All language subtitles for Free-CCNA-OSPF-Part-2-Day-27-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 will continue our studies\nof OSPF.

In part 1 I introduced the basic functions\nof OSPF.

In this video I will cover more important\n

To review, OSPF is item 3.4 on the official\nexam topics list.

You already know the basics of configuring\n

Let’s see what we’ll cover in this video.

First up OSPF’s metric, which as you know\nis called cost.

It’s not so difficult to understand, so\n

The next topic will be how routers become\nOSPF neighbors.

I’ve mentioned OSPF neighbors previously,\n

Finally I’ll introduce some more OSPF configurations.

Make sure to stick around until the end of\n

ExSim is a set of practice exams for the CCNA\n

I highly recommend them, so make sure to check\n

in the video description to get Boson ExSim\nfor yourself.

As you already know, OSPF’s metric is called\n‘cost’.

It is automatically calculated based on the\n

You can also manually configure the cost of\n

The interface’s cost is calculated by dividing\n

The default OSPF reference bandwidth is 100\nmegabits per second.

So, for example a regular Ethernet interface\n

an OSPF cost of 10, because 100 divided by\n10 equals 10.

A FastEthernet interface, with a speed of\n

of 1, because 100 divided by 100 is 1.

Now, what about a gigabit Ethernet interface,\n

It has a cost of 1, even though 100 divided\nby 1000 equals 0.1.

And what about a 10-gig Ethernet interface,\n

It also has a cost of 1, even though 100 divided\n

Well, in OSPF all values less than 1 will\nbe converted to 1.

Therefore FastEthernet, Gigabit Ethernet,\n

So, here is the same network topology as before.

Let’s check out the cost of R3’s F2/0\ninterface.

I used the SHOW IP OSPF INTERFACE F2/0 command.

It’s actually displayed in two places.

As I said, the default cost of a FastEthernet\n

100 megabits per second and the reference\n

Now let’s check out the default OSPF cost\n

I entered SHOW IP OSPF INTERFACE G0/0, and\n

Clearly the default situation is not ideal.

Fortunately, you can change this.

You can, and should, change the reference\n

AUTO-COST REFERENCE-BANDWIDTH, followed by\n

Let’s take a look at that command.

As I showed in the previous slide, the reference\n

I configured 100,000, so what will the cost\n

100,000 divided by 100 is 1000, so that’s\n

100,000 divided by 1000 is 100, so that’s\n

Why configure such a large number for the\nreference bandwidth?

Well, you should configure a reference bandwidth\n

The 100 (*100,000) megabits per second I configured\n

gigabit per second interface, which is 100\n

this network, regular gigabit ethernet.

Finally, notice this message that is displayed\n

‘Please ensure reference bandwidth is consistent\n

So, to provide a consistent cost for each\n

should configure the same reference bandwidth\n

Okay, I set the same OSPF reference bandwidth\n

The OSPF cost to a destination is the total\n

This is just like spanning tree cost.

For example, R1’s cost to reach 192.168.4.0/24\nis what?

To reach 192.168.4.0, a packet would exit\n

So that’s 100 plus 100 plus 100, for a total\ncost of 300.

We’ll check R1’s routing table soon, but\none more thing.

Loopback interfaces have a cost of 1.

So, what is R1’s cost to reach 2.2.2.2,\n

To reach 2.2.2.2, the packet must exit R1’s\n

Now, it doesn’t actually exit any physical\n

but the cost of 1 is added to the metric.

So, R1’s cost to reach 2.2.2.2 is 101.

Here is R1’s routing table before changing\n

so they all have the default reference bandwidth\n

Notice that it has two routes to 192.168.4.0,\n

Even though the connection between R3 and\n

has the same cost of 1 as the gigabit Ethernet\ninterfaces.

And here is R1’s routing table after changing\n

Now R1 only inserts one route to 192.168.4.0\n

Notice the cost to 2.2.2.2 is 101, like we\n

Now let me introduce how to manually configure\n

The command is IP OSPF COST, followed by the\n

You configure this directly on the interface,\n

For example, I configured the cost of R1’s\n

see the cost is 10,000 instead of 100.

One more option to change the OSPF cost of\n

the interface with the BANDWIDTH command.

To review, the formula to calculate OSPF cost\n

I showed you how to change the reference bandwidth,\n

Now, I have to make clear the difference between\n

Although the bandwidth matches the interface\n

doesn’t actually change the speed at which\n

The bandwidth is just a value that is used\n

To change the speed at which the interface\n

This is how you actually change the speed\n

If you change the bandwidth of a gigabit Ethernet\n

still operate at 1 gigabit per second.

However, for the purpose of OSPF’s cost\n

Because the bandwidth value is used in other\n

not recommended to change this value to alter\n

It is recommended that you change the reference\n

to change the cost of individual interfaces\nif you want.

However, if you want to change the bandwidth\n

BANDWIDTH, followed by the bandwidth in kilobits\nper second.

Note that this is different than the reference\n

The interface bandwidth command is entered\n

Before you enter any command like this, I\n

check the units the command is entered in.

For example commands involving time, some\n

For commands involving speed, some are entered\n

Always check to make sure you’re entering\nthe correct units.

There are three ways to modify the OSPF cost.

First is to change the reference bandwidth.

The command is AUTO-COST REFERENCE-BANDWIDTH\n

per second, entered in OSPF config mode.

Next is to manually configure the OSPF cost\n

COST, entered in interface config mode.

Finally you can also change the interface\n

The command is BANDWIDTH, followed by the\n

I already showed you the SHOW IP OSPF INTERFACE\n

the OSPF cost of each interface.

SHOW IP OSPF INTERFACE BRIEF gives a convenient\n

Okay, let’s move on to the next topic.

This is another very important topic in OSPF,\nOSPF neighbors.

Making sure that routers successfully become\n

Once routers become neighbors, they automatically\n

So, you just have to make sure that OSPF is\n

the proper conditions are met to allow the\n

Of course, there are more advanced OSPF configurations\n

However, if routers can’t become OSPF neighbors,\n

So, how do routers become OSPF neighbors?

When OSPF is activated on an interface, the\n

out of the interface at regular intervals\n

These are used to introduce the router to\n

By exchanging hello messages they check that\n

and then negotiate their neighbor relationship.

By the way, the default hello timer is 10\n

OSPF hello messages are multicast to the IP\n

address for all OSPF routers.

Do you remember RIP’s multicast address?

Also, OSPF messages are encapsulated in an\n

the IP header has a value of 89 to indicate\nOSPF.

If you need a review of the IP header, go\n

Okay, for OSPF routers to become neighbors\n

I’ll give a basic overview of each of the\nneighbor states.

I recommend taking notes for this section.

Although it will be just a basic overview,\n

So, let’s assume OSPF is already activated\n

Then, OSPF is activated on R1’s G0/0 interface.

It sends an OSPF hello message to 224.0.0.5.

There are more fields in the hello message,\n

However, R1 doesn’t know about R2 yet, so\n

R1 doesn’t know about any OSPF neighbors\n

This is the first OSPF neighbor state, ‘Down’.

When R2 receives the Hello packet, it will\n

In R2’s neighbor table, the relationship\n

Note that R1 still doesn’t know about R2,\n

Basically, the Init state means that a Hello\n

ID is not in the Hello packet.

R2’s router ID is 2.2.2.2, but the neighbor\n

The next state is the 2-way state.

R2 will send a Hello packet containing the\nRID of both routers.

R1 will insert R2 into its OSPF neighbor table\n

Then, R1 will send another Hello message,\n

Now both routers are in the 2-way state.

The 2-way state means the router has received\n

If both routers reach the 2-way state, it\n

met for them to become OSPF neighbors.

They are now ready to share LSAs to build\na common LSDB.

On the other hand, if they fail to reach this\n

and find what’s stopping them from reaching\nit.

In some network types, a DR (Designated Router)\n

I will talk about OSPF network types and DR/BDR\n

I just wanted to introduce the terms, DR and\nBDR.

At this point, the routers are already OSPF\nneighbors.

Over the next few neighbor states they will\n

Let’s go to the next neighbor state.

After the 2-way state, the two routers will\n

Before that, they have to choose which one\n

So, they will decide which one will be the\n

Note that these are different than the DR\n

This Master/Slave relationship is only needed\n

They decide which will be the Master and which\n

The router with the higher RID will become\n

The router with the lower RID will become\nthe Slave.

So, in this case R2 will be the master and\nR1 will be the slave.

To decide the Master and Slave, they exchange\n

DBD packets are also important in the next\n

Basically, the Exstart state is just to prepare\n

R1 sends a DBD packet claiming to be the master.

R2 has the higher router ID, and says that\n

In the next state, the Exchange state, the\n

These DBDs do not include detailed information\n

their neighbor what LSAs they have.

Basically the routers are telling each other,\n

actually sending the LSAs yet.

The routers compare the information in the\n

own LSDB to determine which LSAs they must\n

After exchanging DBDs, they move to the next\nstate.

The next state is the Loading state.

In the Loading state, routers send Link State\n

neighbors send them any LSAs they don’t\nhave.

In the Exchange state they exchanged DBD packets,\n

So, these LSRs are used to request any missing\n

I’ll just show one side of the exchange,\n

Then the LSAs themselves are sent in Link\n

R2 sends R1 the requested LSAs in an LSU like\nthis.

R1 will also do the same for R2.

Finally, The routers send LSAck messages,\n

Now the loading state is complete, and the\n

We’ve reached the final OSPF state.

In the Full state, the routers have a full\n

But that doesn’t mean things are complete.

They continue to send and listen for Hello\n

to maintain the neighbor adjacency.

To maintain the adjacency another timer called\n

Every time a Hello packet is received, the\n

However, if the Dead timer counts down to\n

If the neighbors remain up, the routers will\n

to make sure each router has a complete and\n

This is the main advantage of dynamic routing\n

to changes in the network and add, remove,\n

Let’s summarize that process.

First of all, the connection between R1 and\n

The first state is the Down state, R1 and\n

send hello packets out of their interfaces.

Let’s assume that R1 sends the first Hello\npacket.

The Init state is when R2 receives that first\n

In the 2-way state, the routers exchange more\n

in R2’s Hellos, and R2’s router ID is\nincluded in R1’s Hellos.

In some kinds of OSPF connections an election\n

I will talk about this more in Day 28.

The routers exchange DBD packets to determine\n

The Master is the router that starts the DBD\n

They exchange DBD packets to tell each other\n

The next state is the Loading state.

They use LSRs, Link State Requests, to request\n

The LSAs are sent in LSU, Link State Update,\npackets.

Finally, LSAck packets are sent to acknowledge\n

Finally, the routers reach the Full state,\n

Do you remember this slide from Day 26?

The three main steps in the process of sharing\n

destination are 1, become neighbors, 2, exchange\n

Looking at this process again, these first\n

three involve exchanging LSAs to synchronize\n

I taught you to calculate the best route to\neach destination.

That’s a basic overview of how OSPF works.

Also, here’s a quick summary chart of the\n

Notice that they are numbered from 1 to 5,\n

I already described the basic purpose of each\n

here or take a screenshot if you want to use\n

After that overview, let’s take another\n

understand the output a little better now.

Here is SHOW IP OSPF NEIGHBOR, I entered it\non R1.

Note the full state with both neighbors R2\nand R3.

Also, both R2 and R3 are DRs.

Again, I will explain DRs in the next video.

This counts down from 40, but resets as soon\n

So, assuming a Hello packet is received every\n

to 40, count down to 30, reset to 40, etc.

Now let’s take another look at SHOW IP OSPF\n

You can see the default Hello and Dead timers\nof 10 and 40 here.

Hello due in 7 seconds means that R1 will\n

in 7 seconds, as it does once every 10 seconds.

Neighbor count is 1, adjacent neighbor count\nis 1.

R1 has only 1 neighbor connected to its G0/0\n

In the next video I’ll tell you the difference\n

Finally, adjacent neighbor 2.2.2.2, designated\nrouter.

As we saw above in SHOW IP OSPF NEIGHBOR,\n

Again, I’ll talk about that in Day 28, but\n

Okay, that’s all for OSPF neighbors for\n

Let’s move on to look at a little bit more\nOSPF configuration.

I already showed you a few new OSPF configurations\n

the AUTO-COST REFERENCE-BANDWIDTH command\n

So, let’s just look at a couple additional\nconfigurations.

First off, do you remember the purpose of\nthe NETWORK command?

It’s the same for RIP, EIGRP, and OSPF.

It simply tells the router which interfaces\n

Well, you can actually enable OSPF directly\n

For example, let’s assume that R1 has no\n

Here’s how to enable OSPF on the interfaces.

You can activate OSPF directly on an interface\n

process ID, then AREA, and the area ID.

Note that this is done from interface configuration\nmode.

Now OSPF is enabled on those interfaces and\n

Next, another method to configure passive\ninterfaces.

You can configure all of the router’s interfaces\n

the command PASSIVE-INTERFACE DEFAULT.

Then, you can use the command NO PASSIVE-INTERFACE\n

This is simply another way to configure passive\ninterfaces.

Depending on the number of passive interfaces\n

faster, or perhaps the normal method is faster.

Either way, the effect is the same.

If you configure OSPF directly on the interfaces,\n

The ‘routing for networks’ section is\n

OSPF on are displayed here, ‘routing on\n

The rest of the output is the same, however.

Before moving on to today’s quiz, let’s\nreview what we covered.

First up I showed you OSPF’s metric, called\ncost.

By default it is automatically calculated\n

actual bandwidth of the interface.

However, if the result is a value less than\n

The default reference bandwidth is 100, so\n

per second has an equal cost of 1.

You can modify the reference bandwidth with\n

You can also manually configure the cost of\n

One more option to modify an interface’s\n

command, although this isn’t the recommended\nmethod.

Finally, a route’s metric is the total cost\n

Next we studied the process routers use to\n

This is probably the most difficult section\nof this lecture.

I recommend watching it a few times, and perhaps\n

states’ to learn more about the process.

Finally I introduced a couple more OSPF configurations.

Instead of using the NETWORK command, you\n

As an alternative method of configuring passive\n

as passive with the PASSIVE-INTERFACE DEFAULT\n

Make sure to watch until the end of today’s\n

for CCNA, a set of practice exams for the\n

Okay, let’s go on to quiz question 1.

Put the OSPF neighbor states in the correct\norder.

Here are the neighbor states, order them from\n1 to 7.

Pause the video now to think about your answer.

Down, Init, 2-way, Exstart, Exchange, Loading,\nand Full.

A full explanation of each state would take\n

remember the order and purpose of each state.

Which statement about OSPF’s default cost\n

b) Ethernet and FastEthernet interfaces have\nthe same cost.

c) FastEthernet, Gigabit Ethernet, and 10Gig\n

And d) Ethernet, FastEthernet, Gigabit Ethernet,\n

Pause the video to think about the answer.

The answer is C, FastEthernet, Gigabit Ethernet,\n

The cost is calculated by dividing the reference\n

The default reference bandwidth is 100 megabits\n

However, anything faster than that will have\n

In which OSPF neighbor state are the Master\n

Pause the video to think about the answer.

A Master and Slave need to be decided in the\nExstart state.

The Master is the router that will start the\n

following state, the Exchange state, which\n

router and backup designated router are selected\n

In D, the Loading state, LSRs, LSUs, and LSAcks\n

Which of these commands can be used to make\n

A, AUTO-COST REFERENCE-BANDWIDTH 100.

Pause the video to think about your answer.

The answer is C, AUTO-COST REFERENCE-BANDWIDTH\n10,000.

Once again, the cost is calculated by dividing\n

A FastEthernet interface has a bandwidth of\n

10,000 divided by 100 equals 100, so you should\n

What are the default OSPF Hello / Dead timers\n

A, Hello, 2 seconds, Dead 20 seconds.

B, Hello 10 seconds, Dead 40 seconds.

C, Hello 30 seconds, Dead 120 seconds.

Or D, Hello 60 seconds, Dead 180 seconds.

Pause the video to think about your answer.

The answer is B, the default Hello timer on\n

default Dead timer is 40 seconds.

Now, I haven’t mentioned this in this video,\n

default OSPF timers are actually 30 and 120,\n

I’ll talk about some other kinds of connections\nin Day 28.

Okay, that’s all for the quiz.

Let’s take a look at a bonus question from\nBoson ExSim for CCNA.

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

You administer the OSPF network shown in the\ndiagram above.

The AUTO-COST REFERENCE-BANDWIDTH 1000 command\n

What is the cost of the route from RouterA\nto RouterC?

Pause the video to think about your answer.

So, you set the reference bandwidth to 1000\n

would mean that these gigabit ethernet connections,\n

1000 divided by 1000 equals 1.

On the other hand, these 100 megabit per second\n

because, of course, 1000 divided by 100 is\n10.

So, ideally we will avoid any fastethernet\n

as a gigabitethernet interface.

So, the shortest route without passing through\n

to RouterB, that is a cost of 1.

RouterB to RouterE, plus 1 so 2.

RouterE to RouterC, plus 1 so 3.

So the total cost from RouterA to B to E to\nC is 3.

Here is Boson's explanation, quite detailed.

And they of course show you the diagram with\n

RouterA to B to E to C. Okay, so you can pause\n

And they also include some references, or\n

OSPF Design Guide: OSPF Cost.

This Cisco documentation is available free\n

So I highly recommend checking it out.

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

These are the practice exams I used myself\n

Once again, follow the link in the video description.

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 Marko, Florian, Daming, Venkatesh,\n

Justin, John, funnydart, Scott, Hassan, Gerrard,\n

Mark, Miguel, Yousif, Sidi, Boson Software,\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.

I'm also a Brave verified publisher and accept\n