IP Routing Explanation

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23 hours 18 minutes
Video Transcription
Hello and welcome back to I see anyone interconnected Cisco networking devices. Part one.
This is upset 513 I p routing explained
I have a friend there when I will be restricted for this course in last video went over some basic features routers how to access them, some of the different cables that used to connect and went over the differences between switches and routers.
This episode of recovering the steps a router actually takes when it decides to Ford packets.
And so we're gonna go through the i P routing process. We're gonna break down each step,
and I'm gonna We're just gonna lay out that way
as always, quick pre assessment here on TV, I figured out what your destination I p, will be any packet from PC one as it is sent over the links to PC to
what is between switch one and router one.
So think about that for a second. I think about you know what's in the frame versus what's in the packet. What gets changed at each length versus what stays. So I'll give you a few seconds.
All right. The destination I p will be PC to remember the data link frame the source of Mac address and the destination Mac address
would be switch once on router one. But the source i p and the destination I p would be p c one and pc to
so quick I p routing process. So what it does is its end, and routing relies on the network layer logic being the layer three deal with packets. We're looking at the source address and destination I p address.
Um, remember that when it is day encapsulated, encapsulated uses that Mac address for the next tops type of thing.
But the source night, he actually tell you where the final destination is and where the origination of the pack iwas.
So the host, the only thing they really determined is they look at the destination address and say, OK, is this on our local land? Okay, little check. It's our cash
and determine if it knows where the GPS or if it knows what Mac addresses it doesn't is gonna use our to learn the i p from that Mac.
All right, you send it out to switch.
It was not on the local land.
It's just gonna send it, writes that default gateway, which is either dynamically set through D A GP or statically set by
the organization. Or you said it. Ah. So what routers do will break down each of these steps and slide
So it goes through F. C s for Ares is going to look at the data link destination address should be for the router.
It shouldn't be Another address is gonna de Caps like that frame to a packet is gonna determine the best route for that to destination I p address based on the routing table.
I was gonna encapsulate that packet with the next top data link destination and Mac address, and that is going to transmit it
so we'll go ahead and jump right into step one here to process or not to process. So you said where it's gonna perform a frame check sequence for errors on that frame? If it does have errors, is gonna ignore it. Uh, but there is no air is we're gonna go ahead and continue processing.
That is gonna go look at the frame and determine if that destination Mac address
is for that router.
Because if you think about ah broadcasts, right, there's static frames whenever.
But it might not be for that router, so it's not gonna, you know, it doesn't need a process it. Ah, but if the Mac address is for that router is gonna go ahead and continue to process it,
so we'll move on to step two here. Day encapsulation, as simple as it sounds, is gonna remove that data like header and trailer
and which just leaves that I p packet, which has thesaurus address or source. I p Destination I p
and all your data, Uh, my protocols So but it just leaves that I p packet.
So here's where we get into the bread and butter of the router here, here's where it goes in. It makes that routing decision was gonna use the i P routing table that it has built in either statically or you can use the different routing protocols
to have these routes pushed to the router.
Um, so each route is gonna have metrics is gonna have affording interface
is gonna have a network associated with Have you seen the picture down below?
Um, you see the network, you see where it iss
connected to?
Ah, the Ford interface being you know, serial zero to our factories in that 10
Some like that. That's a 40 interface, and the metrics you'll see is going to determine each one's different, so you can't really compare different protocols.
So if you look at e j r P O R o S P F versus rip, all their metrics are different. So if you look at a rib metric of 10
and a therapy of like
they're huge numbers, it's like an eight digit number.
They're completely different. They mean nothing comparatively, the
four metrics. So it's actually gonna do when it's gonna look at that destination. I P address that's in the packet is could determine which network to send it Thio
Ah, by the sub net and mask information. So it's gonna look that routing table and determine the most specific route that it can take.
I think most Pacific route is best. That's the winner. So if you have one that was gonna roll down here because remember, the gateway last resort is if it doesn't reach anywhere else in the rowing table, send it out that that is like lowest Lee specific
um, route of all of them, so it'll go down. You know, if you have a 10.0 slash eight
and then you have, ah, 10 that one does 00 slash 16. That's more specific than the slash eight.
So you're looking at submitting for that.
I remember the gateway, the last resort. Ah, we will go through and configure it in one of these lessons. It is the I. P address of zeros and a subject mask of zeros. And it says, basically, if there is no routes that are applicable in the early table, send it out. This interface
One thing you can do if you're curious, like a time if your windows, you could just do a command prompt with route space print
space minus four for MTV four. And then I will give you your routes that is on your Windows machine.
You're just kind of curious. You take it, we'll get it, see what you make of it
and we're onto the next step. After we've determined where the frame is supposed to be sensible about using that running table, we're gonna encapsulate that frame, right?
So we're sending over an Ethernet link. We're going encapsulated in the HDL senior PPP frame
presenting over Ethernet, we're gonna catch let in just your normal Ethernet frame.
And the next hop address for the frame is gonna be that, uh, the next type router will be the max address or the destination, Mac.
Right. But the member of the I P packet will still have the final destination, you know, PC to Ah, I p address. So remember, the source and destination of peas will stay the same. The source and Mac it and decision mag addresses will be corresponding to that specific lander that link.
So he was both assessment here whose source address would is in the data link frame when sending over the serial link from P C. One to PC to. So you see that serial link between Roger one around two in the middle there,
whose source address isn't need data link frame when it is sent over that cereal like give you a few seconds.
It is router one. So
I think back to the cancellation decapitation process. Think about what happens.
And the next episode we're actually gonna go through and break out the party session, and we're gonna look at could figure routes. We're gonna look at the connected wines, and we're gonna look at how to set up your router on a stick.
So it's always a few guys have questions. Need help Full free to shoot the message. Otherwise, thank you for washing this video and four to see the next one.
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