017 Intro to PVST, RPVST MST

hello and welcome to this tutorial so far we've presented standard spanning tree the 802 1d and then the evolution of that into rapid spanning tree and simply stated we presented a lot of details there are a lot of nuances between the two versions and then within each one all of the different port states and the the roles different ports can play and how convergence takes effect there's a lot to know and that makes spanning tree a rather difficult subject and it's not always the strongest area of knowledge for a lot of network admins well we have some more ground to cover however we're not going to get as deep into the new flavours of spanning tree as we have so far with standard and rapid so this is just going to be a brief introduction to three more flavours of spanning tree the first new flavor of spanning tree is known as per VLAN spanning tree plus now sometimes this is written out just as you see a PV st plus and sometimes it's written without the plus now this is a cisco proprietary protocol and what it does is it creates a separate instance of spanning tree for each VLAN now originally all VLANs belong to a single instance of spanning tree so if you think about the port state of a single port on a switch it could be forwarding or blocking well whatever that state is it would apply to every VLAN that is associated with that particular port well with per VLAN spanning tree now we can have different port states for each VLAN on the same port the benefit of doing this is that we get to load balanced traffic now so if we have two links between two switches normally we would have one servicing all VLANs and the other one is in a blocking state for all VLANs well now we can have some VLANs on one trunk and some VLANs on the other and each is blocking for the other VLANs let's take a look at this in a diagram to help illustrate it so like I said if we have two switches with redundant links between them normally we would have all VLANs on one while the other link is blocking all VLANs so now we introduce per VLAN spanning tree and we get rid of this approach and what we'll do instead is let's say this link is now forwarding but it's only going to forward for VLAN one and this link is going to be forwarding for VLAN two that means this link is going to block VLAN two and likewise the other link is going to block for VLAN one so we're splitting our VLANs between the two links each VLAN has a backup link should a particular connection fail but now the primary traffic for VLAN one is here and the primary traffic for VLAN two is here and that would mean we would have different route ports and designated ports for each of the two VLANs okay so with per VLAN spanning tree the main benefit is we split up the VLANs we get to load balanced our traffic and we have more control over the traffic that way ok let's move on to the next type of spanning tree we want to talk about and that is our P vs T which stands for rapid per VLAN spanning tree and this is extremely similar to the per VLAN spanning tree plus and you'll see why in just a second first it's also a Cisco proprietary protocol and what we do here is we create a separate instance of rapid spanning tree for each VLAN so this is pretty much the same as what we just talked about but now we're talking about using rapid spanning tree so the benefit is we still get our single instance of spanning tree running for each vielen but it's not just standard spanning-tree its rapid spanning tree so we get all of the high-speed the quick convergence of rapid spanning tree okay so very so much what we talked about just take out standard spanning tree and replace it with rapid spanning tree and that gives you rapid per VLAN spanning tree okay one more to go okay MST is the last version of spanning tree we're going to talk about and this stands for multiple spanning tree now whereas the previous two versions were Cisco proprietary MST was created by the i3 II so this is the standard and you might see it referred to as 802 1s or sometimes you might see it mi st which stands for multiple instance spanning tree all three of those names refer to the same I three e standard now MST works by creating several rapid spanning tree instances but you don't create one for each VLAN rather what you do is you after you create these several instances you take a group of VLANs and assign them to each instance now the benefit here is we're load balancing traffic but we're reducing the number of spanning tree instances so MST is created for an environment where you have many many VLANs and creating that many separate instances of spanning tree can at some point be too much to run on the switches it's not necessarily efficient to do it that way so here we're we're being smarter about creating fewer instances of spanning tree but we still get the benefit of load balancing all of our traffic let's go ahead and diagram this one as well real quick so again we'll take a look at two switches with redundant links and we'll start off by creating two instances of rapid spanning tree instance a and instance B and to each instance we're going to assign a group of VLANs so on the top will sign VLANs 1 through 49 and to instance B will assign VLANs 50 through 99 now on the top link let's say instance a is in the forwarding state yet on the bottom link instance B is in the floating State that would mean that these VLANs are blocked on the bottom link and likewise these VLANs are blocked on the top link so we have our redundancy here should the top link fail instance a will then fail over to the bottom link so all of our VLANs would then be on the bottom link and vice-versa should the bottom link fail okay so we have our redundancy yet at the same time we've managed to create load balancing half the VLANs on top half the VLANs on the bottom and finally we've done all of this just by using two instances of rapid spanning tree so we're being very efficient with our resources and that's how multiple spanning tree works okay and as promised we didn't get too deep into any of these new types of spanning tree this was just an introduction so to summarize we now know that there is per VLAN spanning tree plus as well as rapid per VLAN spanning tree and they are essentially the same one uses standard the other uses rapid spanning tree and the both Cisco proprietary and then the third one we looked at was multiple spanning tree and that's the i3e standard where we're enabled to run again multiple instances of rapid spanning tree but here we don't run it for each VLAN instead we create just a few instances and we assign groups of VLANs to each instance so it's a bit more efficient for high volume VLAN networks and then finally we looked at the benefits of each one at this point in your studies just be familiar with these three flavors of spanning tree and basically how each one works and the benefits associated with each one okay and so that's it that is the introduction to per VLAN rapid per VLAN and multiple spanning tree thanks for watching

Channel: System Engineer

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Id: 7h_CcM9BCYc

Length: 8min 48sec (528 seconds)

Published: Tue Apr 25 2017