[AUDIO LOGO]
So now we've configured our routing protocol,
we've configured our prefix SIDs,
and we've configured our devices to prefer
segment routing over using the traditional LDP labels.
So at this point, since we've verified
that we have full reachability just with segment routing,
well, we should no longer need LDP.
So the next step, it would make logical sense
to just turn off LDP in our migration
over to segment routing.
So that's what we're going to be doing in this video.
Now, of course, once we turn it off,
we will still want to verify that everything is still
functional, and that we are, of course,
still using segment routing, which there's
no reason we shouldn't be.
But we always want to verify when
we're turning off or disabling a feature.
So we'll bring up the topology just
as a reminder of how everything's configured.
There's really not much to see this time.
But we'll take a look at it just for your reference.
And then we'll jump into the command line
and we'll turn off LDP.
So still on MPLS topology 1.
What we're going to be doing now is disabling LDP
on all of the devices in the core.
So this is going to be routers 1, 2, 3, 4, and 5.
Once this is disabled, we'll verify that we still
have reachability.
So we'll check reachability from router 6 over to router 5,
and from router 8 to router 1 just
to make sure everything is still reachable once we turn off LDP.
So let's jump on to the command line and do just that.
So again we'll start off with that trace
to router 5's loopback.
And there are, of course, a few things we're looking for here.
First is that, of course, it's working
and we have connectivity.
The second is if we look at the second hop,
we see that we are doing MPLS label switching.
So we're not just routing traffic without a label.
And finally, that label that we're using
is the segment routing label.
So this is exactly what we want this to look
like after we disable LDP.
So let's disable LDP and make sure we still
have reachability.
Let's go over to router 1, we'll go into configuration mode.
We can simply type no MPLS LDP.
And say commit.
That's all it takes to turn off MPLS LDP on IOS XR.
So let's go ahead and do this on routers 2, 3, and 4 as well.
So that takes care of router 2, router 3, and router 4.
As usual, IOS XE is a little bit different.
So let's go take a look at router 5.
As we can see here, LDP neighborships
are already going down.
But let's go ahead and just turn it off here on router 5
as well.
To do this, we go into our interfaces.
So in this case, it's interface gigabit 1.3.
We say no MPLS IP.
We do the same thing for gigabit 1.4.
And we can exit configuration.
So let's go ahead and do some verification.
Let's start with a show MPLS forwarding table.
Notice that the only labels left here
are the adjacency labels which are, of course,
still being pulled out of the dynamic pool and the segment
routing labels for the prefix SIDs.
All the other labels are gone.
If we do a show mpls ldp binding,
we're told that TIB is not enabled.
Now that actually means tag information base
because Cisco used to call this tag switching.
But nonetheless essentially what it's telling us
is we're asking to see LDP bindings,
and that protocol is not even enabled.
However, if we were to say show isis database,
we'll ask for verbose and we'll ask for this router.
So router 5.00.00.
What we see here is that for our loopback address 10.5.5.5/32.
we are, in fact, still creating a prefix SID,
and that means this is being sent to the other routers.
Also note that this has the n flag on it
as well, indicating that this is also a node set.
We could also look at this from the perspective
of looking at all of the SIDs that we have in our database.
We could just say include SID.
And here we see the different SID values that we're actually
getting from all of the different routers
in our environment.
So let's go over and do a little bit of verification on router 1
as well.
So we can do this by looking at some of the same commands.
We'll start with our show mpls forwarding table.
Once again, we see nothing but prefix and adjacency SIDs.
So this is clearly using just segment routing.
If we do our show mpls ldp binding,
we can just say it doesn't necessarily
tell us that LDP is not enabled, but it definitely
has zero entries.
If we do a show mpls ldp neighbor, we have no neighbors.
If we do our show mpls label table detail,
we see that all of the labels that are currently in use
are either part of the SRGB or they are adjacency
SIDs for other devices.
And finally, we could look at a show isis
segment routing label table.
And what we see here is simply that we're still
learning all of the prefixes for our environment, which
of course, is as expected because LDP wasn't carrying
these labels anyway.
So it just makes sense that this is all still working.
The real question is, is the data plane and our packet
forwarding still operational?
So let's go back over to router 6 now
that we've turned off LDP, and make sure that our trace still
functions.
As we see from this trace, this is still functioning exactly
as it should.
So turning off LDP has not affected the functionality
of our environment in any way now that we're
doing segment routing.
So in this video, we saw that we can easily turn off LDP
once our segment routing is fully up and operational.
So there's no problem with packet forwarding.
No problem with label distribution.
Everything works fine.
Really it just comes down to LDP is no longer
required for segment routing.
Now this whole time we've been doing this using ISIS
as our IGP.
But we really should take a look at what
changes if we use OSPF instead.
And that's exactly what we're going to do next.
Until then, I hope this has been informative for you.
And I'd like to thank you for viewing.