[AUDIO LOGO]
So now let's jump into Trouble Ticket 3.
This, again, is OSPF Topology 3, so the same topology
we've been working with so far.
This is now a problem with router 8.
Now, if we look over this ticket,
this is sort of the same ticket we just had with router 5.
It currently has no OSPF routes in its routing table.
So again, clearly, we'll be looking at router 8 here.
Again, this is involving its gigabit1 interface,
and we'll probably also do some looking at router 7
here, depending on what we discover the problem is.
But again, mostly, we'll probably
be focusing on this section of our network right
here between router 7 and router 8.
So let's start by jumping into router 8
and verify that there is, in fact, something wrong
and that it's not getting any routes.
So starting here on router 8, let's, of course,
start with our show ip route ospf since that was the ticket,
and we see that it does, in fact, have no routes.
So once again, let's verify our interfaces.
Now here we see that both the loopback0
and the gigabit1 interface are, in fact, running ospf.
So these are the correct interfaces.
Although we can also see the gigabit1 currently
has no neighbors.
We do a show ip ospf neighbor.
We see that we, in fact, don't have a neighbor.
Well, let's then, of course, go see
if router 7 is configured properly on that side.
So let's begin by verifying our interfaces.
In the case of router 7, it's gigabit3 that
goes over towards router 8.
And we can see that is, in fact, configured in area 0
as it should be.
It has the right IP address and mask.
It's set to point to point.
But it's also not showing any neighbors.
So let's do a show ip ospf neighbors.
We're pretty sure that router 8 is not a neighbor here,
and it's not.
So let's try digging into this a little bit deeper.
Let's jump back over to router 8 just
because it doesn't have any neighbors yet
and do some debugging.
Understand we could debug on router 7 here as well.
It'll just be easier to see what's going on router 8.
So first, we'll do term on so that we can see what's going on
since we're in an SSH session.
And let's start with a debug ip ospf hello.
Since this is the first step that
goes on when trying to establish an OSPF neighborship,
let's see what's going on with the hellos.
We'll go ahead and turn off the debugging
because we can already see what's going on.
We see that we're getting mismatched hello parameters
from our neighbor.
We see that for the dead interval,
we're receiving one second, but we're
configured for four seconds.
On the hello, we're receiving zero seconds, which probably
means it's millisecond timers, but R configured is one second.
So if we were to look at the details on R ospf interface,
we, in fact, see here that just like the debug said,
we are configured for one and four.
Let's check out router 7.
We see here on router 7, no big surprise,
that it's set to the hello of 250
and the dead interval of one.
Since these timers have to match,
this is why the OSPF neighborship is not coming up.
So now that we've discovered that the problem is
the timers don't match, well, now
we have to discuss how to fix it.
Now we could, of course, just set all the timers back
to their defaults.
For this type of interface, that would be 10 and 40, which now--
that's pretty high timers.
We generally don't want to go with timers that slow.
So maybe we could go with the one and four
like router 8 is using.
And some routers don't support millisecond timers for OSPF,
so that might actually be something we have to do.
But in this case, both of the routers
do, in fact, support millisecond hello timers,
so the best idea here would probably
be to set router 8 to match router 7 using
250-millisecond hellos and one-second dead interval.
So let's go ahead and go with that solution.
That, of course, means we have to go back over to router 8.
We'll go into configuration mode, interface gigabit1.
The way we configure the millisecond timers is we
actually have to configure the dead interval,
and we use the option here called minimal.
If we try to set it to one second, which
is really what we're doing, but all we can do then
is hit Enter.
And the problem with this is if we take off
dead interval for just a minute and we
look at the hello interval, we see
that there's no way to set the millisecond timer directly.
The lowest we can set this is to one second.
So what I have to do is I have to use the dead interval,
like we said, but we use this other command minimal.
Now, as we see, minimal sets it to one second.
Well, then, how do we set the hello interval?
Well, notice we can't just hit Enter here.
If I try, it'll give me an error.
It'll tell me it's an Incomplete command
because that's not enough information.
It needs-- it requires the hello multiplier.
This is, of course, how many hellos
it's going to send in that one second.
Remember that the goal is to get a 250-millisecond hello timer
with a one-second dead interval.
Well, that's fine, but to get that 250,
what we have to realize is that we
have to take our 1,000 milliseconds that's
in the second and divide that by the 250
that we want for the hellos.
This, of course, is 4.
So this means that our hello multiplier
needs to be four in order to get a 250-millisecond hello.
We see here that our OSPF neighborship has already
come back up, so this is a pretty good indicator
that we've done this correctly.
Let's go ahead and look at the interface detail again,
and we see that our hello and our dead intervals
are, in fact, set to 250 with a dead interval of one.
Now again, we did see the neighborship come up
in our console window there.
However, let's do a show ip ospf neighbor just to verify.
We see that 7 is back up.
And, of course, always verify the original trouble ticket.
So show IP route ospf, and we see
that we have a growing number of OSPF routes
in our routing table.
As we fix more and more problems through our environment,
notice that our OSPF routing table is getting larger.
But the real important point here
is that we have the routes on router 8, which
was the original ticket.
So, in this case, we saw an example of OSPF neighbors
not being able to come up if the hello and dead timers don't
match.
I hope this has been informative for you,
and I'd like to thank you for viewing.