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So currently here on router 11, this is the BGP table.

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And we can see that by doing a show IP BGP.

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And what I'd like to do is let's focus on this route right here.

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And this route is being advertised by R22.

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It's its loopback address.

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It's being advertised into BGP.

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And that's how R11 knows about it.

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It learned about it via R21.

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It also learned about it from R31.

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And that's because R21 also advertised down here.

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And that got advertised here. And that got advertised here.
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And that got advertised here. And that got advertised here.

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And currently R11 has made the decision that it should be using this next top

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of 23.10.20.21 for the best route.

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Because the AS path is shorter.

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So it's basically an AS path of 20 versus 20 and also 40 and also 30 that that

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route went through before it reached a time of system 10 and R11 in AS 10.

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However, that's not the only element.

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The AS path is not the only element that's looked at.

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We have a few others that are considered first, including Cisco with the

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highest weight.
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highest weight.

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So for example, for that one route, the 22 network has its being advertised

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here.

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If R11 believes that the weight coming in from R31, that the weight is 150.

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I'll put the W there.

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And it believes that the weight for that same route coming in from R21 is 100.

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Weight is the first thing considered.

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And as a result, R11 would choose to use the route coming in from R31 as the

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best.

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And it would not use the route coming in from R21 as the best.

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So currently, the route coming in from R21 is the best route as indicated right
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So currently, the route coming in from R21 is the best route as indicated right

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there.

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Then following that, there's local preference, which really applies to internal

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routes within an autonomous system.

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And then there's looking for the next top of 0, 0, 0, 0, 0.

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And then finally, we have the AS path as a consideration.

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So as a demonstration of this currently on R11, the best path is using the next

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top of 23.10.20.21, which is the route coming in from R21.

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And the reason that one was because all other things being equal, the AS path

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was shorter for that route.

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However, if we were to train R11 that the route's coming in from R31,
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However, if we were to train R11 that the route's coming in from R31,

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should have a weight of 150, that Cisco weight would be checked first.

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And as a result, the route would change its mind regarding which is the best

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path.

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And we'd start to think that the path going through R31 with the next hop of .

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31 would be the preferred path.

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So with that in mind, let me walk you through a quick example.

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So to do that here on R11, let's just do a quick show IPBGP to make sure

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nothing changed.

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And sure enough, there's our route to 22.

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It's considered the best.

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And the next top is 23.10.20.21, which is R21.
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And the next top is 23.10.20.21, which is R21.

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So here on R11, let's go ahead and see if there's any route maps.

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Let's do a show route map.

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And there aren't any, so let's create one.

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I'm going to create a route map that does one thing.

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It's going to set the weight.

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So let's create route map.

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And let's call it set_weight in uppercase, space,

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and we'll do a permit and sequence number 10.

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And then we'll do a set_weight and let's see what our values are here.

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How about 673?

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That's a pretty unique weight.

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And then what we'll do is we'll take this route map and we'll apply it to our
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And then what we'll do is we'll take this route map and we'll apply it to our

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neighbor R31.

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So R31 and our topology is down in a Thomas system 30.

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So we'll train R11 that, hey, any routes you get from your good buddy R31,

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just set the weight to 673.

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And currently, if we look at the current weight, which is still on the screen

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here,

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the current weight for the 22 routes and all the routes actually is set to zero

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.

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So 673 is going to be a lot higher than zero.

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So let's do a do showrun, section BGP.

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They are several little bit of typing.
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They are several little bit of typing.

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And then we'll go into router BGP, a Thomas system 10.

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And then we'll go to our neighbor statement here for our neighbor at dot 31,

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which is R31.

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I'll copy paste that.

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And all I'm going to do is add an additional parameter that says,

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you know what, for routes that we receive in from this neighbor, let's go ahead

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and

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apply the route map that we just made.

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So I'll type in route map space.

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Then I do a copy paste of the name that way.

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Don't get a typo.

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So it's called set weight.

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I'm going to go ahead and copy and paste that.

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So that's done space and a question mark and in.
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So that's done space and a question mark and in.

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So effectively, any routes coming in from that neighbor,

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we are going to go ahead and set the weight to 673 based on the route map.

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So again, the route map, do a do show route map.

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It's going to set the weight to 673.

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So we'll get out configuration mode.

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And just to make sure it's a nice fair shake across the board,

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again, in production, you don't want to do this because it's going to be

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devastating.

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But I'm going to go to all routers.

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So I'm going to do a clear IP BGP asterisk and select all the routers.
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So I'm going to do a clear IP BGP asterisk and select all the routers.

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And click here on sends script.

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And that's going to reset every possible BGP neighbor adjacency.

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And that's also going to force us to have new information for updated routes.

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So let's go ahead here on our 11 to show IP BGP summary.

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So currently we have our internal BGP pairing set up.

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That's these two.

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We also have our external ones to router 21 in a ton of system 20.

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And also to our 31, which is an autonomous system 30.

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And currently we have not received any prefixes yet.
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But that's because BGP takes a minute.

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So we'll do a show IP BGP summary.

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And we're going to give it at least a minute.

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And after a few moments, we should see those routes pouring in.

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So go ahead and do a show IP BGP summary.

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There we go.

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We got one from our 12th.

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And we have one from our 21.

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And a pit there for a key again.

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We should have more in just a moment.

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But you also a show IP BGP center that shows the rib.

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So those are the two routes that we currently see here.

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And we'll give it another moment or two to fully converge.
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And we'll give it another moment or two to fully converge.

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Also while we're waiting, let's talk about this little r there.

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So we look at r in the legend.

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That's for a rib failure.

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This simply means that hey, for this route, 12, 12, 12, 12,

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it was learned a different way that has a better AD.

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So the AD for IBGP learned routes is 200.

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And this network is being advertised just in a ton of system 10

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with OSPF, which is an AD of 110.

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So we did a show IP route press enter.

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And we look for that 12, 12, 12 network.
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And we look for that 12, 12, 12 network.

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There it is right there.

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And that's why we did a show IP BGP has a little r there in front of it,

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indicating that the BGP route, even though it's the best one in the BGP table,

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is not the best one in the routing table on the router.

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And I only have one route so far for the 22, 22 network.

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So let's give it just a few more moments to fully converge.

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So for this entry, which is for the 32 network, it has a weight coming in from

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our

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good buddy r 31 of 678, 3 fantastic.

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And also for this one, but I'm still waiting on the route for 22, 22, 22, 22 to
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And also for this one, but I'm still waiting on the route for 22, 22, 22, 22 to

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come in.

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And once we see that because it also have a heavier weight, our 31 should be

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the preferred

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next hop.

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So we'll go ahead and hit the upper key.

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And I don't see that second route coming in.

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Let's go back to r 11 and give it a few more moments.

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So here at r 11, let's do a show IP BGP.

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I still don't see it.

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Let me go ahead and do one more clear here clear IP BGP.

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Asterisk just from r 11.

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So we'll do a show IP BGP summary.

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All right.

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So now it shows three routes being learned from dot 21 and three from dot 31.
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So now it shows three routes being learned from dot 21 and three from dot 31.

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That's much better.

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So now I'm not sure if it's just didn't wait long enough.

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But this was show IP BGP press center.

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So it's currently we look right here.

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It doesn't have any of them marked as the best.

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The greater than symbol isn't there for any of them, but we do have two routes

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for the

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22, 22 network.

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And you'll notice the one with the next top of 23 that 10 dot 30 dot 31 has the

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weight

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of 678, 3.

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So in just a moment, when it's done making its calculations, we hit the upper

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key

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again, it should show that as the best route, which it does.
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again, it should show that as the best route, which it does.

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So this is the next top for the 22 22, 22 network and check this out.

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Even though the AS path is longer than the AS path with the next top of R 21,

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even though

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it's longer here, because the Cisco router checked weight first as its first

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consideration

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and determining the best path, that's why it has that one put in the routing

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table.

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So now if we look at the show IP route for BGP learned routes, it's going to

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show in

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the routing table that the next top is 23 dot 10 dot 30 dot 31 for that 22
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the routing table that the next top is 23 dot 10 dot 30 dot 31 for that 22

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network.

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And to verify that, we can do a show IP route and it was hit space.

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We could also filter that to BGP learned routes, but there's our BGP learned

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route and

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there's the next top of 23 dot 10 dot 30 dot 31.

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And the reason we did that is just want to reinforce the concept of the pecking

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order

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when a router is making a decision, we're getting which route is the best.

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So again, in this case, the weight was considered before the AS path and that's

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why 6, 7, 8,

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3, 1 over 0.

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And it didn't even bother getting to this portion regarding the number of
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And it didn't even bother getting to this portion regarding the number of

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autonomous systems

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in the path.

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Because that's several lower in the pecking order when the router is choosing

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the best path

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and placing it in a routing table.

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Now to verify this, we'd want to go ahead and do a ping from a loopback on

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either R12

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or R22, etc. to one of those destination addresses.

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So let's go to R12 because it has a loopback that's being advertised in BGP.

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And let's ping 22 22 22, which is R22.

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So we'll go to R12 and let's do a ping to 22, etc.
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So we'll go to R12 and let's do a ping to 22, etc.

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And we'll source that from our loopback zero and that works.

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And if you do a trace, it should be taking the long way because of how we

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manipulate a BGP.

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So that traffic should go from R11 down to R31 to R41 to R42 to R21 and then

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finding to

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R22.

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So we'll do a trace route to 22 dot 22 dot 22 dot 22 and we'll source that from

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loopback zero press center.

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So there's the path based on that last octet that's R11, R31.

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In fact, let me bring up the topology while we talk about that.
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In fact, let me bring up the topology while we talk about that.

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So the path would be from R12 to R11, which is an AS10 and then over to R31,

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which is an

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AS30 and then over to R41, which is in AS40 and then to the other router in AS

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40, which

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is R42 and then up to R21, which is an AS20.

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And then over to R22 who own that loopback address and that's the path we have

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through the

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network.

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So in this video, we've had the opportunity to see BGP at work, including IBGP

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and external
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and external

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BGP, as well as how to advertise a route in BGP.

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We also took a look at playing with the weight value just to see that indeed it

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does determine

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which route is considered the best by a router.

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Now watching all this is well and good, but it's not nearly as good as if you

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were able

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to have a chance to practice yourself, which is exactly what I've designed for

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you in the

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next video is to present a hands-on lab so you can get some practice in config

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uring and

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working with BGP.

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So I'll see you in the next video for that hands-on lab.
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So I'll see you in the next video for that hands-on lab.