Subnetting

n our previous model, we relied on a network ID, subnet ID, and host ID to deliver an IP datagram to the correct location. With CIDR ...

the network ID and subnet ID are combined into one.

A single eight-bit number can represent 256 different numbers, or more specifically,

the numbers 0 - 255

Some of the bits in the Host ID are used for what

the subnet ID

Because of the constraints of how logic gates work inside of a processor, it's way easier for computers to

think of things only in terms of zero and one.

If you want to communicate with the IP address 9.100.100.100, core routers on the Internet know that....

this IP belongs to the 9.0.0.0 class A network.

What do we still say there are 256 available address when only 254 can be assigned?

this is because those other IPs are still IP addresses, even if they aren't assigned directly to a node on that subnet.

255.255.255.0 is what in bits?

translates to 1111 1111 . 1111 1111. 1111 1111. 0000 0000 24 ones and 8 zeros

In computer logic one represents what

true

The way the or operator works is you look at each digit, and if either of them is

true, the result is true

A subnet mask is a binary number that has

two sections

CIDR expands on the concept of subnetting by using

ubnet masks to demarcate networks.

The part of the subnet mask that is all zeros tell us what?

what to keep

the subnet mask, which is the part of the number with all the ones, tells us

what we can ignore when computing a host ID.

demarcation point

where one network or system ends and another one begins.

The problem with gateway router looking for the host ID is...

class A networks have 16 million addresses and that is too many devices to connect to a single router.

Each part of an IP address is an octet, this means...

It consists of eight bits xxxx xxxx .xxxx xxxx .xxxx xxxx .xxxx xxxx

Decimal to Binary

decimal: Base10 (10 digits) binary: Base2 (we only have 1's and 0's)

Finally, the host ID is used by that last router to

deliver the datagram to the intended recipient machine.

In computer logic zero represents what?

false

Once your packet gets to the gateway router for the 9.0.0.0 class A network, that router is now responsible for...

getting that data to the proper system by looking at the host ID.

in general, a subnet can usually only contain two less than the total number of

host IDs available

How is X or Y equals Z read?

if either X or Y is true then Z is true, otherwise, it's false.

This practice not only simplifies how routers and other network devices need to think about parts of an IP address,

it also allows for more arbitrary network sizes.

subnet mask

it is used to identify network address of an IP address by perfoming a bitwise AND operation on the netmask. A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address. - are 32-bit numbers that are normally written now as four octets in decimal.E

The operator AND does what it sounds like it does, it returns true

it returns true if both values are true 1 AND 1 = 1 1 AND 0 = 0 0 AND 0 = 0

The size of the subnet is defined by the

its subnet mask

subnetting was introduced when it became clear that address classes themselves were not an effective way to what?

keeping everything organized

So for example, with the subnet mask of 255.255.255.0, we know that

only the last octet is available for host IDs, regardless of what size the network and subnet IDs are.

CIDR basically just abandons the concept of address classes entirely, allowing an address to be defined by

only two individual ids

That gateway router then has some additional information that it can use to (subnet ID)

send that datagram along to the destination machine or the next router in the path to get there.

At the internet level, core routers only care about the network ID and use this to

send the datagram along to the appropriate gateway router to that network.

demarcate

set the boundaries or limits of

gateway router

specifically serves as the entry and exit path to a certain network.

Subnet IDs are calculated via what's known as a

subnet mask

The subnet mask 255.255.255.224 would translate to 27 ones followed by five zeros. What does this mean?

subnet mask that doesn't draw its boundaries at an entire octet or eight bits of address. 1111 1111 . 1111 1111. 1111 1111. 1110 0000

The purpose of the mask or the part that's all ones is to

tell a router what part of an IP address is the subnet ID.

The numbers in the remaining octets that have a corresponding zero are

the Host ID

Individual subnets have there own individual gateway routers serving as...

the ingress and egress point for each subnet.

Addition in binary 0+0=

0

9.100.100.100 As far as an IP address is concerned, having a number 9 as the first octet is actually represented as

0000 1001 (Since each octet needs eight bits we need to pad some zeros in)

The entire representation of the IP address 9.100.100.100 is what in bits?

0000 1001 . 0110 0100 . 0110 0100 . 0110 0100

9.100.100.100 The number 100 is represented as what in binary. (an eight bit number)

0110 0100.

Addition in binary 0+1=

1

addition in binary 1+0 =

1

addition in binary 1+1=

10 - you carry a digit to the next column once you reach 2 when doing binary edition.

9.100.100.100 In this IP address the number 9 is represented by what it bits?

1001

For 9.100.100.100, a Class A network, we know that this is just the first octet. We have how many octets left?

the last three octets

/24 net is 8 host bits

2 to the 8 power = 256

However if you use /23 network which is 9 bits (CIDR)

2 to the 9th power = 512 this means you have 510 hosts available

a 16 bit number in decimal would be?

2 to the power of 16 which equals 65,536

A four bit number would be express how in decimal?

2 to the power of 4 which equals 16

If you have an eight bit number you can just perform the math two to the power of eight, this give you what?

2 to the power of 8 which equals 256

256 - 2 =

254 available ip to assign

even if it's understood that two addresses aren't available for assignment, you'd still say that eight bits of host IDs space have

256 addresses available, not 254.

if you need two networks of this size 254 +254 =

508 available IP host available

Let's take 9.100.100.100 with a net mask of 255.255.255.0. How would this be written with a CIDR notation?

9.100.100.100/24.

How do you represent the ip address 9.100.100.100 with a subnet mask of 255.255.255.224

9.100.100.100/27

Network id

A number used in IP networks to identify the network on which a device or machine exists.

With all three of these IDs representable by a single IP address, we now have a single 32-bit number that can...

be accurately delivered across many different networks.

CIDR (Classless Inter Domain Routing)

A subnetting method that selects a subnet mask that meets an individual network's networking and node requirements and then treats the mask like a 32-bit binary word.

operator

Addition is what's known as an operator and there are many operators that computers use to make calculations.

1 or 0 equals 1 0 or 0 equals 0

both true

The Core router then route the message to a gateway router responsible for the network by...

by looking at the network ID.

With traditional subnetting each class had how many bits available?

Class A = 16 bits Class B = 8 bits Class C = 4 bits

CIDR notation

Classless Inter Domain Routing (CIDR) is a method for assigning IP addresses without using the standard IP address classes like Class A, Class B or Class C. Ex. /24 /32 /16

255.255.255.0

Default Class C Subnet Mask

255.255.255.224

Expressed as a /27 using CIDR notation because there are 27 1s in the subnet mask

Two of the most important operators are...

Or and And

The numbers in the remaining octets that have a corresponding one in the subnet mask are the

Subnet ID IP Address: 0000 1001 . 0110 0100 . 0110 0100 . 0110 0100 Subnet mask: 1111 1111 . 1111 1111. 1111 1111. 0000 0000`

What is the problem with having 2,970,152 class C networks?

That is a lot of entries on a routing table

Subnet ID

The 16 bits, or one block, in an IPv6 address that can be used to identify a subnet on a large corporate network.

Subnetting

The act of dividing a network into smaller logical subnetworks.

Base 2

The name given to the counting system for Binary

Host ID

The portion of an IP address that identifies the host on a network, as determined using the subnet mask.

core router

These main core computers act like traffic cops for packets. They mainly speak to other core routers

Before this, if a company needed more addresses than a single class C could provide, they need an entire second class C. With CIDR,

They could combine that address space into one contiguous chunk with a net mask of /23 or 255.255.254.0.

How many subnet addresses does 255.255.255.224 have?

This means that we have five bits of host ID space or a total of 32 addresses.

The basic equation of an OR operation is...

X or Y equals Z

Base 10

a decimal number system represented by symbols 0,1,2,3,4,5,6,7,8,9

A subnet mask is a way for a computer to use and operators to determine if...

an IP address exists on the same network. This means that the host ID portion is also known, since it will be anything left out.

This means that there might only be 254 classing networks in existence, but it also means

are 2,970,152 potential class C networks.

using a subnet mask of 255.255.255.0, we know that the octet available for host IDs can contain the numbers 0-255. Why are two of those numbers not available?

zero is generally not used and 255 is normally reserved as a broadcast address for the subnet. so only 1 -254 available

The beginning part, which is the mask itself is a string of ones, what comes after this

zeros 1111 1111 . 1111 1111 . 1111 1111 . 0000 0000