the next topic of discussion is I p routing teary.
if you remember, I said routing is a layer three function.
A network layer function. Rowdy is the process of going from one broadcast domain to another broadcast. A mean one layer three broadcast. You mean to another layer three broadcast to me.
So, as you see in this diagram, we have host one and a hostess simply a device with an i P address on it. So we have host one
on network 10 10 10 0 with the i P. Address. 10 10 10.1. You guys should get used to looking at network diagrams like this. I mean, if they're drawn on video, that will look better than this. But
the network addresses usually put separately. And then each host has its address, just the last denoted next to it. So 10 10 10.1 is the I. P. Address assigned to host one.
Now, once again, is there a switch between host one and Router one off course there is, But this is a logical diagram, and I've left. The switch is out of the picture
now. Router one on fast eating at 00
interface on It's fascinating that 00 interface has the I. P address. 10 10 10 to 54
So this is one broadcast domain.
Then you have a second broadcast domain with the network address 2020 20 0 and host to sitting here with the I P address. 2020 22.
Router two's Fascinating as you know, slash one interface has the I. P address 2020 22 54
router one and two are connected to each other with 1/3 broadcast domain with the network address. 202 102 100 0 router ones. Serial 000 Interface being 202 102 101 and router to serial 000 interface being 200. 202 100.
wants to playing host to host one. For some reason. Always wants to play host.
Most one should quit
So Host one wants to paying host, too.
Host One creates an I C and B
Internet control messaging protocol that Pain works with
with a source I P. Address off 10 10 10 1 and a destination. I p address off 2020 22
Then host one needs to create an Internet framed for transmission on the local data link. Remember later, too
controls transmissions on the local data link. Hence it's called the Datalink. Clear the local data link being the link between Host one and Router one. Host one and F 00 off rather one.
So Host one needs to create an Internet friend. Host one is trying to paying 2020 22.
Host one has its own Mac address. Let's again presume that it is a a A. A.
However, Hosts one does not have the Mac address that belongs to 2020 22 which is host to and whose two's Mac, we'll say, is B B B B.
So since Host one does not have host to smack address, Host one sends an ARP request, which remember, it's a broadcast sent to the address to 55255255255 The all post broadcast address.
So Host one sends an art request request requesting the Mac address of the device. 2020 22.
Now, since this our request is a broadcast and broadcast cannot transfers a router by default.
This art request reaches router one
router. One sees that 2020 20 0 is not directly connected to it.
So Router one doesn't know where. 2020 20 0 it's It's a remote destination. So this our request reaches router lon F 00
knows that this is not a locally connected network
router, one replies back to host one
with the Mac address residing on F 00
This is because all routers
by default run a protocol called proxy proxy are on the Internet interfaces.
So basically what rather one does it proxies for host to and returns its own Mac address? Or the Mac address reciting on F 00 to host one.
At this point, Host one can create the Internet frame with the source. Mac Address A and the destination Mac Address being the Mac address off Roader one interface F 00
So Host one creates the Internet frame, encapsulate
the original ICMP echo packet inside of the data portion of the frame and sends the frame over to our one
are one at this point. Receives the frame and matches the destination i p. Destination Mac Address in the frame with the Mac address on F 00
Rather, one sees that this Mac address matches. So Router one discards the frame or Dean capitalist the frame and extracts the packet.
Now, inside of each router, there is a table. Call the I P routing table or the routing table
which has a listing off all the remote destinations that are available to the router and how to get to them
or what interface to send traffic out off the words that remote destination.
So rather one extracts the original packet
and matches or compares
the destination network address in the packet or the destination I p address in that packet
with a listing off all available networks available to that router or all networks available to that router.
Rather, one finds out that network 2020 20 0 is available
out bound off serial 000
So at this point rounder, one needs to create another frame
for transmission on the local data link between router one and router. To
now, as we saw, the default encapsulation type on a serial interface is HDL see and This is a serial link denoted by the thunderbolt.
So Router one encapsulate it's the original echo. Pack it in and HDL see frame and pushes it out. Serial 000 And remember, serial 000 doesn't have a Mac address, and it makes sense. Serial interface is don't have Mac addresses
because once you push something out of a serial interface,
there's only one device at the other end.
Router two is always going to get the information that router one pushes out of cereal 000 So new address ING scheme is required because this is not a monthly access network
in a multi access network, you have several devices that could be connected at the other end. So to differentiate them from each other, you need an address ing scheme like Mac addresses. But on a point to point link, if Ra one pushes out any data out of cereal 000
the only person sitting at the other end is router to,
and it's going to receive it.
So once again, Router one
creates a knish. TLC frame,
encapsulates the original echo packet inside of the SCLC frame and pushes it out serial 000 because rather one discovered looking at its I p routing table that network 2020 20 0 slash 30 is available out Serial 000
So that's the door I have to take.
You get to Network 2020 20 0
router to receive this SCLC frame d encapsulate sit or discards it and extracts the original packet.
The original Echo packet with source address. 10 10 10 1 and destination address. 2020 22
router to then compares the Destination I P address
in the original Echo packet against this I p Routing table again
and router to discovers that Hey, Network 2020 20 0 is directly connected on Fast Ethernet zero slash one
router to at this point, once again needs to create anything that frame for transmission on the local data link between router to at 01 and host, too.
Now, if router to Does not know, Host two's Mac address, which is B B B B router to sends out an art broadcast looking for the Mac address that belongs to I P 2020 22
host who receives the our broadcasts and unique *** back a reply.
Are two at this point. Has host Who's Mac address, which is B B B B
are two at this point. Creates the Internet frame with sore smack, the being the Mac address off the F zero slash one interface and the destination Mac being B B B B
rotter to pushes the frame out
and host to receives the frame and matches the destination. Mac address in the frame with its own map
sense. It matches host to will discard the frame or D encapsulate the frame and extract the original packet
host to will then match the destination i p. Address in the packet with its own I P, which is 2020 22. And since it matches host to will send back an echo reply
I'd be routing to re lecture. Now a few things to keep in mind
what would be the Destiny destination Mac address on the return frame from host to
your answer should be the destination. Mac would be the Mac address off the f zero slash one interface on router to
If you were asked how many times the packet was encapsulated between host one and host to your answer. Should be one encapsulation here
into Ethernet then d encapsulated than one encapsulation hair into h d l C and d encapsulated than another encapsulation here on Internet. So total of three encapsulation.
If you were asked, what is the destination Mac address in the frame as it leaves Router one s 000 You answer should be There is no Mac address in that frame.
This concludes the I P Routing theory lecture.