WEBVTT

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 So now as we're continuing on our journey
 of comparing and contrasting

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 types of routing protocols, we're going
 to look at the third type here,

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 which is advanced distance vector.


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 Some people at Cisco Systems,
 they said, you know what?

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 On the one hand, link state routing protocol
 is good because if the routing

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 table never changes, why re-send it over
 and over and over and over again

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 like distance vector does?

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 That's overkill.

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 And link state is good because it's
 good to actually build a neighbor

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 relationship. Check the ground rules
 first, make sure certain things match

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 before you send your routes.

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 Distance vector doesn't do that.

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 But at the same time, what distance vector
 does have going for it is that

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 in order to know everything
 about everything.

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 All you need to know is about your
 next top neighbors and what routes

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 they're telling you about.

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 You don't really need all the visibility
 into the entire topology, which

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 link state does.

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 So in that regard, distance vector
 is actually a little bit better.

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 We should create a routing protocol
 that has characteristics of both of

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 them. And that is where we get
 advanced distance vector.

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 So in advanced distance vector, like link
 state does require that neighborships

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 be built. Like link state, it will exchange
 all of its routes right the

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 very beginning when the neighbor
 is very first formed.

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 And then it will rely on periodic hellos
 or keep alive to keep those routes

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 believable. Like distance vector, all
 it knows about is itself as directly

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 connected neighbor.

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 It does not have visibility into the
 full topology of your company.

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 It will keep a topology
 table of learned routes.

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 This is actually probably more of a
 distance vector characteristic than

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 a link state characteristic.

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 So actually, let me make that change here
 because that's not really correct.

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 Let's say distance vector
 characteristic.

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 That makes more sense.

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 Topology table of learned routes, that's more
 like a distance vector characteristic.

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 However, advanced distance vector will
 also keep track of a neighbor table.

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 And that is definitely a link
 state characteristic.

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 And EIGRP, the Enhanced Interior Gateway
 Routing Protocol, is an example

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 of an advanced distance
 vector routing protocol.

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 We also sometimes call it a hybrid routing
 protocol because it has characteristics

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 of both distance vector
 and link state.

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 In the next video, we're going to look
 at path vector routing protocols.