CCIE Topic: 1.1e Rapid PVST+

hey everyone i'm charles judd and welcome to this video covering another topic found within ccie blueprint section 1.1e which explores the subtopic of rapid pvst plus or rapid per-vlan spanning tree we're going to look at the enhancements over traditional 802.1d and we'll take a look at the configuration and implementation steps involved and we'll talk about the difference in the convergence times as well in the previous video we looked at regular pvst plus and so here we want to examine the cisco enhancement called rapid per vlan spanning tree or rapid pvst plus this protocol is outlined in the ieee 802.1w standard and the big improvement here is convergence time if you recall from our look at pvst plus the convergence time takes 50 seconds give or take when a topology change occurs we have 20 seconds in the blocking state followed by 15 seconds in the listening state then 15 seconds in the learning state before moving into the forwarding state with rapid pvst plus that convergence can take potentially less than one second so let's talk about how that works with rapid pvst plus we have a separate spanning tree instance for each vlan on the switch and that means that every vlan has the ability to have its own root bridge every designated port in each of these spanning tree instances will send out a bpdu every two seconds and that's the default interval on a designated port if one of those hello message bpdus are missed three consecutive times or if the maximum age timer expires then it's assumed that connectivity to the direct neighbor over that designated port has been lost and then the stp failure detection and convergence mechanism is going to kick in which again is much faster than normal pvst plus now as for the maximum age timer that i mentioned i'll just briefly say that this is the amount of time that information received on a port is stored by the switch with rapid pvst plus this timer generally is not used because when we miss hello messages if we miss three of those consecutively that's going to force convergence long before our maximum age timer expires we generally only see this in use when we need interoperability with older versions of spanning tree with maybe pvst plus if we have that running alongside rapid pvst plus so let's talk about the port states because they are different with rapid pvst plus the first state is discarding which replaces both the blocking and the listening states found within normal stp these states have no specific timer and again they're based on the receipt of hello message bpdus that we receive from neighboring switches we do have that maximum age timer that i mentioned but for all intents and purposes we don't see this mechanism in play if our entire network is using rapid pvst plus so a port will start in the discarding state where it will not forward any frames and it will not learn mac addresses but it will listen for bpdus based on the bpdus that are received we would move into the learning state where the port learns mac addresses and prepares to begin frame forwarding and of course the final stake is the forwarding state where the port has the ability to forward frames normally we also have two new port roles found within rapid pvst plus in addition to the route port designated port and non-designated port roles found within stp we also have the alternative port and the backup port the alternative port allows for an alternate path towards the root bridge through another switch rather than the path that's provided by the current route port and the backup port acts as a backup connection to the same switch as a designated port is connected to so these backup ports are only going to exist if you have multiple connections to a particular lan segment and the backup port would provide another path to that segment in the topology one more thing to note is that cisco recommends we configure ports connected out to a single end station as edge ports ports configured as edge ports will immediately transition to the forwarding state using a technology called portfast and that was previously a cisco proprietary feature but it's become an industry standard edge ports do not generate any topology change notification that's the important thing about those so they will not affect a spanning tree instance when the link state changes here we have the same topology from our previous pvst plus video and we already have some configuration in place we have switch 1 acting as the primary route for vlan 10 and the secondary route for vlan 20 and we have switch 2 as the primary route for vlan 20 and the secondary route for vlan 10. here on switch one let's verify this let's say show spanning hyphen tree and you can see that for vlan 10 we're told this bridge is the route if we look at vlan 20 we're not told that if we jump over to switch to and again say show spanning hyphen tree if we go down to vlan 20 we see that this is in fact the root bridge so again the exact same configuration that we completed in the previous video so what we're going to do here is we're simply going to upgrade pvst plus to rapid pvst plus and that's cisco's preferred implementation of spanning tree now before we do that let's take a look at our current convergence time that we have with pvst plus so that we can compare that because that is the big advantage of changing we're going to have much faster convergence times so i'm just going to clear off a little space on switch one here so that the screen is clear and i'm going to say debug spanning hyphen tree events i'm going to turn on debugging for those events so that we can see all of this happen in real time let me jump to switch 2 now and i'm going to go under global configuration mode interface range gig 0 0 through 0 1 both our trunk interfaces and i'll go under there and what i'm going to do is i'm just going to shut down these ports and then i'm going to quickly jump back to switch one and let's see what happens so i'm going to say shut hit enter i'm going to jump over to switch 1. so this is going to take some time again remember we have quite a bit of time that's going to pass for convergence we have our first 20 seconds when we're sitting in the blocking state we're starting to see some of those messages here we see the message letting us know we've moved into the listening face we're going to sit in this listening phase for 15 more seconds and now we see that we are in the learning state again for another 15 seconds we're gonna sit there and we have finally moved into the forwarding state so this convergence isn't exactly fast it takes 50 seconds for that to happen give or take so let me go ahead and turn off debugging and let's change this over to rapid pvst plus it's really easy to do that let's go under global configuration mode let's say spanning hyphen tree mode if we look at our contextual help options the one we want is rapid hyphen pvst we'll hit enter really simple that's how we do that i'm actually going to copy this command so that i can paste that in and let me go ahead and bring these interfaces back up before i do that on switch 2. and i'm going to paste that command in to change that to rapid pvst i'm going to go ahead and do that same thing on all of my other switches as well so let's jump to switch three paste that in switch four switch five and switch six so now our entire topology has been changed over to rapid pvst mode so now let's again look at the difference in our convergence time we're back on switch one and i'm going to again say debug spanning hyphen tree events so i'm going to turn that debugging back on and here we're seeing a few synchronization messages that are still coming in because we have changed the modes of our switches so still a little bit of synchronization going on in the background that should be all finished up now so let me just clear off some screen space i'm gonna jump back to switch to i'm gonna go back under interface range gig zero slash zero through zero slash one and i'm gonna do the exact same thing i'm gonna shut down these interfaces and then i'm gonna jump over to switch one and we'll see what happens we're gonna see that we're gonna have a much much quicker convergence and there it's already happened we see that um we've now become the root bridge so much much quicker convergence much better much less downtime if we say show spanning hyphen tree we can confirm that for vlan 10 we are the root bridge we should see the same for vlan 20 and we do so the convergence took place much much quicker one last thing to show you is how to configure an edge port remember we do that with rapid pvst plus so that any ports connected directly to a single host will not create any topology change notifications based on their port status so if we have a host that goes offline or if that host gets disconnected we don't want that to create any spanning tree related messages those aren't necessary and that's also a method of protection against someone disconnecting a host and connecting a switch into our network that may take down our current spanning tree topology or change that so let's go over to switch five and you can see in our topology that on gig zero slash one and zero slash two those are connected out to end devices so let's go under interface range gig zero slash one through zero slash two and let's configure these as edge ports so we can say spanning hyphen tree port fast and we want to say edge we'll hit enter on those and you can see our console messages first we have a warning letting us know we should only enable this on a single host connection and we can see another message letting us know that we are enabling this on two interfaces due to our interface range command and that it's only going to work on interfaces in non-trunking mode now of course my interfaces are access ports so that's just fine that's exactly what we want and by the way one more command we can run that's a best practice that i'll point out is bpdu guard this is a layer two protection mechanism that's going to tell our switch that interfaces gig zero slash one and zero slash two in this case it's going to tell our switch that we should never ever receive a bpdu on those ports because we have a workstation connected if we do happen to get a bpdu on this port that means something other than an expected workstation is connected and bpdu guard is going to air disable these interfaces so it's really easy to do that we can say spanning hyphen tree bpd bpdu guard enable and that's going to enable bpdu guard on both of these interfaces under interface configuration mode let me break out of here and let's just verify the configuration really quickly let's say show run pipe to begin the section of interfaces actually need to leave the s off and here we can see under interface gig zero slash one we are an access port for vlan 10 we have our portfast edge configured and we have bpdu guard enabled same thing on gig zero slash two an access port this one dedicated to vlan 20 we are a port fast edge port and we've enabled bpdu guard for protection so obviously we would also want to do this on switch six where our other two hosts are connected as well so that completes a look at rapid per vlan spanning tree plus in the next video i'll be looking at mst multiple spanning tree i hope you found this content useful and i want to thank you sincerely for watching

Channel: Charles Judd

Views: 1,170

Keywords: cisco, ccie, cisco enarsi, ccie enterprise infrastructure, cisco enarsi 300-410, cisco encor 350-401, ccie lab, my ccie journey, ccie training, ccie blueprint, spanning tree protocol, stp, spanning tree, PVST+, per vlan spanning tree plus, rapid pvst+, 1.1e spanning tree protocol, multiple spanning tree, mst, rapid per-vlan spanning tree plus, per-vlan spanning tree, root bridge, spanning tree priority, spanning-tree

Id: qgarw20R31U

Length: 13min 46sec (826 seconds)

Published: Mon Aug 10 2020