Time
31 hours 29 minutes
Difficulty
Beginner
CEU/CPE
30

Video Description

Routing Metrics This lesson discusses routing metrics and the qualities used to determine the best path: - Hop count: how many other routers does a signal need to pass? - Maximum transmission Unit (MTU): The maximum size of a single packet we can send - Casts: reliability - Latency: The amount of delay we have on a link. Routers use different protocols to determine the best path: - Link state: This is a cost-based protocol. An example of a link state is Open Shortest Path First (OSPF) protocol - Distance Vector: Just based on the number of 'hops' - Hybrid: A mixture of distance vector and link state, it uses 'hop' count and cost

Video Transcription

00:04
So we've talked some about how routers communicate and how they actually set up routing tables and how they determine the best way to get from point A to point B. Well, let's take a look now at some of the more specific routing metrics that they use
00:19
now, when we're talking about routing metrics, worth talking about qualities that are routers used to determine the best best path.
00:25
When you hear metrics in computing, you're a metric is a measure of something.
00:32
It's a call. It's, ah,
00:34
analysis of how long it takes to get somewhere how many other routers we have to hit. How much delay there is A metric is a measure of something, so a routing metric is a measure of a different quality that we used to determine the best path.
00:52
Now these different metrics are used when we're talking about are different protocols and when we're determining the best path to use.
01:00
So it's important to know how these metrics are, what is measured in which metrics we use when we're determining the best path.
01:08
One of the most obvious metrics we use is gonna be hop count now. Ah, hop count as we discussed a little bit earlier is essentially how many places, how many other routers, how many stops we go to before we get from point A to point B. Is it just a straight shot from our router to the next router to the server? Or is it our router?
01:29
Two
01:30
com casts router or Verizon's router to another router in a different state, to 1/3 router to an intercontinental router to, finally, to the server that we're trying to get to. So it's important to understand those hot counts and our hot counts. We can see which path we're taking,
01:49
which hops or which locations were hitting
01:51
using the pink command called trace Round.
01:53
Now trace route is spelled out trace Artie,
01:57
and there's actually no space. If we open up a command, prompt and run and type in trace our T space and then a server name or an I P address, so trace our t 8.8 dot eat 0.8.
02:15
Then we'll actually see the route that we take in order to get from us to that other location, and that trace route command will show us all the different hops that we're hitting to get there. So all the different routers, all the different places were hitting in between us, and they're so that's our hop count.
02:34
Next, we have our into you now into U stands for maximum transmission unit. Ah, maximum transmission unit is the size of a single Is the maximum size of a single packet that weaken send.
02:46
So when we're talking about packets, we're talking about the amount of data that we can fit into one box. So think of MT. You a maximum transmission unit as being the largest box that we get in order to fulfill a shipment of bricks.
03:01
So if we're trying to send someone all the bricks that they need to build a house than it would be better if we had larger boxes to send than smaller boxes are maximum transmission unit is going to sort of be our boxes. In this scenario, we have all these bricks we need to send and
03:19
are into you for we hide. We are evaluating two different shipping companies for us
03:24
and shipping Shipping company A says Oh yeah,
03:29
this here is the largest box you can use in order to ship these 2000 bricks and they hand us a box about yea big. We say
03:37
I'm gonna have to send about
03:38
200 of these boxes, you know, probably more. Probably have to send about, you know,
03:44
203 100 these boxes to get everything through. And they say, Yeah, we know
03:47
that's the biggest box of you that we can put on our trucks.
03:52
And so we say, OK, what about shipping company? Be shipping Company B says Okay, I've got this giant big box here that you could put all of your you can put in, ah, 100 bricks at a time, we said, That's what we're talking about. That's what we need. We need a larger empty you. We need a larger maximum transmission unit to get this packet.
04:09
We're talking about into you, though there's another concept we need to know about, which is banned with now. Bandwidth
04:16
is what sort of limiting our into you and bandwidth is
04:21
the width of the data that we can push through on a single length on a single link at once. So it's the maximum amount of data that we can handle either because of the port that we're connecting into the band with maximum Because of
04:39
our Internet service provider, the man with maximum because of the cable type that we have that we're using
04:44
our band with is going to be
04:46
the max amount of data that we can essentially push over a single length at once a single link at once.
04:54
So if we have a router that says, Oh, yeah, my maximum transmission unit is huge,
04:59
but my band with is really small.
05:01
So you I'm gonna allow you to try and push through these massive packets, but my bandwidth is really gonna throttle down what you can use. And it might even chop up some of your packets.
05:14
We don't We don't want that
05:15
very large empty you on a small band, which isn't a good thing. So
05:21
now we have a shipping company B that said, Yeah, I'm gonna give you this giant box that you can use, but the thing is, we only have a couple of trucks in our fleet that can really hold that box. So
05:36
between here and where you're sending, we may actually have to open up that box and break up your box in different boxes and then when it gets to the other end. Put those boxes back back together. But it's Oh, it's It's okay. Well, they may lose a box. Those boxes may get stuck around they Maybe they may get delayed
05:57
so
05:58
large into you on the low band with isn't really a good thing. So we're evaluating our maximum transmission unit as well as our bandwidth on certain links when we're checking our routing metrics. Additionally, we're also evaluating costs.
06:14
Now we're talking about costs. We're not talking. We're not necessarily talking about monetary costs. We're not talking about money here.
06:18
We're talking about reliability, round trip time costs as far as what it takes or how long it takes for our packet to get from point A to point B. This may include things like reliability If we have a, we have a router that isn't always available or is
06:39
kind of sporadic and sometimes goes down sometimes
06:42
sometimes up. Sometimes it down sometimes is up, then it doesn't have a very high reliability rating, doesn't have a very high it isn't. It's not very good there, or we have a round trip time, which takes a long time to go go to one place and then come back to us. It's gonna be high round trip time. These were gonna be costs
07:00
that we have associated with that with that particular route.
07:03
Now we're talking about a particular route. We're talking about a particular link, and we say that it has a low number cost lower number. Cost is good.
07:14
Just like when you go to the store and you're trying to buy something. If you can get a good quality item, you could get the same item. You have two of the same items here, um, at a lower cost. That's good.
07:27
Ah, higher cost is bad. So low cost is good. High cost is bad.
07:33
And then lastly, here we have Leighton. See, Now, Leighton see is the amount of delay that we have on this link on dhe. When we're talking about Leighton, see, and we're talking about delay A lot of times we're talking about how long the distance between one point another,
07:48
or how long it's taking for that other point to respond back, or how long it's taking for us to get there.
07:55
Um, now we have this little guy drawn here, and this isn't a tie fighter. It's Ah, it's a satellite,
08:01
but I do my best.
08:03
And when we think about late and see, we think about satellites because
08:09
when we have our phone
08:11
or we have a mobile hot spot
08:13
or we have ah, device, which is are we have a GPS, we have a Internet connection, which is connecting to a satellite.
08:22
We're getting a very direct, high bandwidth connection from Point A to that satellite
08:30
and compare that to If we plug our laptop directly into our router, we may actually even have less hops
08:39
then, if we just had a satellite connection to an Internet service provider and then that satellite beamed down to their Internet service providers office.
08:46
So there may be a lot of these costs are a lot of these metrics which look better in the case of satellites, we may have a lower hop count we have met. We may have a higher into. You may have a higher maximum transmission unit. We have may have a higher band with Maybe we may have more data that we can send at once,
09:05
but our Leighton see is what's really going to kill us because whereas
09:11
When we have a cable link into a router or we have a white wife, I link toe a local router that's going to be a wired connection to an Internet service provider.
09:22
Our satellite connection is gonna have to go from our location on Earth
09:26
all the way to a satellite, then all the way over to the Internet service provider.
09:35
And then when the Internet service provider gets the information is sent back to us, it has to go from them all the way to the satellite and then all the way back to us.
09:45
That's a latent. See,
09:46
So
09:48
it's taking a long time. We're gonna have a lot of delay on that link. So that's why if say, you have satellite Internet and you're trying to load a page, you may see your your initial your initial search.
10:01
You sit there, you wait. You wait, then, boom.
10:05
You get a bunch of data
10:05
because you may have a high bandwidth. You're getting a lot of data at once, but you have Ah, hi, Leighton Singh is taking a long time for that chunk of data to get to you. You're getting you have a shipping company that is delivering a giant box at your door. But instead of taking two day Amazon prime, it's taking
10:26
a month
10:26
to get to your door.
10:28
So
10:30
in the time it takes for you to get that one big box, you could have shipped 50 smaller boxes and could have added up to more than that twice as much as that one big box does. So that's why Leighton See is also a big issue. So we want to keep that in mind when we're talking about are different routing metrics. So
10:46
rounding metrics qualities used to determine our best path
10:50
we have our hop count
10:52
into you maximum transmission unit are different costs in our Leighton See.
10:56
So now let's take a look at some of our different
11:01
ways that we actually make. We actually determine our connection.
11:07
So next we have our link. State distance vector or hybrid,
11:11
now links the state distance vector and hybrid all refer to protocols and different protocol types that are routers use in order to determine the best path. Now we have a lot more specific protocols that will get into and the specific metrics that those protocols use.
11:30
But when we're talking about our protocols that are routers to use. We have three main protocols that we break those into,
11:35
and that's link State distance, vector and hybrid
11:39
Link state is a cost based protocol.
11:43
When we're talking about routers that use a link state protocol, they are using metrics such as our costs here. So they're gonna use costs and Leighton see into him to you. They're gonna use that cost based. How much effort? How much time does it take
12:01
for me to take this packet and get it from point A to point B
12:05
that's gonna be into you are that's sorry. That's going to be our link state,
12:09
um, example of a protocol that uses link State is O S P F open, shortest path open, shortest path First, that's a link State based protocol.
12:22
Then we have distance. Vector
12:24
distance vector protocols are just based on hops there just based on the distance the number of hops that it takes for me to get from point A to point B. If I have A If I have a way that I could get to this location and it takes me one hop and I have a way that I can get to this location and it takes me two hops.
12:41
I'm going the way that it takes me one hop
12:43
because that's what Distance Vector does. It just bases it on hops
12:48
and examples of protocols that use this R R I, P and R I P version, too.
12:54
And again,
12:56
both of these have their weaknesses and especially dis. Inspector,
13:01
you can't. You can't judge a book by its cover. You can't judge a route by the You can't just judge route by the number of hops. It has that hot, that route that has one hot versus that route that has three hops. That route that has one hop may have a super tiny into you and a lot of Leighton. See, where is that route that has three hops
13:20
as a very nice wide, very nice large into you,
13:24
Very high, very high band with very low latent See So those those costs and those distances can be rolled into our hybrid protocols
13:35
in our hybrid,
13:35
just like our little hybrid cars that drive around used the best of both worlds. They have are sorry
13:43
they have our cost space and they are hops based as well. So our hybrid is going to be distance vector, and they're going to be linked state on dhe. They're going to use both hop count and cost in their analysis of which routes are better.
14:01
So
14:01
that's our routing. Metrics are hop count into you costs Leighton seeing bandwith and how we use those when we're talking about links state distance, Spector or hybrid routing protocols.

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