Okay.
Welcome back everyone.
In this lecture we are going to focus on address resolution protocol or AARP so how AARP works.
You know that they're in every local network every device has an IP address and a MAC address the IP
addresses you get 32 bit numbers there to present how the device is perceived by other devices but if
you want to communicate in the local network for example if you want to communicate with the P.C. that
is connected to the same Wi-Fi connected to a same local network.
Then in order to communicate with that machine what you have to do is you need to know their MAC address
because IP address is only used when you want to communicate with the Internet on the network devices
that are outside.
You heard local network.
What if you want to communicate within your network to do this you have to do to know the MAC address
of this device but how do we know the MAC address to do this are to get the MAC address off other devices.
We use a protocol called ERP so it provides a mapping between IP addresses and the MAC addresses.
So what this protocol basically does is that you input an IP address and a two turns the MAC address
of this device and then once you have the MAC address you can use it to communicate our exchange package
with that device.
So how in this lecture we're going to focus on how we can discover clients on a similar network our
local network.
So let's say we have a P.C. and then we have a router and then we have other devices for example your
phone your desktop P.C. or something else your iPod whatever it is.
So let's say you want to discover which client it is.
So the first idea is to bring the client all the clients in the network.
And once you bring these devices you get the responses bags and then by analyzing their responses you
know what B ratio is and then these devices return and IP value which which represents the address of
this machine.
For example let's say I am sitting in a room and I say whose name is let's say John.
Everyone except John will stay quiet.
And then John will say yes I am John.
So basically this is how AARP works.
So AARP says Who is it ABC.
Who is X.
And then the person or whoever it is whose name is X or John or whatever it is.
He replies back with an answer.
And they've stayed quiet.
So this is how ERP works.
Okay.
So in this lecture we are going to see a practical visual representation of how this algorithm works.
So first thing you have a device let's say this is your device which has an IP address of phone line
to that 16 you don't see two or 13 and this has a MAC address which is this value.
And then there is a router in your network or gateway that is used to communicate with external Internet.
So this address.
His address is when they do that 1 6 8 0 0 dot 1.
And most of the time you will find that every voter has the same address because it's a convention that
is used in the local media and local media network.
And then you have three other devices.
Now let's say you want to communicate with this address on 9 2 1 6 8 0 0 dot 25.
And this is your machine.
So how do you communicate this.
P.S. Our device communicates with this device.
So in order to do this entry it sends an ERP request and there are different types of request but this
type of request will be called who has a request.
So what this request does is basically it sends out an IP address and then it sends this IP address
to everyone abroad broadcasts this IP to add to every device in the network.
So this package goes here here here and here.
So every device receives their address.
And once the request has been reached each device.
This is called broadcasting basically.
So once this has every device will verify this request with its own IP address.
So this will check if it if the request IP address is the same IP address as my own machine.
Similarly this hotel will do the same.
And this machine and this machine will do the same.
Once this has verified that this will be done false because it is 1 9 2 1 6 8 0 0 0 that one is not
equal to this value.
And similarly this will return false and this will returns false but this will return true because this
value is the same value as this one.
So as I know you said that you showed for example whose name is John and then only John will reply because
his name is John.
Similarly this device will now send back and response.
This is called ERP response and then it will say my name.
I have a mac address of this thing.
This value.
So and response it will replay as it will replace his own MAC address reaches 1 1 0 a 95 96 8 2 4.
So in this way this device has an ERP table.
So what the ERP table is basically a list which contains a mappings of IP addresses and their MAC addresses.
So something like this for example device number one the IP address and then the MAC address once the
they get back so response it updates it ERP develop it for example 1 9 2 1 6 8 0 dot 25 and then it
updates the Mac field as this value and then it tries to communicate with it.
So this is how ERP communication or ERP protocol or network works.