WEBVTT

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 So in this last video of this series,
 as we're comparing contrasting at

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 a high level the different characteristics
 of routing protocols, we're

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 now going to look at the last
 one, which is path vector.

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 Like LinkState and like Advanced Distance
 Vector, path vector also requires

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 that neighbors be developed.

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 But there's one critical
 difference.

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 LinkState and Advanced Distance Vector
 are interior gateway protocols,

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 meaning that when they're talking to
 routers, they are talking to routers

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 that are within the same autonomous
 system, within the same company.

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 So it's assumed that the router you're
 talking to is a trusted router.

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 It's not a rogue router, it's a router
 that's owned and maintained by

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 the same IT department.

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 So in Advanced Distance Vector and LinkState,
 routers are, I should say,

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 neighbors are dynamically learned.


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 We basically send out a message saying,
 hey, are there any neighbors out

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 there that are speaking
 the same language as me?

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 And then if somebody responds back,
 you say, great, let's go ahead and

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 check and make sure that we've got
 some basic matching things and then

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 we can talk to each other.

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 Path vector is an exterior gateway protocol,
 meaning that you don't trust

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 neighbors. You're not just going to blindly
 shout out into the wind, hey,

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 who wants to talk to me?

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 Because you don't want to receive hundreds
 of thousands of routes from

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 someone that you didn't want to
 talk to in the first place.

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 So in the path vector routing protocol,
 although you do form neighbor

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 relationships, there's nothing
 dynamic about it.

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 In a path vector routing protocol, you
 actually have to tell the routing

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 protocol, you have to actually configure
 it to say, this is who I want

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 you to talk to. I want you to talk to
 1.1.1.1 and here's the autonomous

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 system that he's in.

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 I want you to talk to 5.5.5.5 and here's
 the autonomous system that he's

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 in. It does not dynamically discover
 neighbors like Distance Vector, like

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 a Advanced Distance Vector
 and Link State will do.

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 Route Maintenance.

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 This is sort of like Advanced Distance
 Vector, where in a path vector

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 protocol, I will tell you everything
 I know about upfront at the very

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 beginning, which might be hundreds
 of thousands of routes.

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 And then at that point, if nothing ever
 changes, I'm never going to send

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 you those routes again.

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 We'll just exchange Keep Alive's Hello
 Pack, it's periodically, and that's

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 all that we'll use.

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 Visibility into the
 network topology.

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 Also, kind of like Advanced Distance
 Vector, where I know who my next

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 hop is, but that's it.

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 I don't know what the network looks
 like behind that next hop.

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 I don't see that.

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 All I know is my next hop and the route
 he tells me about, and that's

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 pretty much it. And the necessity of
 different data structures and tables

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 at the ICND1 label, you don't really
 have to know, but I'll tell you here

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 anyway, I think this now that you have
 to know BGP, you actually have

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 to do know this.

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 So BGP is our one and only example
 of a path vector protocol.

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 And in this way, it's a lot like
 Advanced Distance Vector.

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 It has a neighbor table,
 and it has a BGP table.

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 So all the routes I learn about from
 all of my neighbors are stored in

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 my BGP table. And then the other table
 I maintain is my neighbor table.

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 And that's it. And then my BGP table
 may or may not go into my routing

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 table, depending on if the next hop is
 reachable, depending on the Ministry

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 of Distance, and a variety
 of other factors.

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 So that concludes this video
 series on IP routing basics.

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 And I hope in your CCNA journeys or
 whatever reason you had for watching

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 this, that this series of
 videos was useful to you.