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[AUDIO LOGO]

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So now let's go ahead and
jump into Trouble Ticket 2.

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This is once again
on IS-IS Topology 1,

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and our ticket in this
case is the R7 IS-IS

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neighborships to R6 and
R1 are currently down.

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So we're talking
about this LAN segment

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right here, where
router 7 is supposed

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to be neighbors with
router 1 and router 6

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and the ticket is saying
that it's currently not.

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So let's go ahead
and jump in, verify

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that it's in fact
not working, and then

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do some troubleshooting,
and see if we configure why.

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So let's begin here on router
7 by verifying the ticket.

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We'll do a show IS-IS neighbor.

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We see that we are, in fact,
neighbors with router 3

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and router 8, which we
fixed in our previous ticket

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but we are, in
fact, not neighbors

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with router 1 or router 6.

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So let's look at the CLNS
details for that interface.

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So we'll do a show CLNS
for interface gigabit

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1, what we see is the interface
is, of course, up, up.

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We see that the routing
protocol is IS-IS.

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We see the circuit type is
level-2, which is correct,

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but we currently have
no level-2 adjacencies.

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So everything here appears
to be generally OK.

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We'll do a show IS-IS protocol,
and what we see is our system

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ID is correct.

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We're configured for area
100, but most importantly, we

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see that we are,
in fact, enabled

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for our gigabit 1
interface for IS-IS,

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both for IP and for IPv6.

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So at first glance, everything
looks OK here on router 7.

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Let's take a look
at router 6 and see

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if we see anything wrong there.

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So here on router 6 we'll do
the show IS-IS neighbor again.

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And interestingly, we see
that router 6 is actually

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up with router 1.

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The reason this is interesting
from a troubleshooting

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perspective is we have
three routers here

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that are supposed to be
neighbors on this segment--

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router 1, router
6, and router 7.

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Well, if router 6 and
router 1 are neighbors

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and router 7 is not, that
seems to indicate that maybe

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the problem is on router 7.

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Now that's not always the case.

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There could be exceptions.

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But it's a pretty good
indicator and it would probably

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lead me to believe that
the problem's on router 7

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and I would focus
there a little more.

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We'll find out as we go.

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But just keep that in mind
as a troubleshooting method

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that maybe the one out of
a group that's not working

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is the one with the problem.

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So let's verify our CLNS
interface here as well.

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This again is gigabit 1.

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Once again, we see
that it's up, up.

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We see the routing
protocol is IS-IS.

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It's level-2.

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And this one does, of
course, have one adjacency.

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We just saw that that's
the adjacency to router 1.

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But again, everything
looks OK here.

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Now just another quick note.

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The problem has actually been
seen on these show commands.

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If you know IS-IS well
enough, you may have seen it.

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If not, we're going to
keep troubleshooting

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just a little bit
before I point it out.

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But I will come back and
point out how we can actually

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see the problem already.

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But again before
we do that, let's

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go ahead and look at our logs.

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Let's see if our
logs have anything

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interesting to tell us.

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And in this case,
it really doesn't.

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We see a log entry
for our adjacency

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to router 1 coming up.

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We see that the device was
configured but other than that,

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we don't have any information
here as far as what

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the current problem might be.

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Let's see if router 7
has any information.

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So the only entries we
have here on router 7

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are the IS-IS
authentication failures

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that we had from
our previous ticket,

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and we see the last entry
here is that adjacency

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to router 8 coming up.

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So there's really nothing
going on interesting in the log

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files.

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Let's go ahead and
turn on some debugging

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and see if that can help us.

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First, let's turn
on terminal monitor,

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and then we'll turn on debug
IS-IS adjacency packets.

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We'll go ahead and
turn off debugging

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because the problem actually
can already be seen here.

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So these two entries
right here are

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indicating that we received
the wrong type of Hello

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on the interface.

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We see that a
Multipoint IS-IS Hello

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was received on the
point-to-point interface

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and then ignored that.

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We could actually see
this in Wireshark as well.

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Let's jump over there.

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So let's start off looking at
this Hello here from router 6.

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If we open up the ISO
header, we see here

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that the PDU Type
is an L2 Hello.

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We'll see the same thing if we
look at a packet from router 1.

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So we'll look at
packet 8 here, we

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see that this is
also an L2 Hello.

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However, if we look at
this Hello from router 7,

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we see that the PDU Type here
is a point-to-point Hello.

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So now we've seen both in
the debugs and in Wireshark

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that we have the
wrong type of Hellos

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here, which indicates
were configured

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for the wrong network type.

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Now since they're
of course have to be

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three routers as
neighbors here, this

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has to be a LAN or
broadcast network type,

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and we can clearly
see that router 7 is

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configured for point-to-point.

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So we're going to
have to fix that.

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Before we do,
though, let's go back

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and take a look at that
previous show command

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that I told you if you really
know what you're looking for,

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you could see on the output
of that show command.

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So let's look at that first.

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Then we'll actually fix
the problem on router 7.

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So if we come back
over here to router 6

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and we look at our
CLNS interface again,

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notice this statement
right here--

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Next IS-IS LAN Level-2
Hello in 1 second.

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So we can see that it's sending
IS-IS LAN Level-2 Hellos.

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But if we look at this
same command on router 7,

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we see here that it just
says Next IS-IS Hello.

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It doesn't say LAN Level-2.

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So it's telling us right
there what type of Hello

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it's sending indicating
what type of network it is.

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So now let's go ahead
and fix the problem.

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So all we have to do is
go into our interface.

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And since the default here
would be LAN or broadcast,

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we simply have to say no
IS-IS network point-to-point.

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We can see that our IS-IS
neighborships have already

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come up, but just to verify
let's do a show IS-IS

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neighbor so we can see that now
our neighborships with router

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1 and router 6 are
up as they should be.

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And if we do a show
IP route IS-IS,

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we can see we have routes
in our routing table

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as we should as well.

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So now our neighborships are up,
all of our adjacencies are up,

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so this should take
care of the problem

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with the adjacencies with
router 1 and router 6.

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So in this video,
we explored a ticket

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that involved having mismatched
network types in IS-IS.

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We had two routers that were
configured for LAN or broadcast

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network type and were therefore
sending Level-2 LAN Hellos.

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And we had our router
7, which was configured

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for point-to-point,
which was sending

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IS-IS point-to-point Hellos.

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Clearly, these are incompatible;
therefore, the neighborships

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were not working.

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As soon as we found the
problem and corrected it,

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those neighborships
came right back up.

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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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