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A few quick things about Portfast.

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Portfast is a very important configuration.

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We need to make sure we put on all of our edge ports,

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whether we're running traditional spanning tree,

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I'm not sure why we would in production,

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but even with rapid spanning tree,

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we do have to explicitly state

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which ports are in portfast mode.

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Portfast is telling us that we're connecting

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to not a switch basically.

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So it can connect to other network devices,

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it can connect to routers or firewalls and access points.

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These are network devices that are not switches
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These are network devices that are not switches

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and can't produce a loop.

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And so as long as we have no switch on the other side,

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we can enable portfast.

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Now as a protection mechanism,

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Cisco ignores portfast configuration

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if we configure something for a trunk,

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but some of those devices require trunks.

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So I can also explicitly configure a portfast trunk

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and we'll take a look at that here.

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That's something that we can deploy if required.

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For example, if connecting to a flex connect access point

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that requires trunking,

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I would want to configure it as a portfast trunk.
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I would want to configure it as a portfast trunk.

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Now lastly, even though portfast is an explicit configuration,

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we can enable it to be deployed

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onto all access ports by default.

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And so we're gonna take a look at really all three things,

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configuring portfast, making it the default setting,

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as well as configuring a trunk portfast,

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and we'll wanna take a look and confirm

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that the TCN thing is actually what we said it is,

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that it's not going to produce topology change notifications.

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So as part of all of this,

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we're gonna go ahead and look at switch five,
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we're gonna go ahead and look at switch five,

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and we're going to pretend like gig three slash two here

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is connecting to some kind of edge device.

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Maybe it's a laptop or a PC or for that matter,

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an access point, but either way,

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gig three slash two is going to be our port of choice.

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So normal portfast operation is to do a config T,

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get onto the interface,

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and then I can say spanning tree portfast.
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and then I can say spanning tree portfast.

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And that's it.

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I've just enabled portfast.

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Once again, it is going to warn us

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that this can produce temporary bridging loops.

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I do like that they used temporary,

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'cause we know as soon as we get a BPDE,

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we will fall back to normal spanning tree operation.

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But until we receive a BPDE on the other side,

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it could produce some bridging loops.

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So we have to proceed with caution,

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but we understand that this is the intended behavior

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in this situation.

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So now, if I do a show spanning tree VLAN one,
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So now, if I do a show spanning tree VLAN one,

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we should see that gig three slash one,

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or sleeves three slash two rather,

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says that it's an edge port.

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So that's a rapid spanning tree word

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that's just telling us that it's in portfast operation.

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And it's already in forwarding mode.

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Now, if I go config T interface three slash two,

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and I say shutdown,

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and then no shot.

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Now, it's going to come back online.
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Now, it's going to come back online.

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We'll do a show spanning tree VLAN one,

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and three slash two should already be

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in the forwarding statement, indeed it is.

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So we did not have to go through listening and learning.

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And that's usually the behavior

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that we're really looking for out of portfast.

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Now, really quickly,

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I could configure portfast another way.

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So let's go ahead and say, no, spanning tree portfast.

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But let's say that, again, this is an edge port.

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So I'm going to place this into switch port mode access
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So I'm going to place this into switch port mode access

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and place that into VLAN one.

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So now this port is an access port.

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So if I do show interface gig three slash two switch port,

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another great command,

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we can see that the administrative mode here

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is in access operation.

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So what we can do now is do a global configuration

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to make all access ports into portfast,

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because usually we sync up portfast

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and access mode operation.
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and access mode operation.

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So this makes a lot of sense.

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So I can get on here,

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and I can say spanning tree portfast default.

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Now, again, it's only going to push it to access switches

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or access switch ports rather.

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So won't go on to trunks.

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If I do a show run on interface gig three slash two,

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like this,

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will not see the portfast configuration,

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but I can confirm if I do a show spanning tree interface,

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gig three slash two and add this keyword detail,
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gig three slash two and add this keyword detail,

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I see a lot of information,

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including that it's in portfast edge mode

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and it adds on this by default,

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which would not be there

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if I wasn't using the default option.

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Now let's go ahead and take a look at the trunk situation.

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So if I were to get onto interface gig three slash two

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and say, hey, we're going to configure use this trunk.

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So I'm going to put this into dot one queue operation

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and then switch mode trunk.

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And now it's running as a trunk.
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And now it's running as a trunk.

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So is it running in portfast?

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It's not notice the portfast was removed

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because it's no longer an access port.

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What I can do is get onto gig three slash two

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and say spanning tree portfast

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and we'll see that I've got the ability

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to add an edge and then trunk.

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There it is.

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(laughs)

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iOS, the virtual iOS can be a little different at times.

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So you might see this edge here and you might not.
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So you might see this edge here and you might not.

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Some iOS XCE platforms have it, some do not,

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but either way, I just enabled this portfast

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for trunk operation.

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So now I can do the same show command,

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show spanning tree interface with detail

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and it does say that it's in portfast,

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I can get it, there we go.

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Portfast edge trunk mode.

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So we can run portfast in trunk mode,

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but we do have to explicitly configure it.

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If I were to say remove portfast edge trunk

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and just say spanning tree portfast,
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and just say spanning tree portfast,

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again, this is still a trunk.

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So if I look at the spanning tree interface details,

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we'll find that it's not running in portfast.

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Even though when I look at the interface,

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it's going to appear like it is

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because it's got that portfast.

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Well, again, edge sometimes shows up,

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especially on iOS V, the virtual iOS instances,

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but spanning tree portfast command is there,

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but it's not running in portfast because it is a trunk.
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but it's not running in portfast because it is a trunk.

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So last thing we want to demonstrate

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is the topology change concept.

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So if I do a show spanning tree, VLAN one,

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we will call that this aging time gets reduced

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if the port changes.

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And so I'm going to go ahead and demonstrate

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that it will not change.

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So we're going to go back into switch port mode access on 3, 2,

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and I'm going to enable portfast, so spanning tree portfast.

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And so if I look at the interface,

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so spanning tree interface detail,
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so spanning tree interface detail,

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we see we are running in portfast operation.

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So if I shut this port down and then do a no shut,

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and do a show spanning tree for VLAN one,

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we will see that again, the thing that we typically look at

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is the fact that it went straight into forwarding mode.

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And then we can scroll up just a little bit

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and we can see that the aging time is 300 seconds.

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And so portfast is very important for spinning things up
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And so portfast is very important for spinning things up

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quickly.

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We can apply it to access and trunk ports,

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but it's also super important because topology change

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notifications are suppressed, which is good.

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We're going to see a lot of topology changes out there

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if we don't configure portfast.

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So it's why it's a mission critical configuration.

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We should probably enable it by default on switches,

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which will push it automatically to access ports.