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(futuristic music)

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- So after all of this theory
of OSPF we've been talking

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about, let's finally get around
to configuring this thing.

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So let's talk about implementing OSPF.

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So the initial configuration
of OSPF is pretty simple,

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few things I wanna call to
your attention right here.

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So, you would start out by configuring

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at the global configuration
level your command router,

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OSPF and then a process-id.

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Now I wanna make a
distinct difference between

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a process-id and an
autonomous system number.

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In EIGRP, at the global
configuration level,

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come on,

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you typed router EIGRP,

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and then you had to put your
autonomous system number

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right here.

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And whatever number you put there as your

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autonomous system number
was very important

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because you had to match
on all the routers.

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In EIGRP when a router sends
out an EIGRP hello packet,

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it includes the autonomous system number

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as part of that hello packet

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and those things have to match.

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Well, in this particular case a process-id

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is not sent in any OSPF packets,

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it's simply a locally significant value.

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That's it.

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Now you might be wondering,
Keith, what do you mean

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a locally significant value?

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When I use that term locally
significant that means

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only this router, only this device,

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needs to be aware of that number,

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it's not shared with any other device.

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So, most of the time when
people configure OSPF,

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they use process-id number one.

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You can use whatever you want.

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I mean, theoretically, on
router one you could use

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process one, on router two
you could use process two,

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on router 99 you could use process 99.

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It doesn't really matter,
it does not have to match.

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The main thing to remember is,

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unless you have a real
good reason for doing so,

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you should only have one process of OSPF

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running in your router and that's it.

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As an example, let me
contrast that with EIGRP.

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Once again, with EIGRP, if
I had a router right here,

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let's say this is router x, y and z.

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And let's say that y and
z were part of company...

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Let's say yz,

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and then all of a sudden
we acquire a new company.

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So this is an acquisition.

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And maybe we were already
doing EIGRP in company yz,

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and previously we were using
autonomous system number 200.

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So all the routers here were using 200.

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All of a sudden this new
aquistion we have, well,

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they were also using
EIGRP, but they were using

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autonomous system number 77.

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So, for the time being,
router y actually has to have

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two instances of EIGRP.

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You have to type router EIGRP 200,

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and so that's how he
can exchange routes with

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his own internal company
and then also in router y,

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you'd have EIGRP 77.

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Totally different process
that he can run with router x.

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Now those two processes
will not share routes.

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They will be separate in router y.

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We would have to redistribute
between the two processes

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tell one process sends
his routes into the other,

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and the other process
sends his routes back.

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That's something we'd have
to do manually in router y,

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otherwise they will stay
separate and unique,

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as if they were completely
different routing protocols.

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So that's the only time
when you would really need

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two instances of the
same routing protocol,

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running in one router.

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Well that also holds true with OSPF.

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In OSPF you should only have
to have a single process

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running in your router.

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Only if you're in a situation like this,

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would you possibly need
more than one process,

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but at the CCNA level
just think to yourself

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I'm only gonna type router
OSPF some number and that's it,

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and I'm never gonna do that command again.

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I'm never gonna have to
create another process.

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One process is enough.

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And then you use your network command.

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Now in EIGRP, you had the
option of using a wildcard mask.

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In OSPF, it's not an option.

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In OSPF you have to
include a wildcard mask

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after your prefix and then
you also include the word

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area and then the area number.

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So as an example of that
you might type network,

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I'm just gonna shorten it, 25.70.00,

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and then a wildcard mask that
would be appropriate for that.

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And then I would tell
my router okay any links

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that you have on yourself
that begin with 25.70,

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those links are gonna be part of AREA 1.

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So that's an example of how
you type the network command.

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Now the router will come up
with a router-id by itself,

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but as you saw in the last video,

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where we talked about designated routers

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and backup designated routers,

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you might want to
deterministically set the router-id

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so that you can influence
which router will become the DR

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or the BDR, and remember,
every segment that needs a DR

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is a unique segment.

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In other words, if I'm a router
with two ethernet segments,

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on this segment, there's gonna be a DR,

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it might be me, might be somebody else,

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and on this segment right
here, that's also ethernet,

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there's gonna be another DR.

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Might be me, might be somebody else,

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but every broadcast segment
or non-broadcast multi-access

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segment needs a DR and a BDR.

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Along those same lines
you could also influence

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the ip ospf priority on an interface.

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Remember the default priority
of OSPF on an interface is....

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One. The default is one.

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If you set the priority to
zero, that actually means

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this router can never become
a DR on that interface,

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it is disqualified from becoming a DR.

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Now like it says here, both the router-id

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and the priority, if you change them,

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you need to restart your OSPF process.

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It will not take those changes on the fly.

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And then here's some
verification commands we can use

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to see what OSFP is doing.

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So let's actually do an
example of this in the lab.

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So I'm gonna be using
this typology right here,

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and the routers that you see
with the light blue circles,

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router one, switch one,
router two, switch three,

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and router four, they have
already been pre-configured

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for OSPF so they're
already up and running.

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And I'm just gonna
configure OSFP from scratch

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on switch two and router three.

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Now before I do that, let's for example,

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let's go to router two and issue some

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verification commands to see
what he looks like already.

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Router two.

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Okay, so what command would
I type to see if this router

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has become fully adjacent
with any other OSPF neighbors,

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or if he's learned of any OSPF neighbors

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in any other transitory state?

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Hopefully you said show ip ospf neighbor,

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and you can see he's got
one neighbor 1.2.1.1,

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that is switch one.

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So remember, when switch one was coming up

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with his router-id,
first this you said was

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do I have any loop backs?

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No, I don't.

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Okay, what interfaces do
I have that are either

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up-up, up-down or down-down?

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These two right here.

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Of these two interfaces, which one has

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the highest ip address?

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That would be this, one two one 11.

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So switch one said I'm gonna
create my OSPF router-id

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of 1.2.1.11 and that's
what we can see right here.

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What do you think the router-id
is gonna be of router one?

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It should be it's loop back, right?

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Because the very first this
it's looked at is a loop back.

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So let's go to router one and take a look.

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Which is also gonna answer the question of

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when I'm on a local router, how can I tell

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what it's router-id is?

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You can just do the command show ip ospf.

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And right at the top it
says here is my router-id.

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In this case, just like we thought,

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it's the loop back interface.

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So, show ip ospf shows
you a lot of good stuff,

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as you can see right here.

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And once again, we can
use our favorite command,

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show ip protocols, and that
will give us some information

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about ospf, shows you what
your locally sigificant

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process-id is, I just used
the number one on all of mine.

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It shows you what neighbors you have,

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the administrative distance of ospf.

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Going back here once again,
because router one, switch one

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and router two have already
been pre-configured,

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router two should have
learned about this loop back

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network one 11 one 11 one 11,

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and he should have learned
about one one one zero,

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as ospf routes.

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So let's take a look in
his OSFP routing table,

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of router two, show ip route.

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And there we can see, there's
that loop back network

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that was learned via OSPF,

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and here's that other network
that was learned via OSPF.

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And notice when a route is
prefaced with just the letter O,

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that means that it is an
OSPF intra-area route.

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What does that mean?

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That means that this route
actually lives in the same area

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where this local router is.

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In other words, router two says

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okay the one 11 one 11 one
11 and the one one one,

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they both reside in area
one, and I live in area one.

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So that is an intra-area route.

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Now let's go ahead and
configure switch two for OSPF.

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And if you haven't already
taken a screenshot of this,

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00:10:53,929 --> 00:10:57,776
I would recommend that you do
so, so you can follow along.

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So in switch two what I'm
gonna do is I'm gonna have

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three network statements,
I'm gonna configure OSPF

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then I'm gonna put the two
two two network into area 1,

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I'm gonna put the two three
two network into area 0,

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and I'm gonna put the
three two three network

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also into area 0, so my
configuration will consist

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of a total of four commands.

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Router OSPF one, followed
by three network statements,

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and that will be all
I need for switch two,

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router ospf and you can see here

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my process-id, locally significant value,

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you've got quite a range of
values you can choose from,

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most people usually just start with one.

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Now I'm gonna say network
2.2.2.0, with the appropriate

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wildcard mask, and that's
gonna be in area 1,

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network 2.3.2.0 that's gonna be in area 0,

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so right there, the fact that I have put

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one link in area 1 and one
or more links in area 0,

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means this router is now
an area border router.

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And network 3.2.3.0 also in area 0.

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Now how could I tell that this router,

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now remember it's a switch,
but it's a multi-layer switch,

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I've enabled it for routing
so I'm just calling it

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a router, how do I know
this device is running OSPF?

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Well, once again show
ip protocols and if OSPF

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shows up here, which it does,
I know it's running OSPF.

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It also says right here it
is an area border router,

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so he knows that he's
an area border router.

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And this shows me the various networks,

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where I've activated OSPF
with the network command.

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So now I'll just go ahead
and put my light blue circle

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on switch two, since I've
just finished OSPF for him.

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So at this point, if we go
into let's say router four,

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router four should now have
at least a couple of networks

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that are OSPF intra-area routes.

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He should have learned about
the two three two network,

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and he should have learned about
the three two three network

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as intra-area routes.

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So these two routes should
show up simply as O's in R4.

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And then R4 should also have learned about

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all these routes over here in area 1,

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and in R4's routing table,
all of these will show up

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as O I A in the routing table,

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O I A standing for inter-area routes.

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Routes that originate in some other area

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that router four is not connected to.

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Let's take a look at router four,

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show ip route.

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And there we have it, here
are the intra-area routes,

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that are part of his own area,

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and OSPF as a metric
uses cost, it uses cost,

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which is based on interface bandwidth,

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just like the spanning tree protocol.

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The metric of OSPF is cost, it just uses

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a completely different formula
but the higher the bandwidth,

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the lower the cost.

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And here we see inter-area routes,

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learned from a different area.

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And those have a slightly higher cost,

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'cause they're a little bit further away.

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And at this point I think one
other thing I wanna show you,

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you can actually look at
the database that contains

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your OSPF lsa's, show ip ospf database.

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And it show's you your
different lsa's, now,

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at the CCNA level, like I
said, you don't have to know

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about the specific kinds of
lsa's, you don't have to know

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what their names and type numbers are,

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you don't even really need to be able to

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interpret the output of this command.

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I just wanted to show you
that, it is available to you,

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and once you get to the CCNP
level and you start learning

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about the details of
lsa's then you'll start

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going into gory detail about the output of

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show ip ospf database
and some various keywords

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that you can add to it.

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But I just wanted you to
walk away from this video

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knowing that you can go into the database

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and see various things.

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And, other than that we have gone through

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all of these show commands here,
oh, show ip ospf interface,

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we haven't taken a look at that one yet,

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show ip ospf interface.

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And you can see, it'll
show you every interface

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that has been activated for OSPF,

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because of a network command.

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It shows you the interface,

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it shows you what kind of network it is,

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remember we talked about
that in a previous section,

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this is the broadcast interface,

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00:15:52,391 --> 00:15:54,604
it shows you the OSPF cost, remember,

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cost is based on bandwidth.

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00:15:56,642 --> 00:15:59,583
If I went into the interface
and I changed the bandwidth,

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00:15:59,583 --> 00:16:02,316
that would affect the ospf cost value.

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00:16:02,316 --> 00:16:05,975
So OSPF's metric is
much simpler than EIGRP,

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00:16:05,975 --> 00:16:08,643
EIGRP used all sorts of
factors to come up with

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00:16:08,643 --> 00:16:11,162
a complex metric called distance,

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00:16:11,162 --> 00:16:13,692
OSPF doesn't do that, OSPF
just factors bandwidth

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00:16:13,692 --> 00:16:17,727
and that's it, and it
comes up with a cost value.

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00:16:17,727 --> 00:16:21,300
It also shows you on a link
who the designated router is,

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so you can see that.

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00:16:23,097 --> 00:16:25,475
You can see this particular
device, router four

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00:16:25,475 --> 00:16:28,200
is the backup designated router,

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00:16:28,200 --> 00:16:30,831
and you can see your interface priority.

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00:16:30,831 --> 00:16:35,392
A lot of good information from
the output of this command.

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00:16:35,392 --> 00:16:38,048
And for troubleshooting OSPF,

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00:16:38,048 --> 00:16:42,215
probably one of the best debugs
is debug ip ospf adjacency.

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00:16:44,433 --> 00:16:46,839
That is a great debug
to find out, you know,

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00:16:46,839 --> 00:16:48,790
why do I not have a neighbor?

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00:16:48,790 --> 00:16:50,866
If I'm looking at a
topology diagram and I say,

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00:16:50,866 --> 00:16:53,658
well, router one and router
two should be neighbors

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00:16:53,658 --> 00:16:56,434
with each other but, when
I do show ip ospf neighbor,

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00:16:56,434 --> 00:16:58,871
they're not seeing each other.

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Great debug to turn on,
debug ip ospf adjacency,

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00:17:02,129 --> 00:17:03,898
will tell you what's going on

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00:17:03,898 --> 00:17:06,347
and why they are not neighbors,

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00:17:06,347 --> 00:17:09,460
debug ip packets I would recommend

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00:17:09,460 --> 00:17:11,999
that you not use that debug.

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00:17:11,999 --> 00:17:15,824
That debug can be very verbose,
give you gobs of output

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00:17:15,824 --> 00:17:18,177
in just a couple of seconds,

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00:17:18,177 --> 00:17:20,210
probably not a good idea
to turn that one on.

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(futuristic music)