[AUDIO LOGO]
So moving on to trouble ticket 2,
we're going to see that this is a completely different ticket.
This time, we're on MPLS topology 1.
Well, no.
That's actually the same.
Our core protocol this time is IS-IS.
Well, no.
That's the same too.
But the ticket is probably different.
So this ticket says that router 6 is not
doing label switching to 10.5.5.5,
which is router 5's loopback.
So no, this ticket isn't different at all.
This is the exact same ticket as ticket 1.
As I mentioned during the introduction,
these tickets might be the same.
However, it's a different problem.
Different problems are being introduced
as we go through each ticket.
So just keep that in mind.
Yes, joking aside, this is the exact same ticket.
But I assure you, it's a different problem.
So let's go ahead and jump into the command line.
And as always, we'll start by verifying the ticket.
So that'll take us to router 6.
So again, we'll start with our trace yo 10.5.5.5, source
it from our loopback 0 interface.
So as we can see from the output of the trace here,
once again, the ticket is correct.
We are not doing label switching or segment
routing towards router 5.
So let's start with our troubleshooting.
Let's jump over to router 1 and take a look at its label table.
So again, we'll do our show isis segment-routing label table.
And interestingly, what we see here
is we have prefix SIDs for router 1, which
is the router we're on, router 2, and router 5.
But what we don't have are any prefix SIDs for routers 3 or 4.
So let's go over to router 3 and see what's going on there.
So we'll just do the show isis segment-routing label table
again.
And we see that it has no labels in its label table at all.
So let's try a show mpls label table detail.
And what we see here is there's no labels assigned to the SRGB
or for adjacency labels.
So we have no labels at all here.
Let's do a show run router isis.
What we're looking for specifically
is that segment routing is not enabled under the process
or under the loopback interface.
So that's definitely going to be a problem.
Let's go ahead and start by fixing that.
So we'll go into router isis 1.
Let's start by going into our interface
loopback 0 into the address family IPv4 Unicast.
Let's configure the prefix SID with the absolute value
of 16,003.
And then of course, we have to enable it for the process
as well.
So let's go into address family IPv4 Unicast,
turn on segment-routing for mpls.
And we'll make sure that we have our sr-prefer on there
as well, just in case we're running LDP, which we're not,
but we'll make sure that it's on there.
Let's commit those changes, exit out of configuration.
And let's verify some of those commands again.
Let's look at the show mpls label table detail.
This, of course, looks much better.
We have labels allocated for the SRGB now.
And we can see we're also getting adjacency labels
from IS-IS.
So this definitely looks much better.
Let's look at our label table again.
And we see here that now, we have a label for routers 1, 2,
3, and 5, but we still don't have one for router 4.
Now, the problem with not having one from router 4
is if we go back to router 6 and we
try to verify our ticket by doing our trace again,
what we see on this output is when we're doing our equal cost
multipathing from router 1 going to routers 3 and 4,
when we send the traffic to router 3,
we are, in fact, doing our segment routing
and therefore our MPLS label switching.
We also see that we're using our prefix SID from router 5,
as we should be, the 16,005.
But when we take the path to router 4,
there's no label being used.
So it looks like we have a problem on router 4 as well.
Let's go take a look at router 4.
Let's just start with the show mpls label table detail.
And we see right away that there's no labels allocated
for segment routing.
So my guess is we're having the same problem here.
So if we do our show run router isis,
we can see that once again, it's not enabled under the process.
And we don't have it configured on our loopback.
So again, we need to fix that here.
So again, into our loopback interface,
into our address family IPv4 Unicast,
we'll set up our prefix SID to the absolute value 16,004.
Then, we'll turn it on under the process
again, commit our changes, and exit config.
So now, let's look at our label table detail again.
Now, we have labels allocated for segment routing.
So again, we have allocations for the SRGB
as well as getting adjacency SIDs.
So if we go back over to, say, router 1,
and here, we verify our label table again,
now we can see that we're getting labels
for all of the devices.
So we have our prefix SIDs for routers 1, 2, 3, 4, and 5.
This means that the problem should be completely fixed.
Let's go back over to router 6 again and verify one more time.
So that trace didn't exactly show the multipath thing.
Let's try it one more time, see if we
can get a multipath response.
That's much better.
Now, we can see that we're using our labels both towards router
4 and towards router 3.
Just remember that when you're trying to test something
like multipathing with traceroute,
it can be a little finicky as far as
how it shows the results.
So if you don't see it the first time,
just try to do a trace again.
And most likely, you'll see the multipathing.
But everything's working now as it should.
So that solves trouble ticket 2.
In this video, we saw another example of a ticket
where devices had segment routing
disabled on both the routing protocol and the advertisement
of their prefix SID on their interfaces.
This time, it was on an interim router rather than
the destination, but we saw that the result was very similar.
Once we enabled it and turned our prefix SIDs back on,
then everything started working as it should.
I hope this has been informative for you.
And I'd like to thank you for viewing.