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All right let's go ahead and jump into the lab and just see these macros in

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action. So what we have here is we've got a topology that is the same topology

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that we had in the previous skill. It's just a square of switches. They're all

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set

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to 32,000 so it's the default priority everywhere 32k and just because of MAC

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addresses switch 3 happens to win the root role. Now again that's just because

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it has the lowest MAC address. This is going to be important as we demonstrate

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which switches take over is the root in which situations. So let's go ahead and
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which switches take over is the root in which situations. So let's go ahead and

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clear this and let's run a quick demo. So again they're all at 32k. We know

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that

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switch 3 in theory is the root. Let's just do a show, spanning tree. We'll do

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everything in VLAN 1 here so VLAN 1 root and we do see that I'm the root. I

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know

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that because there's no root port. So that makes me the root even though I've

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got

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the default 32k priority. So let's go and get on to switch 1 here and we'll try

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to make switch 1 the primary and we'll do that using our spanning tree command
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to make switch 1 the primary and we'll do that using our spanning tree command

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spanning tree VLAN 1 and then this is where I could set the priority manually

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and set one of those increments of 4096 or we'll find that I have this root

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command. This is what's going to allow me to set the primary and secondary and

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this is our macro. So I'm going to set root priority or root root primary hit

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enter and let's see what happened here. If I do a show spanning tree VLAN 1
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enter and let's see what happened here. If I do a show spanning tree VLAN 1

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root.

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Now we see that I'm the root because I no longer have a root port and notice my

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configured priority. Now we said that it would go as only as low as needed so

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you could say well why didn't it go to 28k? Well because again the primary

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macro

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is intended to work with the secondary and the secondary uses 28. So that's

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always said the maximum or the highest value that this is going to use is the

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24k value and that's indeed what it shows here. So it shows the 24k let's go
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24k value and that's indeed what it shows here. So it shows the 24k let's go

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back to switch 3 run the same command. We now do have a root port and our root

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has that configuration. So switch 3 is no longer the root it is now switch 1.

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So

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let's go and test the secondary command. I'll get on to switch 2 here and do a

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spanning tree VLAN 1 and again we'll just say root secondary and now let's do a

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show spanning tree for VLAN 1. So we see that the root is switch 1 here with
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show spanning tree for VLAN 1. So we see that the root is switch 1 here with

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its

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priority of 24k and we see that my priority is indeed 28k. So the macros are

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working like we thought. So now we know switch 1 is at 24k what happens if I

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get

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on to switch 3 and run the same command. So let's do or the same macro rather.

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So

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config T here spanning tree VLAN 1 root primary do show spanning tree root

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what happened? Well I didn't filter the VLAN so let's look at VLAN 1 here. So
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what happened? Well I didn't filter the VLAN so let's look at VLAN 1 here. So

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what

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happened was it's no longer the root we or it is it is the root and no longer

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has

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a root port. So we know it took over as the root but notice the priority is the

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exact same. Switch 3 we established has the lowest MAC address as the best MAC

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address. It already won root when everybody had the same priority. So switch

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3 knew that it would win as the root if it just went down to 24k. So that's all

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it had to do it didn't have to go any lower than 24k because switch 1 at 24k
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it had to do it didn't have to go any lower than 24k because switch 1 at 24k

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had the worst MAC address. So switch 3 became the root at 24k. Switch 1 we can

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now run the same command here we see that it does indeed have a root port which

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means it's no longer the root. So once again now let's get into a little war

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here. Now let's go ahead and configure the same thing spanning tree VLAN 1 root

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primary here on switch 1. So before we take a look at what happened what do you

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think is going to happen here? We're telling switch 1 to become the root we
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think is going to happen here? We're telling switch 1 to become the root we

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know that switch 1 and switch 3 are both 24k and switch 3 just went down

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to tie switch 1 to become the primary. So what switch 1 going to do? Well what

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switch 1 is going to do is it's going to say well I can't win at this value so

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I'm

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going to drop down another 4k. We'd expect it to be 20k rather than 24k so if

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I run this command we do see that switch 1 no longer has a root port means it
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I run this command we do see that switch 1 no longer has a root port means it

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is

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the root and it's running 20k. So that's how the primary MACR works it's always

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going to keep battling back and forth until it figures out what the ultimately

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what the value is that I need to do to become or need to choose to become the

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root. So that's how the primary works now notice the primary is now at 20k.

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Let's go back and run that secondary command again and see what happens. So
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Let's go back and run that secondary command again and see what happens. So

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we know that we are running a priority of 28k. We're no longer the backup root

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by

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the way switch 3 still has that priority of 24k. So let's get on here and say

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hey

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I want you to be the secondary. So remember what we said would happen is

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that this isn't going to do much for me. So I just ran that command again

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show VLAN 1 spanning tree and I still have a priority of 28k. So that

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secondary MACR does nothing to ensure that I am the secondary instead it's
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secondary MACR does nothing to ensure that I am the secondary instead it's

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only going to just be set to 28k period that's all it does it's not

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particularly useful relative to the primary but it is useful if we're using

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the primary in a default environment that way the primary should be 24k and

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the secondary would be 28k. So that is how these MACR's come together we can

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continue to play with this. If I wanted to I could get in here and I could say
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continue to play with this. If I wanted to I could get in here and I could say

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you know make a lower priority and see how that comes together as I continue to

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put root priorities these root primary and root secondary commands in but I'd

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encourage you to get into the lab yourself and play with this to make sure

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that we fully understand how these MACR's come together.