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[AUDIO LOGO]

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So now we've configured
our routing protocol,

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we've configured
our prefix SIDs,

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and we've configured
our devices to prefer

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segment routing over using
the traditional LDP labels.

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So at this point,
since we've verified

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that we have full reachability
just with segment routing,

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well, we should no
longer need LDP.

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So the next step, it
would make logical sense

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to just turn off
LDP in our migration

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over to segment routing.

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

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Now, of course,
once we turn it off,

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we will still want to verify
that everything is still

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functional, and that
we are, of course,

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still using segment
routing, which there's

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no reason we shouldn't be.

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But we always want
to verify when

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we're turning off or
disabling a feature.

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So we'll bring up
the topology just

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as a reminder of how
everything's configured.

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There's really not
much to see this time.

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But we'll take a look at
it just for your reference.

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And then we'll jump
into the command line

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and we'll turn off LDP.

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So still on MPLS topology 1.

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What we're going to be
doing now is disabling LDP

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on all of the
devices in the core.

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So this is going to be
routers 1, 2, 3, 4, and 5.

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Once this is disabled,
we'll verify that we still

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have reachability.

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So we'll check reachability
from router 6 over to router 5,

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and from router 8
to router 1 just

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to make sure everything is still
reachable once we turn off LDP.

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So let's jump on to the
command line and do just that.

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So again we'll start
off with that trace

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to router 5's loopback.

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And there are, of course, a few
things we're looking for here.

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First is that, of
course, it's working

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and we have connectivity.

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The second is if we
look at the second hop,

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we see that we are doing
MPLS label switching.

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So we're not just routing
traffic without a label.

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And finally, that
label that we're using

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is the segment routing label.

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So this is exactly what
we want this to look

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like after we disable LDP.

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So let's disable LDP
and make sure we still

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have reachability.

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Let's go over to router 1, we'll
go into configuration mode.

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We can simply type no MPLS LDP.

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And say commit.

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That's all it takes to turn
off MPLS LDP on IOS XR.

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So let's go ahead and do this
on routers 2, 3, and 4 as well.

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So that takes care of router
2, router 3, and router 4.

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As usual, IOS XE is a
little bit different.

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So let's go take a
look at router 5.

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As we can see here,
LDP neighborships

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are already going down.

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But let's go ahead and just
turn it off here on router 5

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as well.

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To do this, we go
into our interfaces.

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So in this case, it's
interface gigabit 1.3.

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We say no MPLS IP.

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We do the same thing
for gigabit 1.4.

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And we can exit configuration.

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So let's go ahead and
do some verification.

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Let's start with a show
MPLS forwarding table.

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Notice that the only
labels left here

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are the adjacency labels
which are, of course,

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still being pulled out of the
dynamic pool and the segment

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routing labels for
the prefix SIDs.

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All the other labels are gone.

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If we do a show
mpls ldp binding,

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we're told that
TIB is not enabled.

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Now that actually means
tag information base

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because Cisco used to
call this tag switching.

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But nonetheless essentially
what it's telling us

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is we're asking to
see LDP bindings,

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and that protocol
is not even enabled.

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However, if we were to
say show isis database,

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we'll ask for verbose and
we'll ask for this router.

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So router 5.00.00.

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What we see here is that for our
loopback address 10.5.5.5/32.

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we are, in fact, still
creating a prefix SID,

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and that means this is being
sent to the other routers.

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Also note that this
has the n flag on it

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as well, indicating that
this is also a node set.

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We could also look at
this from the perspective

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of looking at all of the SIDs
that we have in our database.

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We could just say include SID.

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And here we see the different
SID values that we're actually

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getting from all of
the different routers

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in our environment.

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So let's go over and do a little
bit of verification on router 1

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as well.

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So we can do this by looking
at some of the same commands.

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We'll start with our show
mpls forwarding table.

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Once again, we see nothing
but prefix and adjacency SIDs.

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So this is clearly using
just segment routing.

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If we do our show
mpls ldp binding,

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we can just say it
doesn't necessarily

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tell us that LDP is not
enabled, but it definitely

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has zero entries.

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If we do a show mpls ldp
neighbor, we have no neighbors.

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If we do our show mpls
label table detail,

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we see that all of the labels
that are currently in use

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are either part of the
SRGB or they are adjacency

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SIDs for other devices.

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And finally, we could
look at a show isis

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segment routing label table.

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And what we see here is
simply that we're still

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learning all of the prefixes
for our environment, which

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of course, is as expected
because LDP wasn't carrying

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these labels anyway.

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So it just makes sense that
this is all still working.

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The real question is, is the
data plane and our packet

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forwarding still operational?

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So let's go back
over to router 6 now

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that we've turned off LDP, and
make sure that our trace still

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functions.

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As we see from this trace, this
is still functioning exactly

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as it should.

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So turning off LDP has not
affected the functionality

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of our environment in
any way now that we're

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doing segment routing.

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So in this video, we saw that
we can easily turn off LDP

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once our segment routing is
fully up and operational.

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So there's no problem
with packet forwarding.

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No problem with
label distribution.

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Everything works fine.

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Really it just comes
down to LDP is no longer

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required for segment routing.

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Now this whole time we've
been doing this using ISIS

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as our IGP.

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But we really should
take a look at what

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changes if we use OSPF instead.

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And 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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