[AUDIO LOGO]
So now that we've looked at the different type of LSAs
in more detail, now it's time to jump onto the command line,
take a look at these LSAs in the database
so we can see what they actually contain,
and take a look at the different fields,
and what they represent in our OSPF environment.
So let's start by looking at our diagram.
So remember what our topology looks like
and what our different area types are.
And then we'll jump in to the command line
and take a look at that database.
So for this demonstration, we'll again,
be using OSPF topology 2.
And just some things to keep in mind
as we're going through this, area 200
is configured as an NSSA.
We have router 6 acting as the ABR
between area 0 and area 200.
We have router 1 acting as an ABR,
as well as router 3 for area 100 going into area 0.
And we have router 2 who's an ASBR, redistributing the EIGRP
routes into area 100.
Also as a note, router 10 has a loopback interface
that is also being redistributed into OSPF in the NSSA.
This topology is going to allow us to look
at all of our LSA types.
We'll see 1 and 2 looking in area 0.
We'll see type 3 LSAs coming from areas 200 and 100.
We'll also see some type 5 LSAs, along with type 4 LSAs
coming for the routes from router 9 and from Router 10.
Then we'll take a look at our type 7
LSA in our NSSA area, area 200.
So let's jump in and start looking at the different LSAs.
And we'll be looking primarily at router 7.
But, of course, we'll have to jump up to router 6
to look at our type 7.
But let's begin on router 7.
So let's start by just looking at the routing table.
Just do a show ip route ospf.
And what we see here is we do, in fact,
have a combination of inter-area routes, intra-area routes,
and external routes.
Another good command to keep an eye on is show ip ospf route.
This actually shows the OSPF routing table.
These are the routes that OSPF has chosen as best,
and is trying to put into the routing table.
We can actually see here the routes that
have been chosen as best, and it's trying
to put into the routing table.
Let's talk just for a moment about where
these different components fall into the OSPF decision process.
The first thing is the link state database
with its entries.
This, of course, is what we're going
to be looking at mostly in this demonstration.
The best routes from the link state database
are then put into the OSPF RIB.
This is the O-S-P-F RIB.
And that's what this command we just looked at showed us.
This is what we see with the show ip ospf route.
The routes that are actually marked for entry
into the routing table then get put into the global RIB.
This, of course, is what we see with the show ip route.
And not that it's incredibly important to this discussion.
But just to wrap this up, of course,
all of the entries in the global RIB
then get installed into the FIB, or the Forwarding Information
Base for CEF or Cisco Express Forwarding.
So ultimately, this is the table used for the actual packet
forwarding.
So again, just as a review.
If we do a show ip route, we see this table.
If we do a show ip ospf route, that's when we see this table.
That's the last command we just did.
And, of course, for the rest of this discussion,
we're going to be looking at the database.
So when we do a show ip ospf database,
we'll be looking at the link state database.
And just for completeness, if you want to look at the FIB,
on most platforms, it would just be show ip cef.
But let's go ahead and take a look now
in more detail at the actual database.
So let's just start with the show ip ospf database.
This just gives us a summary of all
of the different LSA types that are currently in our database.
We'll be looking at these in more detail.
But this is just like a summarization.
And if you actually just want a count,
there's also other options here for filtering this.
One of them is database summary.
So it's sort of funny because the command can actually be
show ip ospf database database.
And what this does is just show us
a counter of literally how many of each
type are in the OSPF database.
What we're going to do, though, is focus more
on the individual types.
So let's start by taking a look at the type LSA or the router
LSAs.
So we'll take database off of here, and we will say router.
Now this first entry happens to be
the entry coming from router 1.
The first thing we see is the LS age.
The LS age here is how long this has been in the database.
We also have some options.
We have no TOS capability.
TOS is type of service.
This is simply not supported on Cisco routers.
So this will pretty much always just say no TOS capability.
And then we also see DC here, which is demand circuit.
It just means that this router is
capable of doing demand circuits.
We see the LS type is router links.
That make sense, because that's what we asked to look at.
We see the link state ID, which is the router ID.
And the advertising router is also the router ID.
These are going to be the same on type 1 LSAs.
They'll be different on other types of LSAs.
We also see the sequence number, which
we use to ensure that the database is up to date.
The checksum, of course, for error correction,
the length in bytes.
And we also see that router 1 is announcing itself as an ABR
into the environment.
Then we see that it has four links.
And then it starts breaking them down for us.
So we have one link that's connected to a stub network.
That stub network is 10.1.1.1 with a mask of a /32.
Now just based on our topology and our knowledge,
we happen to know that that's its loopback interface.
Our second link here is connected to another router.
It's a point-to-point link.
And that's connected to router 3.
We also see its IP address on that interface.
If we scroll down, we see that it has another connection
to a stub network.
Notice that it's also listing that as the link 2 router 3.
These point-to-point links are listed
both with a topology entry, as well as a network advertisement
being a stub network.
Then we have the transit network,
which is the multi-access network between routers 1, 6,
and 7.
This is listed as the transit network.
We see who the DR is.
In this case, the DR is actually .7,
which makes sense because it's the highest IP address.
And our interface on that is .1.
Now as we can see, we have other entries
here from other routers, here starting with router 3.
But we're not here to look at the whole database.
We just want to look at the different LSAs.
So next, since we know we have this transit network,
let's take a look at our type 2's.
So we'll take off router, and we'll put in network.
So here's that type 2 LSA.
Notice that it's coming from the DR. Notice
the link state ID is the address of the DR,
and it even tells us that.
Also we see that the advertising router
is in fact router 7's router ID, which make sense since he's
the DR.
And then notice down here it lists the subnet mask in use
on that network.
So the network mask, along with the link state ID would
actually tell us what the network is, 50.0.167.0/24.
Those two pieces of information together define the network.
And then, of course, here at the very bottom,
it lists all of the router IDs attached to that segment.
Notice that the other fields that we didn't mention
are just the same as they are in a type 1.
Next up would be the type 3's.
These are called summary LSAs, of course.
The first thing to notice here is
that the type 3 LSA has this new option on it that says upward.
This is referred to as the OSPF downward bit.
And I know that seems odd since it says upward.
But the thing is the option being
set to upward simply as a way of saying that the downward bit is
not set.
So we generally call this the downward bit.
And we'll talk about this more when we get into MPLS.
This is for MPLS loop prevention when
we're dealing with duplicate PES and things like that.
So we'll get more into this later.
But just for now, be aware that this is where
it's carried in the type 3 LSA.
And if we're not dealing with MPLS and VRFs,
then this is going to be set to upward,
meaning again the downward bit flag is not set.
So next, we see the link state ID,
which in these first two examples here,
notice that they're both 10.2.2.2.
That's actually router 2's loopback interface,
which is over in area 100.
Notice that we're learning this from two different advertising
routers because we have two different ABRs--
10.1.1.1 and 10.3.3.3.
The only other thing to note here
is the network mask is carried down here at the bottom.
So again, if we apply the network mask
with the link state ID, which is the actual network being
advertised, this tells us the actual network.
If we scroll down to something that's a network rather than
a loopback address.
So for example, these entries.
We have an entry here for the network 50.2.61.0.
Now we can see that that's a /24.
So this is telling us that, that network
is available through router 6, which of course, is also
an ABR.
Next up, let's take a look at our type 5's.
So these are going to be external.
And for now, we're just going to focus here
on router 9's loopback.
It happens to be our first entry.
So first thing to note is it again,
has that upward bit or the downward bit that's not set.
So listing it as upward.
And then notice that once again, just like a type 3,
the link state ID is the actual network being advertised.
So it's 10.9.9.9.
But here's the important part.
The advertising router is 10.2.2.2.
That is a router not in our area.
We would have no idea how to get to 10.2.2.2, because we do not
have a type 1 LSA for it.
We'll demonstrate that in just a moment.
But notice we also have the network mask here.
And external type 5 LSAs do carry some extra information
here.
They have the metric type, which can either
be a type 1 or a type 2.
We'll cover that in more detail in a future skill.
We also have a metric listed here, the forwarding address,
which we will also cover in more detail,
as well as any external route tag
that may be set on this route.
Now again, the problem with getting to 10.2.2.2
is if we do our show ip ospf database again,
and this time we say router 10.2.2.2,
notice that there's no entry.
Again, 10.2.2.2 is in a different area.
It's over in area 100.
And we're currently in area 0.
This router, router 7 would have no idea
how to get to this advertising router.
And this is exactly what the type 4's are going to give us.
Let's take a look.
It's actually ASBR summary.
I usually just type ASBR.
But there's the whole command for you.
And notice exactly what this is telling me.
Notice what the link state ID is.
And we don't have to go into a whole lot of detail on these.
Notice that they're almost identical to type 3's
that we just talked about a moment ago.
The only thing that makes these different from a type 3
is what's being advertised.
The link state ID.
And it even tells you in parentheses
afterwards what it is.
It's the AS boundary router address.
Specifically, it is the router ID of the ASBR.
And notice that just like with the type 3's,
we're getting this information from both of our ABRs--
10.1.1.1 and 10.3.3.3.
So finally, let's look at type 7's.
But as I mentioned before, we can't exactly
look at them here because if we say NSSA here,
we're going to have no entries.
Remember that the type 7 only lives inside of the NSSA.
Router 7 here is not in the NSSA.
So we're going to have to jump over
to a router that is in there.
We'll just use router 6.
So on router 6, we'll do our show ip ospf database.
And we'll do the NSSA here.
And we'll see that now we have a type 7 for that loopback
interface on router 10, which happens to be 100.10.10.0.
And as we can see by the network mask here, it's a /24.
The advertising router, of course,
is router 10's router ID.
Notice that this is almost identical to a type 5 LSA.
And it doesn't really need to be any different,
because we're just using the type
7 to get this through the NSSA.
We'll be covering this in more detail in a future skill
when we cover OSPF area types in greater detail.
But all we really need to see for right now
is the fundamental difference on this LSA from a type 5,
is this option here that says type 7/5 translation.
It's basically the originator, in this case router 10,
asking our ABR, in this case, router 6,
to translate this into a type 5 LSA.
And in fact, if we say show ip ospf external
and filter it by self originated,
notice we are, in fact, translating it.
There it is.
This is us generating the type 5 on behalf of the type 7.
We are doing the translation.
If we do a show ip ospf, and if we
look at our information for area 200,
notice it even says perform type 7 to 5 LSA translation.
And we can see that router 6 is.
Again, we'll be covering this in more detail in a future skill.
But I at least wanted you to see the type 7's for now.
So you can get an idea of how these work.
In this video, we jumped into the command line,
and really got a detailed look at each of these LSA types,
what they look like, what information they contain.
We even got to see how our ABR between an NSSA
and a normal area, in our case, area 0,
how that ABR is translating the LSA from a type 7 to a type 5.
I hope this has been informative for you,
and I'd like to thank you for viewing.