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[AUDIO LOGO]

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So finally, let's
use BGP as our CEPE.

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And one of the things
we want to focus on

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is we work through this is
how little work actually

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has to be done on the PE router
in order to accomplish this.

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Yes, of course, we will have
to configure BGP neighborships

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for the customer routers, but
there's no additional protocols

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to run.

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There's no redistribution
that we have to do.

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It really does save a
lot of work on the PE

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and offloads that
work to the CEs.

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We're going to be setting
this up for customer B

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in our environment, and we
will explore the one caveat

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that we do normally
have to work with when

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handling BGP as the CEPE.

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That's simply that the customers
will usually have the same AS

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number at multiple sites.

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In fact, they may only
have one AS number total.

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And it may even be a private
AS number that we gave them.

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And that's something that
we'll have to deal with

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or the customer will.

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So we'll explore some
of those options.

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So that said, let's take
a look at our topology,

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so we can see where we're
going to be running this.

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And then, of course, we'll
jump into the command line

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and get BGP up and running
as our CEPE for customer B.

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So as we mentioned, we will be
configuring BGP for customer B

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down here, between
their headquarters

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and their remote site.

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Now, the first thing we're going
to need here for customer B

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is going to be an AS number.

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So we'll go ahead and
configure their AS number

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on both sides as 65001.

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So we'll use this
private AS number

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at both of their locations.

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And as we mentioned,
that's going

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to push the redistribution job
out here to the CE routers.

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Now, since all of the
networks are directly

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connected to the CEs, we'll just
do a redistribute connected.

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However, of course,
in the real world,

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the customer would redistribute
whatever core protocol

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they happen to be using.

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

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Let's just start on router 7
and get the customer routers

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configured first.

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So let's go ahead and begin by
configuring router BGP 65001.

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Then, we'll configure
our neighbor.

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Our neighbor here is
going to be 192.168.27.2.

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That's router 2's address.

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And the service provider
is remote AS 100.

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Then let's do a
redistribute connected

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and do a configuration.

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That's all there is.

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Now, obviously,
the customer might

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want to redistribute something
else, but, in this case,

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connected will be fine.

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We're going to do the same
configuration on router 10.

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Of course, the
neighbor's address

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is going to be different
here, 192.168.51.5.

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It's, of course,
in remote AS 100.

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And we'll still do
redistribute connected.

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Now, we'll configure the PEs.

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Let's start on router 2.

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Let's begin by seeing, if
we have any of our BGP route

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policies on this router, let's
do a show rpo route policy.

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And we actually see that
we don't have any route

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policies on this router.

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So that's going to
be the first thing

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we're going to want to do.

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Let's do a route policy.

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Let's call it RP_ALL because
all we're going to do

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is pass all the routes.

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So we'll end that policy.

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So now, we have a route policy
to pass all the routes through.

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Now, we're going to router BGP
100 into the VRF for customer

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B, into our address
family for IPv4 unicast,

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and we'll configure
our neighbor.

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The neighbor here
is going to be .7.

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That neighbor is
a remote AS 65001.

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And for the address
family, IPv4 here.

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We're going to put in
our filters, RP_ALL.

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We'll use that same filter
inbound and outbound

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to that neighbor.

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Because, at this
point, at least,

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we want to send and receive
all of the customer routes.

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We're not trying to
do any filtering here.

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Let's commit our changes.

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And we can exit configuration.

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So here on the console, we
see that neighborship just

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came up, which means
that we should actually

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have some prefixes.

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So let's do show bgp vpnv4
unicast for the VRF customer B.

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And we see that we are,
in fact, receiving updates

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from router 7.

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So, so far, this
is looking good.

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Let's actually jump over
and configure router 5 next.

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So router 5, we go
into router BGP 100,

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into the address family ipv4
four unicast for the VRF

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customer B, and we configure
our neighbor, 192.168.51.10,

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which is in remote AS 65001.

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We see the BGP neighborship
come up, so let's verify.

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We'll do a do show bgp vpnv4
unicast for the VRF customer B.

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And we see all of the routes
being learned through BGP.

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So this is looking good.

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Let's go ahead and
jump out to router 10,

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and let's just do
a show ip route.

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And unfortunately,
we see nothing

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but local and connected.

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Well, we already know
what the problem is here,

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but let's do a debug
ip bgp update and clear

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our inbound BGP session.

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We'll turn off
all the debugging.

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And we already see here
what the problem is.

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We're getting all
of these prefixes,

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but they're, of course, denied
because they contain our AS

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number.

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Now, there are a few
ways we can fix this.

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So let's take a look
at a couple of them,

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and we'll talk
about one of them.

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So we could simply do this.

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We could go back to router 5,
go back up to our neighborship

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and just change the option
and say as override.

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Let's go back over to router
10 and clear the updates again.

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We won't even leave
the debug on this time.

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We'll just say what happens.

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And we see, just
like that, we're

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now receiving all
of the BGP updates

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because the AS is being removed.

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If I were to say, show ip bgp,
we can see that what's happened

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is the 65001 that
was put on by router

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7 has been removed and
replaced with AS 100

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from the service provider.

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So as you can see, this is
a very nice, clean solution,

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which is partially
why it was created,

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that we can use to simply
replace the customer's

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AS with the service providers.

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So now, let's go over and take
a look at a different option.

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Let's configure this
one on router 7 itself.

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Because we'll look
first, but router 7

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is having the same problem.

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So again, jumping over to router
7, if I do a show ip route,

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we can see we have
the exact same issue.

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Now, we don't have to do
the debugging everything.

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We know what the problem is.

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However, we could fix it a
slightly different way here.

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We could simply say,
to allow our own AS

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in from that neighbor.

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If we do that, if we do our
show ip route, give it a second.

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But here, we come across
an interesting problem.

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Notice that after several
refreshes of the routing table,

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and, in fact, I can
do it again, we're

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still not getting the updates,
even though we should be.

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So let's turn on our debug
and see what's happening.

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Let's do our refresh again.

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That's a lot of input.

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Notice, all these routes--
wait, no, there's no routes.

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Let's go up to router 2 and
see what's going on here.

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Because we're not even receiving
the updates here on router 7.

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It's not a matter of our
own AS being in the AS path.

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So let's go up to router
2 and see what's going on.

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On router 2, let's do a show
BGP for the VRF customer B.

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And for our neighbor 7,
let's see what routes

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are being advertised to it.

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We can see that this is a very,
very long list of nothing.

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This explains a lot of
what's going on router 7.

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It's not getting
any of the updates.

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And the reason for this is
because of IOS XR's behavior.

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It already knows that
the path contains 65001,

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and it's not going to send
those updates to a device

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that it knows is in 65001.

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So even though allow
AS in is possibly

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a solution we could
use here, it's

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not going to save us from
having to do AS override here

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on router 2.

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So let's go back into
configuration, back into router

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BGP 100, back into customer B.

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Then, we're going to configure
our neighbor, 192.168.27.7,

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into the address family IPv4
unicast for that neighborship,

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and we're going to
configure AS override.

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We'll commit those changes
and exit configuration.

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Now, if we hop back
over to router 7,

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we can see, since our
debug was still running,

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that as soon as we got
done configuring router 2,

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it went ahead and sent
us all of the updates.

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Now, we'll turn off the bugs.

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We'll do a show
ip bgp, and we'll

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see that the AS override is,
in fact, what's in effect.

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So can allow AS in be
an appropriate solution?

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Yes, but only if the
other device is actually

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sending us the routes.

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Another possibility could be
to have the service provider

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remove private ASs, assuming
that the customers are

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using private ASs.

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So there could be multiple
solutions to this,

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but the best one is going
to be the AS override.

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Just to make sure
everything is working,

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let's ping 10.10.10.10 and
source it from our loopback

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zero interface.

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We can see that this is working.

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So now, we have BGP up
and running as our CEPE.

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So in this video, we
set up BGP as our CEPE.

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And as we saw, that
was very easy to do.

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We configure a
few neighborships.

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We have the prefixes
go right through,

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no redistribution,
no extra protocols.

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The only issue we had was
when the neighboring sites

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are using the same AS number.

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So we had to do AS
override or, possibly,

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one of the other
solutions to fix that.

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But AS override is
definitely the best solution.

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So that covers
everything we need

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to discuss in this
skill, which leaves us

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with just a review in
the form of a quiz,

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and we're going to do that next.

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Until then, 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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