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In this video, we're going to focus on internal BGP.

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That's IBGP for short.

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And that basically means that the two ends of our BGP

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session, the two routers that are participating in BGP,

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are both in the same autonomous system number.

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And the syntax is really simple.

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We go into configuration mode and then from configuration mode,

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we type in router, space, BGP, space,

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and then our local autonomous system number.

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So in this case, that pair for a autonomous system 10,

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we put a 10, and then we press enter.

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And that puts us into router configuration mode for BGP
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And that puts us into router configuration mode for BGP

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autonomous system number 10.

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And then from there, what we would do

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is simply specify who our neighbors are.

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So the syntax would be neighbor.

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And then the address of that neighbor, B, C, D,

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in the case here of R12, we could point the loop back.

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And on the loop backs are the same as the router number.

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So R12 has a loop back of 12, 12, 12, 12.

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R13 has a loop back of 13, 13, 13, 13, 13.

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R11 has a loop back of 11, 11, 11, 11, and so forth.

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And within an autonomous system, I've already

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got OSPF running, already advertising those loop backs.
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got OSPF running, already advertising those loop backs.

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So all the loop backs here in a autonomous system 10

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are reachable to other devices in the same autonomous system,

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same thing over here in AS20 and AS30 and inside of AS40.

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So we'd say neighbor, space, if we want to point to a loop

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back address of our peer we can, and then space,

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then we're going to use the command remote, dash AS.

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Now, even if our peers in the same autonomous system,

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that's the keyword, remote, dash AS in the space.

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And then we specify the AS number of 10.

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So we'd use this command on our 12, our 13, and our 11
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So we'd use this command on our 12, our 13, and our 11

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as we peer with each other to their loop backs.

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Now, if we are peering to the loop backs,

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we need to one of their statement that is neighbor,

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same neighbor IP address, space, and we use the command

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update source, and then loop back zero, if that's the IP address.

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And that way, when we start our session, for example,

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from our 12 or our 13, we'll be sourcing it from loop back zero.

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And if we target 13.13.13.13.13, then we're

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specifying the correct IP address for the peering on both sides.

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The loop back zero here, we're going to loop back over here.
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The loop back zero here, we're going to loop back over here.

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So in order to source it from our loop back, instead of just

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the interface, from a routing table closest to that destination,

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we want to use that update source command,

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and specify the source IP address.

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In this case, the interface associated

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with the source IP address, we want that session to begin from.

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And when we reach out and we start the session,

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we're going to be using TCP.

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And the destination port is 179.

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So part 12 was starting the session.

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So we would use some high numbered unused port at the moment,

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and connect over to our 13 at port 179.
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and connect over to our 13 at port 179.

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And they can both use that session as they negotiate

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and set up their BGP neighborship.

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But the destination well known port for BGP

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is TCP port 179.

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So if we wanted to configure this autonomous system

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in the IBGP neighborships, we'd basically

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do this configuration on a routers 12, 13, and 11.

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And we would point, for example, in our 12,

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we'd point to the loop back address on our 12 for the peering.

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And from our 12, we'd point to the loop back address of our 11

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and vice versa.

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From our 11, we'd point to the loop back over on our 12.

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And from our 11, we'd point to the loop back over here
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And from our 11, we'd point to the loop back over here

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on our 13.

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So with that in mind, let me go ahead and walk you

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through sitting up the IBGP neighborships

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here between our 11, our 12, and our 13.

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So let me bring up the topology here,

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just to confirm our topology looks good.

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And we're going to be focusing on AS10.

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So let me go ahead and double click here on server 1

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and hug, bring it up, give that a moment to initialize.

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There it is.

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Fantastic.

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And here's tabs for all of the routers.

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So currently in our 11, our 12 and our 13,
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So currently in our 11, our 12 and our 13,

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I believe BGP has already configured.

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So if we do a show, IP protocols and press center, sure enough.

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I've got here, I've got OSPF running.

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That's great.

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And if we hit the space bar, I've got BGP already running.

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So I'm going to remove BGP from our 11, our 12 and our 13.

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So we can demonstrate the entire configuration of the IBGP

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neighborships from scratch.

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So I'm going to use this icon right here,

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the little carriage return icon right below the help.

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And click on that.

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And we're going to go into configuration mode
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And we're going to go into configuration mode

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on all three routers, and do a no, router, BGP,

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and a ton of system 10, and type in end.

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And we're going to apply that to our 11, our 12 and our 13.

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And we'll click on send script.

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And it is done.

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We've just removed BGP.

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So now we do a show, IP protocols, press center.

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I've got OSPF.

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If we hit the space bar, but we don't have BGP running anymore.

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All right, so let's start on our 11.

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Now we want to peer from our 11, we want to peer with our 12,
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Now we want to peer from our 11, we want to peer with our 12,

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at our 12's loopback of 12, 12, 12, et cetera.

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And we also want to peer from our 11 with our 13,

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at its loopback of 13, 13, 13, 13.

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And so we can verify, first of all,

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those routes from the routing table do a show IP route, press center,

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and sure enough, there's 12, 12, 12, 12, and 13, 13, 13,

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13, both in the routing table.

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Because if we can't reach those loopback addresses,

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you're not getting me able to peer to those IP addresses with BGP.

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So we're relying on the interior, get me a routing

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for a call, in this case, OSPF, for reachability to those loop
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for a call, in this case, OSPF, for reachability to those loop

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backs.

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So here in our 11, we'll go into configuration mode.

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We'll type in router, BGP.

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And we want to use a ton of system 10, press enter.

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And then we'll specify our first neighbor.

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Let's go ahead and use our 12.

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So we'll type in neighbor.

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And I'm going to go ahead and just copy and paste the 12, 12, 12,

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12 from right here.

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And then the keyword remote AS.

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And then R12 is also in a ton of system 10.

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So even though the keyword is remote, dash AS,

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think of it like what AS is the remote device in.

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It's also in 10.

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And so effectively, once we're done configuring the other side
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And so effectively, once we're done configuring the other side

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as well, R12, it's going to configure an internal BGP

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neighbor ship, because both routers are 11 and 12

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are both in the same ton of system.

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Now because I'm going to be sourcing it,

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I want to source it from my loop back address,

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going to their loop back address.

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I'm going to hit the upper of key into a neighbor 12, 12, 12, 12 again,

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and specify update source loop back zero, just like that.

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And then I'll do the same process for R13.

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So if you look at our topology, R13 is in the top of a ton of system 10.

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And we're going to pair to it at its loop back address of 13, 13, 13, etc.
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And we're going to pair to it at its loop back address of 13, 13, 13, etc.

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So we'll type in neighbor, 13.13.13.13.13.

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And that's also in the same AS, we'll do remote AS 10 enter.

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And then we want to go ahead and specify for that neighbor

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that we want to use our update source of loop back zero, just like that.

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And we'll do a do show run section router.

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And here's our BGP configuration for BGP, a ton of system 10.

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We have two peers at 12, 12, etc., and 13, 13.

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And we've also specified that for those purings,

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we want to use our own local loop back zero address,
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we want to use our own local loop back zero address,

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which on R11 is 11, 11, 11, 11.

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All right, so next, let's head over to R12.

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So here at R12, we'll do a similar treatment.

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We'll go into configuration mode, router, BGP, a ton of system 10.

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And we'll specify that we have a neighbor, or we want to have a neighbor,

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over at 11.11.11.11.

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And the remote AS is 10.

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And for that same neighbor, we want to use update source loop back zero.

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And then similar treatment for 13, 13, 13, 13.

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We also just got an up notification at the console,

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regarding that neighbor ship, fantastic.
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regarding that neighbor ship, fantastic.

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So we'll do a neighbor for 13.13.13.13.13.

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Remote AS 10, and also update source using our local loop back zero.

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So we do a show run, right, section router.

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Take a look at that.

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Here's our configuration for BGP, a ton of system 10,

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that we just configured on R12.

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So next, we'll go to R13 and do something extremely similar,

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except we'll point to the IP addresses of R11 and R12's loop back zero

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addresses for those purings.

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So we'll go to R13 and FIGT, Router, BGP, 10.
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So we'll go to R13 and FIGT, Router, BGP, 10.

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Neighbor is going to be 11.11.11.11 in the remote autonomous system of 10,

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same as ours, that makes it an IBGP peer.

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And for that neighbor, we want to use update source loop back zero.

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And then neighbor 12.12.12.12, remote autonomous system 10, same as ours.

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It'll be an IBGP neighbor ship.

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And for that same neighbor, we want to use update source loop back zero.

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And we'll do a show run, pipe section router.

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Actually, it's to pipe section BGP, press enter, that'll work even better.
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Actually, it's to pipe section BGP, press enter, that'll work even better.

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So there's our BGP configuration that we just configured on R13.

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Now, in a production environment, you wouldn't want to do a full reset of BGP

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because BGP is fairly slow to convert, and it may take a while.

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However, in this case, in a lab environment, it won't be too bad.

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So let's go ahead and hit the character trunite icon up here.

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And I'm going to do a clear IP BGP asterisk.

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Now, in a production environment, with hundreds of thousands of routes,

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this is a really bad idea.
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this is a really bad idea.

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You want to do a soft reset.

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But this is a hard reset.

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We'll do a clear IP BGP and press enter.

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And we'll apply that to R11, R12 and R13.

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Click on send script, and it is done.

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So just be aware that after you do a clear IP BGP asterisk,

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it may take up to 60 seconds, or it may be even a little longer

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for them to fully become adjacent and share any routing information

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and provide all the updates.

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So if we go to R11 in our topology, and in our topology,

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that's this guy right here at the edge of a time system 10.
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that's this guy right here at the edge of a time system 10.

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And so go ahead and do a show.

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Oh, this guy didn't get a clear because he was in configuration mode.

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Let me take a look at 12 and 13.

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Oh, they did.

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So because everybody else forced a clear, we're good to go as well.

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So R11, if you do a show, IP BGP summary, which is a great command, press enter

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,

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is showing us that we have two neighbors, one at 12, 12, 12, 12.

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That's the identity of that neighbor.

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And the way that BGP chooses a router ID is exactly the same as it does for OSP

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F.

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If you've got one hard configured, it's going to use that.
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If you've got one hard configured, it's going to use that.

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If you don't have one hard configured, it's then going to use the highest IP

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address

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on a loopback interface.

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And if you don't have any IP addresses on loopbacks, it's then going to use the

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highest IP

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address on any other active interface at the time BGP comes up.

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So for the lab, it's going to match the actual loopback zero address because we

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're not

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configuring manually the router ID, but we do have those loopbacks.

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And that's why the ring used as the router ID.

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So here we have those two neighbors.

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Great.

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We haven't received or on the far right hand side.

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We haven't received any networks yet.
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We haven't received any networks yet.

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We do have the neighborships.

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And we also can do a show IP, BGP, and press enter.

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And that will show us any BGP routes from the routing information base.

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And again, we haven't been advertising any yet.

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So we shouldn't see any.

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And we can also show IP, BGP, neighbors, press enter.

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So here's the command show IP, BGP, neighbors.

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It's showing us details about that neighbor, including the neighbor ID.

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What AS it's in.

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Well, version of BGP is running.

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10:23.680 --> 10:25.240
The current state, which is established.

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10:25.240 --> 10:27.160
It's going to be a question up further over two minutes.

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10:27.160 --> 10:29.920
And some of the capabilities regarding that BGP speaker.

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10:29.920 --> 10:32.040
And then if we scroll down, it has some stats.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

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And then if we scroll down, it has some stats.

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We're getting sent and received.

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10:33.600 --> 10:38.640
And if we continue to scroll down by default, BGP4 is supporting IPv4 unicast.

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10:38.640 --> 10:41.760
And if we scroll down far enough, we'll get information on our next peer.

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10:41.760 --> 10:43.000
And here it is right here.

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10:43.000 --> 10:45.440
That neighbor is 13, 13, 13, etc.

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And as we continue to scroll down, it has neighbor capabilities.

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10:48.280 --> 10:51.160
And other stats we're getting sent and received for that peer.

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All right.

248
10:52.160 --> 10:53.160
Fantastic.

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10:53.160 --> 10:58.330
We have AS 10 and the internal BGP neighborship setup between our 12, our 13

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10:58.330 --> 10:59.480
and our 11.

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10:59.480 --> 11:03.400
In the next video, let's turn our attention to setting up external BGP
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

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In the next video, let's turn our attention to setting up external BGP

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neighborships between

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11:04.280 --> 11:11.370
our 11 and its 2B neighbor, our 21 and also our 31, which are an AS 20 and AS

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30 respectively.