[AUDIO LOGO]
So let's begin by jumping in and taking
a look at the reasons or advantages of doing
route summarization.
Now, the main things we're going to be looking at
and there are many different advantages.
But the two main focus is first, reducing
the size of the routing table.
Obviously, this is going to help increase performance
and help with scalability.
Our network can get larger and larger as long
as we're summarizing properly.
This is a big deal particularly with OSPF
since all of the routers have to maintain a database.
The other main thing we want to focus on is fault isolation.
So if a route fails in another area,
should all of the areas really have
to recalculate their database and update their routing table
because of some remote failure.
Now, keep in mind we can only do summarization between areas
or for external routes as they're brought into OSPF.
Now, that being the case, we would not
be talking about type I or type 2 LSAs here.
So we would not be rerunning Dijkstra.
So this is not about saving us having to run the SPF
algorithm within an area.
However, when these type 5 or type 3
LSAs depending if they're inter area or external routes,
when these change they disappear or they
come into the routing table.
That at least causes everybody to have
to update their database and update their routing table.
So let's begin by looking at our topology diagram learning
where our routes are coming from that we're going to summarize.
And then in this video, we'll just
be looking at what actually takes
place when those routes flap so when
they disappear and reappear in the routing table.
So again, let's start by looking at that topology.
So what we've done for this lab is we've configured router 10
to send in four routes that are pretty much within what would
be a /16 subnet.
All of these routes start with 100.100.
And then they are different in the third octet.
We'll be taking a look at this, of course, in just a moment.
We've done the same thing on router 9.
It is also bringing in four routes
into in this case EIGRP which, of course,
router 2 is then being the ASBR and redistributing those routes
into OSPF.
So those four routes, of course, are coming in as external.
These all begin with 200.200.
Again, these could be summarized easily with a /16.
So let's jump in.
And we're of course, going to start off
by looking at router 7, which is a router very
comfortably inside of our OSPF area 0 environment meaning
it is not an ABR or an ASBR in any way.
It's just an internal router in area 0.
And what, of course, we'll be looking
for here is what these routes look like on router 7
and what happens if those routes go away and come back,
what happens with our database, and running Dijkstra.
So let's jump into the command line on router 7
and get started by looking at these routes
before we start taking them away and bringing them back.
So let's begin by looking at those routes
that we were just discussing.
We'll just do a show IP route OSPF.
And what we see is this block of four 100.100 networks.
These are the ones that are coming through router 6
from router 10.
And then down here at the bottom,
we have the x channels in the 200.200 range coming from
router 9 through router 2 and then, of course,
through router 1.
Let's also take a look at how many times
the spoof algorithm has executed in this area.
As of right now, it is 21.
Let's also turn on our d bugs for OSPF.
So now let's go up to router 10 and cause a failure in one
of those 100.100 networks.
We'll just bring down interface loopback.
110.
We'll simply do a shot.
And let's go back and observe what happens on router 7.
So the first thing we see here is
we definitely see the change.
We see that we're processing the fact that this 100.100.110.0/24
is now being removed from our routing table.
We do a show IP router OSPF again.
We see that in fact that network is gone.
We, of course, have the remainder
of the other three networks.
But that one is missing.
And notice that OSPF has executed 21 times.
Now, keep in mind this is the behavior we would expect.
Remember, the point of splitting OSPF up into areas
is to as so we don't have to run OSPF every time
something changes in a different area.
So this is expected either with or without summarization.
What we're going to be looking for from summarization
is for router 7 not to have to process an update at all.
So just so we're clear on that difference.
We're still getting an update.
We're still having to process that update,
modify our database, and update our routing table.
What we are not doing is running OSPF
because it is a different area.
So once we get into summarization,
we'll see how that changes and we don't have to do anything.
That's our goal.
So now let's go back to router 10.
We'll go ahead and bring that interface back up.
So this is basically acting like a flap
of the network on router 10.
And if we go back over to router 7,
we see that once again we had to process this update.
Did we have to run OSPF?
No, we're still at 21 times.
However, we did have to process this update that came in
for our database and, of course, that
means we had to update our routing table.
Now we have that 100.100.110.0 back in our routing table as we
should.
We'll see that external routes are processed the same way.
Let's just go ahead and demonstrate it just
for completeness.
Let's jump over to router 9.
And we'll shut down one of these loopbacks as well.
So for example, interface loopback 210, we'll do a shot.
Once again, hop back over to router 7.
We see once again it has to process this.
It looks a little bit different because it's
an external route however, it's the same basic process.
If we look at our show IP route for OSPF,
we see that route is missing.
And if we look at SPF we see that it has still only executed
21 times here in area 0.
So although it looks a little bit different,
this is functioning exactly the same way
as the type 3 LSA coming from area 200.
Let's go ahead and bring that back up.
We look at router 7 again.
We see that it has again learned that update.
We still have not run OSPF any additional times.
And our route is back in our routing table.
In this video, we took a look at the two major disadvantages
to not running summarization.
First, we have a large number of routes in our routing table.
Now, in this case, it's only eight routes.
We're bringing in 4 from one router and 4 from another.
So it's not a really large number of routes,
but it is 8 where it could possibly be 2.
And more importantly, we took a look
at how each router in every area.
We focused on router 7 but all the other routers
would be the same.
They have to process these updates
and modify their routing table.
Do they have to run Dijkstra or OSPF algorithm?
No, that's taken care of by the areas themselves.
But it is still a little bit of work
that has to be done on the routers.
And when you're talking about scaling up
a protocol like OSPF, this becomes critical.
I hope this has been informative for you.
And I'd like to thank you for viewing.