Alright, let's pick up with our Spanning Tree Configuration. We've made Core 2 the Spanning Tree Root for VLAN 1, our only VLAN at this point and if we left it like this and Core 2 were to go down, who would become the root of Spanning Tree? Well let's think this through, all the other priorities are at the default, so if Core 2 goes down, I could just go in there and unplug it and we could see which one becomes the root, but let's try to figure out. All the other priorities are at the default therefore the lowest MAC Address would win again, therefore that Access 2 Switch would be the root of the Spanning Tree if Core 2 went down. Again not really something we probably want to let happen, so let's set Core 1 to be the Secondary Root for the Spanning Tree. So we'll go into Core 1 first of, we'll do Show Spanning Tree again on this guy. Now you'll notice that the Fast Ethernet 02 port is Blocking, where before if we scroll back up here, we see that they were all Forwarding before. That's because this switch decided that, that would be the redundant link and so all of the traffic's going to go from Core 1 down to that Access 2 switch or actually the Access 1 Switch, that's the one connected to Core 1. That's where this interface goes. So let's go ahead and configure this guy to be the Secondary Root of Spanning Tree. You'll see there's my Bridge ID, it's got that priority 32,769 which 32,768 with VLAN 1 added to it and we'll go over that when we talk about multiple VLAN Spanning Tree. So Config T, we'll do Spanning Tree VLAN 1 Root and we'll do Secondary. So once we do that, Spanning Tree reconfigures itself again, I'll go ahead and write the Config real quick and we'll do Show Spanning Tree. The root's priority is 24,577, hey I wasn't too far off, only a 1,000 off on my guess at the priority there. If you go over here to Core 2, obviously nothing's changed there, so let's look at the Access Switches down here and see what they say. So we'll do Show Spanning Tree and if you're configuring Spanning Tree or you're messing with Spanning Tree in your core network, this is always a good thing to do as far as the verification step. Make sure that all of the switches agree on who is the Root Bridge, in this case, the Root Port is off Port 1, Fast Ethernet 01 which if we do Show CDP Neighbor, Fast Ethernet 01 points at the Core 2 Switch. So this switch believes that Core 2 is the root of Spanning Tree. Let's go over to Access 1 and do Show Spanning Tree on this guy and he believes the same thing, Port 2 is Fast Ethernet 02. We do Show CDP Neighbor, we see that Fast Ethernet 02 points at Core 2. So all of the Access and all of the Core Switches are in agreement that Core 2 is the root of Spanning Tree at this point. So now that we've got Spanning Tree all set up, let's break it, that's how you learn stuff. It's about breaking it and see what happens or at least that's how I learn things. Now as you'll recall from our lab diagram, we have two PCs or two machines with IP addresses connected to the switches. One's connected to Core 1 and one's connected to Access 2. Now I'm on this machine here, this 10.10.1.1 on Access 2 and I'm going to ping 10.10.1.10 across the network. I've already done it as a test here but I'll Up Arrow and you'll see that it actually does work. And so now I'm going to demonstrate what happens when Spanning Tree fails. Now you'll recall we're not running the Rapid Spanning Tree so obviously when Spanning Tree fails, it's going to take a while to re-converge. Now I'm not going to pause the video at any point during this, I want you to exactly how long this takes just with the Default Configuration and the Default Timers, it's going to take awhile, a lot longer than it should in my opinion. So we are here on this machine and we'll verify on Access 2 that Fast 02 is Blocking. So let's go back to here and go back to Access 2, Fast Ethernet 02 is Blocking because it is an alternate link and it's sending all of the traffic out Fast Ethernet 01. So what I'm going to do is I'm going to go in here to Config T. I'm going to do Interface Fast Ethernet 0 slash 1 and I'm just going to shut down this interface. Now a true test would be to go in there and pull the cable, but since my lab is actually in another physical location from where I'm at, I can't easily go in there and, and grab the cable and pull it out. So we'll start this ping here,/T and I'm going to shut down this port and I want you to see how long this ping takes before it comes back. So we'll do Shut on that port, bring up the pings, it's transitioned to down and we're dropping packets at this point. Spanning Tree is, said hey, something's happened you know, I'm, I'm not getting this hello, I'm waiting 20 seconds before I figure out exactly what to do. At this point, all of your Voice Over IP calls have dropped. Any file transfers that were going on in the network, they've just stopped. Your cell phone is starting to ring, all kinds of nice things are happening. You've got people walking into your office, hey Fred, is the network down? And you'll see it took it a good 15, 20 seconds there before it figured out what was going on. Now your machines, your workstations could probably recover from that, but any, like I said, any Voice Over IP calls that you had in progress just dropped because that's very sensitive to delay and, and packet loss. So if we go back out here now and we do Show Spanning Tree, we'll see that Fast Ethernet 02 is now the Root Port. Do Show CDP Neighbor, we only have one connection back to Core 01, we've lost our link to Core 2. However, it says I can still get to the Root Bridge going out this Fast Ethernet 02 and so it re-converges after 20, 30 seconds and life's happy and grand again. And what I'll do is, I'll go re-enable that port. Config T, Interface Fast Ethernet 01, No Shut and even when we restore it, Spanning Tree says, well hey I've had a State Change and you'll drop packets even when you bring it back up. So even trying to fix the problem, you're going to introduce down time and latency and make your phone ring off the hook even when you find the problem and you fix it. Oh someone tripped over the cable, just let me plug it back in real quick. Well you know, you're really causing more harm than good at this point. So that's it for our discussion of Spanning Tree, you've seen how we can verify what switch is the root of Spanning Tree, how we can force the switches we want to be the root of Spanning Tree. And what happens when just the plain vanilla non Rapid Spanning Tree breaks. That concludes our discussion of Spanning Tree.
|Course:||Implementing Cisco IP Switched Networks (642-813 SWITCH)|
|Duration:||8.5 hrs / 102 lessons|
|Captions:||Available on CD and Online University|
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