Seven-Second Subnetting - N10-008 CompTIA Network+ : 1.4

Summary

This 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

• 🔢 The 'seven-second subnetting' is a shortcut method for quick subnetting during exams, minimizing complex math.
• 📈 It relies on pre-made charts for subnetting values, making calculations faster and more accessible.
• 💻 The method is especially useful for online exams where a digital whiteboard is provided for note-taking.
• 📝 It's beneficial to practice creating and using these charts to become proficient before an exam.
• 🖊️ Having a chart ready is crucial for the seven-second subnetting method to work effectively.
• 📑 The script suggests creating a chart summarizing CIDR-block notations for each octet of an IP address.
• 🔄 The process involves converting IP addresses and subnet masks to decimal values for easier calculation.
• 📉 The method also includes calculating network and broadcast addresses, as well as usable IP address ranges.
• ⏱️ With practice, subnetting calculations can be performed quickly, often in seven seconds or less.
• 📝 It's recommended to bring your own dry erase marker to exams for easier chart writing and reading.
• 🤔 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

00:00

🔢 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.

05:00

📝 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.

10:00

📉 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.

15:02

🖊️ 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.

Keywords

💡Subnetting

Subnetting refers to the process of dividing a network into smaller networks, known as subnets. This is crucial for efficient IP address allocation, traffic management, and network organization. In the video, subnetting is the central theme, with the presenter discussing methods to perform subnetting calculations quickly, such as the 'seven-second subnetting' process.

💡Magic Number Method

The Magic Number Method is a shortcut for performing subnetting calculations. It involves using predefined numbers to determine the network and broadcast addresses. The video mentions this method as an alternative to the 'seven-second subnetting' process, suggesting that viewers compare both methods to find the one that suits them best.

💡CIDR Block Notation

CIDR (Classless Inter-Domain Routing) Block Notation is a system used to define IP address spaces. It is represented as a combination of an IP address and a prefix length, such as /24. In the video, CIDR notation is used to explain how to quickly convert between CIDR and decimal notation for subnet masks.

💡Subnet Mask

A Subnet Mask is a 32-bit number that divides the IP address into network and host portions. It is crucial in determining the network address, broadcast address, and the range of IP addresses within a subnet. The video discusses how to convert CIDR notations to subnet masks and their role in subnetting.

💡Decimal Value

Decimal Value in the context of networking refers to the numerical representation of an IP address or subnet mask in decimal form. The video emphasizes the importance of converting CIDR notations to decimal values for subnet masks to facilitate quick subnetting calculations.

💡Network Address

The Network Address is the identifier for a specific subnet and is used for routing purposes. The video explains how to calculate the network address by using the subnet mask and the given IP address, which is essential for understanding subnetting.

💡Broadcast Address

The Broadcast Address is used to send data to all devices on a particular subnet. The video describes how to determine the broadcast address by using the subnet mask, which is key to understanding how data is transmitted within a network.

💡Usable IP Address

Usable IP Addresses are the IP addresses within a subnet that can be assigned to devices. The video explains the calculation of the first usable IP address (one more than the network address) and the last usable IP address (one less than the broadcast address).

💡Seven-Second Subnetting

Seven-Second Subnetting is a method described in the video for quickly calculating subnetting values. It involves using charts and shortcuts to perform calculations rapidly, which is particularly useful for certification exams where speed is important.

💡Digital Whiteboard

A Digital Whiteboard, as mentioned in the video, is a tool that can be used to create and manipulate charts and diagrams during an online exam. It is relevant to the discussion of subnetting in a testing environment where physical whiteboards might not be available.

💡Certification Exam

Certification Exams, such as those for Network+ or other IT certifications, often require knowledge of subnetting. The video is tailored towards individuals preparing for these exams, emphasizing quick and efficient subnetting methods to succeed in a timed testing environment.

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.