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Well, Rapid Spanning Tree is going to make some other changes, including the

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fact that

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the port states are going to be slightly different.

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Now we think about 802.1D, traditional spanning tree, we had five different

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port states, starting

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with disabled, saying that the port just isn't working right now, at least from

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a spanning

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tree perspective.

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And then of course we have blocking, which says that we're receiving BPDUs, but

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we're

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not doing anything else.

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And then listening, learning, and forwarding, which is our traditional path to
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And then listening, learning, and forwarding, which is our traditional path to

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bring a port

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online.

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Well, 802.1W, Rapid Spanning Tree, recognized that these three states largely

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have the same

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function.

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Even those different situations, especially for example listening, we know that

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we're

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trying to bring a port online, but functionally it's doing exactly what

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blocking is doing,

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which is we're not doing anything.

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We're not learning MAC addresses, we're not sending any packets or anything

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like that.

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So 802.1W, again, Rapid Spanning Tree calls this the discarding state, which is
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So 802.1W, again, Rapid Spanning Tree calls this the discarding state, which is

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abbreviated

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as DIS.

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Now notice DIS over here stood for disabled.

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Now it stands for discarding.

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So we're discarding packets regardless of what the situation is, which yes

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means that

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when I bring a port online, it's going to sit in the discarding state for 15

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seconds

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by default, then it will go to learning for 15 seconds, and then it will go to

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forwarding.
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forwarding.

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So it still takes 30 seconds to come online.

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We're just not going to see LIS listed.

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We're going to see DIS listed because we're discarding for 15 seconds.

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And this is important because again, even though we are getting rid of the

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listening

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state, we haven't gotten rid of what the listening state was doing.

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So that process still plays out.

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And when we look at our Cisco iOSXE later, we're going to see that yes indeed,

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we do

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still have to wait for those 15 seconds.
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still have to wait for those 15 seconds.

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Now that said, when we do connect two switches together using Rapid Spanning

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Tree, we're

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going to use those negotiations to spin things up a whole lot faster to the

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point that we

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really don't see this process pan out very often.

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Specifically, we're going to see that when we get a superior BPDU sent across

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this link,

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that this port here decides that, hey, this is my root port.

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Or potentially, maybe it's not my root port, but let's just say it's the root
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Or potentially, maybe it's not my root port, but let's just say it's the root

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port.

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It's going to alert the other side that, hey, I have decided this is my root

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port, which means

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that this side knows immediately it can be an affording state.

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This side can immediately be an affording state because it's its root port.

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And this is why it comes up so quickly.

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And so the odds of us even paying attention to this enough to see that there's

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no listening

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are pretty low.

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We don't see the listening and learning process, which is now discarding and

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learning.

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We don't see that process play out very often.

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We also need to pay attention to the edge ports because our edge ports are
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We also need to pay attention to the edge ports because our edge ports are

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again going

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to transition directly into forwarding just like they did before.

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Now before this is interesting, as we talk about our port types, we have a port

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type edge

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now defined officially in rapid spanning tree.

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So remember Cisco created the concept of port fast and port fast allowed an

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edge port

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to transition immediately to forwarding.
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to transition immediately to forwarding.

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And that would hopefully just allow us to bring end devices online immediately

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without

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a risk of there being a loop.

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Furthermore, they do not trigger TCNs as topology change notifications.

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That's a very important part of the edge port concept.

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And if a BPDU is received, it's going to transition to normal operation,

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meaning it's

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going to go back to this process and more likely to the negotiation process of
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going to go back to this process and more likely to the negotiation process of

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rapid

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spanning tree.

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So Cisco created this concept with traditional spanning tree, but they created

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their own

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way of doing it with port fast.

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Well now again, it is part of the rapid spanning tree standard.

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They basically copied and pasted port fast and said, okay, this is now in rapid

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spanning

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tree.

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However, this is still a manual configuration.

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I can do it per interface.

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I can do it globally as we described before.
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I can do it globally as we described before.

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But this is not something that spanning trees is going to be able to figure out

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on its own.

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We need to indicate to rapid spanning tree, which ports are edge ports in some

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capacity.

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And the beautiful thing about this is that in iOS Xe, the configuration still

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uses the

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port fast commands.

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Even though on the back end, it's configuring the standardized version of it.

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We understand that there's value in keeping commands the same.

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And so we still enable it with spanning tree port fast.
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And so we still enable it with spanning tree port fast.

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However, in other platforms, for example, Cisco's Nexus platform, NXOS, we don

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't have

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port fast because we don't use many Cisco terms on NXOS.

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We always want to run standardized commands.

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Or at least that's how Cisco built it is to run port channel commands instead

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of ether

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channel commands, as we talked about earlier.

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And so instead, we're going to see a much longer command where we say spanning

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tree port

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type edge in NXOS.
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type edge in NXOS.

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And so the command might look different.

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Technically, NXOS's version is more accurate because we are no longer running

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Cisco port

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fast.

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We're running the rapid spanning tree official version of that.

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But do understand that the command is the same, even though it's not react

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ivating port

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fast, it is, however, activating all of the same features that poor fast had.