Welcome to Jeremy’s IT Lab. This is a free, complete course for the CCNA. If you like these videos, please subscribe to follow along with the series. Also, please like and leave a comment, and share the video to help spread this free series of videos. Thanks for your help. In this video we will continue our study of spanning tree, focusing instead on an updated version called rapid spanning tree. More specifically, we’ll be looking at Cisco’s version, rapid per-VLAN spanning tree. You saw in the previous lecture that classic spanning tree can be quite slow, taking up to 50 seconds for the network to converge after a change in the topology. As the name implies, rapid spanning tree improves this time, only taking a few seconds to respond to changes in the network. Because rapid spanning tree is superior to classic spanning tree, it is the default on most devices now, and the CCNA exam topics only mention rapid spanning tree. However I think it is important to understand classic spanning tree, and now that you know about classic spanning tree, rapid spanning tree will be much easier to learn. Let’s take a look at what we’ll cover in this video. First up, let’s take a few minutes to compare different versions of STP. In the past few videos I’ve mentioned multiple versions, STP, PVST+, rapid STP, rapid PVST+, multiple spanning tree. Just so there is no confusion, I will summarize each version, and clarify between the industry standards and the Cisco proprietary versions. Then the rest of the video will be all about rapid spanning tree, specifically the version which operates on Cisco switches, rapid per-VLAN spanning tree plus. Also, make sure to watch until the end of today’s quiz, I will once again feature a bonus question from Boson Software’s ExSim for the CCNA, a set of practice exams for the CCNA which I highly recommend. Ask anywhere on the Internet for CCNA practice exam recommendations, and people are going to recommend Boson. If you want to get a copy of ExSim to prepare for the exam, follow the link in the video description. Let’s start by summarizing the different versions of spanning tree. On the left I will list the industry standard versions, the IEEE standards. On the right I will list the Cisco proprietary versions, Cisco’s upgrades to some of the standard versions. First up, the classic spanning tree protocol, IEEE standard 802.1D. This is the original spanning tree protocol, according to Wikipedia it was originally published in 1990, although the original spanning tree was actually created in 1985, before being standardized. In classic STP, all VLANs share one STP instance. Therefore, we cannot load balance using classic STP, because there is only one instance, we cannot block different ports in each VLAN to achieve load balancing. So, Cisco decided to improve upon this. They developed Per-VLAN Spanning Tree Plus. Actually, before that they developed regular Per-VLAN Spanning Tree, which as I mentioned before only supported ISL trunk encapsulation, no dot1q, but let’s forget about that version since everyone uses dot1q for their trunk encapsulation these days. It’s Cisco’s upgrade to 802.1D. Each VLAN has its own STP instance. In the previous lab video when we configured STP we had to include the VLAN number in each command, for example spanning-tree vlan 1 root primary. That’s because a separate STP instance is running for each VLAN. Why is this good? Well, as you know already, we can load balance by blocking different ports in each VLAN, in each STP instance. We can use our network bandwidth more effectively, since we don’t have any connections going totally unused, just waiting for another connection to fail. Now, as you also know, classic spanning tree and PVST+ are quite slow. The max age timer is 20 seconds, and the listening and learning states are 15 seconds each, so it can take up to 50 seconds to respond to changes in the network. That’s simply not fast enough for modern networks. This was solved in rapid spanning tree protocol, IEEE standard 802.1w. It is much faster at converging and adapting to network changes than 802.1D. However, just like 802.1D, the industry standard rapid spanning tree protocol runs only one STP instance, shared by all VLANs. Therefore, it also cannot load balance. Cisco once again developed an improved version of the industry standard, Rapid Per-VLAN Spanning Tree Plus, or Rapid PVST+. It is Cisco’s upgrade to 802.1w, featuring the improved speed of rapid STP, plus it runs a separate STP instance for each VLAN. Therefore, it can load balance by blocking different ports in each VLAN, just like the previous PVST+. The final version is Multiple Spanning Tree Protocol, IEEE standard 802.1s. It uses modified RSTP mechanics. But the main improvement is that it can group multiple VLANs into different instances, for example if there are 10 VLANs, VLANs 1 to 5 in instance 1, and VLANs 6 to 10 in instance 2, to perform load balancing. Finally an industry standard version of STP that allows load balancing, and actually its superior to Cisco’s rapid-PVST. If you have many VLANs, let’s say 200, in your network, configuring primary and secondary root bridges in each VLAN is a lot of work. However, with MSTP, all you have to do is assign VLANs 1 to 100 to instance 1, and VLANs 101 to 200 to instance 2, and then configure the primary and secondary root bridges for instance 1 and instance 2, so its much easier to configure and manage. Actually, Cisco hasn’t developed their own version of MSTP, Cisco devices simply run the industry standard 802.1s. For large networks, it’s best to use MSTP, however for small to medium networks without a huge number of VLANs, Cisco’s Rapid PVST+ is what you’ll probably run on your switches, and that’s the version we’ll be focusing on today. It’s also the version that is mentioned in the official exam topics list. Also, all of this information here applies to the standard 802.1w, but that’s not the version that runs on Cisco switches. The good news is, since you already understand classic STP and PVST+, it will be much easier to learn rapid STP and rapid PVST+ by comparing it to the previous versions. Let’s get started. Before getting in to the details, here is Cisco’s summary of RSTP. RSTP is not a timer-based spanning tree algorithm like 802.1D. Therefore, RSTP offers an improvement over the 30 seconds or more that 802.1D takes to move a link to forwarding. The heart of the protocol is a new bridge-bridge handshake mechanism, which allows ports to move directly to forwarding. So, that’s the big difference between RSTP and 802.1D STP. 802.1D uses long timers to determine when it’s safe to move to the next state, and these timers are quite long, to ensure that no loops are accidentally created when a port starts forwarding. Back when the original STP was created, it was acceptable that a port could take 30 to 50 seconds to react to a change and start forwarding traffic. However that’s no longer the case. So, RSTP uses a ‘handshake’ mechanism, which allows switches to actively negotiate with other switches and move ports immediately to the forwarding state if appropriate. Okay, now I will introduce some of the specifics of RSTP. By the way, I will probably say RSTP sometimes, and Rapid PVST+ other times. Really, I’m talking about the same thing. Cisco’s Rapid PVST+ operates the same as RSTP, but with the addition of a separate instance for each VLAN, so I will use the two terms interchangeably. Let’s summarize some similarities between STP and RSTP. First of all, RSTP serves the same purpose as STP, blocking specific ports to prevent Layer 2 loops. RSTP elects a root bridge with the same rules as STP. I’m sure you know it by now, the switch with the lowest bridge ID becomes the root bridge. RSTP also elects root ports with the same rules as STP. So, the interface with the lowest root cost becomes the root port, with the same tie-breakers, neighbor bridge ID and then neighbor port ID. You studied this in day 20’s video, our first video on STP. Finally, RSTP elects designated ports with the same rules as STP. So, the interface on the switch with the lowest root cost will become designated and the interface on the other switch will be non-designated. If there is a tie, the switch with the lowest bridge ID will set its interface to designated. Cisco has said that RSTP isn’t a ‘revolution’ of STP, just an ‘evolution’. It made some major improvements to speed up STP, but it didn’t change it completely, as you can see here. Now let’s look at some of the differences of STP and RSTP. First up, port costs were updated for rapid spanning tree. Classic spanning tree defines port speeds up to 10 Gbps, and I believe port speeds faster than this are all given a cost of 1. To accommodate for faster speeds, RSTP’s cost values were expanded. 2 million for 10 mbps, 2 hundred thousand for 100 mbps, 20 thousand for 1 gbps, 2000 for 10 gbps, 200 for 100 gbps, and 20 for 1 Tbps. Beyond this, a 10 terabit-per-second interface would have a cost of 2. Use the flashcards to remember the port costs of both classic STP and rapid STP. Here’s a slide from day 21, the different port states of classic spanning tree protocol. Hopefully you remember these states, which ones send and receive BPDUs, which one forwards traffic, which ones learn MAC addresses, etc. However, rapid spanning tree simplifies the port states, reducing them to just 3, by combining three of these states into one. The three states that are combined into one are blocking, listening, and disabled. Actually, a more accurate way is to say the blocking and disabled port states were combined into one, and the listening state is simply not used. So, the listening state is gone, and the blocking and disabled states have become the discarding state. If a port is administratively disabled, meaning it has the shutdown command applied to it, it will be in a discarding state in RSTP. This was previously the disabled state. If a port is enabled but blocking traffic to prevent Layer 2 loops, it is also in a discarding state. This was previously the blocking state. Next, how about port roles? Remember, the three original port roles are root, designated, and non-designated. The root port role remains unchanged in RSTP. The port that is closest to the root bridge becomes the root port for the switch. Of course, ‘closest’ means the port with the lowest root cost. Also, the root bridge is the only switch that doesn’t have a root port. So, these points are the same as what you already learned about classic spanning tree. The designated port role also remains unchanged in RSTP. The port on a segment (which is another name for a collision domain) that sends the best BPDU is that segment’s designated port, and there can only be one designated port per segment. The other port on the segment is either a root port, or a non-designated port in classic spanning tree. However, the non-designated port role was divided into two separate roles in RSTP. Those are the alternate port role and the backup port role. Let’s break down those two roles. First up, the alternate port role. The RSTP alternate port role is a discarding port that receives a superior BPDU from another switch. This is the same as what you’ve already learned about blocking ports in classic STP. In our little topology down here, SW1 is the root bridge. When BPDUs are sent in this topology, SW3 receives a superior BPDU from SW2. It’s superior because the bridge ID of SW2 is lower than SW3. So, SW2’s interface is designated, and SW3’s is an alternate port. An alternate port basically functions as a backup to the root port. If the root port fails, the switch can immediately move its best alternate port to forwarding, as the new root port. If SW3’s root port fails, its alternate port is ready to immediately become the root port, with no transitional states. This immediate move to forwarding state functions like a classic STP optional feature called UplinkFast. Because it is built into RSTP, you do not need to activate UplinkFast when using RSTP or Rapid PVST+. We didn’t look at UplinkFast in the previous videos, its not mentioned in the exam topics list, but try to remember that its functions are built into rapid spanning tree, you might get asked about that on the exam. So, UplinkFast is one STP optional feature that was incorporated into RSTP. Since I just mentioned one, I’d like to briefly explain one more that was incorporated into RSTP. Neither of these are on the exam topics list so you don’t have to learn them in depth, but just be aware of their general functionality, because they are part of RSTP. One more STP optional feature that was built into RSTP is BackboneFast. Let’s say SW2’s root port is cut off, so it stops receiving BPDUs from the root bridge. It will then assume it is the root bridge, so it will send it’s own BPDUs to SW3. However, SW3 is now receiving BPDUs from both SW1 and SW2, but SW2’s BPDUs are inferior, they have a higher bridge ID. Without this backbonefast functionality, SW3 would just ignore these BPDUs from SW2 until it’s non-designated port, in classic STP, finally changes to a forwarding state and forwards the superior BPDUs to SW2, which then accepts SW1 as its root bridge again. However, BackboneFast allows SW3 to expire the max age timer on that interface and rapidly forward the superior BPDUs to SW2. This functionality is built into RSTP, so it does not need to be configured. So, that’s a very basic explanation of BackboneFast. Let’s look at a quick summary on the next slide. UplinkFast and BackboneFast are two optional features in classic STP. They must be configured to operate on the switch, but it’s not necessary to know how to do so for the CCNA. Both features are built into RSTP, so if the switch is running RSTP, you do not have to configure them. They operate by default on all switches running RSTP. Finally, You do not need to have a detailed understanding of them for the CCNA. I recommend that you know their names and their basic purpose, which is to help blocking or discarding ports move to forwarding without delay. If you want to learn more, do a Google search for ‘spanning tree uplinkfast’ or ‘spanning tree backbonefast’. Learning how to effectively search on Google for information is an essential part of being a good network engineer, to be honest. We Google things all the time in our daily work, and you can bet I Google things a lot when preparing these videos. So, if you ever want to learn more about a topic in one of these videos, take the chance to improve your Google skills and try to search for some good resources. Okay, after that little detour, let’s look at the last port role in RSTP. We just saw the alternate port role, which is just like the non-designated port role we saw in the previous lectures. Next up lets look at the backup port role. The RSTP backup port role is a discarding port that receives a superior BPDU from another interface on the same switch. This only happens when two interfaces are connected to the same collision domain, via a hub. Notice that there is now an ethernet hub connected between SW2 and SW3. When BPDUs are sent in this nework, the BPDU sent out of SW2’s designated port is flooded by the hub, and as you can see here it receives that same BPDU on a different interface. That’s why this interface is a backup port, not an alternate port. However, I’ve already told you that hubs are not used in modern networks, so you will probably not encounter an RSTP backup port. It’s still something you should know. RSTP backup ports function as a backup for a designated port. If SW2’s designated port fails, its backup port immediately begins forwarding traffic as a designated port. Now, as for how the switch chooses which port will be the designated port and which will be the backup port, the interface with the lowest port ID will be selected as the designated port, and the other will be the backup port. Before moving on let’s try out a quiz question. Identify the root bridge, and the RSTP port role of each switch interface in this network. By the way, the hub doesn’t participate in spanning tree. Hubs aren’t sophisticated enough to use spanning tree, so it just floods all frames it receives. Okay, pause the video here to find the answer. Okay, let’s check the answer. The root bridge is SW1, because all switches have the same priority and SW1 has the lowest MAC address, it is elected as the root. Its interfaces are designated ports. These are the root ports for each switch. SW2 and SW3’s root ports are obvious, they have the lowest root cost. How about SW4’s root port? The hub doesn’t participate in STP so it doesn’t add any cost to the BPDU, so why did SW4 choose G0/1 over G0/0? It’s because the neighbor bridge ID is lower via G0/1, because SW2 has a lower MAC address than SW3. SW2’s G0/1 connected to SW4’s G0/1 becomes designated. Now, how about the connection between SW3 and SW4? First of all, which switch sets its interface to designated? Well, SW3 has a lower root cost, so one of its interfaces will be the designated port. Which one? G0/0 has the lower port ID, so it will be the designated port in this collision domain. How about SW3’s G0/1 and SW4’s G0/0? SW3’s G0/1 receives the superior BPDU, with the lower port ID, from the same switch, so it's a backup port. SW4’s G0/0 receives the superior BPDU from a different switch, so it is an alternate port. Okay, those are the answers. Hopefully you answered correctly. If not, don’t worry, there will be more practice at the end of the video. Now let’s take a quick look at the CLI, I’m on SW3 here. As I showed you in the last video, there are three STP modes you can run on a Cisco switch, MST, PVST, and rapid-PVST. Rapid-PVST is the default on modern Cisco switches, so you probably won’t have to use this command, but I entered SPANNING-TREE MODE RAPID-PVST to make sure it runs in rapid pvst mode. Then I used SHOW SPANNING-TREE to confirm. Notice that it says ‘Spanning tree enabled protocol rstp’. Previously when we were using classic STP, it said ‘ieee’, now it says ‘rstp’. Although it says ‘rstp’, this is in fact Cisco’s Rapid PVST+ running. Now, the only other difference I want to point out is this. As shown in the network diagram, SW3’s G0/1 interface has the ‘backup’ role. The status is still listed as BLK for ‘blocking’, although this state is actually called ‘discarding’ in rapid STP. I used the SHOW SPANNING-TREE command on SW4 also. As in the network diagram, SW4’s G0/0 interface is an ‘Alternate’ port. Once again, this command lists the status as ‘blocking’, but remember the rapid STP name for this state is actually ‘discarding’. Just one note about running different STP versions, Rapid STP IS compatible with classic STP. The interface, or interfaces, on the rapid STP-enabled switch connected to the classic STP-enabled switch will operate in classic STP mode, with the same timers, the same blocking to listening to learning to forwarding state process, etc. So, if you have a really old switch that doesn’t run rapid STP, you can still use it in a network of rapid STP-enabled switches, they will adjust the operation of those specific interfaces to match the slower switch. So, in our network diagram, if SW4 was running classic STP, SW2 and SW3 would make these interfaces run in classic STP mode, but their interfaces connected to SW1 would remain in rapid STP mode. Next let’s look at the updated BPDU for RSTP. Here on the left is the classic STP BPDU for comparsion, I made it smaller so you can see the rapid STP BPDU better. Most of the BPDU remains unchanged, but there are some differences you should know. As I mentioned last time, you don’t need to memorize the BPDU, that’s more depth than is required for the CCNA. You just need to know a few aspects of it and what kinds of things are included in it. The first difference to know between these two BPDUs is here . Notice that the RSTP BPDU has a protocol version of 2, whereas classic spanning tree has a version of 0. Remember these version numbers for the exam, 0 for classic STP, 2 for rapid STP. The rapid STP BPDU also has a BPDU type of 2. Now, the next difference is here. The classic STP BPDU uses only two bits of the BPDU flags, the 1st bit and the 8th bit. However, the rapid STP BPDU uses all 8 bits. These flags are used in the negotiation process that allows rapid STP to converge much faster than classic STP. That’s all you really need to know about the rapid STP BPDU itself, compared to the previous version. But there is one more major difference. In classic STP, only the root bridge originated BPDUs, the other switches just forwarded the BPDUs they received. In rapid STP, ALL switches originate and send their own BPDUs from their designated ports. Let’s go through a few other differences. First, as I just said, all switches running rapid STP send their own BPDUs. Switches also ‘age’ the BPDU information much more quickly. In classic STP, a switch waits 10 hello intervals, which is 20 seconds. In rapid STP, a switch considers a neighbor lost if it misses 3 BPDUs, which is 6 seconds. It will then ‘flush’, meaning delete, all MAC addresses learned on that interface. Why does it do this? Because the neighbor is down, it knows it cant reach anything through that interface any more. For example, in this network traffic from PC1 to PC2 usually follows this path. But what if this connection is cut off? This switch will think: I can’t reach this neighbor anymore. I’ll clear all entries for this interface from my MAC table, and its other interface will become the root port. Then, if PC1 wants to send traffic to PC2 again, it will go through the normal process of flooding until it learns the MAC address on this new interface, and traffic will now follow this path. That’s just a quick look at how topology changes are handled in rapid STP. There is a lot of depth that we could go into about this, but its not necessary for the CCNA. If you want to go on to get your CCNP and CCIE, you’ll definitely have to study these processes more in depth. Before I summarize everything and move on to the quiz, there is one more concept of RSTP you should know, the RSTP link types. RSTP distinguishes between three different ‘link types’. The first type is edge. An edge port is a port that is connected to an end host. It moves directly to forwarding without negotiation. Does this sound similar? It sounds like portfast. Well, the portfast functionality was built into RSTP. So, there’s another STP optional feature built into RSTP by default, UplinkFast, BackboneFast, and now PortFast. The next link type is point-to-point. This is used for direct connections between two switches. However, there is one more type, although it is one you probably won’t use at all. That type is shared. This is a connection to a hub, like we saw earlier in the video. These connections must operate in half-duplex to avoid collisions. Don’t confuse these link types with the spanning tree port roles or port states. Basically, the point-to-point and shared link types just distinguish between full- and half-duplex connections, and the edge type is a port that uses portfast. Okay, let’s take a quick look at each type. As I said, edge ports are connected to end hosts. Because there is no risk of creating a loop, they can move straight to the forwarding state without the negotiation process. They function like a classic STP port with PortFast enabled. In fact, you configure an edge port simply by enabling portfast on the port. Here is the command, just like in classic STP. So really, portfast and an RSTP edge port are the same thing. In this network down here, which ports should be configured as edge ports? Pause the video if you want to think about it. Got the answer? All of these ports, the ones connected to the PCs, should be configured as edge ports. Next up, point-to-point. These ports connect directly to another switch. Because they connect to a switch, not a hub, they function in full-duplex mode. You don’t need to configure the interface as point-to-point, the switch should be able to detect that it is connected directly to another switch and will operate in full-duplex as a point-to-point port. However, if you want to explicitly configure the point-to-point link type, use this command: SPANNING-TREE LINK-TYPE POINT-TO-POINT. So, which connections in the diagram are point-to-point? Pause the video to think about it. Did you find the answer? It’s these three, the direct connections between two switches. Finally, shared ports connect to a hub. Due to the nature of hubs and the likelihood of collisions, these links must function in half duplex. Once again, you don’t need to configure the interface in shared mode, the switch will detect it. However, to manually configure it, use this command: SPANNING-TREE LINK-TYPE SHARED. Although you should be aware of this type of RSTP link, as I already said, you will probably never actually see this link type in real networks, hubs are old technology that have been fully replaced by switches. So, which connections in the diagram are shared connections? I think the answer is fairly obvious now, all of the remaining ones, which are connected to the hub. So, these connections here are shared links. Before moving on to the quiz, let’s summarize what we covered today. First up, we compared the different versions of STP. The classic STP is 802.1D, and Cisco’s upgrade is PVST+, which runs a separate spanning tree instance for each VLAN. Then the next standard version is 802.1w, rapid spanning tree protocol. Cisco’s version of this is Rapid PVST+, which again runs a separate instance for each VLAN. Then there is one more industry standard, multiple spanning tree, with which you can create multiple spanning tree instances, and group multiple VLANs within each instance. There is no Cisco version of MSTP, Cisco switches run the industry standard protocol. Then we looked at Rapid PVST+, but actually all of the information we looked at applies to the industry standard RSTP as well. RSTP is an evolution of classic STP. Instead of using timers, it uses a negotiation process to allow it to rapidly move the necessary ports to a forwarding state, and rapidly adjust to changes in the network topology. I didn’t mention any specifics of the negotiation process, that level of depth is not necessary for the CCNA. I told you about the port states in RSTP, there are only three. Discarding, Learning, and Forwarding. The listening state was deemed unnecessary, and in fact the learning state is often skipped due to the built-in features of rapid STP, like UplinkFast and BackboneFast. We talked about RSTP port roles, there are four. Root and designated ports are the same, but RSTP distinguishes between two types of ports in the discarding state. Alternate ports are discarding ports which receive a superior BPDU from another switch, this is the usual case. Backup ports, on the other hand, receive a superior BPDU from an interface on the same switch. This only occurs if connected to a hub, which is a situation you’ll probably never encounter, hubs are no longer used. I also mentioned some optional features of classic STP which were built into RSTP. First I showed you UplinkFast and BackboneFast, but PortFast is also built in, through the edge port function. Although you have to know PortFast for the CCNA, you don’t need a detailed understanding of UplinkFast and BackboneFast. I briefly showed you the RSTP BPDU, just remember that the protocol version in an RSTP BPDU is 2, whereas in classic STP it’s 0. Also remember the important point that in RSTP ALL switches send BPDUs, not just the root bridge. Finally, I showed you the RSTP link types. Edge ports are connected to end hosts, and you configure an edge port by enabling portfast on the interface. Point-to-point means it is connected directly to another switch, and shared means it is connected to a hub, and must use half-duplex. As I said before, hubs aren’t really used anymore, so you probably won’t see a ‘shared’ link type in any real networks. Okay let’s move on to the quiz. After a few quiz questions, let’s take a look at my favorite set of practice exams for the CCNA, Boson Software’s ExSim. Back before I started this YouTube channel, I used Boson ExSim to prepare for my CCNA and CCNP exams, and I really think ExSim played a big role in me passing all of my exams on the first try. The questions are very similar to the questions on the real CCNA exam, and Boson gives in depth explanations which really help deepen your understanding of the topics. Okay, now continuing on from quiz question 1, which we did earlier in the video, let’s go to quiz question 2. Which IEEE 802.1D optional features were built in to the IEEE 802.1w standard, and allow ports to move rapidly to the forwarding state? Select three. A, root guard, B, portfast. C, BPDU guard. D, uplinkfast. E, backbonefast. F, loop guard. Or G, rootfast. Pause the video to think about your answers. The answers are B, portfast. D, uplinkfast, and e, backbonefast. A, root guard, C BPDU guard, and F, loop guard, are spanning tree optional features, but they are not features built in to RSTP that allow ports to move rapidly to the forwarding state. G, rootfast, is not a real STP optional feature. B, portfast, allows edge ports, connected to end hosts, to move rapidly to the forwarding state. D, uplinkfast, and E, backbonefast, allow ports to move rapidly to forwarding in certain cases of interface failure. Let’s go to question 3. You want to configure an 802.1w edge port, so that hosts connected to the interface can begin sending traffic over the network immediately. Which command should you use? A, spanning-tree link-type edge. B, spanning-tree mode edge. C, spanning-tree link-type portfast. Or D, spanning-tree portfast. Pause the video to think about your answer. The answer is D, spanning-tree portfast. Although ‘edge’ is a link type in RSTP, you don’t use the spanning-tree link-type command to configure it, and the command doesn’t even include the word edge. To configure an RSTP edge port, simply configure portfast on the interface with the command SPANNING-TREE PORTFAST. Okay, let’s do one more quiz question. Identify the root bridge in this network. What is the RSTP port role of each switch (port)? What is the appropriate RSTP link type of each connection between devices? This is a pretty long question, I recommend taking a screenshot and writing the port roles and link types on the screenshot so you can remember everything. Pause the video now to find the answers. Okay, hopefully you solved it. The root bridge is SW1, it has the lowest priority. How about all of the root ports in the network? Here they are. SW4 picked it’s G0/0 interface because SW3 has a lower bridge ID than SW2, even though they have the same root cost because the hub doesn’t add any cost. So, these are the designated ports. Why was an interface on SW2 and not SW4 selected to be designated? Because SW2 has the lower root cost. Finally, the discarding interfaces. Notice that there is one backup interface, SW2’s G0/2 interface. This is because it receives a superior BPDU from an interface on the same switch, the G0/1 interface. Now, how about the link types? All of these ports connected to end hosts should be edge ports. All of these full-duplex connections between switches are point-to-point links, and these half-duplex connections with the hub are shared links. If you had trouble with this, you should review the spanning tree videos, including this one, and if you still don’t understand feel free to ask a question in the comment section. Okay, now let’s check out a question from Boson ExSim for CCNA. Okay, for today's Boson ExSim practice question, I picked a question that mentions edge ports, something you just learned about. So here's the question. Which of the following optional STP features reduces convergence time by immediately placing edge ports into a forwarding state? Select the best answer. So there are five options. A, root guard. B, BPDU guard. C, PortFast. D, BPDU filter. And E, loop guard. Pause the video to think about your answer. Okay, did you find your answer? So, first of all what is an edge port? Well it's a port at the edge of the network, meaning it's connected to end hosts, it's not the internal network between the switches. So, which optional feature places ports connected to end hosts immediately into a forwarding state? You should know the answer by now, it is C, PortFast. If you're actually doing a practice exam you can click next to go to the next question, but let's check the answer, show answer. Okay, and we are correct. So you can see it gives quite a detailed explanation, and this is really the great thing about Boson ExSim, about their practice exams. Not only does it tell you why PortFast is the correct answer, but here it gives you a brief summary of each of these other optional features. Loop guard, root guard, BPDU guard and BPDU filter. So you can know why they are not the correct answer. After all that it gives some references to the official cert guide here, this is from chapter 9, optional STP features. And then also some Cisco documentation that you can read online for free, and this is another great study resource by the way, Cisco's official documentation. Okay, if you want to get a copy of Boson ExSim for yourself, please follow the link in the video description. I used Boson ExSim myself for my CCNA and CCNP and I really think they were essential in helping me pass all of my exams on the first try. So once again, please click that link in the video description and get a copy of Boson ExSim. There are supplementary materials for this video. There is a flashcard deck to use with the software ‘Anki’, download it from the link in the description and use the flashcards to review the concepts you learned in this video. There will also be a packet tracer practice lab so you can get some hands-on practice. That will be in the next video. Before finishing today’s video I want to thank my JCNP-level channel members. Thank you to tibi, vikram, Joyce, Marek, Samil, velvijaykum, C Mohd, Johan, Mark, Miguel, Yousif, Kone, Boson Software, the creators of ExSim, Sidi, Magrathea, Devin, Charlsetta, Lito, Yonatan, Mike, Aleksander, Vance, and Gerrard. Sorry if I pronounced your name incorrectly, but thank you so much for your support. One of you is still displaying as Channel failed to load, if this is you please let me know and I’ll see if YouTube can fix it. This is the list of JCNP-level members at the time of recording by the way, May 27th 2020, if you signed up recently and your name isn’t on here don’t worry, you’ll be in future videos. Thank you for watching. Please subscribe to the channel, like the video, leave a comment, and share the video with anyone else studying for the CCNA. If you want to leave a tip, check the links in the description. I'm also a Brave verified publisher and accept BAT, or Basic Attention Token, tips via the Brave browser. That's all for now.