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Please read the lecture article again to review before trying this exercise, So the first portion of this lab is the same as the practice quiz questions. We did at the end of the lecture article Identify the root bridge then identify the spanning tree port role of each switch interface, Either root designated or non-designated, But since we're in Packet Tracer, We can now use the CLI to confirm our answers. I didn't want to make the lecture article too long, So I didn't show any CLI commands. So please read this article to see which commands you can use to confirm spanning tree First up which switch is the root bridge.
First, We must compare the bridge priorities and if there is a tie, Compare the MAC addresses Those are the two components of the spanning tree bridge ID and the switch with the lowest bridge ID becomes the root bridge. In this case, The answer is fairly obvious. Sw3 has the lowest priority 24577, So it will be the root bridge.
So we now know port role of each interface on SW3. All of its interfaces must be designated ports because it is the root bridge. Just to make things easier to remember, Let me make labels Click on the note button up here and let me make 4 Ds for designated and after you have made them, Let's move them into position. So all four interfaces on SW3 are designated ports.
Next up let's find the root ports. Each other switch in the topology must have a single root port. The first criteria to determine the root port is the root cost. The interface with the lowest root cost will become the root port. How about SW1 Via either F0/1 or F0/2, It would have a cost of 19 plus 4 for SW1's, G0/1 and plus 4 for SW4's, G0/2, So 27 Via f0/3 or f0/4.
It has a cost of just 19, So it will be either F0/3 or F0/4, But we don't know which so let's look at the tiebreaker neighbor bridge ID Well. Both are connected to the same switch SW3. So that is a tie as well.
The final tie, Breaker is the neighbor switch's port ID the lowest one wins It's important to remember that this isn't the LOCAL switch's port ID it's, Not SW1's port ID It's, The neighbor switch's port ID SW3's port ID F0/1 is lower. So that means SW1's F0/4 interface. Will be the root port? Let me create that label, And then I will move it over to SW1.
next, Which will be SW2's root. Port F0/3 is directly connected to the root bridge, So it might look obvious that this will be the root port. However, Via F0/3, It has a root cost of 19 Via G0/1. It has a root cost of 4 plus 4 for SW4's G0/2, So only 8.
Therefore G0/1 will be the root port. That also means we can label SW4's G0/1 interface as designated. The interface connected to a root port is always designated So SW4's root.
Port is now obvious, Since G0/1 is designated it's. Other port G0/2 must be the root port. It also has a very low cost. Only 4 so we have found and labeled all of the root ports. Next up in each remaining collision domain, We must determine which side will be designated and which will be non-designated First up, Two very obvious ones: SW1's F0/3 is connected to the root bridge, So it must be non-designated.
The same goes for SW2's F0/3. It is connected directly to SW3, So it is non-designated. Sw3's port is already designated. All that remain are F0/1 and F0/2 on SW1 and SW2. The first criteria is the root cost. The interfaces on the switch with the lower root cost will be designated.
The other side will be non-designated. Sw1's root cost is 19 via F0/4. However, SW2's root cost is 8 via G0/1, So SW2 has the lower root cost. Therefore, Its F0/1 and F0/2 interfaces will both be designated.
The other side, SW1's, F0/1 and F0/2 will both be non-designated. In a blocking state, Now that we've figured out the answers, Let's actually check by using the CLI Let's go on the root bridge. Sw3 first So enter privileged exec mode with ENABLE And the first command I want to show you is SHOW SPANNING-TREE At the top here. It shows the VLAN number If there were multiple VLANs on these switches. You would see all of this information listed separately for each VLAN.
In fact, You can filter the output of this command to show a single VLAN like this SHOW SPANNING-TREE VLAN 1, But we only have a single VLAN, So it doesn't matter here Under that spanning tree enabled protocol IEEE. This means we are using the ‘classic' spanning tree. Actually it's Cisco's PVST, But this means it's in ‘classic' mode, Rather than the newer rapid spanning tree, Which we will look at in a future article. Then there are two big sections Root ID which lists information about this spanning tree's root, Bridge and bridge ID which lists information about this switch's information. In this case, SW3 IS the root bridge, So t are the same with a few differences in the information t present Under Root ID.
It just lists the priority of 24577, But down here it shows that really its the priority of 24576 plus the extended system ID of 1 for VLAN 1 In the root ID section it clearly states this bridge is the root. Then there are some timers listed. I'll talk about these timers in the next lecture article.
Finally, At the bottom, Each interface participating in spanning tree is listed. You can see the role status, Cost interface, ID and interface type, And I won't talk about the interface type in this course. By the way, It's not necessary So because this is the root bridge, We expect all interfaces to be designated ports and to be forwarding, As you can see, T are so we were correct Now before moving to another switch. Let me briefly show another couple: commands SHOW SPANNING-TREE DETAIL, Lists similar information to SHOW SPANNING-TREE, But, As you might expect, With more details, I won't go through everything here, But feel free to take a look if you want And one more command SHOW. Spanning-Tree SUMMARY This lists.
Each VLAN and shows how many interfaces are in each STP state. I told you about Blocking and Forwarding already, But these two here listening and learning are transitional states which I will teach you about in the next article. The final column, STP active just lists. How many interfaces are STP activated in total By default, Every interface that is connected to another device and enabled will have STP running Next let's? Take a look at SW1 Enter privileged exec mode with ENABLE SHOW SPANNING-TREE As expected. F0/4 is the root port and is forwarding, And the other interfaces are blocking Note that slightly different terminology is used here, ‘alternate' instead of non-designated, But the meaning is the same, Also notice that the root ID section shows SW3's information. But now the bridge ID information is different.
This is SW1's own information, So our answers for SW1 were correct. Next, Up let's go to SW2, ENABLE SHOW SPANNING-TREE Looks like we were correct, Again, F0/1 and F0/2 connected to SW1 are both designated and in a forwarding state. Although really these connections are disabled because SW1 is blocking, Those ports, F0/3 is blocking and G0/1 is the root port. By the way something I should have mentioned before, The COST displayed here is just the cost of this interface, Not the total root cost, So it only displays 4 here.
If you want to see the total root cost use this command. I showed you SHOW SPANNING-TREE DETAIL Here. It says: cost of root path is 8 because there are two gigabit ethernet interfaces in the path.
Finally, Let's check on SW4 ENABLE SHOW SPANNING-TREE So G0/1 is designated and G0/2 is the root port. So we successfully calculated the spanning tree topology, That's all for this lab Next up, Let's take a look at a lab in Boson NetSim, For today's Boson NetSim for CCNA lab preview. I will once again do something a little bit different Here in the 'network access' section of NetSim for CCNA you'll notice.
There are no labs for spanning tree. Why is that? Why does Boson not include spanning tree in NetSim for CCNA? Well, Let's check the exam topics list: These are the exam topics for the CCNA 200-301 current version, 25 'describe, The need for and basic operations of, Rapid PVST+ spanning tree protocol and identify basic operations' So 'describe' and 'identify' There's no mention of 'configure'. Like these other topics.
'Configure configure configure configure' This one 'describe' and 'identify'. So, According to the exam topics list spanning tree configuration is not on the CCNA exam. So that's probably why Boson didn't include it in NetSim for CCNA. However, I still think it's a good idea to get some hands-on practice in the CLI observing and configuring spanning tree.
So that's why I include labs in my course. However, If you check out the CCNP ENCOR 350-401 exam topics list here, 31c configure and verify common spanning tree protocols, So configuration is included in the CCNP exam topics list. So instead of a CCNA NetSim for CCNA lab, Let's do a NetSim for CCNP ENCOR lab. There are quite a few spanning tree labs here, Starting here, 'spanning Tree 1'. All the way down to here 'Implementing, Multiple Spanning Tree Protocol', The one we're going to take a look at today - is this one simply titled 'spanning Tree Protocol' Click on the lab and click 'load lab', But I've already done that so 'lab instructions'.
So there are four switches here: P1ASW1 ASW2, P1DSW1, DSW2 ASW mean 'access switch', 'access, Layer, Switch' And DSW is 'distribution layer switch'. These are two common layers of network design, Good network designs - and I haven't actually talked about them. Yet in my course, So you can wait for that in the future Just know their meaning now: 'access switch', 'distribution, Switch' Notice, The hosts connect to the access switches and then the access switches connect to the distribution switches. So just for today's preview, I will do this step here, Step 1 On P1DSW1 issue, The SHOW SPANNING-TREE VLAN 1 DETAIL. I just showed you this command SHOW SPANNING-TREE DETAIL to display the spanning tree for VLAN 1 Use the output to answer the following questions. So let's go into the CLI of DSW1 here: Click on the device and click on 'console', And we're in ENABLE SHOW SPANNING-TREE, VLAN, 1 DETAIL.
So question A which spanning tree is VLAN 1 executing. We aren't actually going to do any configuration in this step by the way. This is just answering questions And actually that's something I really like about NetSim. T ask you good questions to really test your understanding of the topic So anyway, Which spanning tree It says it right here.
'Vlan 1 is executing the ieee compatible Spanning Tree Protocol'. This means classic spanning tree protocol, The one I taught you in the lecture article. This is not rapid, Spanning tree protocol. So that's the answer, Regular classic spanning tree B.
What are the priority sys-id? This is the extended system ID the VLAN number and MAC address. T are stated here. Bridge identifier, Bridge ID has priority 24576 sysid 1, Which actually gets added to the priority. So it's really 24577 in total, And this is the MAC address, So that's question B: Why is there no root port? Well, Let's confirm.
Is there a root port Here? Fastethernet0/1 is designated forwarding, So it's not a root port. It's a designated port 0/2 designated 0/3 designated designated designated and designated, So there are in fact, No root ports. Why is that? Well? The answer is here: We are the root of the spanning tree. This switch is the root bridge. As you know, Every port every interface on the root bridge must be designated.
So that's why there are no root ports. So that's C And then D. Why are there no blocked ports for VLAN 1? Well, That's the same reason, Because it's the root There will be no blocked ports on the root bridge. T should all be designated ports in a forwarding state, E: what is the timer value for sending BPDUs bridge protocol data units? So I haven't talked about the timers yet in the lecture article, So I will talk about them in the next lecture article Day 21.
But the answer is here Configured time. Time is the interval at which it sends those BPDUs t're called ' BPDUs'. So 2 means 'every 2 seconds', So it will send 1 BPDU every 2 seconds. What is the maximum age for a BPDU Here? It is 20 seconds Again. I will talk about this, This maximum age timer in the next article And what is the value of the forward? Delay? Timer? It is 15 seconds.
Sorry there we go 15 seconds. These are the defaults. 2. 20. 15. ! So that's the answer for G . So there is one more step here to this lab and then lab solutions highlighting all of the different outputs.
You can see pretty much everything we just looked at , So there it is Boson NetSim. If you want to get a copy of Boson NetSim for CCNA, And I highly recommend you do look at all of these guided labs, T have here for all the exam topics From network fundamentals, Network access, IP connectivity, IP services, Security fundamentals. So if you can, I highly recommend getting a copy of NetSim for CCNA.
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