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Our mission should we choose to accept it is to go ahead and configure this

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autonomous system,

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a autonomous system 20 with the IBGP nameorship and the two external BGP name

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orships as shown,

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and then advertise R22's loopback so that it's advertised via BGP. So we're

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going to start off by

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going to R21 and R22, we'll remove the existing config, and then we'll follow

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these steps and

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put it all back. With that being said, let's make a road trip over to the lab

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environment. So here in

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the lab environment, let's go to R21, let's just look at our topology real
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the lab environment, let's go to R21, let's just look at our topology real

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quick. Here it is,

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let's double click on that to open it up. All right, so let's go up to R21 and

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R22. In fact,

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we can remove the configurations just by going to this icon right here, the

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carriage return icon,

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and from there, we'll do a config T and no router, BGP, autonomous system 20,

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and end, and that should

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do it. So we must then enter R21 and R22. I'll select those two routers, click

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on send script, and

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it is done. So all those routers, if we did a show, run, section, BGP, not BGT,

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but BGP. There is
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but BGP. There is

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no configuration for BGP whatsoever. So the first step is done. We've removed

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the configuration for

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BGP from both R21 and R22. So let's go back to R21 and begin our config. So we

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'll go into configuration

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mode. We'll type in router, BGP, autonomous system 20, and our neighbor, I'm

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going to point

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to the loop back address at 22.22.22.22 and say, remote, autonomous system,

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same as ours, which is 20,

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and I'll hit the up arrow key and say, update source, loop back zero. Also,
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and I'll hit the up arrow key and say, update source, loop back zero. Also,

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while I'm here, I'm going to say

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that neighbor 22, 22, etc. that I was supposed to add next top self as I

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learned routes from other

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external neighbors and I send them to this internal BGP neighbor. I'll set that

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next top to my address.

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All right, so that's our internal neighbor. And while we're here, let's also go

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ahead and do the

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external neighbors as well. So we're going to neighbor with R11 at 23.10.20.11

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and we're going to neighbor

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with R42 at 23.20.40.42. And for each of the routers, you can either go look at
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with R42 at 23.20.40.42. And for each of the routers, you can either go look at

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the IP addresses on

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those interfaces or just realize that the last octet on every router matches

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its router number.

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So let's configure the external BGP neighbor ship between R21 and R11. So we'll

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say neighbor and

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R11 address is 23.10.20.11 and the remote AS that they're in is 10. That's R11.

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And I'm just going

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to pause here for a second because R11 is already configured. And so it should

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give me a console message

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in just a moment. There it is that that neighbor ship is up. Then we'll do
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in just a moment. There it is that that neighbor ship is up. Then we'll do

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another neighbor statement

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for 23. We want to go down to R42, which is at 23.20.40.42. And that's in the

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remote autonomous system

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of 40. So we'll put that in. Oh, look at all those characters. I have like a

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five octet IP address.

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So it's 23. I have one to many 23s in there. So let me go ahead and fix that up

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. Neighbor 23.20.40.42

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in press center much better. And we'll verify that the neighbor comes up as
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in press center much better. And we'll verify that the neighbor comes up as

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well. Fantastic. So then

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that we have that done. Let's go ahead and go configure R22. So R22 is right

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here. So we'll go into

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configuration mode and type in router, BGP. And we're in a system 20. And our

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neighbor is going to be

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21.21.21.21.21.21. And the remote AS is the same as ours, which is 20. And we

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're going to say

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for that neighbor, we want our update source to be loop back zero. And if you

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use the actual physical

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interface on that directly connected network, you wouldn't need to worry about

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doing the update source.
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doing the update source.

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So I'm going to go ahead and do that. And then on both router 21 and 22, I'm

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going to do a clear IP BGP

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asterisk. And it is the same thing on router 21 to clear IP BGP asterisk. And

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that's going to give us

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a nice fresh establishment of our sessions and also a nice fresh update of all

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the routes. And

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again, it may take a moment or two for that to fully converge. So while it's

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happening, we need to show

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IP BGP summary. And that wasn't too bad. So we have three routes that we've

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learned from R11. And
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learned from R11. And

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we also have three routes that we've learned from router 42. And we haven't

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learned any routes yet

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from R22. And that's because we have not yet advertised any routes. So if we do

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a show IP BGP,

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that'll show us the routes that we've learned in the rib. And at the moment, we

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don't have any greater

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than symbols, but that will rectify itself here in a moment once R21 decides.

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So while it's still

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thinking about that, let's go to R22. And let's advertise our loop back address

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with a show IP

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interface brief, verify what our loop back address is. And the IP address is a
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interface brief, verify what our loop back address is. And the IP address is a

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32 bit one who do a show

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IP route, a little confirm it for us. So there it is right there. It's a 32 bit

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route. So we're going to

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configuration mode router, BGP, autonomous system 20, all type in network 22.22

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.22.22.22 space the keyword

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mask, and then the 32 bit mask, beautiful type in end. And that's a show IP BGP

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press center. And there

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are all the routes. So that's the route that we just added on our 22. That's

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why the next top is

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0, 0, 0, 0. And then we have the routes for the 12, 12, 12. That's the loop
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0, 0, 0, 0. And then we have the routes for the 12, 12, 12. That's the loop

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back on R12. We have the

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route for router 32. And we have the route sourced by router 43. So now here

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from router 22, we should be

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able to ping those other respective loop backs sourcing it from our loop back

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because they also have

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reachability back to us. And let's test that next. So in R22, let's go ahead

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and do a ping over to

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how about let's go down to R32, which is 32.32.32.32.32. And I got excited that
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how about let's go down to R32, which is 32.32.32.32.32. And I got excited that

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I forgot to say,

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hey, source this from my loop back zeros. So we're sourcing this from the IP

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address on our gig 1/0

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interface here on R22. And what I need to do is do a source it from loop back

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zero, which is the

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22 22 22 to address. And because the destination R32 has a route back to our

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loop back at 22 22, etc,

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we should be able to get a response. And that looks much better. It's also a

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trace and verify the

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path. So we'll do a trace route to 32.32.32.32.32.32.32 and we'll source it

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from loop back zero.

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And if you just take a peek just for a moment at the edge router R21 and we do
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And if you just take a peek just for a moment at the edge router R21 and we do

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a show IP BGP, as we

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try to go to 32, its preferred route is using the next top of 23.10.20.11,

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which is R11. So after

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the packet goes to R21, the next hop in the path should be R11. We can verify

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that by doing the trace.

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So do the trace and sure enough, the first top is R21 and the next top is R11,

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then to R31, then finally

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to R32. And if you just show IP BGP summary, that'll show us who our neighbors
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to R32. And if you just show IP BGP summary, that'll show us who our neighbors

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are and how many

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prefixes we've learned from that neighbor. And if you just show IP BGP enter,

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it'll show us the

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BGP rib, the routing information base with all the routes that we know about.

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And for the routes

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in the routing table, we can just show IP route. We can also show IP route

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followed by BGP, just to

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narrow it down to the BGP learned routes in the routing table. So thanks for

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joining me in this

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fundamental look at the world of BGP, where we had an opportunity to look at

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and configure and

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verify internal BGP, external BGP. And if you're interested in even more and
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verify internal BGP, external BGP. And if you're interested in even more and

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more detail on BGP,

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which there's a lot more detail to it, come see us in one of our additional

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professional level

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courses for Cisco, such as an RC, which provides an even deeper look and goes

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into more of the

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methodologies and options in tweaking and tuning BGP. But for now, thanks for

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joining me in this set

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of videos. And I look forward to seeing you in another set very, very soon. And

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until then,

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I hope this has been informative and I'd like to thank you for viewing.