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In the last lesson, I talked about the fact
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that we can use dynamic routing protocols
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so routers can tell each other the routes they know.
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But I said we would talk more
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about those specific writing protocols later on.
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Well, in this lesson, we're going to cover
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each and every one of those
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that you're going to need to know for the Network+ exam.
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Now there are two different types
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of dynamic routing protocols.
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There are internal ones and external ones
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and these are the basic categories.
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Now, interior ones are things like
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interior gateway protocols that operate
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within a network or within an autonomous system.
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External gateway protocols will operate
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between autonomous systems on those exterior networks.
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So for example, the internet
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is a really large exterior system
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so it's going to be using exterior gateway protocols.
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Your networks inside your intranet,
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even if you have multiple routers and switches there,
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are going to operate using interior gateway protocols.
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And we're going to go through some examples
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of both of these types of protocols in this lesson.
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Now first, let's talk about the router advertisement method.
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This is a characteristic of every routing protocol.
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Every dynamic routing protocol is going to look at routing
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just a little bit differently, though.
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Some of them are going to use things
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known as distance vectors and others
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are going to use things known as link states.
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Now some of them don't fit neatly
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into either of these two categories
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and they become a hybrid of both of them.
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Now, what this means is that there's some method
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for the route to be received, advertised,
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and provided to somebody else.
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And you have to figure out how you're going to do that.
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There's different ways of doing it.
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It can be based on the measurement of cost.
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That would be something like a distance vector.
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If could be based on how many routers
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you have to go through,
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it might be something based on the link state of it.
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All of those are valid ways,
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depending on the protocol you're using.
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And this is where you become much more concerned
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with the different ways of doing things.
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For instance, if you're going to be using a link state vector,
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this is where you're going to be concerned more with link speed
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and what is the quickest method of getting there?
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If you have to go through four routers,
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but it's quicker than going through just one.
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That's okay if we're dealing with link state,
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but if we're dealing with distance, that would be backwards.
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We only want to go through one router, even if it's slower.
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This is the way we have to look at these different things
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and figure out what's going to be best for us.
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Now, we're going to talk about all of these
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as we go through this video
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and hopefully it'll make a little bit more sense to you.
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First, let's talk about distance vectors.
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Now, when you're dealing with a distance vector,
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this is about the number of routers
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you're going to be connecting through
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for a particular route.
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And so if you're dealing with a distance vector,
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it's going to send a full copy of its routing table
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to everybody else who's directly connected to it
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at regular intervals.
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Now, the bad thing about this is it has
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what's known as a slow convergence time.
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Now, what is convergence?
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Well, convergence is the time it takes
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for all of the routers to update their routing tables
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in response to a topology change.
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So if I add a router or I take one away,
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how long is it going to take for everyone on the network
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to know that happened?
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So in this example, you'll see I have three routers.
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I have routers one, two, and three.
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And if I added a fourth router in,
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it's going to take some amount of time for router four
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to tell the other three routers that it's there
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and how it's connected.
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That's the idea of convergence time.
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Now, once everybody knows all the same information
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across all four routers
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then you have what's known as a converged network.
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Now, one of the ways that we can speed up
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our convergence time is to actually use a hold-down timer.
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So instead of updating our routing tables every 30 seconds,
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we might update it every three minutes.
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Now, by doing that, it's going to allow us
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to converge faster
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because there's less changes across the network.
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Now, if there's more changes,
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it's going to take us more time to converge.
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So if we do less changes and we spread that out
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from 30 seconds to three minutes, maybe to six minutes,
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that's going to be better for us
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in terms of convergence time.
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Now, when we deal with a distance vector,
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it's really also concerned about a thing known as hop count.
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And this is how many times
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I have to go through another router to get somewhere.
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So in this example, what's the quickest way
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to get from router three to router two?
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Well, if you're only concerned with hops
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or the number of routers you have to go through,
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you're going to go directly from three over to two
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over that slow, one-megabit-per-second connection.
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Now, if you're concerned with link state on the other hand,
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you're going to be concerned with the fastest way
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to get there by going where the most bandwidth is available.
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And that would actually be going
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across the 100-megabit-per-second connections.
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So I go from router three to router one to router two,
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and that will be much faster than going directly
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to router two from router three.
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Now that's again not going to account for the fact
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that if we're doing a distance or link state vector.
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If we're using a distance vector, we don't consider speed.
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We just count the hops.
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So we're going to go direct from two to three,
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but if we're dealing with a link state vector,
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we're going to go based on speed.
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And that's the big difference here.
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So you have to think about that as you're figuring out
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which protocol you're going to use
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and which is going to be the best way
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for you to have information flow in your network.
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Now, when we deal with link state, we start worrying
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about the cost and the speed of all these connections.
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This is going to require all of our routers
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to know about all the paths of all the other routers as well
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so it can figure out what the best path is
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to send the information around.
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Now, this information is flooded out
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through the link state domain when you're using OSPF,
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which is one of our routing protocols.
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Another one we can use is IS-IS
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and this again is a link state protocol
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to ensure the routers have a synchronized information
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inside their routing tables.
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Now, with that synchronized information,
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they can then make the best routing decisions.
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Now, we're going to talk specifically
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about these two protocols in just a little bit here
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so hang in with me.
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Now, the link state does have a faster convergence time
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than distance vectors and it does use that cost
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and other factors as metrics
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when it figures out what the best way of routing traffic is.
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Now, this also includes things like your link speed,
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because the link speed is really important
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of how much bandwidth you have to send the data across.
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Each router is going to construct
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its own relative shortest path based
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on where it sees itself in the logical diagram
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and then it calculates the distance
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of how it's going to get to the other places.
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So let's take an example of you sitting in Florida,
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and I'm sitting here in Washington, DC,
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and we both want to get to California.
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Now we can have different methods to get there based
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on where we sit in the typology of the United States, right?
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If we're both going to get in our car and drive there,
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we have to figure out based on the highway speeds
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and the slowness of those speeds
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and which traffic there is
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and how many states we have to go through
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and which highways we're going to go to get over there.
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So let's say we had to go 3,000 miles
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to get to California from Washington or from Florida.
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Well, if I can go 60 miles an hour the whole time,
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but you can only go 30 miles an hour,
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well, I'm going to get there a lot faster, right?
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Because I can go two miles for every one that you go.
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Now that's the idea.
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So as we start figuring out
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how we're going to go through this using link state,
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we can start taking speeds into account and figuring out,
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hey, maybe I'm going to take this highway
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versus that back road.
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Or, there's a lot of traffic on that highway
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so I'm going to take the back roads instead.
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Well, our routers do the same exact thing
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using those links state protocols.
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Now let's talk about the first routing protocol here.
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This one is known as RIP, R-I-P,
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and it's one of the oldest routing protocols out there.
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It stands for the Routing Information Protocol
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and it is an interior gateway protocol
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that is used internal to your networks.
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This is a distance vector protocol
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and so it's going to rely on hop count
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to figure out the fastest path.
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Now it's all about how many routers
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we're going to have to go through
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and the maximum number of hops you can hit is 15 with RIP.
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Now, if you hit 16 or more routers,
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the connection is going to be considered dead
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and it's just going to drop the packet
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and wait for you to retransmit it.
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Now, again, this is the oldest dynamic routing protocol
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out there and it does provide updates every 30 seconds
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and so it becomes really hard to maintain convergence
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when you're dealing with a RIP network.
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Now, RIP is really easy to configure
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and it sends out its information using UDP as its protocol
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and so it does have that fire and forget method.
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The next routing protocol we have is known as OSPF
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which is really popular.
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This is known as Open Shortest Path First.
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OSPF is another interior gateway protocol,
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but unlike RIP it doesn't use distance vector.
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It uses link state.
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So it is concerned with costs and this way
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it's going to be a lot more efficient.
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Now, going back to our example of having the three routers,
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router one, router two, and router three,
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what is the shortest path for us to go
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from router three to router two?
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Well, it's actually going through router one
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because the speed there is going
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across a 100-megabit-per-second link
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instead of going over a 10-megabit-per-second link.
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Cost here is based on link speed not on hop count.
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And so OSPF will help you get there fastest
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using that link state variable.
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Next, we have
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the Intermediate System to Intermediate System
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known as IS-IS.
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This is another interior gateway protocol
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and it functions a lot like OSPF.
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It again is going to use cost as its link state measurement.
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And this cost is based on link speed between two routers.
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It functions a lot like OSPF,
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but OSPF is still dominant in the marketplace
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and used very widely where IS-IS
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didn't really see widespread adoption.
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The next routing protocol we have to discuss is EIGRP
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or the Enhanced Interior Gateway Routing Protocol,
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which you can probably guess
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is the interior gateway protocol based on its name.
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Now this is an advanced distance vector protocol
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that uses both bandwidth and delay to make it a hybrid
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of the distance and link state protocols.
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It does count the delay that exists,
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which is how many hops there are,
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as well as the cost that's available
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with each of those links to figure out their speed,
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00:09:13,090 --> 00:09:14,860
making it that nice hybrid.
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Now, this hybrid protocol was developed by Cisco
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as an upgrade to OSPF and it is very popular
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if you're using a Cisco-only network.
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Because it's proprietary,
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meaning you can only use it with all Cisco products,
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you're not going to see it a lot if you're using Juniper
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or Brocade or other routers in your network.
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Again, it hasn't gotten the widespread acceptance
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that OSPF has because OSPF can be used on any device
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in any networks, not just Cisco.
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The last protocol we're going to talk about is BGP
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or the Border Gateway Protocol.
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This is an external gateway protocol and on the exam,
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if you're asked which of these
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00:09:49,020 --> 00:09:50,880
is an exterior gateway protocol,
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the only answer you should be looking for is BGP
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because all the other protocols we talked about
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are interior protocols.
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Now this gateway protocol is going to use a path vector
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to use a number of the autonomous system hops
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that it needs to use instead of router hops.
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00:10:06,220 --> 00:10:07,920
Now, I'm not concerned with how many routers
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I have to go through necessarily,
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but I'm more concerned with how many systems
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00:10:11,600 --> 00:10:12,860
I have to go through.
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00:10:12,860 --> 00:10:14,700
Again, this makes sense when you start thinking
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about the fact that BGP is used
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as the backbone of the internet.
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It's made up of lots of different autonomous systems
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as we move from one ISP to another
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and so this is what we want to think about
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00:10:24,600 --> 00:10:26,580
when we talk about autonomous systems.
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Now this has gained widespread utilization
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and is used all across the internet.
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BGP makes the internet run.
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The big problem with it is that
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it doesn't converge very quickly
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because of the large scale of all of these networks.
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So if you add a new router or a new system to the internet,
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it can take an hour or two
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before it starts getting populated
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and even more as it goes across the entire internet
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to let them know that it now exists.
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When we talk about these routers,
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we have all of these different routes
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00:10:51,470 --> 00:10:54,560
and we have to think about the believability of a route.
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Now, what exactly does that mean
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when we talk about believability of a route?
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Well, let's say I have a network that's using
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00:11:00,320 --> 00:11:02,010
more than one routing protocol
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because my routers can support multiple protocols.
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I might be running RIP, and I might have OSPF.
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Both of them being used on the same router
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in the same network.
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00:11:10,460 --> 00:11:11,690
Now, how do I know which one
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00:11:11,690 --> 00:11:13,480
I'm going to go with when I'm a packet
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00:11:13,480 --> 00:11:15,980
and the router needs to move me around the network?
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Well, these routing protocols
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are going to be considered more or less believable
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based on some different factors that we have.
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For example, RIP is considered less believable than OSPF.
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Now, why is that?
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Well, this is because routers use an index of believability,
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which we're going to call AD
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00:11:33,328 --> 00:11:35,070
or the administrative distance.
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00:11:35,070 --> 00:11:37,470
Now, if a route has a lower administrative distance,
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it's going to be considered more believable,
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and it's going to be better to have a lower number.
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00:11:41,410 --> 00:11:43,520
So I like to think about this like golf rules,
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00:11:43,520 --> 00:11:45,500
the lower the number, the better it is
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00:11:45,500 --> 00:11:47,250
in terms of believability.
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00:11:47,250 --> 00:11:49,720
Now here's a chart for you with the administrative distances
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00:11:49,720 --> 00:11:51,830
of the different protocols we talked about.
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If you're dealing with a directly connected route,
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this is going to be the most believable.
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Why?
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Because the router is directly connected
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to another router so it knows itself
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and it trusts its own opinion that it's connected.
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00:12:03,030 --> 00:12:04,750
Now, this makes a lot of sense, right?
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00:12:04,750 --> 00:12:06,890
So if I know you personally, we're holding hands,
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00:12:06,890 --> 00:12:09,820
we're both connected and therefore the trust would be zero.
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00:12:09,820 --> 00:12:12,180
That's the idea here with the directly connected route.
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00:12:12,180 --> 00:12:13,800
It is fully trusted.
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00:12:13,800 --> 00:12:15,420
Now a statically configured network
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00:12:15,420 --> 00:12:17,410
is going to have an AD of one.
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00:12:17,410 --> 00:12:19,040
That's the next most believable
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00:12:19,040 --> 00:12:20,640
because routers do what they're told.
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00:12:20,640 --> 00:12:22,820
And if you, as a network administrator
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00:12:22,820 --> 00:12:26,200
went in and configured a static route, you told that router,
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00:12:26,200 --> 00:12:28,400
I want you to believe this above everything else,
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00:12:28,400 --> 00:12:30,700
unless you're directly connected to somebody else.
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00:12:30,700 --> 00:12:33,000
Beyond that, you're always going to believe me.
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349
00:12:33,000 --> 00:12:35,710
After our directly connected routes and our static routes,
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00:12:35,710 --> 00:12:38,720
we're then going to trust EIGRP next.
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00:12:38,720 --> 00:12:42,090
After that we believe, OSPF and then RIP,
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00:12:42,090 --> 00:12:44,230
and then external EIGRP.
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00:12:44,230 --> 00:12:46,510
And then as we go all the way to the bottom of our chart,
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00:12:46,510 --> 00:12:50,420
we see the worst believability, the unknown or unbelievable,
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00:12:50,420 --> 00:12:53,050
which means that it's going to have a rate of 255
356
356
00:12:53,050 --> 00:12:54,750
for its administrative distance.
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357
00:12:54,750 --> 00:12:57,510
The reason why we set it at 255 is basically we say,
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00:12:57,510 --> 00:12:59,300
I can't find this network anymore.
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359
00:12:59,300 --> 00:13:00,800
It is totally unbelievable
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360
00:13:00,800 --> 00:13:03,190
and so I don't want to run traffic that way.
361
361
00:13:03,190 --> 00:13:06,370
Now for the exam, do you have to memorize all these numbers?
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362
00:13:06,370 --> 00:13:09,520
No, but you should have an idea that directly connected
363
363
00:13:09,520 --> 00:13:12,240
is the most believable, then static,
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364
00:13:12,240 --> 00:13:16,210
then followed by things like EIGRP, OSPF and RIP.
365
365
00:13:16,210 --> 00:13:17,550
If you think about the fact that RIP
366
366
00:13:17,550 --> 00:13:19,300
was one of our earliest protocols,
367
367
00:13:19,300 --> 00:13:21,440
it would be one of our least believable.
368
368
00:13:21,440 --> 00:13:23,010
OSPF was an improvement to RIP
369
369
00:13:23,010 --> 00:13:24,710
so it's a little bit more believable.
370
370
00:13:24,710 --> 00:13:27,670
And then we had EIGRP, which was an improvement to OSPF.
371
371
00:13:27,670 --> 00:13:29,600
So again, it's more believable.
372
372
00:13:29,600 --> 00:13:31,370
This is kind of a memory game that I use
373
373
00:13:31,370 --> 00:13:33,290
to try to remember which ones are most believable
374
374
00:13:33,290 --> 00:13:35,090
and which ones are least believable.
375
375
00:13:35,090 --> 00:13:38,200
Lastly, we have metrics associated with all of these routes.
376
376
00:13:38,200 --> 00:13:39,530
And when we look at these metrics
377
377
00:13:39,530 --> 00:13:40,700
and we look at these routes,
378
378
00:13:40,700 --> 00:13:42,270
there's going to be a routing protocol
379
379
00:13:42,270 --> 00:13:44,640
that's able to choose which path it's going to go on.
380
380
00:13:44,640 --> 00:13:46,510
And we do this based on metrics.
381
381
00:13:46,510 --> 00:13:49,220
These are things like hop count, believability,
382
382
00:13:49,220 --> 00:13:53,970
reliability, bandwidth, delay, costs, or other metrics.
383
383
00:13:53,970 --> 00:13:55,980
Each protocol uses a different metric
384
384
00:13:55,980 --> 00:13:57,720
to determine which route it should use
385
385
00:13:57,720 --> 00:14:00,570
and which one is it going to be considered faster or slower.
386
386
00:14:00,570 --> 00:14:01,980
Depending on which route it is,
387
387
00:14:01,980 --> 00:14:04,410
it's going to determine which metric you're going to use.
388
388
00:14:04,410 --> 00:14:05,710
And so when we're dealing with metrics,
389
389
00:14:05,710 --> 00:14:07,430
it's always going to be thinking about the fact
390
390
00:14:07,430 --> 00:14:10,670
that lower numbers are better, higher numbers are worse,
391
391
00:14:10,670 --> 00:14:12,270
when we deal with routing.
392
392
00:14:12,270 --> 00:14:13,820
Anytime we talk about hop count,
393
393
00:14:13,820 --> 00:14:15,480
we want the least number of routes.
394
394
00:14:15,480 --> 00:14:17,240
If we start talking about bandwidth,
395
395
00:14:17,240 --> 00:14:19,290
we want the lowest cost of bandwidth.
396
396
00:14:19,290 --> 00:14:21,420
And that gives us the highest amount of bandwidth.
397
397
00:14:21,420 --> 00:14:23,040
And so lower costs becomes better.
398
398
00:14:23,040 --> 00:14:23,970
If we're dealing with delay,
399
399
00:14:23,970 --> 00:14:25,790
we want the least amount of delay.
400
400
00:14:25,790 --> 00:14:27,610
Believability, we want the lowest number.
401
401
00:14:27,610 --> 00:14:29,750
We want a zero for directly connected, right?
402
402
00:14:29,750 --> 00:14:32,380
Or one for static route or one of those lower numbers
403
403
00:14:32,380 --> 00:14:33,930
for the administrative distance.
404
404
00:14:33,930 --> 00:14:34,763
That's the idea here.
405
405
00:14:34,763 --> 00:14:36,450
Lower numbers are always going to be better.
406
406
00:14:36,450 --> 00:14:37,650
You see this trend in routing
407
407
00:14:37,650 --> 00:14:40,040
where the metrics lower is always better.
408
408
00:14:40,040 --> 00:14:41,980
And so remember that for the exam.
409
409
00:14:41,980 --> 00:14:44,330
Lastly, I wanted to give you this summary slide
410
410
00:14:44,330 --> 00:14:45,430
here on the screen.
411
411
00:14:45,430 --> 00:14:47,160
This is one of those things I'd like you to write down
412
412
00:14:47,160 --> 00:14:48,410
in your notes so you can remember
413
413
00:14:48,410 --> 00:14:50,310
all about the routing protocols.
414
414
00:14:50,310 --> 00:14:52,090
This summarizes everything nicely.
415
415
00:14:52,090 --> 00:14:54,393
From RIP, OSPF, EIGRP.
416
416
00:14:56,020 --> 00:14:57,870
IS-IS, and BGP.
417
417
00:14:57,870 --> 00:14:59,600
It shows you which ones are interior,
418
418
00:14:59,600 --> 00:15:02,350
which ones are exterior, which ones are distanced vectors,
419
419
00:15:02,350 --> 00:15:03,660
which ones are link states.
420
420
00:15:03,660 --> 00:15:04,810
And hopefully this will help you
421
421
00:15:04,810 --> 00:15:06,417
as you study your different routing protocols
422
422
00:15:06,417 --> 00:15:08,040
and remember the key facts and figures
423
423
00:15:08,040 --> 00:15:09,543
for them before the exam.