So, guys, going forward, our protocol works using two types of messages, the up broadcast request
message and our reply message.
Now note that that the OP's request message is actually a broadcast message, whereas our reply message
is a unicast message.
Now, what does it mean by broadcast message and unicast message?
You will understand when we will be discussing the functionality of our protocol in detail in the coming
sleights.
Our messages never crosses the subnet boundary.
Now here are messages means board.
That is our request message and our reply message.
So other type of AAFP messages never cross the subnet boundary.
So for example, in this diagram, suppose host machine E issues the broadcast request message and places
that message on the wire.
So you can see that this our broadcast request message will be received by all the machines present
in the same subnet.
But this message will never cross the subnet boundary.
So the gateway entry throughout all of a sudden it is the demarcation of subnet boundary.
Whether it is our request, message or a public message, always remember that our messages never,
ever crosses the L3 Lauter, which is a gift we offer subnet.
So our message will never go on the other side of this ultimate daughter, right?
So in other words, I'll out demarcate the boundary of the subnets.
All machines in the same subnet are set to be neighbors, so we have already discussed this point that
all the machines which are present in the same subnet are set to be neighbors of each other.
So the neighbors of the host machine E, for example, will be host machine, the host machine F and
the router itself.
Now, going forward now, let us discuss the Arpad format specification.
So you can see that this diagram shows the standard message format of our message type.
You can see that there are various fields in this optimizers type.
Let us discuss the meaning of each of these fields which are shown in this arc, message, format,
specification.
So the first field is the hardware type, so the value of this field is set to one, if the wiring that
is being used is Ethernet cable and if this wiring is used using optical fibre cable, then the value
specified is 18.
Of course, there are other types of communication channels, but these are the most common communication
channels which is used in networking.
And therefore, we will limit our discussion only to these two hardware type values, that is one for
Ethernet cable and 18 for optical fibre.
Then the second feel is the protocol type here protocol, I feel, represent whether the ARB resolution.
Is being done for IPV for address or IPV six address, if the resolution is being done for IPV for address,
then this value is zero x zero eight zero zero.
That is, the hexadecimal value of this field will be zero x zero eight zero zero.
Then Hardwell at Rossland, this value is six bytes, of course, the hardware address is always the
Mac address.
The most common hardware address that is used in networking today is Mac address, and the length of
the Mac addresses are six bytes.
Therefore, the most common value of this field is six bytes.
Then the next bill is the protocol at Rossland Field.
So simply, if the resolution is being done for IPV for address, then the value of this will is for
bite's.
And if the resolution is being done for IP address, then the value of this field is 16.
Right.
So it is some type of mistake here.
So remember, this field represents the land of the protocol address.
So what is the land of IP before I address the land of IP?
Before address is four bytes.
Right.
And the land of IP address is 16 bytes right now.
The next will is the upgrade.
This upgrade represents the type of this ARPA message.
That is whether this AAFP message represents our request message or it represents our reply message.
So if the value of the upgrade is one that this message represents the OP's request message and if the
value of the upgrade is to, then this message represents the R reply message.
Remember, the same message specification format can be used to represent our request message or our
reply message based on the value of our code.
Then the next field in this message format is the standard hardware address, you can see that the size
of this field is forty eight bits.
That is 32 bits plus 16 bits, so the total sizes, 40 Edwards and this will represents the Mac address
of the sender sender means a whole machine, which is generating this type of message.
That is Apricus message or message.
So this will will be the Mac address of the sending machine.
Then the next field is actually a 32 bit field, which actually represents the IP address of the sending
machine.
So you can see that the specification allows you to specify only four bytes to specify the Sanders IP
address.
Therefore, send a protocol address can only be IPB for addresses, and the next field is the Target
hardware address.
So this will represents the recipient Mac address.
That is the Mac address to which this message is destined to.
And the final field is the target protocol address, which is actually the destination IP address for
which this message is designed.
So it will be the recipient IP address.
It is not IP address.
It can only be IP before address because you can see that the message specification allows you only
to specify a 32 bit as a target protocol address.