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Next up, we need to learn about the port states. The port roles tell us a lot

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about

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where in the network a port is. Is it the best path to the route, for example?

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Is it

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not the best path? Is it a downstream port? But the port state is actually

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going to

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determine whether it's blocking or forwarding as well as a couple of other

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behaviors. And so there's five different states that we need to worry

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about. First of all, is listening abbreviated as LIS. We also have learning
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about. First of all, is listening abbreviated as LIS. We also have learning

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abbreviated as LRN. And this is something that we see by the way at Cisco CLI.

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So

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for an iOS XE, we're going to see these usually abbreviated. So then we've got

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forwarding like forwarding ports, FWD. We also have blocking. We've already

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used

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this shortcut BLK for blocking. And then lastly, we have disabled, which can be
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this shortcut BLK for blocking. And then lastly, we have disabled, which can be

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abbreviated as DIS. Now, just to get a couple of these out of the way, as we

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can imagine, blocking means that we have no traffic forwarding. This is going

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to be

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our loop prevention mechanism. The port in our topology that we had on the

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previous video, when we were blocking here, this was in a blocking state.

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Remember,

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that's the state. But the role was a non designated port or a blocking port. So
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that's the state. But the role was a non designated port or a blocking port. So

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we do need to make sure we understand the distinction between the role and the

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state. The other one to knock out here is disabled. Disabled means that it's

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administratively shut down. So if I've got a port on this switch and I log into

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it and I disable it, well, at that point, from a spanning tree perspective, it

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's

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considered to be disabled and not part of the spanning tree topology. So the

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more

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interesting states are these three up here, because what we'll find is that
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interesting states are these three up here, because what we'll find is that

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both

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designated ports and root ports are going to go through a process that starts

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with

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listening, goes to learning, and then goes to forwarding. In fact, we might

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actually find that a non designated port can do the same thing. It can start at

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listening, go to learning, and then go down to blocking. So let's zoom in here

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and take a look. Let's say that we just brought a connection online. And let's

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specifically look at this port right here. Now, when spanning tree is looking
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specifically look at this port right here. Now, when spanning tree is looking

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at a

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brand new port, it's going to want to know, hey, is there a loop here? Because

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maybe we already have a connection to the switch, or maybe we don't. Either way

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,

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our primary concern is loop prevention. We care greatly about loop prevention,

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speed, at least with the original spanning tree, not really a priority. We'd

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really rather take our time and make sure that there's not a loop before we

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turn this port into a forwarding port. And so what we're going to do is we're
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turn this port into a forwarding port. And so what we're going to do is we're

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going to start in the listening state. The listening state means that we're

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effectively blocking. But we're also doing absolutely no MAC address learning.

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So basically, we're doing nothing other than receiving traffic and potentially

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allowing the upstream device to recognize that this port is online. It's

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more or less a massive buffer. The learning state changes this. It is still

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blocking effectively, but we are going to start to learn. What do we mean by
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blocking effectively, but we are going to start to learn. What do we mean by

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learning? Well, that means that we're going to insert entries into our cam

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tables. What kind of traffic might I be getting on a port that hasn't sent any

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traffic? Well, maybe we're going to get broadcast traffic, or maybe we're going

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to get flooded traffic. But either way, if we do get traffic, then we can add

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MAC addresses into the cam table so that that will reduce flooding once we

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finally come online because we'll have more entries and fewer situations where
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finally come online because we'll have more entries and fewer situations where

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we need to flood. Now, if this process goes well, and I'm sending a superior

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BPDU out this port, that means that this is a downstream port and it must be

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designated. This means that I'm going to transition from learning to

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forwarding. If indeed, I'm in a designated port role, which is determined by

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the

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BPDU flow, we are determining the role somewhere in here. Usually during the

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listening state, we're already determining our role. But what happens if we
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listening state, we're already determining our role. But what happens if we

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determine that the situation is reversed? What if we're sending superior BPDU's

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this way, and I can't send those? Well, at that point, I still progress through

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listening and learning. And as I indicated up here, at that point, we're

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going to decide, hey, since I am a non designated port, then I'm going to move

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into the blocking state. So again, we determine the role pretty early as fast

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as we can. And once we have our role, then eventually we can transition over to
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as we can. And once we have our role, then eventually we can transition over to

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our particular state. Now, we're going to learn about timers, but our listening

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and our learning, by default, each take 15 seconds. Because they each take 15

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seconds, we have to do both of these, that means that it actually takes a total

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of 30 seconds to bring a port online. And yes, this, this actually applies even
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of 30 seconds to bring a port online. And yes, this, this actually applies even

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to somebody with a laptop. If I'm a college student, and I come home from a

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class, and I hard wire my laptop in to a switch, if we don't have anything else

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configured other than standard spanning tree operation, it will take 30 seconds

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for spanning tree to trust that this is a designated port. And yes, it is a

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designated port. It's going away from the route. It's going towards a device

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that's not even sending me BP to use. So it will decide to become a designated

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port, but it will still take 15 seconds for it to move to the forwarding state.
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port, but it will still take 15 seconds for it to move to the forwarding state.

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So back to our topology up here, we know that this was in a non designated or

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blocking port role. And we already said it's in the blocking state. Everything

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else is going to be in the forwarding state when we're in steady state

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operation, meaning that we've already gone through, or we've already been

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online

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for a while. Therefore, we're all going to be, oops, I missed one, there we go.

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We're all going to be forwarding other than this port right here. However,
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We're all going to be forwarding other than this port right here. However,

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if I do connect a new switch, well, at this point, that's a really weird

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connection. There we go. At this point, we're going to transition from

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listening

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to learning before we get to forwarding. And that's going to apply to both this

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port here and this port on the other side. It doesn't matter, even if this is

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the

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route bridge, we still have to go through this process. And so it is going to

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come

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back to taking 30 seconds for us to bring ports online using traditional

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spanning tree mechanisms.