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Internet Structure | Internet Hierarchy | Internet Backbone | ISP | DHCP| How IP Address is Assigned - YouTube
Channel: ISO Training Institute
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this first illustration models the mysterious聽
cloud view of the internet casual users see聽聽
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information go into and come out of the internet聽
and they understand what kinds of information and聽聽
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services are available female services web聽
pages online retailers banking institutions聽聽
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and more but they may not understand how that聽
information is networked together let's take a聽聽
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closer look at the structure of the Internet聽
so the cloud is not so mysterious this next聽聽
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illustration begins to show how the Internet is聽
networked together in a little more detail it聽聽
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shows how the Internet is arranged loosely into聽
a hierarchy at the top of the hierarchy is what聽聽
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is referred to as the backbone of the Internet聽
the backbone of the Internet consists of the聽聽
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largest set of Internet service providers or ISPs聽
as they're called an ISP is an organization that聽聽
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owns controls and maintains a large number of聽
the computer networking cables and networking聽聽
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devices that make the internet possible these聽
largest ISPs include corporations governments聽聽
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and in some cases large academic organizations the聽
connections linking the biggest ISPs together are聽聽
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modeled by red arrows in this illustration these聽
arrows represent the network cables that carry聽聽
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the most information most Internet traffic must聽
travel through one of these backbone connections聽聽
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at some point as it travels across the net as聽
we work our way down the hierarchy we see that聽聽
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there is a tier of medium-sized ISPs these medium聽
sized ISPs are responsible for considerably less聽聽
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Internet traffic and considerably fewer cables聽
and networking devices then the backbone ISPs are聽聽
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but they are still responsible for a huge amount聽
of traffic in this illustration the blue arrows聽聽
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represent the Internet traffic between these聽
medium ISPs and the backbone ISPs above them聽聽
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the green arrows represent the connection聽
between the medium ISPs and an organization聽聽
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further down the hierarchy as we can see in the聽
illustration a business with its own private聽聽
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internal network might connect its many users聽
directly to one of these blue medium-sized ISPs聽聽
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however a residential user might connect to the聽
media of ISPs through an even smaller local ISP聽聽
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these small local ISPs that connect residents聽
to the Internet are often controlled by a local聽聽
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cable company or a local phone company the聽
connection between the smallest tier of ISPs聽聽
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and an individual residence is represented here聽
by a purple arrow the connection represented by聽聽
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the purple arrow might carry a lot of information聽
streaming video file downloads or maybe online聽聽
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games but that quantity of information is just聽
nothing compared to the quantity represented by聽聽
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the arrows higher up on the hierarchy so there it聽
is this illustration shows us how Internet service聽聽
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providers are organized into a hierarchy with聽
the ISPs on the top handling the most data and聽聽
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the ISPs and residents on the bottoms handling the聽
leased data this next illustration shows something聽聽
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else as you may already know every device that聽
is connected to the Internet has a unique address聽聽
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called an IP address this illustration shows聽
a couple different ways that IP addresses get聽聽
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assigned to devices this diagram includes three聽
fictional networks the X Y Z office network聽聽
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the ABC office network and the Jose coffee shop聽
network to keep the diagram relatively simple the聽聽
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rest of the Internet has been condensed down into聽
a cloud in the middle of the illustration first聽聽
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let's take a look at the XYZ office network on the聽
left side of the illustration those red numbers聽聽
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are the IP addresses for the whole network every聽
IP address is numerical like that they are always聽聽
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written as four sets of digits each separated聽
by a period each of these four sets of digits聽聽
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can be any number from 0 to 255 so take a look at聽
the IP address of the XYZ network it's 1 97.1 2聽聽
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15.0 all of the devices connected to the XYZ聽
network will be assigned IP addresses that聽聽
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begin with the first three sets of digits one聽
nine seven point one to point one five device聽聽
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IP addresses ending in zero are restricted and聽
device IP address is ending in 255 are also聽聽
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reserved so in practice the range of possible IP聽
addresses for devices on this network are point聽聽
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one to point two fifty four as we can see in the聽
illustration the router at the XYZ office network聽聽
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has been assigned the IP address ending in point聽
two five four meanwhile Carole's desktop computer聽聽
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has been assigned the IP address ending in point聽
one zero there are 252 IP addresses remaining聽聽
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and the available range for this network the XYZ聽
office network uses static IP address assignments聽聽
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static IP addresses are unchanging that means聽
that for the foreseeable future Charles desktop聽聽
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has been permanently assigned this particular IP聽
address 197 point one to point one five point one聽聽
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zero is permanently reserved for her computer聽
the opposite of static IP address assignment is聽聽
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dynamic IP address assignment for an example of聽
dynamic IP address assignment let's take a look聽聽
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at the ABC office network over on the right side聽
of the illustration the ABC office network is at聽聽
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the IP address two 07.10.2012 the network can use聽
any IP address starting with those first three聽聽
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numbers and ending with any number from 1 to 254聽
for example on this network if the router took the聽聽
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IP address ending in 254 Bob's computer took the聽
address ending in 1:5 and Alice's computer took聽聽
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the address ending in 5 but unlike the XYZ network聽
the ABC office Network uses dynamic IP addresses聽聽
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instead of static IP addresses this means that聽
some of these IP addresses are subject to change聽聽
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you see the ABC office network has a special piece聽
of hardware called a dynamic host configuration聽聽
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protocol server or a DHCP server as it's often聽
abbreviated the dynamic host configuration聽聽
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protocol server assigns a device one of the 254聽
possible Network IP addresses each time a device聽聽
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begins a new internet session the DHCP server will聽
lease each IP address for a set period of time and聽聽
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after that time passes then the device will have聽
to renew its lease I know that I'm throwing a lot聽聽
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of new information at you but I promised that the聽
underlying concept isn't very difficult all we're聽聽
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saying is that for example Bob's computer has the聽
IP address is ending in 0.15 for now but it might聽聽
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be assigned a new IP address once the hour is聽
up what are the advantages and disadvantages of聽聽
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dynamic IP addresses versus static IP addresses聽
well the advantage of a static IP address like聽聽
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Carol has on her computer is that her IP address聽
is always available to her she has a reserved聽聽
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place on Browder when IP addresses are assigned聽
to dynamically as they are for Bob's computer聽聽
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over here then there's a chance that there won't聽
be any room for him Lee tries to connect to the聽聽
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network if the DHCP server has already assigned聽
all the IP addresses available to it then there聽聽
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won't be any left for Bob the advantage of dynamic聽
IP address assignment is that dynamic assignments聽聽
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are more flexible thousands of different devices聽
could connect to the ABC network and as long as聽聽
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they don't all try to connect at the same time the聽
DHCP server can assign them all an IP address on聽聽
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the network let's look down at the bottom of this聽
illustration to see one more network configuration聽聽
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that also uses dynamic IP address assignments聽
Joe's coffee shop network is at IP address two聽聽
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zero seven point one zero point three point zero聽
this means that device is connected to it can聽聽
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take the IP addresses beginning with those three聽
numbers and ending with a number between 1 and 250聽聽
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for over the course of say a month a coffee shop聽
could probably expect to have many more than just聽聽
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254 devices connect to their wireless connection聽
but at any given time throughout this day it would聽聽
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probably have only a few devices connected that聽
maybe 50 or so this is a perfect situation for聽聽
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dynamic IP address assignments the network only聽
has 254 IP addresses that it can assign but it can聽聽
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easily accommodate all of its users by assigning聽
these addresses on a temporary basis only to the聽聽
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users for active on the network but remember聽
when we were examining the ABC office network聽聽
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connection we saw that a network needs a dynamic聽
host configuration protocol server in order to聽聽
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accommodate dynamic IP addressing where is the聽
DHCP server at Joe's coffee shop the answer is聽聽
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that it Joe's coffee shop the DHCP server is聽
combined with the internet router instead of聽聽
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the router and the DHCP server being two separate聽
devices they're integrated together into a single聽聽
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device this is pretty common most home internet聽
routers also have DHCP servers built into them聽聽
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and so most home networks can accommodate聽
dynamic IP address assignments so what are聽聽
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the big takeaways from this illustration I want聽
you to see that a computer's IP address usually聽聽
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depends on a routers IP address I also want you聽
to see that your device's IP address can change聽聽
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depending on what network it's on and depending聽
on whether the network uses dynamic or static IP聽聽
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address assignment finally I want you to note the聽
structure of an IP address that it's four numbers聽聽
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separated by periods the last illustration that we聽
will examine in this lecture models the difference聽聽
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between a public IP address and a private IP聽
address in our discussion of IP addresses so far聽聽
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we have not been making the distinctions between聽
public and private IP addresses I've been speaking聽聽
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as if all IP addresses are the same but there is a聽
significant difference between public IP addresses聽聽
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and private IP addresses this illustration shows聽
two different networks that are connected to the聽聽
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Internet Alice's home network and Bob's home聽
network Alice's home network is composed of two聽聽
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devices a router and Alice's computer Bob's home聽
network is composed of four devices a router Bob's聽聽
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computer Carol's computer and a printer let's take聽
a look at Bob's home network on the right side of聽聽
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this illustration Bob's local Internet service聽
provider has only assigned him one IP address聽聽
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that he would like to connect two computers to聽
the Internet his in Carol's and furthermore he'd聽聽
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like to connect his wireless printer to his home聽
network the rules of IP require that every device聽聽
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has its own IP address but Bob's internet service聽
provider has only given him one IP address to work聽聽
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with so what does Bob do he will use his router聽
to create a private home network to connect his聽聽
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four devices together and then he'll connect聽
his entire home network to the public Internet聽聽
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through the IP address that his internet service聽
provider has assigned him from the perspective聽聽
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of somebody outside on the public Internet Bob聽
appears to have only one device connected to the聽聽
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Internet and that's his router but Bob's router聽
can coordinate Bob's public internet connection聽聽
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with multiple devices on his private network so聽
from within the private network we can see that聽聽
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there are really three more devices connected聽
to the public Internet through Bob's router now聽聽
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let's compare Bob's home network to Alice's聽
home network on the bottom left portion of聽聽
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the illustration both networks have a public IP聽
address and those public IP addresses are unique聽聽
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indeed every public IP address must be unique聽
however Bob's and Alice's routers help them聽聽
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to create private networks and these private聽
networks can reuse the same IP addresses for聽聽
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example we can see that Alice's computers private聽
IP address is identical to Bob's computers private聽聽
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IP address this repetition is possible because of聽
the distinction between their private IP addresses聽聽
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and their public IP addresses it's kind of like聽
how every apartment building in a city must have聽聽
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a unique street address for the post office聽
to deliver mail to but at each unique street聽聽
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address the apartment buildings can reuse the same聽
apartment numbers okay I know that we've covered聽聽
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a lot of ground here with these illustrations so聽
let's take a break in the next video we'll examine聽聽
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a few more illustrations that will help us to see聽
how information is routed through the Internet
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