In this lesson,
we're going to cover Routing Protocols.
Now, there are two different types
of dynamic routing protocols.
There are internal ones and external ones,
and these are the basic categories.
Now, interior ones are things
like interior gateway protocols that operate
within a network or within an autonomous system.
External gateway protocols will operate
between autonomous systems on those exterior networks.
So for example, the internet is
a really large exterior system,
so it's going to be using exterior gateway protocols.
Your networks inside your internet,
even if you have multiple routers and switches there
are going to operate using interior gateway protocols.
And we're going to go through some examples of both
of these types of protocols in this lesson.
Now, first, let's talk
about the Router Advertisement Method.
This is a characteristic of every routing protocol.
Every dynamic routing protocol is going to look at routing
just a little bit differently though.
Some of them are going to use things known as distance vectors,
and others are going to use things known as link states.
Now, some of them don't fit neatly
either of these two categories,
and they become a hybrid of both of them.
Now, what this means is that there's some method
for the route to be received, advertised,
and provided to somebody else,
and you need to figure out how you're going to do that.
There's different ways of doing it.
It can be based on the measurement of cost.
That would be something like a distance vector.
It could be based on how many routers
you have to go through.
It might be something based on the link state of it.
All of those are valid ways depending
on the protocol you're using,
and this is where you become much more concerned
with the different ways of doing things.
For instance, if you're going to be using a link state vector,
this is where you're going to be concerned more with link speed
and what is the quickest method of getting there.
If you have to go through four routers,
but it's quicker than going through just one,
that's okay if we're dealing with link state.
But if we're dealing with distance, that would be backwards.
We only want to go through one router, even if it's slower.
This is the way we have to look at these different things
and figure out what's going to be best for us.
Now, we're going to talk about all of these
as we go through this video,
and hopefully, it'll make a little bit more sense to you.
First, let's talk about distance vectors.
Now, when you're dealing with a distance vector,
this is about the number of routers
you're going to be connecting through for a particular route.
And so, if you're dealing with a distance vector,
it's going to send a full copy of its routing table
to everybody else who's directly connected
to it at regular intervals.
Now, the bad thing about this is it has
what's known as a slow convergence time.
Now, what is convergence?
Well, convergence is the time it takes
for all of the routers to update their routing tables
in response to a topology change.
So if I add a router or I take one away,
how long is it going to take for everyone
on the network to know that happened?
So in this example, you'll see I have three routers.
I have routers one, two, and three,
and if I added a fourth router in,
it's going to take some amount of time
for router four to tell the other three routers
that it's there and how it's connected.
That's the idea of convergence time.
Now, once everybody knows all the same information
across all four routers, then you have what's known
as a converged network.
Now, one of the ways that we can speed up
our convergence time is to actually use a hold-down timer.
So instead of updating our routing tables every 30 seconds,
we might update it every three minutes.
Now, by doing that, it's going to allow us to converge faster
because there's less changes across the network.
Now, if there's more changes,
it's going to take us more time to converge.
So if we do less changes,
and we spread that out from 30 seconds to three minutes,
maybe to six minutes, that's going to be better
for us in terms of convergence time.
Now, when we deal with a distance vector,
it's really also concerned about a thing known as hop count,
and this is how many times I have to go
through another router to get somewhere.
So in this example, what's the quickest way
to get from router three to router two?
Well, if you're only concerned with hops
or the number of routers you have to go through,
you're going to go directly from three over to two,
over that slow one megabit per second connection.
Now, if you're concerned with link state, on the other hand,
you're going to be concerned with the fastest way to get there
by going where the most bandwidth is available,
and that would actually be going across
the hundred megabit per second connections.
So I go from router three to router one, to router two,
and that would be much faster than going directly
to router two from router three.
Now, that's again, not going to account
for the fact that if we're doing a distance
or a link state vector.
If we're using a distance vector,
we don't consider speed, we just count the hops.
So we're going to go direct from three to two,
but if we're dealing with a link state vector,
we're going to go based on speed.
And that's the big difference here.
So you have to think about that
as you're figuring out which protocol you're going to use
and which is going to be the best way for you
to have information flow on your network.
Now, when we deal with link state,
we start worrying about the cost
and the speed of all these connections.
This is going to require all of our routers
to know about all the paths, all the other routers as well,
so it can figure out what the best path is
to send the information around.
Now, this information is flooded out
through the Link State Domain when you're using OSPF
which is one of our routing protocols.
Another one we can use is IS-IS,
and this, again is a Link State protocol
to ensure the routers have a synchronized information
inside their routing tables.
Now, with that synchronized information,
they can then make the best routing decisions.
Now, we're going to talk specifically about these two protocols
in just a little bit here, so hang in with me.
Now, the link state does have a faster convergence time
than distance vectors, and it does use that cost
and other factors as metrics when it figures out
what the best way of routing traffic is.
Now, this also includes things like your link speed,
because the link speed is really important
of how much bandwidth you have to send the data across.
Each router is going to construct its
own relative shortest path based on
where it sees itself in the logical diagram,
and then it calculates the distance
of how it's going to get to the other places.
So let's take an example of you sitting in Florida,
and we both want to get to California.
Now, we can have different methods to get there based on
where we sit in the topology of the United States, right?
If we're both going to get in our car and drive there,
we have to figure out based on the highway speeds
and the slowness of those speeds,
and which traffic there is,
and how many states we have to go through,
and which highways we're going to go to get over there.
So let's say, we had to go 3,000 miles to get
to California from Washington or from Florida.
Well, if I can go 60 miles an hour the whole time,
but you can only go 30 miles an hour, well,
I'm going to get there a lot faster, right?
Because I can go two miles for every one that you go.
Now, that's the idea.
So as we start figuring out how we're going to go
through this using link state,
we could start taking speeds into account
and figuring out, hey,
maybe, I'm going to take this highway versus that back road,
or there's a lot of traffic on that highway,
so I'm going to take the back roads instead.
Well, our routers do the same exact thing
using those link state protocols.
Now, let's talk about the first routing protocol here.
This one is known as RIP, R-I-P,
and it's one of the oldest routing protocols out there.
It stands for the Routing Information Protocol,
and it is an interior gateway protocol
that's used internal to your networks.
This is a distance vector protocol,
and so it's going to rely on hop count
to figure out the fastest path.
Now, it's all about how many routers we're going to have
to go through, and the maximum number
of hops you can hit is 15 with RIP.
Now, if you hit 16 or more routers,
the connection is going to be considered dead,
and it's just going to drop the packet
and wait for you to retransmit it.
Now, again, this is the oldest dynamic routing protocol
out there, and it does provide updates every 30 seconds,
and so, it becomes really hard to maintain convergence
when you're dealing with a RIP network.
Now, RIP is really easy to configure,
and it sends out its information using UDP as its protocol,
and so, it does have that fire-and-forget method.
The next writing protocol we have is known as OSPF,
which is really popular.
This is known as Open Shortest Path First.
OSPF is another interior gateway protocol,
but unlike RIP, it doesn't use distance vector.
It uses Link State, so it is concerned with cost,
and this way it's going to be a lot more efficient.
Now, going back to our example of having the three routers,
router one, router two, and router three,
what is the shortest path for us
to go from router three to router two?
Well, it's actually going through router one
because the speed there is going
across a hundred megabit per second link,
instead of going over one megabit per second link.
Cost here is based on link speed, not on hop count,
and so, OSPF will help you get their fastest
using that link state variable.
Next, we have the intermediate system
to intermediate system known as IS-IS.
This is another interior gateway protocol,
and it functions a lot like OSPF.
It, again, is going to use cost as its link state measurement,
and this cost is based on link speed between two routers.
It functions a lot like OSPF,
but OSPF is still dominant in the marketplace
and used very widely where IS-IS
didn't really see widespread adoption.
The next routing protocol we have to discuss is EIGRP
or the Enhanced Interior Gateway Routing Protocol,
which you can probably guess
is the interior gateway protocol based on its name.
Now, this is an advanced distance vector protocol
that uses both bandwidth and delay
to make it a hybrid of the distance
and link state protocols.
It does count the delay that exists
which is how many hops there are,
as well as the cost that's available
with each of those links to figure out their speed,
making it that nice hybrid.
Now, this hybrid protocol was developed
by Cisco as an upgrade to OSPF,
and it is very popular if you're using a Cisco-only network.
Because it's proprietary, meaning you can only use it
with all Cisco products,
you're not going to see it a lot if you're using Juniper
or Brocade, or other routers in your network.
Again, it hasn't gotten the widespread acceptance
that OSPF has because OSPF can be used on any device
and any networks, not just Cisco.
The last protocol we're going to talk about is BGP
or the Border Gateway Protocol.
This is an external gateway protocol,
and on the exam, if you're asked which
of these is an exterior gateway protocol,
the only answer you should be looking for is BGP
because all the other protocols we talked about
are interior protocols.
Now, this gateway protocol is going to use a path vector
to use a number of the autonomous system hops
that it needs to use instead of router hops.
Now, I'm not concerned with how many routers I have
to go through necessarily, but I'm more concerned
with how many systems I have to go through.
Again, this makes sense when you start thinking
about the fact that BGP is used
as the backbone of the internet.
It's made up of lots of different autonomous systems
as we move from one ISP to another.
And so, this is what we want to think about
when we talk about autonomous systems.
Now, this has gained widespread utilization
and is used all across the internet.
BGP makes the internet run.
The big problem with it is
that it doesn't converge very quickly
because of the large scale of all of these networks.
So if you had a new router or a new system to the internet,
it can take an hour or two
before it starts getting populated,
and even more as it goes across the entire internet
to let them know that it now exists.