where the first IP
address is 128.
So we're going to bring down the 128, making our network address
18.172.128.0.
Let's now calculate the broadcast address.
If the mask is 255, we're going to bring down our address.
If the mask is 0, we're going to bring down the value of 255,
and then we'll have a look at our third octet, where
we have the value 200.
We know in that particular range it
goes all the way to the end, which means
that it is going to be 255.
Our broadcast address, then, is 18.172.255.255.
And now you can add 1 to your network address
to get the first IP, so the first IP is 18.172.128.1.
And we subtract 1 from the broadcast address
to get the last IP, so that will be 18.172.255.254.
I recognize that the seven-second subnetting method
requires that you have these charts available in order
to perform these calculations.
But for me, when I'm in the middle of an exam,
this provides me with a lot of speed,
especially if I get a lot of subnetting questions.
With Network+, this might be a little bit overkill,
because you might get one, two, or maybe three subnetting
questions.
But if you take other certification exams
during your career that have much more subnetting,
you may find that this method helps you quite a bit.
So you might want to practice creating these charts
prior to starting your exam.
Try writing down the charts or try typing them out online,
so that you can be prepared for whatever method
you'll be using during your exam.
You'll find that it will take probably a minute or two to be
able to write down everything you're
going to need to perform a seven-second subnetting
process.
If you go into a testing center, they usually
give you a piece of laminated paper or a whiteboard
that you'll use for your exam.
One of the challenges, though, is
they often give you a pen with a very fat tip, making
it difficult to write out these very detailed charts.
I will often bring my own dry erase marker.
I'll check in with the front desk,
I make sure that they look over the pen,
and I ask permission to use that dry erase marker on the exam,
and they've always allowed me to do that on previous exams.
This makes the process of writing the chart
and perhaps more importantly reading the chart much easier
during the exam process.
Ultimately, you want to find the process that works for you.
If you think seven-second subnetting is too tedious,
try to have a look at the magic number method,
or find some happy medium between both
of these that is the perfect process for you to use
to be able to perform these subnetting calculations.
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