[AUDIO LOGO]
So now let's go ahead and jump into Trouble Ticket 2.
This is once again on IS-IS Topology 1,
and our ticket in this case is the R7 IS-IS
neighborships to R6 and R1 are currently down.
So we're talking about this LAN segment
right here, where router 7 is supposed
to be neighbors with router 1 and router 6
and the ticket is saying that it's currently not.
So let's go ahead and jump in, verify
that it's in fact not working, and then
do some troubleshooting, and see if we configure why.
So let's begin here on router 7 by verifying the ticket.
We'll do a show IS-IS neighbor.
We see that we are, in fact, neighbors with router 3
and router 8, which we fixed in our previous ticket
but we are, in fact, not neighbors
with router 1 or router 6.
So let's look at the CLNS details for that interface.
So we'll do a show CLNS for interface gigabit
1, what we see is the interface is, of course, up, up.
We see that the routing protocol is IS-IS.
We see the circuit type is level-2, which is correct,
but we currently have no level-2 adjacencies.
So everything here appears to be generally OK.
We'll do a show IS-IS protocol, and what we see is our system
ID is correct.
We're configured for area 100, but most importantly, we
see that we are, in fact, enabled
for our gigabit 1 interface for IS-IS,
both for IP and for IPv6.
So at first glance, everything looks OK here on router 7.
Let's take a look at router 6 and see
if we see anything wrong there.
So here on router 6 we'll do the show IS-IS neighbor again.
And interestingly, we see that router 6 is actually
up with router 1.
The reason this is interesting from a troubleshooting
perspective is we have three routers here
that are supposed to be neighbors on this segment--
router 1, router 6, and router 7.
Well, if router 6 and router 1 are neighbors
and router 7 is not, that seems to indicate that maybe
the problem is on router 7.
Now that's not always the case.
There could be exceptions.
But it's a pretty good indicator and it would probably
lead me to believe that the problem's on router 7
and I would focus there a little more.
We'll find out as we go.
But just keep that in mind as a troubleshooting method
that maybe the one out of a group that's not working
is the one with the problem.
So let's verify our CLNS interface here as well.
This again is gigabit 1.
Once again, we see that it's up, up.
We see the routing protocol is IS-IS.
It's level-2.
And this one does, of course, have one adjacency.
We just saw that that's the adjacency to router 1.
But again, everything looks OK here.
Now just another quick note.
The problem has actually been seen on these show commands.
If you know IS-IS well enough, you may have seen it.
If not, we're going to keep troubleshooting
just a little bit before I point it out.
But I will come back and point out how we can actually
see the problem already.
But again before we do that, let's
go ahead and look at our logs.
Let's see if our logs have anything
interesting to tell us.
And in this case, it really doesn't.
We see a log entry for our adjacency
to router 1 coming up.
We see that the device was configured but other than that,
we don't have any information here as far as what
the current problem might be.
Let's see if router 7 has any information.
So the only entries we have here on router 7
are the IS-IS authentication failures
that we had from our previous ticket,
and we see the last entry here is that adjacency
to router 8 coming up.
So there's really nothing going on interesting in the log
files.
Let's go ahead and turn on some debugging
and see if that can help us.
First, let's turn on terminal monitor,
and then we'll turn on debug IS-IS adjacency packets.
We'll go ahead and turn off debugging
because the problem actually can already be seen here.
So these two entries right here are
indicating that we received the wrong type of Hello
on the interface.
We see that a Multipoint IS-IS Hello
was received on the point-to-point interface
and then ignored that.
We could actually see this in Wireshark as well.
Let's jump over there.
So let's start off looking at this Hello here from router 6.
If we open up the ISO header, we see here
that the PDU Type is an L2 Hello.
We'll see the same thing if we look at a packet from router 1.
So we'll look at packet 8 here, we
see that this is also an L2 Hello.
However, if we look at this Hello from router 7,
we see that the PDU Type here is a point-to-point Hello.
So now we've seen both in the debugs and in Wireshark
that we have the wrong type of Hellos
here, which indicates were configured
for the wrong network type.
Now since they're of course have to be
three routers as neighbors here, this
has to be a LAN or broadcast network type,
and we can clearly see that router 7 is
configured for point-to-point.
So we're going to have to fix that.
Before we do, though, let's go back
and take a look at that previous show command
that I told you if you really know what you're looking for,
you could see on the output of that show command.
So let's look at that first.
Then we'll actually fix the problem on router 7.
So if we come back over here to router 6
and we look at our CLNS interface again,
notice this statement right here--
Next IS-IS LAN Level-2 Hello in 1 second.
So we can see that it's sending IS-IS LAN Level-2 Hellos.
But if we look at this same command on router 7,
we see here that it just says Next IS-IS Hello.
It doesn't say LAN Level-2.
So it's telling us right there what type of Hello
it's sending indicating what type of network it is.
So now let's go ahead and fix the problem.
So all we have to do is go into our interface.
And since the default here would be LAN or broadcast,
we simply have to say no IS-IS network point-to-point.
We can see that our IS-IS neighborships have already
come up, but just to verify let's do a show IS-IS
neighbor so we can see that now our neighborships with router
1 and router 6 are up as they should be.
And if we do a show IP route IS-IS,
we can see we have routes in our routing table
as we should as well.
So now our neighborships are up, all of our adjacencies are up,
so this should take care of the problem
with the adjacencies with router 1 and router 6.
So in this video, we explored a ticket
that involved having mismatched network types in IS-IS.
We had two routers that were configured for LAN or broadcast
network type and were therefore sending Level-2 LAN Hellos.
And we had our router 7, which was configured
for point-to-point, which was sending
IS-IS point-to-point Hellos.
Clearly, these are incompatible; therefore, the neighborships
were not working.
As soon as we found the problem and corrected it,
those neighborships came right back up.
I hope this has been informative for you,
and I'd like to thank you for viewing.