[VIDEO LOGO]
Next up is trouble ticket 4.
For this one now, we're going to be using IS-IS IPv6 topology 1.
That would be because this ticket involves IPv6.
So let's take a look at our ticket.
It says that router 5 is missing the IPv6 routes to R2 and R4's
loopback interfaces.
So R2 and R4, of course, have loopbacks.
Each of these have IPv6 addresses on them.
And according to the ticket right now,
router 5 does not have these routes.
So let's start, as always, by jumping in and verifying
the ticket, and then let's see what the problem is.
Let's go ahead and jump into the CLI on router 5.
So we'll start off on router 5 by just looking
at the show IPv6 routing table.
And what we see here is we're actually
getting an IPv6 default from router 2 and router 4.
Now, this is actually fairly significant from
a troubleshooting standpoint.
The reason I say that is we can actually skip over things like
are the neighborships up?
Clearly, the neighborships are up
because we're getting routes from them.
Are we getting the routes that the ticket
says we should be getting?
No, but we are getting routes.
So this doesn't appear to be a neighborship issue.
Honestly, it looks more like a filtering issue possibly,
or maybe those routers aren't bringing their loopback
interfaces into IS-IS.
So this looks like some other, sort of,
an issue other than neighborship.
So let's skip over the neighborship troubleshooting
at least for now, and start going after other things.
My first guess would be filtering.
However, I will say that before we jump right into filtering,
we probably should at least make sure that router 2 and router 4
do, in fact, have the interfaces in IS-IS.
So before we go right for filtering,
let's jump throughout or R2 and do a little bit
of troubleshooting there.
So on router 2, let's do a show IS-IS interface brief.
And we see that, in fact, loopback 0 is in IS-IS.
And just for curiosity, let's see if router 2
has router 4's loopback.
So let's do a show route IPv6 IS-IS,
and we can see that it does.
Right here is a route to router 4's loopback.
So this indicates that at least router 4
is bringing its loopback in.
We already saw that router 2's interface is enabled for IS-IS.
So it really seems like 2 and 4 are advertising properly.
Of course, just to be completely sure,
we could look at router 4.
Just to show route, IPv6 IS-IS.
And here, we see router 2's loopback.
So yes, both sides are advertising their loopbacks
into IS-IS.
So this would bring up the question
that maybe it's filtering.
Well, let's take a look here.
Let's do a show run router IS-IS.
So if we look at this output, there's
no filtering or no configuration at all for the address family
IPv6.
Now, it is enabled under our interfaces.
However, there's no configuration where
we're doing any filtering.
Let's check router 2 as well just to make sure.
And we see the same thing here.
We do have some propagation in such setup,
but again, these are under address family IPv4.
Nothing for IPv6 aside from enabling it
under the interfaces.
Well, maybe the filtering is happening on router 5.
So let's go look there.
On router 5, we'll do a show run section router IS-IS,
and we see there's absolutely nothing configured here either.
We simply have address family IPv6
and then exit address family.
There's no IPv6 configuration here on router 5.
So this doesn't look like it's a filtering issue.
So maybe we should just go right for looking at the database.
Let's do a show IS-IS IPv6 topology,
and we see that there's actually no information
in the IPv6 topology.
So this is interesting.
Let's maybe take a look at some debugs.
So let's turn on terminal monitor and let's debug IS-IS.
Let's go for adjacency packets since, again, this
seems to possibly be an issue with the databases.
So we've got a lot of debugs there fairly quickly.
So we turn them back off.
We have an interface level mismatch on gigabit 2.
But is that really our problem?
The link between router 2, 4, and 5
is a Multi-Access segment.
Now, we have level 1 and level 2 adjacencies configured
between routers 2 and 4.
Router 5 is actually only configured
for level 1 adjacencies.
This is why we're getting these messages.
Now, that may or may not be a good design.
We won't get into that argument right now,
whether we should have these type of HELLOs
going on a network where not all the neighbors are
participating.
That's another discussion.
It's probably not the best design.
However, it's also not our problem.
So let's go ahead and keep digging
a little further because this debug, although it's giving us
some information, isn't anything that's actually causing us
a problem for this particular ticket.
So maybe, in this case, we need to go to Wireshark for help
once again.
So let's start by looking at this HELLO coming
from router 4, and let's expand the IS-IS HELLO header.
So looking over the HELLO, we see
that it's set to circuit type level 1 and level 2.
That we saw in the debug.
And we already discussed the fact
that 2 and 4 are both set that way.
So that's not really a concern.
Our System ID is correct.
Our PDU is 1497, which we know is the default.
If we look at our protocols supported,
we can see that we're supporting both IP and IPv6.
If we scroll down, we see something here
that may be of interest.
We see that this is set to Multi-Topology.
So this has a TLV type 229 for Multi-Topology.
But we just looked at the configuration on router 5.
Router 5 had nothing in its configuration for IPv6.
It was empty.
So we know that IOS XE actually defaults to single topology.
But here, we have router 4 sending a Multi-Topology packet
onto the wire.
Let's check router 2 and router 5,
and I bet we're going to find a difference here.
Now, router 2 here, we can see does have the Multi-Topology
TLV.
However, if we look here at router 5,
we can see that as we suspected, it does not
have the Multi-Topology TLV.
So even though we have the correct protocols supported
here, IP and IPv6, we have to match on Multi-Topology.
So what we need to do here is change router 5
to Multi-Topology.
We could, of course, change router 2 and 4
to Single-Topology.
But in this particular case, it would make more sense
to change router 5 to Multi-Topology.
So let's jump into Configuration on router 5,
do that, and see if it solves our problem.
Now, again, this is a reminder here.
If we do show run section IS-IS, we
can see that there is no configuration under address
family IPv6.
Again, we saw this earlier, but I just
wanted to bring it up again as a reminder.
So let's go to Configuration mode, into router IS-IS 1,
into address family IPv6, and simply
change it to Multi-Topology.
If this solves our problem, we should
be able to verify the original ticket with a show IPv6 route.
And we can see that we do, in fact, now have router 2
and router 4's loopback in our routing table.
So Multi-Topology was, in fact, the issue.
So in this video, we took a look at a ticket
involving a Single-Topology versus
a Multi-Topology mismatch.
Keep in mind that we can support both IPv4
and IPv6 in either Single-Topology
or Multi-Topology.
However, the devices within the area
do have to agree on whether it is Single or Multi-Topology.
I hope this has been informative for you,
and I'd like to thank you for viewing.