All language subtitles for 28 - Routing - Understanding and Configuring OSPF-eng

>> Is something broken?

Did I click on a new nugget
and I'm sitting here?

This isn't-- this isn't the title slide.

There's no learning goal.

There's no witty story from
Jeremy to start it off.

That-- that's right.

We're crazy here at CBT Nuggets.

We're going to start nuggets a
little differently this time.

We're going to start right here where we
left off in the last nugget which is OSPF.

Yes, in the last nugget.

I tried to cram it all together,
routing protocols

and OSPF all in one manageable sitting.

It's just not possible.

Don't do it.

We're starting OSPF a little
different this time.

Now, the fact that we're even talking

about OSPF is a radical change
from previous editions of CCNA.

If you've-- if you've heard some,
if you've been in the CCNA realm,

you know that we always learn RIP first.

And-- and I've been teaching it that way for
so long it almost escaped me how-- how silly.

It's like-- it's like now that
I-- now that I look back I'm like,

does anyone really realize how
irrelevant RIP is to the world.

But my father had to learn it and his father
had to learn it, so you'll learn it too.

Well, not anymore.

RIP is done.

Rest in peace, that just came
to me, rest in peace, RIP.

You are now replaced by OSPF.

Now does that mean RIP as a protocol is gone?

No, it's still out there.

The beauty and the reason that-- the
reason we've learned it for so long is

that it's the simplest of all routing protocols.

But the fact is you walk out of your door
right now and walk in any network in the world

and chances are very good it's
not going to be running RIP.

If it is, e-mail me.

I want to hear from you.

But-- but most of the-- most of the
networks of the world run on OSPF,

most popular routing protocol in the world.

Now the reason it was in CCNA is
because this was the simplest.

But somebody sat down and
sharpened their pen and said,

you know what, OSPF is just a little bit more.

I mean it's not that much more
to understand the foundations.

Now keep in mind, OSPF.

Think of it-- think of-- I got a little
beach here, a little beach umbrella,

some people on a lawn chair
sitting, the waves coming in.

And you got all this sand on the beach, right?

And then sitting on that sand is a bucket.

Looks like a large bucket in
perspective of that person, but it's not.

It's full of sand because all this
sand represents OSPF in all its glory.

And you're going to learn what's in that bucket.

You're not going to learn all
of it but you will learn enough

that you'll be proficient with OSPF.

You'll be able to recognize the configuration.

You'll be able to set it up
yourself and get it running.

You'll be able to hold your own with OSPF.

That's what my goal is.

Before we dive into how to get OSPF
working, I want to take a step back,

big picture, what's OSPF do again?

It lets our routers talk about what
they think is most interesting.

Router one is going to talk to
router two about everything it knows.

And it knows things that it's plugged into.

It knows about the 192.168.1 network.

Why? Because you as an administrator
configured it in that network,

so it knows, hey, I'm plugged in there.

And I know I'm plugged into 192.168.2.0 network.

Why? Because you configured it to know that.

So it then talks to router two and
says, hey, I know about 2.0 and 1.0

and router two says, that's
great I knew about 2.0.

This is our common ground.

This is where we talk about, so
yeah that's great, I'll just,

you know, FYI, you know, whatever.

But I didn't know about 192.168.1.0,
ooh, that's news.

I'm adding that to my routing table
and I'm going to use you, router one,

I'm now talking as router two, playing the role.

I'm going to use you, router
one, as my next hop to get there

because you told me about
it, that just makes sense.

And router two says, and by the way,
there might be something you want

to know about I know about 192.168.3.0.

I just-- just got out of that
conversation with my kids.

They love-- I love this suspense
that kids have when you--

when you talk to them and I'm
like guess what, guess what.

And they're like, what, what, what?

We're going to go to Dairy Queen and
they're like, "Oh, Dairy Queen, ice cream!

Yehey!" You know it's like that's--
routers go through that all the time.

He's like, hey, I know about 192.168.3.0

and router one is like, yehey,
I never knew about that.

I'm adding it to my routing table.

Now, I have a way to get there.

Way, which way?

You, router two, 'cause you told me about it.

So that's how they inform each other.

Now-- now let's dig a little bit deeper.

That's routing protocols and
all routing protocols do that.

That's their goal.

How does OSPF do it that's a
little different than say RIP?

Well, OSPF uses something
known as a Hello packet.

Oh, so different than RIP.

See RIP never really forms a relationship.

It's just a bunch of passerby
screaming information out.

If these guys are running RIP, you know,
router one and router two are just yelling.

They don't really care who gets in there.

They're just sending a big broadcast or
multicast message saying, "Hey, everybody,

I know about this, this and this and this."

There's no-- there's no acknowledgement
that anybody got that.

They don't really follow up with that to make
sure the information was received in any way.

They just broadcast it out
and hope it gets there.

Now, OSPF is much more methodical than that.

OSPF says from router one's
perspective the very,

very first thing he sends out is a Hello packet.

And they should have called it a Hello
package because it really contains all kinds

of interesting information about router one.

It contains for instance a series of timers
like router one inside of this Hello package,

you know, when router two opens it up he's going
to see a little piece of paper that says, hey,

you know what, I say hello once every 10
seconds and I have a dead timer of 40 seconds.

What's that mean to router two?

That means I can expect that router one is
going to be like, hey man, every 10 seconds just

to make sure that I'm online, that I'm
available and I can also hear from router--

router one that he's available
once every 10 seconds.

Same thing if he doesn't hear from somebody--
if he doesn't hear from a friend and neighbor

in 40 seconds, then he's going
to consider that neighbor dead.

So router two now knows, okay, when speaking to
router one, I know if he doesn't hear from me

in 40 seconds, he's going to
consider me offline and he's going

to mark all of my networks unreachable.

Now, the reason that this is a big deal is
OSPF is very picky about its relationships.

If the timers don't match, if router one
is saying hello once every 10 seconds

and router two is like I'm a speedy
router, I say hello once every second.

Hello, hello, hello, hello, hello.

If he's-- if he is that way, they're not
going to form a neighbor relationships.

Timers must match.

The area that they're configured in must match.

And you might say, well, what's an area?

And that's part of the buckets
of the sand of the seashore

that we're not really going
to talk too much about.

But let me give you the high level view.

OSPF allows you to break your network
up into kind of groups of networks.

So here's the idea, right?

All networks start really
small, maybe it's two offices.

Over here is an office in Minnesota or
Michigan 'cause I don't know the abbreviation

for Minnesota.

And then over here is an office in Texas, right?

And that's just where the business begins.

And then it kind of grows from there.

It grows, you know, you add more offices and
more offices and you get to 10, 20, 30, 40, 50,

60 offices, it's starting to
get a little chaotic, right?

You've got all of these different
routers that are connected together

and your routing table is getting bigger
and bigger and bigger and bigger and bigger.

And here is the fact, the bigger your
routing table, the slower your router.

So our goal as a network administrator is to
say, I want to keep my routing table small,

and areas is what help us do that.

See, as I grow this, I eventually can say, okay,
I'm going to break this whole group of routers

into an area and we'll call it area zero.

Now area zero happens to be very special.

It's the very first area
that you create with OSPF.

As a matter of fact, you can't run OSPF.

You can't get OSPF working
without designating an area.

And for what we're going to talk
about, everything will be in area zero.

Now how big can area zero grow?

However big you want it to, 50 routers,
100 routers, a thousand routers.

Sure, you can do that.

But as-- as the area grows bigger and bigger and
bigger, eventually you're going to reach a point

where you're like, ah, it's too big.

Our routers are running out of memory.

They're slowing down.

There's too many-- too many
changes like a network goes down

and everybody is like, oh,
I have to know about that.

And all these-- these updates flood my network.

You reach a point where it just gets too big.

Now, I will say big in terms of today
like 2013 is much different than big

as it was in 2005, and big in 1993.

And I mean big that that term changes
because our routers are beefier.

They got more memory, more process and all that.

But eventually, you go, what's an area.

So an area is where you say, okay, at
this office I want to add a dividing line.

I want to break this into area one.

And now I have a whole section
of routers down here.

Okay, you say.

And, you know, I don't know.

Over here is area two.

Let's add a couple, why not while we're at it.

Area two, and here's a bunch of routers.

Okay, what does that mean?

What does that do?

Areas, and this is-- this
is huge, huge concepts.

Hang with me.

Areas represent a point of summarization.

It's a point where you're
able to summarize entries

in your routing table down to a bigger network.

Let me give you an example.

Let's say up here I have,
you know-- and sometimes we--

we draw these pictures of routers connected to
routers and you lose kind of the perspective.

And think of each one of those
little circles as an office.

Like this is-- this is the Texas office, right?

And over here is 10.1.1.0/24, right?

We got that network.

And then over here is the-- the Michigan
office and they've got 10.1.2.0/24.

And then-- and then over here is the
California office and they've got 10.1.3.0/24.

Are you seeing the theme, right?

Each one of these offices,
this one might be 4.0.

This one might be 5.0.

The point is they all start with 10.1.

So when we hit this area
boundary we now have a choice.

Do we advertise all of those networks to
where down here this router now knows, okay,

10.1.1.0 is up here and 10.1.2 and
10.1.3 and I've got all these entries

in my routing-- my routing table.

And my router is running
slow 'cause I have all these.

Do we do that or do we make a move?

I would say we make a move.

And we call that summarization to where we
take all those 10.1 networks and we say instead

of taking all the individual networks and
advertising them down here, let's just do this.

Let's just say I've got 10.1.0.0/16.

Can he do that?

Yup, we can do that.

I'm a little weird today.

I'm in one of those weird moods.

So-- so what that does is now suppress
all of these individual update.

So, now this router in his
[inaudible] I mean I drew five.

But imagine that was 50 or 500 routers.

Let's go crazy, right?

This guy, instead of having 500 routes,

and I guess we can't really
get 500 routes out of that.

Let's just say 200.

How's that?

Instead of having 200 routes in his
routing table, he's going to have one.

He's going to know 10.1.

anything slash 16, right?

That means these two are the significant digits.

10.1. anything is up there, right?

And now I've suppressed all
those more specific things.

One, number one, two things it does.

Number one makes our routing table much
smaller, meaning our routers become much faster,

much more efficient at what they do.

Number two is it hides problems.

See here's the deal with OSPF,
everything in an area has

to know what's-- what each other is doing.

Like if a network goes down over here,
everybody in that area has to know about it.

And it comes up, okay, everybody
in the area has to know about it.

It's the rule of OSPF.

Everybody in an area must be synchronized,
like they all know the same stuff.

Well, that's a problem when we start
spanning this is-- this is our--

our WAN connection from the United
States over to India, right?

We-- we have tech support offices in India.

And we have this WAN link going over that.

I don't-- I don't want to flood that LAN link
'cause it's slow with unnecessary information.

So let's-- let's summarize.

So when this network goes down,
everybody knows about it up to here.

So, what that does that mean?

Do they not know that the
10.1.1 network is down?

That's correct, they don't.

They don't know it's down at all and that's okay
because when they started sending information,

it's going to go right here, this router, and
he's going to be like, oh, sorry man, it's down.

You know, drop, drop, drop, drop, drop.

So it drops all the packets.

And so communication won't happen.

And that's okay, we want to be able
to high-- I mean, think about it.

Are there-- are there-- like did the network
on the internet just go down right now?

Yes. Did it come up right now?

Yes. There are thousands and thousands of
networks on the internet going down and going

up every minute that we sit here and talk.

We don't have to know about it.

Our routers don't have to know about it.

They just send it as far as it can
get and then it's like, oh sorry,

microsoft.com is down, if that were to happen.

So, that's what an area is.

But we're not going to talk about that, right?

Areas in summarization and that--

that configuration, that's what you do when
you go beyond this-- this sand bucket of OSPF.

But the key is that area has to match.

These guys have to be-- I have to be let's
say an area zero on both of these routers

or else we won't form neighbor relationship.

We have to have matched authentication,
like if I have a pass code.

Like I will only be your-- your OSPF
neighbor if you have the key Cisco, right?

And both of these have the same
key that has to match between that.

You can define a password that way
you don't have evil routers coming in

or computers pretending to be routers.

They have those coming in and trying to
form a neighbor relationship with you.

And lastly, they have to
have the same subnet mask.

You can't have, you know, slash 24 here

and maybe he's got a slash
16 or something over here.

They're going to be like, oh,
we're not going to do that.

We're not going to form neighbors.

Now if all of these things match up,
then the Hello is accepted on both sides,

and they will become a full
neighbor relationship,

meaning they will start exchanging routes.

Okay, so let's take that and now
go into how to get OSPF working.

And just starting off with
a very basic scenario.

We've got two routers, right?

Each one is connected to a network
that the other doesn't know about,

so we're not going to be able to reach it.

Like router one over here is not going to be
able to reach router two's 192.168.3 network

because we have nothing in place to allow that.

Let's prove that.

I'm going to go to GNS3.

Let's just right click on router one
and open a console connection to it.

And so I've got router one.

Let's first off get our bearings, you
know, see if I can squeeze this over here.

Let's get our bearings.

Always show IP interface brief.

My favorite command to just
say, okay, what's what.

And I can say right here
I've got a serial connection,

192.168.2.1 lines with what I
see there on my network diagram.

I have 192.168.1.1 which is
the LAN network over here.

Now that all looks good.

Let's do a show IP route.

And I can see that this router
knows about only connected routes.

It knows it's plugged into 192.168.1.0 because
I configured an IP address in that network.

Same thing with 2.0, I've got
an IP Address in that network.

So-- so, it's all looking good.

And I can absolutely guarantee that if I type
in ping 192.168.3.1 which is the LAN interface

of router two over here, we're going to fail.

And we can guarantee that because
when we look at the routing table,

we're trying to reach anything
that's not shown here.

The router is just going to say,
I have no idea what you're doing.

So, last nugget-- no, two nuggets ago.

We got static routing to get this setup going.

We go into global config.

And let's do first off turning on OSPF.

The command is router and then
the protocol you want to run.

Now I mentioned remember the jellybean slide.

We had BGP, EIGRP, ISI's.

I mean all these different protocols that are
out there, some that we didn't even talk about

but they're out there, other routing protocols.

We just need to pick the one that we want.

In this case, we are using OSPF.

So I'll fill that in and hit the question mark.

And now it ask me for a big
question, what is your process ID?

You ever gone in-- in Windows?

Let me bring something out.

Tell me if this looks familiar to you.

That guy. Isn't this machine awesome?

It's got like 8 processors.

It's amazing.

I didn't do that just to show you this machine.

I showed-- I wanted to show
you this process tab.

Have you ever gone in here?

Have you ever gotten into-- to
Windows where things go bad?

I mean your-- you're sitting,
nothing's done bad at Windows, right?

No. But, you know, you're in here.

You've got, you know, whatever running.

You know, Dynamips is freezing or whatever.

You know something goes bad.

And you're trying to kill a
process and have you ever gotten

to a point in Windows where it won't die?

Have you ever got in there?

One of the things that you can do
and see, this isn't a Windows course.

But you can actually-- I'm
going to pull up Google.

And obviously I had recently gone through that
experience 'cause Google Chrome did not shut

down correctly.

So, I'm going to do what is it?

Task kill, right?

That's the command, yeah.

So this is a command-- if you didn't know
about this command, oh, if you're in Windows,

you live by this command 'cause
things break all the time.

Task kill is like I'm going to
kill a process absolutely dead on--

you know, I'm cutting it off.

You're probably going to
get some file corruption

but that's all good 'cause
that's normal in Windows.

And we're going to make-- we're going to
make your computer stable again, right?

So-- so task kill requires that you
identify a process by its process ID.

And you can actually go in task manager.

And let's see, where is it?

Properties.

There's a way-- now of course,
no, I'm not going to view.

Oh wait, select comms, there it is.

Select comms and process ID.

Voila, right there.

And this column PID is what
you need for task kill.

Like, oh man, mom.

Mom is totally acting up and we got to kill her.

This is just not good.

But-- but anyway, we've got
to kill the mom process.

I need 3828 and I'm good.

So you're going, okay, that's kind of cool.

So I-- I would go to command
prompt typing task kill.

Now I don't know what mom is
so I don't want to kill her.

But that's what this is.

A process ID just identifies
the OSPF process to the router.

I might say, well, what--
what numbers should I use.

Yeah, whatever you want to use.

But you got to remember it.

You got to remember it.

Does it have to be the same on
all the routers in your network?

No. Because I mean just like if
I went to another computer in--

in my house, I would see that
there's other-- there's other--

I mean, maybe mom or DWM is running

with a different process ID on
a different computer, right?

So-- so process ID doesn't really matter.

However, you have to remember what it is.

So, the reason you have to remember is
because you'll constantly be typing it

in to go into this configuration mode.

So, let me just tell you this.

Use one. That's it.

And I know, I-- this, this section right here.

This little process ID just
in the past has gener--

whoa, has generated so many questions that
it's just I'm telling you just use one.

I know questions like, well, can
I have multiple OSPF processes?

Yes, you can.

No, you don't want to.

Can I use, you know, process ID one and
then process ID 50 on another router?

Yes, you can.

No, you don't want to.

Why? Because then you have to remember.

Well, this one is 1, this
one is 50, that one is 392.

Just use one, okay?

So we're in OSPF.

And actually we've done step one.

We've turned it on.

OSPF, it's like the little
light switch on our router.

There's-- there's a light switch.

We just went from off to on, right?

So it's now running but it's not doing anything

because we haven't told it
what interfaces to use.

Okay, big, big command here.

OSPF works based on this command called network.

The network command I would say this is--

this got to be one of the
confusing commands in all CISCO.

And they're actually making it
go away as we move into IPV6.

The network command is actually
gone because CISCO knows it's crazy.

It's a crazy command.

The reason why is it's one command that does
two very similar yet very different things.

When I type in network I'm number one
identifying, you might write this down,

if you're taking notes write this down.

Embed this in your mind.

It identifies, identify-- hang on.

Beauty of a pause button, right?

It identifies what interfaces
to send Hello Packets on.

I know if you're a grammatical person,
you're like you can't end in a preposition.

But I just did 'cause that's
the only good way to say that.

It identifies what interfaces
to send Hello Packets on.

So when I type in network, so here--
let me show you the command, right?

I type in network 192.168.2.0, right?

Now-- now there's more to this command.

But let's just start there
and hit the enter key.

Now it's going to say, wait there's more to this
command and we'll talk about that in a second.

But when I type in network
192.168.2.0 it says okay,

let's see what interfaces do I
have in the 192.168.2.0 networks?

And it's going to go no,
nope, nope not that one.

Oh that's one, 192.168.2.1.

That's in the 192.168.2.1, 2.0 network.

So I am going to start sending
Hello Messages on these interfaces.

Why? Because it wants to form a neighbor.

It wants to find friends
to exchange routes with.

So we're telling it I want you
to send hello messages out there.

So when I type this-- this command in, it's
going to start sending hello's on there.

Is it going to send hello's out here?

No, it's not because that's not
the 192.168,2 network, right?

Okay, so that's-- that's
the first big thing it does.

Second thing it does, it identifies
what networks to advertise.

So what we're doing when we type in
network 192.168.2.0 is it says I'm going

to number one form neighbor
relationships out that interface.

And number two I'm going to tell people
about the 192.168.2 network, right?

Because maybe-- maybe I don't want
to tell people about this network.

Maybe this is a secret ninja network
where we have top secret Apple development

on the iPhone 9 or-- or something like that.

You know it's-- it's-- we don't want people
to know about the network then I wouldn't type

in the network advertisement because that is
what tells the router to advertise that network.

So now let me-- let me fill this-- this in here.

Let's say I type in this command
network 192.168.2.0 and hit the enter.

What have I done?

This router now is going to try and form
a neighbor relationship on that interface.

And as long as router two is doing the same
thing as long as I've typed that same command

in router two, they're both going to be
like, "hey man it's good to meet you."

And as long all these things are-- are up
to par which we're going to talk about those

in just a second so it's there up to
snuff in there-- they're all matching--

they're going to be like, let's be neighbors.

And then router one is going to say okay,

I got some really good information
for you to router two.

I know about the 192.168.2.0 network.

That's it.

Router two looks and goes,
"that was not interesting at all

because I'm connected to that network.

I already knew about that network.

You are worthless to me router one."

It doesn't really say that
but it kind of feels that way

because router one is not giving
it any information beyond that.

No, so what do we have to type in to let
router one tell router two something it didn't

know about?

Come on take a guess.

Come on. We would type in network.

Well, in addition now, it's going to
give me an incomplete command, right?

Because there's more to this
but let's just go with it.

So I would also have to type
in network 192.168.1.0.

Hit the enter key.

Okay, now again, filling in the-- the end of it.

So let's just focus on the base command first.

If I type in that now it's going to number
one send hello's out that interface as well

as the 192.168.2 'cause you now have, I
mean, they kind of go together, right?

It's not like you just type one.

So I'm going to type in, I send hello
messages out the 192.168.1.0 interface.

And-- and I'm going to start advertising
that network to other routers as well.

Now router two is like wow, you just became
a lot more interesting to me router one.

You're telling me about something
I didn't know about, 192.186.1.0.

Now of course you might have you're like okay,

well does he have to send
hello's out that interface?

I mean does he really have to?

Well not really.

I mean it's just kind of pointless hello's.

He's like hello.

I mean think of it like, you know, one of
those weird movies walking through hello.

Hello, anybody here?

But without the guy with the knife
jumping out from behind the door.

That's what this guy is doing.

He's sending empty hello's to an empty LAN.

Now is that a waste?

Yes. I would say on-- on the-- the least
amount of consequence it's a waste of--

of bandwidth, a waste of resources.

Number two is that a security hazard?

Yes, it is.

The reason why is he's saying
hello out to a user community.

If you've got a user, how many of
you know you can't trust your users?

Absolutely a fact.

That smiling guy in the cubicle,
he's trying to destroy you.

He's trying to hack your network because if
he starts seeing hello's coming in from OSPF,

he's going to try and sabotage your
network by becoming an impostor, you know.

Acting like an OSPF router and forming
a neighbor relationship with you.

Now I'd say well why would
somebody want to do that?

Well I would say on the least amount of
damage they can really mess up your network.

They can-- they can go in there and
they could start advertising routes

that don't really exist.

They could, I mean, they could
just sabotage your routing cable.

And that's number one you don't want that.

But I'm telling you if somebody's trying
to do that, what they're probably trying

to do is set off some kind
of man-in-the-middle attack.

Ever heard of that?

Man-in-the-middle is where you try to inject
yourself meaning a computer or some device

in the middle to where you make this
router believe you're a good exit point

to the internet.

And then you do some wizardry behind the scenes

to really say oh well actually
I can get you to the internet.

So essentially all of the routing goes
through your computer and, you know,

maybe it's not a WiFi connection.

Maybe, I mean you can, there's
all kinds of tricks you can play

to do the man-in-the-middle attack.

But you-- you get it to where it's going.

But now you are in the middle so
that you can start opening a tool

like Wireshark and capturing all of the data.

So now you can start seeing what
people are doing on the network.

You can start gathering information.

You can, I mean, there-- there are--
it's easy to do with Wireshark.

Start reassembling, you know, excel files
that people were working on, spreadsheets,

e-mails that were being sent, voice over
IP conversations that were being had.

You can actually capture
those if you're in the middle.

And put them all back together.

And now you've got scary data
that you can walk away with.

So you don't want that.

So and you might say okay, well what
if I want to advertise that network?

Now I'm going to advertise that to this router.

But I don't want to send hello messages there
'cause I know I won't ever have a neighbor.

Is there a way to split this network
command and say well do number two.

This is good.

Don't do number one.

I-- I don't want that.

Yes, there is.

That is actually known as the
passive interface command.

Check it out.

I'm going to go back on router one and
I'm going to type in notice I'm under--

I'm under OSPF configuration mode.

I'm under this router config mode.

I can type in passive interface
and say well I want

to be a little passive on we'll say [inaudible].

I don't remember what it was,
zero slash zero whatever.

You know, I'm not going to type it in
'cause I don't remember what it was.

And if I-- if I do the wrong one, you know,
then, then it's not going to send hello's

out this interface and no
neighbor relationships will form.

So-- so passive interface I know it's
almost like worth the foundations of OSPF.

So here is how it works and I'm already
introducing the passive interface,

the reason why is it's that important.

You want to use the passive.

As a matter of fact, I'll tell
you what, a lot of people do.

'Cause I'll actually type in passive interface
and then let me show you a question mark again,

passive interface default which
says turn off all routing updates.

Turn off all hello messages on all interfaces.

Type that in just like that.

Then no more hello messages anywhere.

You know like well, that says it--
that kind of defeats the point, right?

Well yes because now, you can go
in and do no passive interface.

And then I can do-- I got
to figure out my interfaces.

Show IP Interface Brief, right?

I can do no passive interface and do serial 0/0.

So now it's saying okay, everything is passing.

Nothing is sending hello messages
unless you as an admin go in.

And that's a really good practice.

What I just did right there,
really good security practice

to make sure you're not sending hello
messages where they don't belong.

Remember anywhere you send a hello that's where
a potential neighbor relationship conform.

Okay. Let's get back.

We've got to get back to configure.

Let me-- let me just clear
this off for a second.

All right, there we go.

That's a little better.

Let's-- let's get back to
the-- the core of everything.

We are in the middle of telling
it what interfaces to use, right?

And we kept seeing that incomplete
command when I was typing it in.

So we need to say router one use
these two interfaces for OSPF.

So I'm back in and still under, here let
me exit out 'cause I cleared the screen.

So router OSPF one.

I'm back into the router configuration mode.

I'm going to type in network 192.168.2.0

but you remember we kept
getting this incomplete command.

What's it looking for?

Space question mark.

Let's find out.

It says enter the wild card bits, okay?

What's a wild card bit?

Well let me first say we will unpack wild
card bits fully when we get into access list.

That's a big, big, big part of access
list understanding it in its entirety.

For now I'm going to give you enough about
wild card bits to-- to configure OSPF.

Now wild card bits think of
these as identifiers, right?

We're-- we're trying-- we're going
to try and identify in this--

in this IP address that we typed in.

What should the router really care about?

Here's what I mean.

First off, wild card bits are
completely opposite of the subnet mask.

So let's just write it up here.

I'm going to type in network 192.168.2.0.

Now let me give you a sample wild
card mask that we would use for this

and then I'll-- I'll describe what it means.

I'm going to do 0.0.0.255.

Now, I know it's wild, right?

That's why I gave it the name.

No one really knows why CISCO decided
to do it this way but they did.

What-- what it is, is completely
opposite of the subnet mask.

I mean when you think about a subnet mask
for 192.168.2.0 you're typically thinking

of class E, 255.255.255.0, right?

Well looking at that wild card mask it's
exactly the opposite and here's what it means.

Just again high level view right now wherever
you see a zero, line it up to the IP address

because that's something that the
router is saying look at this.

So let me draw the arrow there, right there.

The router is thinking, I'm getting
used to this pause thing, look at this.

So 192 is significant to me.

So I am going to identify interfaces by--
if they start with 192 that's-- that's key.

I'm going to start sending
hello packets on them.

If they-- if they start with 192, I'm going
to start advertising those networks, right?

But wait there's more.

Wait, no cost to you.

There's more.

168 that's the second octet.

It's saying look at this.

So look at this router when you're
trying to identify only turn on OSPF.

Let me-- let me just go back to this.

And when I say turn on, it
means these two things.

Only turn on OSPF on interfaces
that start with 192.168.

And then we look at the third
octet dot two, right?

Look at this.

Look at the two, 192.168.2 is significant.

Now the 255 means I don't care period.

I don't care what is in that
last octet because I mean what--

what really is happening when I type
this command is the router is going

to look at all of its interfaces.

Now let me-- let me get back here.

I mean do I show IP Interface Brief.

So when I type in network 192.168.2.0 and I
type in 0.0.0.255 what the router is going

to do is this going to say okay, let me look.

Do I have any interfaces that start with 192?

Yes, I do.

Do I have any interfaces that have
168 because again it's a look at this?

Yes, I do.

I actually have two of them.

Do I have any interfaces that have
192.168.2 because again it's uh look at this.

Look at this-- this third octet right here.

And it's going to say oh, oh yes I do.

This one qualifies.

Now this last octet it's going to say okay, dot
zero and it's going to go, oh that's dot one.

But wait a sec, you know what?

I don't care.

I don't care what IP Address
is in that last octet.

I just want to identify any interface
that starts with 192.168.2, right?

So that is how the wild card mask works.

So let's-- let's do a little more example.

Let's say-- let's say I wanted
to turn on OSPF for both

of these interfaces at the same time, right?

Here is something I could type.

I could type in network 192.168.0.0 with
a wild card mask, come on, think about it.

Can you guess it?

0.0.255.255.

That would be a way of turning on OSPF on
both of these interfaces at the same time.

Why? Because this one says look at this.

Look at the 192.

Turn OSPF on any interface that starts with 192.

Oh, look at this, second octet 168.

That is significant.

Look at any interface that's
starting with 192.168 for OSPF.

And then it looks at these last two octets.

And it says I don't care.

I don't care.

I don't care that this is
the one and this is the two.

That doesn't matter to me.

That's fine.

And I don't care that this has
a dot one and this has a dot one

in the-- in the fourth octet right here.

And I don't care because they
start with 192.168 something.

I'm going to turn on OSPF on them, okay?

Okay, let me go one step further.

What if I wanted to turn on OSPF on every
interface on my router that have right now.

And any interface I add in the future?

Go on and pause it right now.

Think of it, think of it and I know
you can think of it, okay unpause.

Network 0.0.0 with wild card
mask, 255.255.255.255, done.

It would work because that says
turn on OSPF on I don't care,

I don't care, I don't care, I don't care.

Anything, anything now or in the future
and now you might say well that seems easy.

Why don't we do that?

Not good. And Cisco says don't
do it because there's a lot

of times you're configuring your
router and you're adding an interface.

You're deleting it there.

And if you accidentally add an
interface, it's automatically whoop

within the OSPF before you're even
ready for that interface to be active.

You don't want to do that.

As a matter of fact, we might say
well what is Cisco's best practice?

It's none of these, seriously, none of these.

What Cisco actually sets to do
is use a network of, you know,

do a show IP Interface Brief right here.

And say network 192.168.1.1
with what wild card mask?

0.0.0.0. Network 192.168.2.1
with what wild card mask?

Oops, 2.1.

0.0.0, same things 0.0.0.0.

What that does is it's like a sniper
rifle-- we're turning on to OSPF.

You're like exactly this interface.

An interface that has 192.168.1.1
as it's IP Address,

exactly that interface turn on OSPF, right?

That's-- that's the scoop.

I mean that's-- that's your best practice.

Why is that the best practice?

It's a lot more typing.

It's a lot more and we're
even like well this is easy.

Beware of easy things in the Cisco
world because it's too far reaching.

It's too auto-magic.

We want to make sure that we know
exactly where OSPF is running.

So we literally type in a network command

for every single interface
and it starts advertising it.

Now another big misunderstanding
of the network command or comment.

I-- I remember when I first
learned-- I still remember this.

When I first learned network command I was
like okay, so does this actually affect,

you know, like what is advertised?

Like when I type in 192.168.0.0
is this guy going

to say I know about the 192.168.0.0 network?

No, it's not.

This is simply an identifier.

Just-- just like when I type in this,

it's not going to say I know
about the 192.168.1.1 network.

What happens when I type in this
network command is the router goes--

goes and says oh look I have that interface.

It's in that network or I know I guess
I'm based on the command I type below.

I have that interface.

So it says okay, well let me-- let me
look at that interface's configuration.

I'll do a sure-run interface 0.0.0/0.

And it says oh, well it looks

like this interface has the configuration
192.168.2.1 with this subnet mask.

So it looks and it goes oh okay, so it's
really connected to the 192.168.2.0 network.

The router is smart enough to
put all the pieces together.

This network command does not impact the
actual network that is being advertised.

Now, it could just happen to
line up for example if I type

in this command right here network 192.168.2.0
that that does happen to be the network

that is advertised over to router two.

But that just happens then.

All of these other, every single
one of these commands would work.

This would make OSPF work.

This would.

This would.

These would.

They all do the same thing.

And all their goal is to identify.

Think of it-- think of these
routers as standing and looking

at its interface like a line up of people.

And it's about ready to play dodge ball, right?

And it's like I want you and I want
you and I want you on my team, right?

And the little interfaces walk
forward and they're like yes.

And he goes okay, now who are you?

And he's like oh my name is 192.168.2, right?

So-- so this, the network command
just picks the people for dodge ball.

It picks the interfaces for dodge ball.

It does not actually dictate that this
is exactly what is being advertised.

Okay, good.

Now there's one more piece.

I told you it's the biggest
command, most important command

in everything that we're doing here.

One more piece to this network command, right?

And notice I hit the enter key.

And it's like okay, you got the wild card
mask but it's still an incomplete command.

Like there is more to this
command than what you've type in.

So I go okay well what else do you want?

And it would say, oh you need to
tell me what area this network is in.

Now this is that bucket of sand
I was talking about a moment ago.

We're just going to configure
everything in the backbone area,

the very first area we create
which is always area zero, okay?

Now we hit the enter key and we get nothing.

Nothing is always good in Cisco.

That means it took the command.

It's now working in that configuration.

So I can say okay, you've identified
well hey let's-- let's do this.

I'm going to say no network.

I'm going to remove that command and
I'm going to use Cisco's best practice.

Let's do 2.1, right?

With a wild card mask of 0.0.0.0.

Identify specifically that when
interface to use over to the other office.

And then let's hit the upper
row and identify 1.1.

The LAN interface to use up here.

So-- so we are again remember the two things we
are now sending hello's out these interfaces.

And we are identifying both of these
as networks advertised to our friends.

Now I said sending hello's out both

to these interfaces although it's
not happening here 'cause we use--

remember that passive interface default command?

And that's-- that's still in there.

It's still taking effect and that's fine.

We don't have any neighbors
outside of that interface.

Okay. So now we can come over to
router two so router two, right there.

Bring them into the picture.

Let's do get a quick orientation of router two.

We'll go much faster now
without all the descriptions.

So we've got 192.168.3.1.

Looks good.

That's the LAN interface looking at the diagram.

191.168.2.2 that's the LAN interface.

Let's just make sure we can ping 192.168.2.1,

just kind of getting some trouble
shooting all the way before we get there.

And then I'll do router OSPF.

And it says, what's your proximity?

Could I make this 60,000?

Yes, I could.

And it would work just fine but then I got

to remember 60,000 every time
I go and configure this router.

No, just use one.

So then I'm going to go in here and
type in network 192.168.2.2.000 area 0.

Hit the enter key and network oh, oh it happened
so fast 192.168.3.1.0.0.0 oops-- 0.0.0.0 area 0.

Did you see that message?

See why these messages are so golden?

You don't want to turn those off.

And it says OSPF adjacency change.

That's what that ADJ change means.

Process ID one, we just saw
a neighbor 192.168.2.1.

That's-- that's our friend.

That's router one over there on serial
0, I just went from loading to full.

Later on, you'll actually
learn about all of the--

the phases that a neighbor goes through
initially it could go through and an in-it phase

and you go through a two-way phase.

And you go through X start
exchange, loading, full,

you go through all these
different phases of neighbor.

But it only reports the big one, meaning
I now have a full neighbor relationship.

How do we verify that?

Let's go back and do a show IP OSPF neighbors.

That would say that's your number one
troubleshooting command right there for OSPF.

And I can see right there on the screen it
says 192.168.2.1 is at a full neighbor state.

We've-- we've-- we're now fully
exchanging routes between them.

So how do I prove that this
is working to me, okay?

I do show IP Route and this is
from router two's perspective.

And I can see in my two connecting interfaces
and-- OSPF whoa, has done its deal 192.168.1.1

or 1.0 network it now knows about it.

OSPF has advertised that to us.

I can see it now-- what's all these other stuff.

This, the 110 represents
the administrative distance.

Remember from the last nugget
the believability of OSPF.

How believable is that route to me?

I can see 74, that's the actual metric.

That's the cost.

How much-- how much does
it cost me to get there?

Now how was that figured out?

Well it was-- it was based on
the interface bandwidth in--

in megabits per second, divided by 100.

Now it-- it-- I'm trying to figure
out how-- how to end up getting to 74.

But, you know, essentially just doing the
math whatever this bandwidth is set to for

that LAN link, I think it's
two megabits per second.

And then this bandwidth is set
too for-- for that LAN link.

I don't know what it is.

But it puts it into this formula.

Totals them up and says okay,
that's going to be--

that is actually equal to the
cost which is the metric of OSPF.

So it cost me 74 to get there.

Where did I learn about it?

192.168.2.1, how long have
I known about this route?

59 seconds.

How-- how what interface do I
go out of to reach that route?

00/0, so now of course the
ultimate test is always

to ping it 192.168.1.1 and success we are there.

Let's shoot over to router one because
it should be feeling the same way.

Notice without typing anything it gave us
that status message we have a new neighbor.

Show IP OSPF Neighbor.

Verify that the neighbor is there.

Show IP Route.

And I can see I've learned
about the 192.168.3.0 network.

Got to ping it just to feel
good about ourselves.

And there it is.

We're pinging it.

We're successful.

This is the neighbor that we
learned from OSPF is in action.

Okay, only other troubleshooting
commands, like verify.

Let's see-- how else can we see this is working?

I can do a show IP Protocols.

Show IP Protocols shows us what routing
protocols are running on our router.

And I can see OSPF process one is running.

I can see it's advertising or routing for
the networks 192 and it shows, you know,

the network commands that I've typed in.

It says here are the interfaces
that are configured as passive.

That's kind of cool.

It's even showing us that and
you'll notice serial zeros.

So zero is the only one not in that list.

And then down here I see the sources.

This is-- this is some neighbors.

These are some friends that I've learned about.

Last update was three minutes ago because, you
know, now they're sitting there nice and idle.

What are they doing?

I mean if I were to do a debug
IP OSPF, what do we got here?

Let's do packet.

All I would see, there is hello messages.

Now you might say well, how did
you know it's a hello message?

'Cause I know that's all I should see.

You can actually-- you can actually go and
break down each one of these-- these fields.

And they mean something to where you
can see this is OSPF version two.

This packet is type one.

It just so happens that type
one is a hello packet.

There are all kinds of different
types of packets that are out there.

What is the length of the packet?

What is the router ID, essentially
what is my name when I'm--

when I'm or the name of the
router that's sending this packet?

What is the authentication ID?

I mean you can actually configure
authentications really easy to make sure

that oh what am I-- did say
authen-- no I just made that up.

Area ID, I don't know why I
was thinking authentication.

Area ID. It actually puts
it in the IP address format.

This is area zero.

You'll see little check sum on there.

You know this is the-- that's why I was saying
authen-- this is the authentication here.

What kind of authentication are you using?

OSPF supports clear techs, not very good.

And MD5 hashing, very good--
authentication between the different devices

and then what interface they came in on.

Now-- now, I'm seeing this is like--
and those are coming in every so often.

I can do a show IP OSPF Interface and say well
show me, you know, for instance serial 0/0.

And I can say oh serial 0 is
a point to point interface.

That's the kind it is.

And I'm saying hello every 10 seconds on there.

Somebody is going to be considered dead
if they don't speak for 40 seconds.

And do you get that feel about how often
these-- these little packs are showing up?

It's about once every 10 seconds.

There it is.

There is it.

So-- so some key show commands
that you can use to really see kind

of dig a little bit more of what's going on.

Essentially watch the magic happen

but understand a little more
of how the magic is working.

Can you believe that I thought I
could fit all that into one nugget?

Yeah, crazy right?

So-- so let me-- let me just
wrap this all up because I want

to give you the big picture perspective.

I don't know how long this nugget
is because I'm still talking.

But-- but it probably is I'm
guessing about 30 minutes long

or so that we've been talking about this now.

But I want you to notice, all of this
boil down to really two commands, right?

Router, OSPF and we did the
process ID one, right?

And then network and then
we typed in the network,

the wild card mask and the
area ID and that was it.

And now I threw in the passive
interface and some show commands for fun.

But really 30 minutes boil down to two commands.

Now, I know your-- that wasn't efficient.

We could-- we could have done that in 5 minutes.

Well the point is, there's a ton
of configurations in Cisco that--

that are two minutes long but it takes
hours of understanding the concepts

of what you're doing behind there.

The thing I'm trying to convey right now
is make sure that sometimes it's so easy

to get caught up in I've got remember syntax.

I've got to remember these commands.

And yes, yes you do have to
remember commands to type in.

But remember that the commands
are the easy part.

Anybody can go on Google and type

in give me example OSPF configurations
and be like oh there it is.

I can-- I can type that in
and it starts working.

But to really understand it, that's the key.

That's what Cisco wants at the CCNA
levels, the understanding of what--

what is that network command doing?

What-- what are those two things that it impacts
when you go under the-- the network commands?

So between this nugget in the last, we have
seen what routing protocols are all about,

the jellybean jar of protocol choices,

all the different flavors and
features that are out there.

And then finally this nugget, we
looked OSPF concepts and configuration.

I hope this has been informative for you
and I'd like to thank you for viewing.