All language subtitles for Free-CCNA-Spanning-Tree-Protocol-Part-2-Day-21-CCNA-200-301-Complete-Course_en

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In this video we will continue our study of\nspanning tree.

In part 1 we focused on the basic purpose\n

In this video we will look into more detail\n

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

First of all we will take a look at spanning tree states and

You already know the blocking and forwarding\n

states between those two, and some timers\n

I’ll show you the spanning tree BPDU (bridge protocol data unit,

Then we’ll take a look at some optional\n

tree ‘toolkit’, some additional features\n

tree, we’ll cover some of them briefly.

Finally, we’ll cover spanning tree configurations.

Spanning tree runs by default so you don’t\n

you should know how to change which switch\n

make sure traffic follows the best path.

Also, make sure to stick around to the end\nof today’s quiz.

I will feature one practice question from\n

of practice exams for the CCNA.

Pretty much everyone who uses them agrees\n

and are an essential part of preparing for\nthe CCNA.

They definitely helped me pass all of my CCNA\n

If you want to grab a copy of ExSim, please\n

First let’s take a look at spanning\ntree port states.

You are already familiar with two, BLOCKING\n

BLOCKING and FORWARDING are the two ‘stable’\nstates.

Root and Designated ports remain stable in a Forwarding state, and

Note that they only remain stable as long\n

If a new device is added, an interface is\n

they may have to change states.

But as I said, as long as the network is stable,\n

Now, there are also two transitional states.

Listening and Learning are transitional states\n

is activated, or when a Blocking port must\n

change in the network topology.

Actually, there is one more state you might\n

This simply refers to an interface that is\n

We won’t really talk about the disabled\n

any role in spanning tree, the interface is\nshut down.

Okay, let’s take a look at these states,\n

Non-designated ports are in a Blocking state.

Interfaces in a Blocking state are effectively\n

This is what makes spanning tree work, disabling\n

Interfaces in a Blocking state do not send/receive\n

Any regular traffic that arrives on an interface\n

However, Interfaces in a Blocking state do\nreceive STP BPDUs.

They need to receive and process BPDUs to\n

to transition toward a forwarding state if\nthey need to.

But, interfaces in a Blocking state do NOT\nforward STP BPDUs.

Finally, interfaces in a Blocking state do\n

If regular traffic arrives on the interface\n

After the Blocking state, interfaces with\n

Let me just repeat that only Designated or\n

That’s because Listening is a transitional\n

state, so there’s no need for a Non-designated\n

The Listening state is 15 seconds long by\ndefault.

This is determined by a timer called the ‘Forward\ndelay’ timer.

You’ll soon see that this timer isn’t\n

Anyway, remember that it is 15 seconds by\ndefault.

An interface in the Listening state ONLY forwards/receives

It does NOT send or receive regular traffic.

If a regular unicast frame is received on\n

An interface in the Listening state also does\n

that arrives on the interface.

I said the same thing about the Blocking state,\n

As you know well already, when a frame arrives\n

source MAC address field to ‘learn’ that\n

table with the MAC address, interface, and\nVLAN information.

However, if an interface is in the spanning\n

The traffic is simply dropped, and the MAC\n

After the Listening state, a Designated or\n

The Learning state is 15 seconds long by default.

This is determined by the Forward delay timer,\n

and Learning states, meaning by default it\n

both states and enter a forwarding state.

Same as in the Listening state, an interface\n

Also, it does NOT send or receive regular traffic.

However, here is the difference between the\n

An interface in the Learning state learns\n

So, an interface in the learning state is\n

some of its MAC address table beforehand.

Finally, we have the forwarding state.

Root and Designated ports are in a Forwarding\n

A port in the Forwarding state operate as\nnormal.

A port in the Forwarding state sends and receives\nBPDUs.

It sends and receives normal traffic.

Also it learns MAC addresses from the frames that\n

So, it’s a switchport operating as normal.

For review, here’s a summary of each spanning\ntree port state.

For reference, I’ve also added the Disabled\n

is the spanning tree state of a shutdown,\n

Pause the video if you want to take a look\n

You can also review using the flashcard deck,\n

Now let’s talk about each of the timers\nused in Spanning Tree.

I’ve already mentioned the Hello and Forward\n

First up let’s look more in detail at the\nhello timer.

It determines how often the root bridge sends\n

Other switches in the network do not originate\n

However, there is one thing I didn’t mention\nbefore.

The switches will only forward BPDUs on their\nDESIGNATED PORTs.

First off, I showed you this slide in day\n20’s video.

Assuming these switches all come online at\n

bridge, and each will send BPDUs out of all\ninterfaces.

However, once the network has converged and\n

roles, only the root bridge sends BPDUs.

Then, the other switches will forward these\n

information like the bridge root cost, sending\n

Then, two seconds later, the root bridge will\n

again forward these BPDUs on their designated\nports.

Note that they do not forward the BPDUs out\n

Next up, the forward delay timer.

This is the length of the Listening and Learning\n

Note that this is the length of each of the\n

So, with the default Forward delay timer of\n

for the switchport to move through both states\n

Then the final timer, one I haven’t told\n

This timer indicates how long an interface\n

So, this will need some more explanation.

Remember that each collision domain has one\n

So, all root ports and non-designated ports\n

The root bridge, SW3, sends BPDUs, and then\n

To demonstrate the Max Age timer, let’s\n

It just received a BPDU, so the max age timer\nis reset to 20.

And then the root bridge sends BPDUs, because\n

they are forwarded by the other switches,\n

But what if a failure occurs on the connection\n

The root bridge will send BPDUs, and other\n

G0/0 interface is down so SW2 no longer receives\n

So, the max age timer continues counting down.

15… and if the failure doesn’t recover\n

its G0/1 interface, SW2’s max age timer\n

First of all, If another BPDU is received\n

the time will reset to 20 seconds and no changes\nwill occur.

However, If another BPDU is not received,\n

switch will reevaluate its STP choices, including\n

After these decisions, if a non-designated\n

root port, it will transition from the blocking\n

learning state (again for 15 seconds), and then finally\n

So, it can take a total of 50 seconds for\n

Well, tThese timers and transitional states\n

created by an interface moving to forwarding\nstate too soon.

I showed you in the previous lecture how dangerous\n

That’s why spanning tree protocol is very\n

However, a forwarding interface can move directly\n

about creating a loop by blocking an interface.

But, as I just said, a blocking interface\n

It must go through the listening and learning\nstates.

So let’s move on to check out the spanning\n

First off, in the Ethernet header section,\n

Cisco’s PVST+ uses the destination MAC address\n

I recommend remembering this, it’s a little\n

For remembering little facts like these, I\n

deck I include with this video.

I mentioned PVST in the previous lecture,\nbut what’s PVST+?

Well, PVST is an older version which only\n

PVST+ is a newer version which supports dot1q.

I might use the term ‘PVST’ sometimes,\n

By the way, since I mentioned the MAC address,\n

PVST or PVST+, uses a destination MAC address\nof 0180.c200.0000.

Again, you probably should remember that fact\nfor the exam.

Now let’s move on to the spanning tree BPDU\nitself.

I don’t think you need to memorize the BPDU for the CCNA, but I

give you an introduction to what is included\nin the BPDU.

The first three fields are the protocol identifier,\n

The protocol version identifier is set to\n

a different value here when we look at rapid\n

Finally, the BPDU type is hexadecimal 00 for\n

There are other types of BPDUs, but we don’t\n

Next up are some flags, these are used to\n

Again, I don’t think we need to go in depth\n

Next up is the root identifier, which gives\n

is the VLAN ID, 10 in this case, and the bridge\n

I set the MAC address to all A’s in this\ncase.

It’s 0 in this case, so you know that this\nis the root bridge.

You can also know this is the root bridge\n

The information in the bridge identifier field\n

meaning this is the root bridge.

After that is the port identifier, the interface\n

8 0 in hexadecimal is equivalent to 128, which\n

0 2 is the number of the port itself.

Message age is something I haven’t mentioned\n

and is increased by 1 each time it is forwarded\n

It is subtracted from the max age when a switch\n

is passed through 5 switches, when it reaches\n

its max age timer to 15, meaning each time\n

to 15 instead of 20, even though the max age\ntimer is 20.

I don’t think that’s an important topic\n

After that we have the three timers we talked\n

By the way, the spanning tree timers on the\n

for the rest of the switches in the network,\n

Next let’s talk about some optional features\n

These are features that can be enabled to\n

The first one is called portfast.

It solves one problem of spanning tree.

Portfast can be enabled on interfaces which\n

interface on each of these switches.

These are designated ports, in a forwarding\nstate.

However, when they are first turned on or\n

the Listening and Learning states first before\n

15 seconds for Listening and 15 seconds for\n

I want you to open up Packet Tracer and try\na little experiment.

For this experiment, make sure Show Link Lights\nis enabled.

You can enable it by clicking on options,\n

I want you to place a switch and a PC like\n

At first you should see that the link light\n

This is the same if you connect a real physical\n

It’s because the port is not Forwarding\n

However, 30 seconds later you should finally\n

The port is finally forwarding.

I told you why spanning tree goes through\n

forwarding state, it’s because Layer 2 loops\n

wants to be absolutely sure no loop will be\n

However, only interfaces connected to another\n

There is no risk of forming a loop with an\nend host.

So, wouldn’t it be nice if these ports connected\n

away, without having to wait 30 seconds to\n

Well, that’s what portfast does.

Portfast allows a port to move immediately\n

If used, it must be enabled only on ports\n

If enabled on a port connected to another\n

The purpose of the listening and learning\n

them is risky when connected to another switch.

We haven’t looked at any other spanning\n

operates by default even without configuration.

We will look at general spanning tree configuration,\n

Portfast is enabled at the interface level\n

Then we get a warning about what I just told\n

There is also a message saying that, even\n

take effect if the interface is in a non-trunking\n

That’s because trunk ports are typically\n

You can still configure portfast on a trunk\n

You can also enable portfast with the following\n

This enables portfast on all access ports,\nbut not trunk ports.

So, portfast is a great feature for getting\n

quickly without having to wait 30 seconds.

However, it can still be a risk.

What if an employee plugs another switch into\n

This employee doesn’t necessarily have malicious\n

Because portfast is putting these interfaces\n

Portfast can also cause loops if the network\n

perhaps a host is moved to a different switchport\n

Anyway, the point is that there is a risk\nto using portfast.

However, there is an additional spanning tree\n

If an interface with BPDU Guard enabled receives\n

will be shut down to prevent a loop from forming.

BPDU guard is very simple to configure.

From interface configuration mode, use the\n

Similar to portfast, there is also an option\n

From global config mode, use the command SPANNING-TREE\n

This enables BPDU Guard on all portfast-enabled\ninterfaces.

Notice that the commands are a little different,\n

spanning-tree bpduguard enable, no mention\nof portfast.

However to enable it globally, you have to\n

I took this screenshot in packet tracer, so\n

than the previous one, but I connected a switch\n

you can see what happens when a BPDU arrives\n

The port is disabled, it is effectively shut\ndown.

What if you want to enable the port again?

To enable a port that was disabled by BPDU\n

You can see that the interface comes up.

However, if you didn’t actually solve the\n

you can see here that the interface will immediately\n

So, make sure you actually solve the problem\n

In terms of spanning tree optional features,\n

I also showed you BPDU guard because it is\n

There are many other optional features that\n

all of them for the CCNA, but let me just\n

least know the name and basic purpose of,\n

They are Root Guard and Loop Guard.

If you enable root guard on an interface,\n

bridge ID) on that interface, the switch will\n

The interface will be disabled.

This helps maintain the spanning tree topology\n

either with bad intent, or perhaps without\n

If you enable loop guard on an interface,\n

The interface will be disabled.

This prevents loops that can happen if an\n

what is called a ‘unidirectional link’\n

to forward it, or the opposite.

So, those are two other optional spanning\ntree features.

However, as I said, You probably don’t have\n

such as UplinkFast, Backbone Fast, etc) for\nthe CCNA.

But make sure you know Portfast and BPDU Guard.

If you want to read more about the others\n

Finally, let’s look at some basic spanning\n

You can configure the spanning mode the switch\n

and then you can see there are three options.

MST, multiple spanning tree, is not a topic\n

PVST is the classic spanning tree but with\n

Rapid-PVST is an improved version I will tell\n

Modern Cisco switches run rapid-PVST by default,\n

However, if you want to try out the classic\n

these demonstrations, you can enable it with\n

You can also manually configure the root bridge\n

With these MAC addresses and the default priority\n

However, we could configure SW3 to be the\nroot bridge.

We could also configure something called a\n

next in line to become the root bridge if\n

Let’s see how to configure that.

This is how to configure the root bridge,\n

SPANNING-TREE VLAN, followed by the vlan number,\n

Now you can see that this bridge has become the\nroot.

This command sets the STP priority to 24576.

If another switch already has a priority lower\n

to 4096 less than the other switch’s priority.

So, it makes this switch have the lowest priority,\n

If you then check the running-config, you\n

applied in this case is SPANNING-TREE VLAN\n1 PRIORITY 24576.

So, this commands tells the switch to apply\n

with the priority 24576, or 4096 less than\n

The command to set the secondary root bridge,\n

SPANNING-TREE VLAN, vlan number, ROOT SECONDARY.

Now the priority has been set to 28672.

So, this command sets the spanning tree priority\n

However, like the root primary command, the\n

So, for both of these commands, you could\n

as you see here to configure the root bridge,\n

way to do it without remembering the different\n

You may remember from the last lecture, that\n

of 4096, so the root command is easier to\nuse.

The interface between SW1 and SW2 is disabled\n

This topology is running Cisco’s PVST+,\n

Perhaps there is another VLAN, VLAN 2, in\n

It will look like this, the default topology,\n

In VLAN 2, the connection between SW1 and\n

between SW2 and SW3 will be disabled.

This allows for what’s called spanning tree\nload balancing.

If you have multiple VLANs in your network,\n

a waste of interface bandwidth.

That connection will be doing nothing, just\n

However, if you configure a different root\n

will disable different interfaces.

Okay, to check if you understood that explanation,\n

This is quiz question 7, because in day 20’s\n

Two VLANs are active in this network, 10 and\n20.

By default, SW3 is the root bridge for both\nVLANs.

Configure SW1 as the primary root for VLAN10\n

Configure SW2 as the primary root for VLAN20\n

Which two commands should you issue on SW1,\n

So, use the commands I just showed you, the\n

You don’t have access to the CLI so just\n

We want to make SW1 the primary root bridge\n

essentially it acts like a backup root bridge\nfor VLAN20.

So, these are the commands to issue on SW1.

On SW2 we want to do the opposite.

It should be the root bridge for VLAN20, and\n

so it will have the second lowest priority\n

These are the commands to issue on SW2, basically\n

So, did you get the correct answers?

Please watch the next video which will be\n

learn in this video, you can practice with\n

own labs in packet tracer to practice.

So, with those settings, perhaps the VLAN10 topology\n

And then perhaps the VLAN20 topology looks like this.

So, different connections are used in different\n

interfaces, this is called load balancing.

Before moving on to the rest of the quiz questions\n

show you how to configure some spanning-tree\nport settings.

There are two main settings you can configure\n

The cost, and the port priority, and as you\n

on a per-VLAN basis like the bridge priority.

It’s the root cost, remember the chart I\nshowed you in day 20.

FastEthernet costs 19, gigabit ethernet costs\n4, etc.

It’s used primarily to determine the root\n

selecting designated and non-designated ports.

How about the priority, do you remember what\nit is used for?

Well, it is the first half of the port ID,\n

Why would you want to change either of these\nvalues?

Well, to change the result of the root port\n

I won’t give a detailed example here, but\n

video, so make sure to watch that.

First I configured the cost of this interface,\n

Then I set the port-priority, which is configured\n

Those are the only spanning tree interface\n

Again, stay tuned for the lab video to try\nthem out.

We covered the different spanning tree states\nand timers used.

We took a brief look at the structure of a\n

the spanning-tree optional features, focusing\n

Finally we did some basic spanning tree configurations,\n

different root bridges in different VLANs\n

interfaces, and then some basic spanning tree\n

Okay, for today’s quiz we’ll do 3 more\n

After that, one special practice question\n

far the best practice exams for the CCNA there\n

If you want to get a copy of Boson ExSim,\n

Now let’s go to question 8 of the quiz.

So, continuing from quiz question 7 we did\n

You connect a PC to a switch, however for\n

Which two options could fix this issue and\n

Each answer is a complete solution.

A, enable portfast on the switch port you\nconnect the PC to.

B, reduce the STP hello timer.

C, reduce the STP forward delay timer.

Or D, reduce the STP max age timer.

Pause the video to think about your answer,\n

The answers are A and C. A, portfast, allows\n

spanning tree states and enter the forwarding\n

As for C, the forward delay timer determines\n

If you shorten this timer, the switch will\n

However, it is recommended that you leave\n

default settings were chosen for a reason.

A packet capture indicates that a switch port\n

What is the STP port priority of this port?

Pause the video to think about your answer.

The first half of the port ID, hexadecimal\n

Hexadecimal 8 0 is equivalent to 128 in decimal,\n

You want to make sure that a Layer 2 loop\n

Which spanning tree optional feature achieves\nthis?

Pause the video to think about your anwer.

BPDU guard will shutdown an interface if a\n

It should be enabled on portfast-enabled switch\n

Okay, that’s all for the quiz, let’s take\n

Okay, for today's Boson ExSim practice question\n

as in Day 20's video because at the end of\n

enough to answer the questions from Boson\n

Well, now we can answer at least some of them.

So, let's read the question one more time.

You want to decrease the amount of time that\n

PortFast is not configured on any of the switch\n

You issue the SPANNING-TREE PORTFAST DEFAULT\n

Which of the ports on SwitchA will use PortFast?

A, no ports because PortFast cannot be enabled\nglobally.

Okay, you should know the answer to this question.

Please pause the video here to think about\nyour answer.

So, you should know, we just talked about\n

Or at least I think it is, let's check.

To check your answer click down here, 'show\nanswer'.

Okay, so not only does it tell you it's correct,\n

explanation of why it's correct.

Why D is correct, and why A, B, and C are\nincorrect.

That's one of the great things about Boson\n

Personally I think a practice exam that just\n

you why it's correct or why it's incorrect,\nisn't very useful.

So let's read just at least this first part\n

All access ports on SwitchA will use PortFast.

PortFast enables faster connectivity for hosts\n

If PortFast is not enabled, a switch port\n

learning states before it enters the forwarding\nstate.

This process can take as long as 30 seconds\n

In addition, port initialization can take\n

I haven't talked about this yet in the course,\n

PortFast transitions the port into the STP\n

STP listening and learning states.

Okay, and there's more explanation down here.

Plus references, here to the official cert\n

And some Cisco documentation you can read\nfor free online.

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

I used them myself for my CCNA and CCNP, please\n

There will be supplementary materials for\nthis video.

There will be a review flashcard deck to use\n

Download the deck from the link in the description.

There will also be a packet tracer practice\nlab.

Please be sure to watch the practice lab and\n

practice with the configurations you learned\nin this video.

Before finishing today’s video I want to\n

Thank you to Vikram, Joyce, Marek, Samil,\n

Miguel, Yousif, Kone, Boson Software, the\n

Charlsetta, Lito, Yonatan, Mike, Aleksandr,\nand Vance.

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 members at\n

2020, so if you signed up recently and your name\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