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[AUDIO LOGO]

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So now that we've taken a
closer look at Multiarea OSPF,

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let's jump into the command
line and take a look

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at some of our database commands
to see what this actually looks

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like in the OSPF database.

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So we'll start off by
looking at our topology, how

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our areas are currently set up.

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Then we'll jump in, we'll
take a look at the databases,

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as well as watching how
Dijkstra's algorithm actually

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runs now that we have different
areas in our OSPF environment.

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So let's start off by
looking at that topology.

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So for this demonstration, we
will be using OSPF topology 2.

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And what we see here is now
do we not only have area zero,

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but we also have area
100 and we have area 200.

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The way things are
configured we have

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router 6 is acting as an ABR.

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So is router 1 and router 3.

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We also have router 2 over
here, which is an ASBR bringing

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in external routes from EIGRP.

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Now in this demonstration,
we're simply

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going to be focusing on what's
happening inside of OSPF

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with our different areas.

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So we won't really be looking
at the external routes coming

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from router 9 at this point,
we'll be using that later.

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But for now we're going to focus
on what happens when failures

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occur in these different
areas now that we're not

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in one big area.

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So let's jump into
the command line,

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and we're going to start
by looking at area 200

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since this is a very small
area and let's see what happens

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when a failure occurs there.

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So let's start here on router 6.

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And let's turn on a
debug of IP OSPF SPF

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and we'll go over to router
10, and let's shut down

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one of its interfaces.

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Specifically, we'll just shut
down its loopback 0 interface.

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Now let's go back
over to router 6,

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we'll turn off our debugging.

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And what we want to notice here
that SPF ran and notice that it

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only took 8 milliseconds
for this to occur,

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which is significantly
faster than what

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happened when we ran this
earlier when everything

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was one big area.

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So even in an environment
as small as this,

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we're definitely getting
a performance increase

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by having multiple areas.

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So let's bring that interface
back up on router 10.

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So now let's take a look
at what happens when

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a failure occurs between areas.

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For this demonstration,
let's keep an eye

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on what happens on
router 7 when we

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create a failure on router 5.

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So we'll start by doing our
observations on router 7.

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Let's start with the
show IP route OSPF.

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Notice that we do have an
entire area route for 10.5.5.5

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which is router 5's loopback.

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If we do a show
IP OSPF database,

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notice that we also have
numerous type III LAs here,

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which are the summary
net link states.

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And notice that we in fact,
have one for 10.5.5.5.

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In fact, we have two, one
coming from each of our ABRs.

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And finally, let's
do a show IP OSPF.

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And when we want to
look at specifically

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is for area zero how many times
SPF has actually executed.

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At the moment it's 129 times.

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So let's take a look at what
happens now if we shut down

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that interface on router 5.

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Let's turn on our debug.

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So we'll debug SPF
here on router 7

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then we'll go over to
router, 5 and we'll

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shut down that interface.

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Let's go back over to router 7.

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We notice here that it
definitely did calculations.

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We can see where the
network is being removed,

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and we see that it
processes things.

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But what's not here is any
calculation for how long it

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took to run SPF
because it didn't.

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If we say show IP
OSPF again, notice

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that the execution of the SPF
algorithm is still at 129 times

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even though we
recognize the failure.

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And if we do a
show IP route OSPF,

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we'll see that the 10.5.5.5
is now in fact missing,

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and we don't have it
in our database either.

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So we've removed it
from our database,

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we've removed it from
our routing table

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but we did not execute SPF.

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This is the big advantage of
having multiple areas in OSPF.

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When a change or a
failure or anything

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happens in another area,
yes we learn about it.

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Of course we do, this wouldn't
be much of a routing protocol

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if we didn't, but
we're not running SPF.

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We still remove it
from the database,

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we still remove it
from the routing table,

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but we don't have to run SPF
every time something changes

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in another area, that would
even include the route coming

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back up.

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Let's go back over to router 5
and bring that interface back

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online.

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So we'll pop over here,
we'll do a no shut

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to bring the interface back
up, back over to router 7.

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Notice once again, we're
adding the routes back

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into the routing table.

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We do a show IP
route OSPF, there's

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the 10.5.5.5 back
in our table again.

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We do a show IP OSPF
database, the 10.5.5.5

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is again here in the database.

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However, if we look at
our show IP OSPF, notice

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still the SPF algorithm has
only executed 129 times.

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We're not running SPF
because the changes are not

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occurring in this area.

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In this video, we took a look
at how the database reacts

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and how the execution
of SPF reacts

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when changes occur both
within our smaller areas,

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as well as what
happens between areas

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when we have a
failure that's not

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in our directly connected area.

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So we saw that within
the area things

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happen faster because
it's a smaller area.

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And we saw that between
areas although we of course

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lose the database entry
and therefore the route,

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we don't run SPF when something
changes in a different area

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when we're doing Multiarea OSPF.

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And this is what adds
to the scalability

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of doing Multiarea OSPF.

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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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