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[AUDIO LOGO]

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We know that MPLS creates
a label for every route

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in the routing table.

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That doesn't necessarily
mean, however,

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that we want to
advertise those labels

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to every one of our peers.

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So what we have is a
way that we can limit

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or filter which labels
are sent to which peers.

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This is a relatively
easy process.

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However, there are some
rather unique rules

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that we want to look at
before we just jump into this.

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So that's actually what
we're going to do first.

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Then, of course, we'll take
a look at our topology,

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just to see what
we're going to build,

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and jump into the command
line and make this happen.

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But on the other
side, there's also--

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we may not want to
receive all labels.

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That's a much easier process.

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We don't have to worry
about a bunch of rules,

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it's just the filter.

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But we're going to be taking
a look at that as well.

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So again, let's go ahead
and jump into that topology,

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take a look at what we're
going to build and look at,

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and then, of course, get
this up and operational.

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So let's begin by looking
at these filtering

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rules around our conditional
label advertisement.

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So the first rule
is, if there is

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no ACL about a particular
label, that label is

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going to be sent to everyone.

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And you could argue that this
is the default condition.

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There is no ACL
about any labels.

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And therefore, those labels
are sent to everyone.

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But what we mean
here is that if we

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don't create an ACL
about a particular label,

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then anything else we do
is not going to affect

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that particular label.

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The next rule is, if there
is an ACL about a label,

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then that label
will be sent only

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to the configured neighbors.

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In other words,
it will stop being

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advertised to the neighbors
that are not listed.

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Another rather interesting
rule is these ACLs

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that we create can only be
applied to one neighbor.

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So in that ACL,
you're going to have

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to list all of the prefixes
that you want labels advertised

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to that particular neighbor.

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And again, this is
related to the first rule,

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but it's saying that
if there is an ACL

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to a particular neighbor,
but a particular label is not

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addressed, it will
still be sent.

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Like I said, closely
related to the first rule,

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but it's just a
little bit different

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because, in this case,
there actually is an ACL.

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It's just not addressing
that particular label.

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And then, the last one here
isn't necessarily a rule,

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but a modification of the rules.

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We can actually turn off
all label distribution

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and only send things if
they are explicitly allowed,

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which would effectively
kill the first rule here.

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We're saying, no, no, no, we
don't send labels to anybody,

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unless we have an ACL
saying that we should.

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If you want to look
at it this way,

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the default behavior is
pretty much a permit all.

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We send labels to everybody.

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And then, we
implement our filters

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to say where we
don't want them sent.

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But with this
bottom choice, we're

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changing that to a default deny.

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We don't send labels to anybody,
unless our ACLs say we should.

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So let's go ahead and jump
into our topology diagram,

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take a look at where we're going
to implement this, and then

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let's jump into that command
line and get this working.

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Now, the way we have this
configured right now,

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particularly since we're doing
prefix suppression on all

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of the transit
networks, we're really

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not generating and sending
labels for any prefixes

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that we don't need.

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So we've already optimized
our network here.

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So that means we can
really filter anything

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without breaking something.

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So what we're going
to do is, we're just

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going to create a new loopback
interface on router 2,

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just so we can filter out its
label and see how all of this

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works.

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

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Of course, we'll be
starting on router 2,

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creating that loopback.

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So what we're going
to do is just create

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an interface loopback 22 here.

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We'll give it an IP address,
and we'll just make it a /32

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address of all 22s.

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We'll go into router
OSPF 1 into area zero,

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and we'll bring interface
loopback 22 into OSPF.

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And the same thing
with MPLS LVP.

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We'll enable that on
the interface as well.

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We'll commit those changes.

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So now, routers 3
and 4 should have

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a label for this new network.

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Let's go over and verify.

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So we'll do our show
MPLS forwarding table.

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And we see that we have this
22.22.22.22 network, which

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is configured as
pop, which is fine.

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It's doing PHP.

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We should see the same
thing on router 4.

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And we see that router 4 has
the exact same configuration.

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So now that we have this
network and label on router 3,

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of course, you know
what we're here for.

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We're here to filter it.

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So now, let's
configure router 2 so

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that it no longer sends
the label for 22.22.22.22

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to router 3.

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But, of course, we still
want router 4 to get it.

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So let's jump back over
to router 2 and configure

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our filtering.

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So on router 2, what we
need to do is create an ACL.

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So we'll say, IPv4 access list.

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And we'll just call this ACL_R4.

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Because what we're
going to be doing

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is configuring this to only
send this prefix to router 4.

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So we're going to say to
permit IPv4 host 10.4.4.4 any.

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So that configures
which peer we're

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going to be applying this to.

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Then, we're going to
need another IPv4 ACL.

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And let's call this
one actually OUT.

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This is going to
be almost the same.

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But for this one, we're going
to be listing the network

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that we're talking about.

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So in this case, 22.22.22.22.

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So which prefixes do we want
to advertise to which peers?

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That's the purpose
of these two ACLs.

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To apply this, we
go into MPLS LDP.

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We're going to
address family IPv4.

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We say label local
advertise for.

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and then, of course, it wants
to know which prefixes, so

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for which prefixes.

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This would be where we
put in the ACL_R4_OUT.

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And then we say who
we want to send it to.

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And this, of course,
would be the ACL_R4.

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Now, remember our
fundamental rules here.

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If we configure ACLs
to go to a neighbor

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to advertise a
particular prefix,

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it means that
prefix is no longer

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advertised to anybody else.

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So by telling it what
to send a router 4,

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we're telling it not to
send this one to router 3.

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So let's go ahead and
commit those changes.

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We'll exit configuration.

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And just to make sure
everything's up to date,

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particularly since this is
just a lab, let's just go ahead

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and clear our MPLS
LDP neighbors,

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just to make sure
everything's up to date.

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And then if we go
back over to router 3,

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we should lose the label
for the 22.22.22.22.

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And we can see that we have.

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We, of course, still
know about the prefix.

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The prefix still exists.

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However, notice that the
outgoing label is unlabeled.

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That means we did not receive
a label, even the pop label,

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for that prefix.

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So our filtering is
working correctly.

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If we go over to router
4, router 4 still

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has that prefix listed as pop.

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Because router 4 is
still getting the label.

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So that pretty much covers how
to control conditional label

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advertisement.

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We've set this up so that
router 4 gets the label,

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but router 3 doesn't.

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It's, again, fairly
straightforward, as long

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as we keep the rules in mind.

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But what about accepting labels?

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Well, since we're filtering
things, why not configure

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router 4 here to not accept
the label for this prefix,

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since we know that
it's still getting it.

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Let's go ahead and do that.

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So once again, we're
going to want an ACL.

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So let's start by
creating this access list.

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We'll call it
ACL_LABELS_R2, which

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is going to list the
prefixes that we're

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willing to accept labels for.

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So in this case, it's just
going to be router 2's loopback.

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So once again, let's
go into MPLS LDP

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Into the address family IPv4.

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We'll say label.

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But this time,
it's label remote.

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Which remote labels
are we going to accept.

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We're going to say from.

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And here, we put in
the LDP here that we're

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going to accept this from,
colon, the label space.

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The label space
is currently zero.

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So we're going to put in the
host address, colon, zero.

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And then, we're going to say
for, and we put in our ACL.

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We'll commit those changes
and exit configuration.

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Then, let's look at our show
MPLS forwarding table again.

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And what we see is
that to 10.2.2.2,

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which we are still accepting
the label for, says pop.

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But now, the 22.22.22.22, which
we just effectively filtered

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out, is now set to unlabeled,
exactly as it should be.

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So now, we have our outbound
and our inbound label

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filtering working as we want.

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So in this video, we saw how
to configure conditional label

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advertisement, as well as
conditional label acceptance,

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if we don't want to get
labels or send labels

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for every prefix in
the routing table.

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We can see that this is
fairly easily filtered out.

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And as long as we follow
the rules correctly,

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we should get the labels
where we want them

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on the devices that need them.

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So that pretty much
wraps up everything

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we need to talk about in
this skill, which leaves us

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with just one more thing to do.

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And that's our review
in the form of a quiz.

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That's exactly what
we're going to do 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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