All language subtitles for Free-CCNA-OSPF-Part-1-Day-26-CCNA-200-301-Complete-Course_en

This is a free, complete course for the CCNA.

If you like these videos, please subscribe\n

Also, please like and leave a comment, and\n

In this video we’re going to begin a series\n

It’s the only dynamic routing protocol that\n

the CCNA, so we’re going to go quite in\n

brief overview given for RIP and EIGRP.

OSPF is topic 3.4 of the CCNA exam, which\n

and verify single area OSPFv2’, with the\n

point-to-point, broadcast, and router ID.

We’ll cover all of these topics and more.

This first video, however, will focus on some\nbasics of OSPF.

Consider this a high-level introduction to\n

then in later lectures we will go lower down\n

So, let’s see what we’ll cover in this\nvideo.

First I’ll introduce some of the basic operations\nof OSPF.

This will be just a quick introduction, in\n

Then I’ll talk about OSPF areas, which is\n

networks into smaller sections.

Finally I’ll show you some basic OSPF configurations,\n

Watch until the end of the video’s quiz\n

ExSim is a set of practice exams for the CCNA.

I used them myself when studying for my CCNA,\n

really think ExSim is an essential study tool.

If you want to get ExSim, follow the link\n

Okay, let’s get started with OSPF.

First up, here’s the same chart of the different\n

Remember that OSPF is a Link State dynamic\nrouting protocol.

You’ll see in this video that it functions\n

routing protocols RIP and EIGRP.

To review, distance vector protocols use ‘routing\n

about the routes they know and their metric\n

However, the routers don’t have a complete\n

their neighboring routers tell them to determine\n

Now let’s review how link state protocols\nfunction.

Here’s another slide I showed you in Day\n24’s video.

When using a link state routing protocol,\n

To allow this, each router advertises information\n

These advertisements are passed along to other\n

develop the same map of the network.

This is important, all routers have the same\n

Then, each router independently uses this\n

Due to this process, Link state protocols\n

It’s more demanding on the router.

However, link state protocols tend to be faster\n

So that’s a quick review of link state routing\nprotocols.

Now we’ll start to go in depth about how\n

of what all this means, and see how different\n

So, let’s get started with OSPF.

OSPF stands for ‘Open Shortest Path First’.

The OSPF protocol uses the ‘shortest path\n

Another name for the algorithm is ‘Dijsktra’s\n

There are three versions of OSPF.

Version 1 was released in 1989.

It’s old and not in use anymore.

Version 2 was released in 1998, and this is\n

Take a look at the exam topics again.

The version of OSPF in the exam topics list\n

these videos I will be talking about version\n2.

There is also OSPF version 3, which was developed\nfor IPv6.

It can also be used for IPv4, but version\n

Okay, now a couple general points about OSPF.

Routers store information about the network\n

are organized in a structure called the LSDB\n

LSA and LSDB are two important terms for OSPF.

I’ll talk more about them throughout these\nvideos on OSPF.

Routers will flood LSAs until all routers\n

network, meaning the same LSDB.

So, those are two more important terms, ‘flood’\nand ‘area’.

You already know the term flood, switches\n

In the case of OSPF, it means they send the\n

OSPF ‘areas’ are a unique aspect of OSPF,\n

Let me briefly elaborate on the last two points\n

So, let’s say this network of four routers\nis running OSPF.

All of these routers are OSPF neighbors, they\n

Then, OSPF is enabled on R4’s G1/0 interface.

So, R4 needs to tell the other routers about\n

So, R4 creates an LSA to tell its neighbors\n

An OSPF LSA contains more information than\n

of the basic information in an LSA is the\nRID, the router ID.

For this demonstration, R4’s router ID is\n4.4.4.4.

None of its physical interfaces have an IP\n

interface with the IP address 4.4.4.4 or the\n

The network on the G1/0 interface is, of course,\n

I’ll talk more about OSPF’s metric, called\n

The LSA is then flooded throughout the network\n

This results in all routers in the OSPF area\n

The LSDB is like this, containing LSAs for\n

Now that OSPF has been activated on R4’s\n

I’m going to repeat this many times I’m\n

for all routers in the OSPF area.

Each router then uses the SPF algorithm, Dijkstra’s\n

Remember, each of these routers has a complete\n

So, for example, you and I looking at this\n

192.168.4.0/24 is this route via G1/0.

Well, R2 is basically looking at the same\n

traffic via G1/0 is the best route.

It’s not looking at a visual diagram like\n

Finally, note that each individual LSA has\n

The LSA will be flooded again after the timer\n

In OSPF, there are three main steps in the\n

best route to each destination in the network.

Step 1 is to become neighbors with other routers\n

In the network in the previous slide, for\n

Step 2 is to exchange LSAs with neighbor routers,\n

Then, each router independently calculates\n

I will cover these steps in depth in the next\nlecture.

Just keep in mind this basic process of OSPF.

Let’s move on to another fundamental concept\n

OSPF uses areas to divide up the network.

However, small networks can be single-area\n

For example, this network with four routers\nis a small network.

When configuring OSPF in a network like this\n

there won’t be any degradation of network\nperformance.

In larger networks, however, a single-area\n

For example, if the OSPF network had 500 routers\n

and just a few subnets, using just a single\n

You should divide a large network like that\n

Now, what are some of the negative effects\n

Well, for example the SPF algorithm takes\n

It also requires exponentially more processing\n

Each router sharing a single, huge link state\n

On top of that, every small change on the\n

activated, would caused LSAs to be flooded\n

would have to do the SPF calculation again.

By dividing a large OSPF network into several\n

Checking the exam topics once more, notice\n

So, I will only give a brief overview of OSPF\n

I’m not going to make a diagram with 500\n

It’s possible to make this one large, single-area\nnetwork.

All interfaces on all routers are assigned\n

You’ll see soon that area 0 is of special\n

Now, instead of one large area I’ll show\n

Now, there are some rules and terminology\n

It’s a set of routers and links that share\n

Looking at this diagram once more, how many\nareas are there?

Area 0, Area 1, Area 2, and Area 3.

Each of these areas maintains a unique LSDB.

Next, the backbone area (which is area 0)\n

Let’s check that network diagram again.

Notice that area 1, area 2, and area 3 all\n

This kind of network design, for example,\n

Notice that area 1 is not connected to area\n

It is only connected to area 2.

Next up, routers with all interfaces in the\n

So, in this diagram which routers are internal\nrouters?

If all of the router’s interfaces are in\n

This router here is internal to area 0.

These routers are internal routers in area\n1.

Same for these routers in area 2, and these\nrouters in area 3.

So, those are internal routers, routers with\n

Next up, routers with interfaces in multiple\n

because they are the border between different\nOSPF areas.

In this network, which routers are ABRs?

This router, connected to area 0 and area\n1, is an ABR.

This router, connected to area 0 and area\n2, is also an ABR.

And this router, connected to area 0 and area\n3, is an ABR.

So remember that ABRs, Area Border Routers,\n

One more bit of information about ABRs.

ABRs maintain a separate LSDB for each area\n

It is recommend that you connect an ABR to\na maximum of 2 areas.

Connecting an ABR to 3+ areas can overburden\nthe router.

So, a design like I show here is good OSPF\n

Next, routers connected to the backbone area,\n

This includes area border routers, by the\nway.

So, which routers in this network are backbone\nrouters?

Of course, this router is connected only to\n

It is a backbone router and an internal router,\n

This router is also a backbone router, on\ntop of being an ABR.

Same for this router, and this router.

They are both backbone routers and area border\nrouters, ABRs.

Next term, an ‘intra-area route’ is a\n

For example, from a router in area 1 to a\n

For example, if this router learns a route\n

route, because the destination is in the same\n

An ‘interarea route’ is a route to a destination\n

For example, if a router in area 1 learns\n

If this router in area 1 learns a route to\n

The router and the destination are in two\ndifferent OSPF areas.

So, those are some important OSPF terms regarding\nOSPF areas.

Make sure you learn and understand these,\n

Area, backbone area, internal router, area\n

route, and interarea route, remember those\nterms.

Next up, let’s cover a few additional rules\nabout OSPF areas.

First up, OSPF areas should be ‘contiguous’.

It means that each individual area should\n

It’s easier to demonstrate with the network\ndiagram.

So, this network satisfies that rule.

Now let’s look at what it means to be non-contiguous.

Instead of all being connected, half of area\n

This kind of network design is not allowed\n

So, instead of having area 1 split up and\n

you should make this section on the right\n

Now all of the areas are contiguous and OSPF\n

Next rule, all OSPF areas must have at least\n

I actually already mentioned this, but it’s\nworth repeating.

Let’s look at the network diagram again.

So, notice that area 1 has an ABR connected\n

connected to both area 2 and area 0, and area\n

This is correct OSPF network design.

As I showed you before, a network like this\n

problems, because area 1 does not have an\n

One more rule, OSPF interfaces in the same\n

If they’re not in the same area, they won’t\n

information about the networks they know about.

In a future video I will go more in detail\n

to become OSPF neighbors, but for now let’s\n

In this example, these three routers all have\n

This router also has an interface in the 192.168.1.0/29\n

Even though all four interfaces are in the\n

area 1 router will not become OSPF neighbors\nwith the others.

This time, the area 1 ABR’s interface in\n

So, all four routers will become OSPF neighbors.

Here’s a summary of those three rules.

Of course, I will cover many more points about\n

I will go in depth about OSPF neighbors, OSPF\n

But now let’s cover some basic OSPF configurations\n

So let’s use the same network topology that\n

Although it’s important that you understand\n

the CCNA you only have to configure single-area\n

I’ve already configured R2, R3, and R4,\n

Here is the basic OSPF configuration, let’s\nwalk through it.

First up, to enter OSPF configuration mode\n

A router can run multiple OSPF processes at\n

Typically you’ll just use a single OSPF\n

If you remember the EIGRP configuration, you\n

For EIGRP routers to become neighbors, their\n

However, the OSPF process ID is different.

The OSPF process ID is locally significant.

Routers with different process IDs can become\nOSPF neighbors.

Usually I just use process ID 1, but you\n

process ID 2 on R2, and they would still become\n

Note that this process ID is totally unrelated\nto the area.

You’ll see next that the area is configured\nseparately.

So, next I attempted to use the network command\n

Note that OSPF uses wildcard masks just like\nin EIGRP.

If you need to review them, go back and watch\nDay 25’s video.

Basically, it’s an inverse subnet mask.

Anyway, I tried to use that command but then\n

That’s because the OSPF network command\n

So I activated OSPF on all of these interfaces,\nin area 0.

Once again, for the CCNA you only need to\n

For single area OSPF it’s actually possible\n

Before moving on, let me review the function\n

The network commands tells OSPF to look for\n

in the range specified in the network command,\n

For example, in the first network command\n

R1’s G0/0 interface has an IP address of\n

So, OSPF will be activated on G0/0 in area\n0.

When OSPF is activated on the interface, the\n

with other OSPF-activated neighbor routers.

In this case, R1 will become OSPF neighbors\nwith R2 and R3.

I’ll explain that process in depth in the\nnext video.

So, just remember that the NETWORK command\n

It doesn’t tell the router ‘advertise\nthese networks’.

But we already covered that in the last video,\n

First up, the PASSIVE-INTERFACE command.

You already know this command from RIP and\n

The passive-interface command tells the router\n

OSPF uses hello messages to tell other routers\n

However, the router will continue to send\n

subnet configured on the interface.

So, although R1 won’t send hellos out of\n

still tell its other neighbors about the 172.16.1.0/28\nnetwork.

You should always use this command on interfaces\n

It’s a waste to continuously send hello\n

So, that’s the PASSIVE-INTERFACE command,\n

Next up let’s see how to advertise a default\n

So, I’ve added an Internet connection to\nR1.

Then I configured a default route on R1, and\n

Here is that information in the routing table of\nR1.

Feel free to pause here if you want to check\n

Just like I showed you in RIP, the command\n

DEFAULT-INFORMATION ORIGINATE.

In OSPF this will cause the router to create\n

I checked R2’s routing table, and you can\n

R3 and R4 would also do the same.

Now let’s take a look at the SHOW IP PROTOCOLS\n

check out some other commands as well.

Up top it says ‘routing protocol is ospf\n1’.

1 is the process ID I configured earlier.

OSPF also uses a router ID, and the router\n

Here is the order of priority when determining\n

First up, if you manually configure the router\n

If you don’t manually configure the router\n

If the router has no loopback interfaces with\n

physical interface will become the router\nID.

Currently R1’s router ID is 172.16.1.14,\n

router ID, and I also haven’t configured\n

Let’s see how to manually configure the\nrouter ID.

From OSPF configuration mode, use the ROUTER-ID\ncommand.

This is a little different from EIGRP, in\n

So, I entered a router ID of 1.1.1.1, but\n

Reload or use ‘clear ip ospf process’\n

So currently, the router ID is still 172.16.1.14,\n

reload the router or use that command to clear\n

I did that, from privileged exec mode I used\n

This basically resets OSPF on the router.

This is a bad idea in a real network, and\n

for a short time and won’t be able to forward\n

In a lab like this, however, it’s not a\nproblem.

As a side note, notice the ‘no’ in square\nbrackets.

When you see this after entering a command,\n

If you just press enter, the router will assume\n

However I typed ‘yes’, so it was cleared.

Then I did SHOW IP PROTOCOLS again and you\n

Now let’s look at the rest of the command.

Take a look here, ‘It is an autonomous system\nboundary router’.

An autonomous system boundary router, or ASBR,\n

R1 is connected to the Internet.

By using the DEFAULT-INFORMATION ORIGINATE\n

OSPF network to the Internet.

So, that’s why we see this output here on\nR1.

Next up, number of areas in this router is\n1.

These are three different types of OSPF areas,\n

types for the CCNA, just wanted to point out\n

router is in, just one because this is single-area\nOSPF.

Unlike EIGRP, OSPF doesn’t support unequal-cost\n

over a maximum of 4 paths by default.

To change the maximum number of paths, use\n

Here I changed the number to 8.

The ‘routing for networks’ section shows\n

To repeat myself, this only determines which\n

tell OSPF to flood LSAs for these specific\nnetworks.

Here’s the passive interface we configured,\n

Notice the router IDs, I configured these\n

their IP addresses became the router IDs.

Finally, down here OSPF’s AD is displayed,\n

If you want to change it, the command is the\n

From OSPF configuration mode, just use the\ncommand DISTANCE.

For example, I changed it to 85, so OSPF routes\n

We covered a lot of information, but lots\n

learned about RIP and EIGRP.

Of course, there was plenty of new information\ntoo.

Before moving on to the quiz, let’s review\nwhat we covered.

I gave a basic overview of OSPF operations,\n

we will cover in more depth later.

Although the CCNA only requires you to configure\n

Make sure to remember those basic OSPF rules\n

autonomous system boundary router, ASBR.

Finally we looked at some basic OSPF configurations.

Most of these were the same as in RIP and\n

Make sure to watch until the end of the quiz\n

CCNA, the best practice exams for the CCNA\n

If you want to get Boson ExSim, follow the\n

Which of the following statements about OSPF\nare not true?

A, In multi-area OSPF networks, all non-backbone\n

B, Single-area OSPF must use area 0.

C, Two OSPF routers with different process\n

D, The OSPF area must be specified in the\nnetwork command.

E, An ASBR connects the internal OSPF network\n

And F, The OSPF process ID must match the\narea number.

Pause the video to think about the answers,\nselect two.

The answers are B and F. Although it is common\n

you can actually use any area.

And the OSPF process ID does not have to match\nthe area number.

In fact, in multi-area OSPF there will be\n

so it’s impossible to match the process\nID to all area IDs.

The other statements are all true.

You want to activate OSPF on R1’s G0/1 and\n

G0/1’s IP address is 10.0.12.1/28, and G0/2’s\n

Which of the following commands should you\nuse on R1?

Here are the commands, A, B, C, and D. Pause\n

The answer is C, NETWORK 10.0.12.0 0.0.1.255\narea 0.

This is the only option that contains both\n

one that activates OSPF on both interfaces.

Answer the following questions about the OSPF\nnetwork below.

1, How many backbone routers are there?

And 3, How many ASBRs are there?

Pause the video now to answer each of these\nquestions.

Okay let’s check each of them.

How many backbone routers are there?

These 4 routers are backbone routers because\n

These 3 routers have interfaces in 2 separate\n

Finally, how many ASBRs are there?

Just one, This router here connects the OSPF\n

a default route into the OSPF domain.

Which of the following commands will make\nR1 an OSPF ASBR?

A, B, C, and D. Pause the video to look at\n

The correct answer is B, which first configures\n

OSPF using the DEFAULT-INFORMATION ORIGINATE\ncommand.

Option A simply configures two network commands\n

Option C activates OSPF on ALL interfaces\n

Option D is not a real command.

Which command can be used to manually configure\n

A, B, C, and D. Pause the video to examine\n

The correct answer is A, ROUTER-ID 1.1.1.1,\n

The command to manually configure the EIGRP\n

Option C configures an IP address on a loopback\ninterface.

If the router ID isn’t manually configured\n

ID, but it’s different than manually configuring\nthe router ID.

That’s all for the quiz, now let’s do\n

Okay, here's today's Boson ExSim practice\nquestion.

You administer the OSPF network above.

You issue the DEFAULT-INFORMATION ORIGINATE\ncommand on RouterA.

Which of the following statements are true?

A, OSPF will advertise RouterA's gateway of\nlast resort.

B, RouterA will become the OSPF ABR.

C, OSPF will summarize all of RouterA's directly\n

D, RouterA will become the OSPF ASBR.

And E, OSPF will redistribute all of RouterA's\n

Okay, so pause the video here to think about\nyour answer.

Okay, so let's check the answer.

We used the DEFAULT-INFORMATION ORIGINATE\n

as well as the previous video on RIP and EIGRP.

So, what this command does is it advertises\n

So that means A is one of the correct options.

OSPF will advertise RouterA's gateway of last\n

Okay, next, it's either B or D, is the second\ncorrect choice.

Will RouterA become the OSPF ABR, or will\n

So, an ABR is an Area Border Router.

It is an OSPF router that has interfaces in\n

backbone area, and one other area.

Now, an ASBR, Autonomous System Boundary Router,\n

external network, outside of the OSPF domain.

And it shares information into the OSPF domain\n

So that makes D the correct answer, because\n

the Internet, for example, and RouterA advertises\n

Click on 'show answer' down here.

So this is Boson's explanation of this question.

Not only why A and D are the correct options,\n

So, pause the video here if you want to read\n

In addition to Boson's explanation, there\n

OSPF Command Reference: default-information\noriginate.

So, Cisco's documentation is a really great\nstudy resource.

If you ever have any doubts about some certain\n

and Cisco's documentation often comes up.

So, you can use that as an additional study\nresource.

Okay, so if you want to get a copy of Boson\n

These are the practice exams I used when I\n

So once again, follow that link in the video\ndescription.

There are supplementary materials for this\nvideo.

There is a flashcard deck to use with the\nsoftware ‘Anki’.

There will also be a packet tracer practice\n

That will be in the next video.

Sign up for my mailing list via the link in\n

the flashcards and packet tracer lab files\nfor the course.

Before finishing today’s video I want to\n

Thank you to Venkatesh, kone, Joshua, Jhilmar,\n

funnydart, Scott, Hassan, Gerrard, Tibi, Joyce,\n

Yousif, Sidi, Boson Software, Charlesetta,\n

Sorry if I pronounced your name incorrectly,\n

One of you is still displaying as Channel\n

me know and I’ll see if YouTube can fix\nit.

This is the list of JCNP-level channel members\n

If you signed up recently and your name isn’t\n

Please subscribe to the channel, like the\n

with anyone else studying for the CCNA.

If you want to leave a tip, check the links\nin the description.

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