Video Transcript
Quantum Networking (Part 2)
7m 2s
00:08
Welcome back. We've discussed schemes used for managing IP addresses
00:12
which naturally leads us to the concept of IP subnets.
00:16
We want to break off certain machines and put them into groups that we can talk to you at once.
00:21
In order to facilitate that we add what's called a subnet mask
00:26
which is a way to mask off a number of machines that will receive a certain broadcast.
00:31
When expressing subnets, we have the same concept as an IP address, 4 octets.
00:37
To give the simplest explanation,
00:39
a 255 in an octet means that the corresponding octet of the device IP will have to match to make that group.
00:47
A zero in an octet means a device can have any IP address in that place and be a member of the group,
00:53
as long as it meets the other conditions.
00:56
Values other than 255 and 0 are allowed in subnets, but we'll discuss those later.
01:02
So let's look at a common case.
01:04
Here is a subnet that includes the IP address 192.168.1.101
01:11
with a subnet mask of 255.255.255.0.
01:16
We know that all machines on this subnet must have 192.168.1
01:23
in the address due to the 255s in those corresponding places in the subnet mask.
01:29
We have a 0 in the last place, which would suggest that 0 through 255
01:35
would all be allowable values for an IP address to have in its last place and still be included in this subnet.
01:43
However, there are two special cases. The first address in the subnet range (0 in this example) is reserved to define the subnet.
01:54
And the last address is reserved as the broadcast address for that subnet.
01:59
So that leaves us with the following:
02:01
A subnet address of 192.168.1.0 , which defines the subnet.
02:08
A host range of 192.168.1.1-254, which are IP addresses that machines on the subnet can have.
02:19
And a broadcast address of 192.168.1.255;
02:25
that’s the address we can use to talk to all of these machines at once.
02:30
When subnets were originally specified, they were what we refer to now as ‘classful subnets’.
02:38
Each range was specifically defined.
02:41
A lot of the IP schemes we see now are holdovers from those original definitions.
02:46
Class A networks are defined as having first octets 1-126 with a subnet mask of 255.0.0.0.
02:57
The most commonly used subnet in the range is 10.0.0.0.
03:02
Note these subnets have up to almost 16.8 million possible hosts.
03:09
That’s never done these days, so if you’ve seen it, it’s mostly in the form of a more restrictive subnet.
03:16
Class B networks use the subnet mask 255.255.0.0 with the first octets of 128-191.
03:27
This allows for a little over 65,000 hosts per subnet, which is still a large number of devices.
03:34
The most common address schemes coming from this class are ones beginning in ‘172’.
03:40
Class C networks are the most common ones we see,
03:44
from your own home networks to those in our workplaces, etc.
03:48
These are small subnets with up to 254 devices.
03:52
Almost everyone has seen a 192.168.0.x or 192.168.1.x IP address if they’re looking.
04:03
And now that routers are so much less expensive and prevalent, subnets tend to be in this range or smaller.
04:10
There’s no need for a giant class A or class B subnet anymore.
04:14
Note that the IP ranges in the Class A, B and C network definitions are NEVER found on the internet.
04:23
These ranges are specifically set aside for internal networks.
04:27
Addresses of machines on the internet themselves
04:30
are very carefully set aside and assigned to avoid catastrophe.
04:36
We mentioned before that subnets could be defined outside of the rules
04:41
and classifications we just discussed.
04:42
Doing this is referred to as Classless Inter-domain Routing, or CIDR.
04:50
To explain, we’ll need to convert an IP address to binary… which is even more fun than hexadecimal.
04:57
Let’s say we wanted to start with IP address 192.168.1.1 and create a subnet smaller than class C.
05:06
The binary representation of that address is to the right.
05:10
Note a class C subnet would be represented as 24 ‘1’s from the right, with 8 ‘1’s representing 255 as a decimal.
05:21
To make our subnet one size smaller, we add a 25th ‘1’ to the subnet mask going from the right.
05:30
Every 1 in the subnet mask represents the bits in the address that define the network, so they’re called the ‘network’ bits.
05:39
The hostrange of the subnet is determined by the 0s in the subnet mask (represented here in dark blue).
05:47
If we convert all of this back to decimal we have a subnet mask of 255.255.255.128.
05:56
In what we call CIDR notation we specify the subnet address,
06:00
which is 192.168.1.0 with a slash and then the number of network bits, which is 25 in this case.
06:10
This makes the allowable hostrange 192.168.1.1 to 192.168.1.126.
06:19
The final address, 192.168.1.127 that becomes the broadcast address for the subnet.
06:27
So, does your head hurt yet? 'Cuz mine does!
06:31
You know, all of this seems complicated, but there are online calculators to make this easy.
06:37
Here are a couple of examples.
06:39
If you’re given an IP and netmask by corporate IT, you can easily find the host range.
06:46
If you need to define a custom subnet, you know can do that as well.
06:49
So, let’s take a break here, and in the next section we’ll dive into how to actually troubleshoot
06:56
some of these issues when you’re on a project site.
Video Transcript
Quantum Networking (Part 2)
7m 2s
00:08
Welcome back. We've discussed schemes used for managing IP addresses
00:12
which naturally leads us to the concept of IP subnets.
00:16
We want to break off certain machines and put them into groups that we can talk to you at once.
00:21
In order to facilitate that we add what's called a subnet mask
00:26
which is a way to mask off a number of machines that will receive a certain broadcast.
00:31
When expressing subnets, we have the same concept as an IP address, 4 octets.
00:37
To give the simplest explanation,
00:39
a 255 in an octet means that the corresponding octet of the device IP will have to match to make that group.
00:47
A zero in an octet means a device can have any IP address in that place and be a member of the group,
00:53
as long as it meets the other conditions.
00:56
Values other than 255 and 0 are allowed in subnets, but we'll discuss those later.
01:02
So let's look at a common case.
01:04
Here is a subnet that includes the IP address 192.168.1.101
01:11
with a subnet mask of 255.255.255.0.
01:16
We know that all machines on this subnet must have 192.168.1
01:23
in the address due to the 255s in those corresponding places in the subnet mask.
01:29
We have a 0 in the last place, which would suggest that 0 through 255
01:35
would all be allowable values for an IP address to have in its last place and still be included in this subnet.
01:43
However, there are two special cases. The first address in the subnet range (0 in this example) is reserved to define the subnet.
01:54
And the last address is reserved as the broadcast address for that subnet.
01:59
So that leaves us with the following:
02:01
A subnet address of 192.168.1.0 , which defines the subnet.
02:08
A host range of 192.168.1.1-254, which are IP addresses that machines on the subnet can have.
02:19
And a broadcast address of 192.168.1.255;
02:25
that’s the address we can use to talk to all of these machines at once.
02:30
When subnets were originally specified, they were what we refer to now as ‘classful subnets’.
02:38
Each range was specifically defined.
02:41
A lot of the IP schemes we see now are holdovers from those original definitions.
02:46
Class A networks are defined as having first octets 1-126 with a subnet mask of 255.0.0.0.
02:57
The most commonly used subnet in the range is 10.0.0.0.
03:02
Note these subnets have up to almost 16.8 million possible hosts.
03:09
That’s never done these days, so if you’ve seen it, it’s mostly in the form of a more restrictive subnet.
03:16
Class B networks use the subnet mask 255.255.0.0 with the first octets of 128-191.
03:27
This allows for a little over 65,000 hosts per subnet, which is still a large number of devices.
03:34
The most common address schemes coming from this class are ones beginning in ‘172’.
03:40
Class C networks are the most common ones we see,
03:44
from your own home networks to those in our workplaces, etc.
03:48
These are small subnets with up to 254 devices.
03:52
Almost everyone has seen a 192.168.0.x or 192.168.1.x IP address if they’re looking.
04:03
And now that routers are so much less expensive and prevalent, subnets tend to be in this range or smaller.
04:10
There’s no need for a giant class A or class B subnet anymore.
04:14
Note that the IP ranges in the Class A, B and C network definitions are NEVER found on the internet.
04:23
These ranges are specifically set aside for internal networks.
04:27
Addresses of machines on the internet themselves
04:30
are very carefully set aside and assigned to avoid catastrophe.
04:36
We mentioned before that subnets could be defined outside of the rules
04:41
and classifications we just discussed.
04:42
Doing this is referred to as Classless Inter-domain Routing, or CIDR.
04:50
To explain, we’ll need to convert an IP address to binary… which is even more fun than hexadecimal.
04:57
Let’s say we wanted to start with IP address 192.168.1.1 and create a subnet smaller than class C.
05:06
The binary representation of that address is to the right.
05:10
Note a class C subnet would be represented as 24 ‘1’s from the right, with 8 ‘1’s representing 255 as a decimal.
05:21
To make our subnet one size smaller, we add a 25th ‘1’ to the subnet mask going from the right.
05:30
Every 1 in the subnet mask represents the bits in the address that define the network, so they’re called the ‘network’ bits.
05:39
The hostrange of the subnet is determined by the 0s in the subnet mask (represented here in dark blue).
05:47
If we convert all of this back to decimal we have a subnet mask of 255.255.255.128.
05:56
In what we call CIDR notation we specify the subnet address,
06:00
which is 192.168.1.0 with a slash and then the number of network bits, which is 25 in this case.
06:10
This makes the allowable hostrange 192.168.1.1 to 192.168.1.126.
06:19
The final address, 192.168.1.127 that becomes the broadcast address for the subnet.
06:27
So, does your head hurt yet? 'Cuz mine does!
06:31
You know, all of this seems complicated, but there are online calculators to make this easy.
06:37
Here are a couple of examples.
06:39
If you’re given an IP and netmask by corporate IT, you can easily find the host range.
06:46
If you need to define a custom subnet, you know can do that as well.
06:49
So, let’s take a break here, and in the next section we’ll dive into how to actually troubleshoot
06:56
some of these issues when you’re on a project site.
Downloads and Links
Quantum Networking (Part 2)
7m 2s