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[AUDIO LOGO]

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So now that we have
a game plan together,

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our first step
with configuration

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is going to be to configure
our iBGP peers in AS 65001

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and 65002.

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So that's what we're going
to be doing in this video.

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Let's once again
bring up our topology

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just as a reminder of what
we're going to be building here,

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and then we'll jump
into the command line

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and get these neighborships
up and running.

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So the part that we'll be
setting up in this video

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is we'll be neighboring up
router 1 to router 2, router 1

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to router 5, router 1 to router
4, and router 1 to router 3.

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Then we'll jump
over to AS 65002,

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and we'll set up that
neighborship between router 6

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and router 7.

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Keep in mind with this design
of iBGP neighborships in 65001,

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we're ultimately going to
need router 1 to be a route

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reflector.

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This, of course, is because
of BGP's rule of split horizon

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where we can't take an
update from an iBGP neighbor

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and send it to
another iBGP neighbor.

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That's of course why iBGP
normally has to be a full mesh,

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and as we can see here,
we're clearly not building

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out 65001 as a full mesh.

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So we're going to have
to do more in that AS

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as we go through
our design here.

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But for now, we want
to leave it as it is.

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In other words, just
building the neighborships

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so we can actually
see the problems that

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come up before we make
router 1 a route reflector.

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So again that will
happen, but it

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will happen a little bit later.

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Now technically in 65002
we do have a full mesh

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because there's only
two routers and they're

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going to peer with each other.

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So 65002 is not going to have
a problem, but 65001 will.

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Just so we're aware of it
going in, we're expecting that,

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but we also want to examine it.

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So now let's go ahead and
jump into the command line

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and get started.

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We may as well begin on
router 1 since clearly it has

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the most amount of work to do.

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So the first thing we have
to do is create our process.

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So it's going to be
router BGP and, of course,

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the AS here is 65001.

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We'll set our router ID.

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We'll just set it to its
loopback address, which

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is 10.1.1.1, and then we'll
begin configuring our address

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family IPv4 unicast.

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Since router 1 is actually going
to have a significant amount

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of configuration
here, let's go ahead

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and use a neighbor
group on router 1.

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We'll call it iBGP_PEERS.

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And since they're
iBGP, that means

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that they're going to be
in the same remote AS.

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We also said we were going
to peer using our loopbacks,

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so we'll set our update
source to loopback 0.

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And, of course, we want to
activate the address family.

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Next, let's configure
our neighbors

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to actually use
this neighbor group.

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So first we'll do
neighbor 10.2.2.2,

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And we'll say use
neighbor-group,

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and we'll put in
our name iBGP_PEERS.

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Now we're going to do the
same thing for the other three

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neighbors.

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So let's just go ahead
and change the addresses.

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It's going to be neighboring
up with 3, 4, and 5.

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We'll commit our changes,
and we'll exit configuration.

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So next let's hop over
and configure router 2.

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Again, this is going
to be in 65001.

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We'll set its BGP router ID,
enable our address family,

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and here we'll just
configure router 1.

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Again, iBGP so it's
the same AS number.

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We'll set our update source,
and activate our address family.

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Exit configuration.

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And we should see that
neighborship come up.

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So it got buried in the
other console messages

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there a little bit, but
if we look at this line,

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we can see that the
neighbor did come up.

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To make it easier, we'll
do a show BGP summary,

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and we can see that the
neighborship with router 1

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is in fact up.

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It's been up for 17 seconds.

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It hasn't exchanged
any prefixes yet.

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However, the fact
that that is a number

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indicates that it's actually up,
even though that number is 0.

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Next, we configure
routers 3 and 4.

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They get an identical
configuration to router 2,

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so we'll do a little bit of
copying and pasting here,

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but we will have to
change the router ID.

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So let's start off putting
that configuration in Notepad.

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So this is the configuration
we're going to be using.

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We just need to change our
router ID here to be router 3.

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Highlight everything
and copy it.

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And then back on router
3 we simply paste it.

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We should see router 1 come up.

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It did.

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So then we can see that router
1 has been up for 4 seconds,

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and now let's grab the
config for router 4.

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Again, we'll change
the 3 to a 4.

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Highlight everything, copy
it, and paste it on router 4.

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And again router 1 is up.

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Now we can't exactly copy and
paste directly onto router 5

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just because it is iOS XE,
so it's slightly different.

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We'll just do that one manually.

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Still, of course, we
create the BGP process.

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We'll still set the router
ID, but here we go directly

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to neighbor configuration.

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So it's router 1.

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And then, of course, the
settings for those neighbors

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actually go on the neighbor
statements in iOS XE.

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So we'll set the update
source to loopback 0.

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So here we can see
that router 1 came up,

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but we'll still do
our show BGP summary.

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And we can see that router 1
has been up for 22 seconds.

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So that takes care of all of
our neighborships in AS 65001.

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Now let's go do AS 65002.

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We'll just jump into router 6.

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Again, this is 65002.

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Well, of course, at the
BGP router ID still,

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and we'll set up router 7
as our neighbor of course

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in the same AS since it's iBGP.

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Update loopback 0, and
we'll exit configuration.

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It's going to be a very similar
configuration on router 7,

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but since we have to mirror 3
out of our 4 commands anyway,

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it's not really necessarily
worth using Notepad here.

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So again, BGP process.

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Set the router ID, the remote
AS, and set the update source.

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Now something to note here, see
that our neighborship came up

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before I even hit Enter
on the update source

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loopback 0 command.

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The fact of the matter we're
only creating a TCP session

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to exchange our BGP updates,
and that session only

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has to happen between
one pair of IP addresses.

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You don't technically need
the update source loopback 0

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on both sites in a
connection like this.

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If you have it, what it'll do
is it'll create two TCP sessions

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and then tear one of them down,
and at the end of the day,

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you only have one session left.

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Just like when my
neighborship came up here,

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it had only formed
one TCP session.

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And we know this
because, of course,

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BGP will only accept
the TCP connection

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from the neighboring
address that

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matches its neighbor statement.

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So since router 6 was configured
with a neighbor statement

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of 10.7.7.7, it would not
have accepted our neighborship

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until we set the
update source here.

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However, here on router 7, I
set the neighbor as 10.6.6.6

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so I accepted its
packets on TCP port 179,

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and our neighborship
was established,

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and we came right up.

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It only ever established
that one TCP session,

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but actually that's all we need.

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So you might be looking
at this and maybe you're

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thinking to yourself,
well, if we only

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need update source
loopback 0 on one side,

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why do we always put
it on both sides?

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And the answer is
honestly best practice.

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It doesn't really have
to be on both sides,

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but we normally put
it there anyway,

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I just wanted to
point that out so you

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can understand why our
neighborship came up here

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before I even hit Enter on
that update source loopback 0.

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So after that
whole discussion it

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might be a little
bit of a moot point,

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but let's still just
do our show BGP summary

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just so we can verify
that it is in fact up.

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And after all that
explanation I did,

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it's actually been
up 3 minutes now.

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So now we have our four iBGP
neighborships up on router 1,

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and our one BGP neighborship
up between routers 6 and 7

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in AS 65002.

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So in this video, we jumped
into the command line

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and we got our iBGP
neighbors set up

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in two ASs that need iBGP
neighborships, AS 65001 and AS

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65002.

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Now, of course, we have to
start setting up neighborships

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between our
confederations, and that's

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exactly what we're going
to do in the next video.

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I'll see you there.

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I hope this has been
informative for you,

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and I'd like to thank
you for viewing.

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