Master Spanning Tree (STP) Topologies in 3 Steps

here's what I want to do so if you want to um if you want to hang out and see a little bit about spanning-tree you can so I'm gonna what I'm gonna do is put this diagram up this my friends is the Cisco three-tier hierarchy and also a great complex network to demonstrate how spanning tree does what it does now the reason I said this is going to take about 15 minutes is because it's not easy let me actually I'm gonna open a couple of my pen utilities hang on one saying I gotta get these open just so I've got them I had to do this I literally use three different bends so I can clear one and not not have the other so that by the way this is my my epic pen tool that pops in the little screens let me move those aside move those aside okay that way I can get some multiple colors going on okay so here is so first and foremost let me if you're if you're brand new to the world of spanning tree let me give you the flyby spanning tree protocol has one function and that is to stop loops right because building redundancy into your network is a is a big deal you want to have redundancy and and this is the ideal design for a redundant network but without spanning tree this network would crumble in a matter of seconds because as soon as somebody would send a broadcast message it would come into the switch and switches send a broadcast everywhere so it goes out both of those ports these guys receive it and they go oh okay well send it out all the ports all the ports except it was received on by the way if if you're studying for exam all the ports except the one that was received on so it goes everywhere these guys get it they send it everywhere he gets it he goes so so within a matter of a second of sending a broadcast you're gonna it's done so what spanning-tree does is it looks around the network and it says I'm going to identify the redundant links and it goes ah redundancy right there now I know some of you're like well that should be either channel well we're not talking about ether yet so so spanning-tree will go okay I'm gonna disable that link oh we're done I'm gonna disable that I'm gonna sew it so it picks links to disable and it disables all of the redundancy to stop famed geeks got it a broadcast storm so HJ John if you if you enable spanning tree the big thing is a big thing is is how does it do what it does well the one thing and the funny thing is I probably I for the new CCNA I just finished probably an hour and a half of just straight lecture on how spanning tree does what it does I'm not gonna do that right now I'm just gonna cut to the chase and get to it hour-and-a-half lecture one command that's literally all you have to do for spanning tree one command and the command lets you pick the root bridge c spanning tree does everything based around the switch that it calls the root bridge and the root bridge just in plain english is it should be the center of the network but by default spanning tree will choose the oldest switch in the network i'm not talking like the remote run time I'm talking manufacturer date and when I first learned Spanish I was like that's dumb why does it pick the oldest switch in the network why it should pick the newest switch because if it picked the newest wish then every time you brought in a new switch if you didn't modify Spanish P it would completely reconfigure the whole network so that's why they did it that way so the problem is it's gonna pick some if you don't step in and configure it's gonna pick some closet access which is the root bridge so but it like spoiler alert here's the end of the story your job is to go in and just say I want this switch let's just say whichever whichever switch you would consider the center of your network I want that one to be the root bridge and maybe if that one goes down I want that one to be as backup that is done using something called the spanning tree bridge ID so there's your dictionary term so so every single switch will have a bridge ID you can either configure it by setting the priority or you can just let it be as default so I'm just gonna let's just let I'll just say these are all the bridge IDs and by the way the bridge ID is not a short little number like that like you're a default bridge ID might be something like thirty two thousand seven sixty eight dot you know 1 1 1 1 dot 2 2 2 2 dot 3 3 3 3 if the bridge ID is actually the priority which we can change plus the switches MAC address which we can't change I know some people like well you can spoon it you can't not not with spanning tree that is static you can't change that one so so so here now here's where this the confusion comes in how does spanning tree do what it does so first thing it does is pick the root bridge and in our case that's that's the easy part because we did we just said that one is the lowest bridge ID that will be the root bridge okay now all of the switches this here's the magic of spanning tree all the other switches are like I must go to the center of the network they're like little zombies I must go so they will find I'll say step one is find their root port which is the the fastest way that they can reach that root bridge now how do how does how does it find that root port well it actually and this is it's like I said it's it's complex everything has a process the first thing it's going to use is the paths with the lowest cost no I'll explain this in just a second if that's tied it will go okay I'm gonna use the lowest bridge ID I know some of you are like up you lost me right here don't don't worry don't worry hang with me I'm gonna explain this the third one that breaks the tie will be the lowest port number okay so now let me explain I just I just need to get that on the screen so cost is based on a table there's only two values that I would really recommend knowing if you're studying for the exam 100 megabits per second is a cost of 19 gigabit per second I'll just put 1g is a cost of 4 just just remember those two and you'll be all set so so for the sake of this example let's just say that all these links are gigabit per second so 4 4 4 they're all it cost a 4 4 4 all the way down foot so just imagine fours all over the place right so we've got fours for craziness right so let's just say I am I am this switch right here he's gonna say okay how do I find the best way to get to the root you know what's the lowest the lowest cost to get there it looks it goes okay can go this way and it's a cost of 4 or I could go this way and it's a cost of 4 and then I'd have to go what that way that's it cost of 4 you know plus 4 so you know I could go that way 4 4 4 so that would be a cost of 12 right so it's going no no no I'm gonna go I'm gonna go this way so hey I'm let me change change my pen colors here you'll see why it's a lot easier to understand so that's going to be my root port which is the one that I used to reach the root bridge and freeze for a moment there's a lot of stuff that I'm not telling you because I'm glancing at the chat and I'm like ah BPD use BP to use bridge protocol data units that's how they do this whole thing that it's like that's like their sonar it's like how they figure out the network right so so I'm kind of letting that to the side because this piece is the most confusing piece for most people it's how do how does it do it okay so so that guy's like okay that's my report this guy's like okay I would go this way and it's for or you know maybe this way and then I'm then I'm at 12 so so it's gonna say that's my route port all these guys that's nice and easy you know report report report report report report step one of spanning tree oh it's almost done no what about what about this guy forgot to forgot that guy well okay actually that guy's a great discussion look at him if he goes this way he's got a cost of 4 plus 4 that's 8 right ok he goes this way or that way or any of these the ways okay that's that's also four plus four so that'd be that'd be a cost of eight so this is where the lowest cost is a tie okay so it's gonna come down here and go okay my next one would be the lowest bridge ID I'm gonna take the path that has the lowest bridge ID so it looks that this guy goes oh your bridge ID is 10 yeah nope because I've got a friend right here his name is 3 you know you're a friend that's great you know but but three is lower so that will be my root port right so you see how that second the second thing works right Oh cut off my team so we've got our root port selected that's the first part of the process second part and this is where most people get lost hang with me the second port is it will light up I'll just put a turn on one designated port per segment so let the questions flow what is a designated port simple it's a port that is forwarding that's it so a designated port equals a port that's active a port that's alive a port that's forwarding right so okay let me read it again each switch will turn on one designated port percent oh okay second question what's the segment any one of these this is a segment this is a segment the switch link a switch link is a segment so let me let me just tell you if you plug in a computer right here spanning tree will run on this link and we'll say oh this is a designated port because I've got one per segment okay so so let's do that so let me use let me use the color let's use green designated port that's one per segment right okay designate port one persimmon and by the way I can tell you the root bridge that's its reward it has all designated ports because if you look every segment is going to have a root port connected to it right because it's it's the root so does the import doesn't any port you could just that rubriz DP DP DP DP right so all of these are forwarding is essentially what it's saying now and where I'm gonna do the rest of the switches in just a second but I want to make sure I say this a lot of people look at their like why like why is it doing that like what's the point remember you and I can look at this diagram and you can be like oh that's redundant let me let me block that oh that's redundant let me let me block that we can human beings can look at that computers are dumb they don't know that all day there are zeros and ones so they need rules to make this happen so somebody who's really smart said if we follow three rules and that's by the way where we're going three rules you've got one we've got two three rules every single time we will end up with turning spaghetti into a perfect spanning tree Network right to the just the rules that they figure it out right so we've got that root port oh there's one dozen airport right one per segment so pretty much anywhere I see a root port I can go to the other side and put DP okay now are we done no because what about links like this we need to light up a designated port right there how do I know which which side yet cuz only one side is allowed to get it remember one designated a port per segment you can't have two otherwise you end up with the loops so it uses the same strategy to figure it out it says okay I've got three and four we've got to light up one designated port on these on these interfaces so first one I'm gonna say the switch with the lowest cost to the root bridge is going to be the winner right so you've got a cost of 4 you've got a cost of 4 2 so we're tied there you you both have a cost of 4 you both are really good switches okay so the next one it says okay the switch with the lowest bridge ID you're gonna be the one with the bridge with a dozen airport so he's like woohoo I win does the airport does any port right and then these two are like okay competitions on he's like oh I got the lowest cost he's like oh man I'm a loser taking Airport right because he has a cost of 4 he has a cost of 8 to get to the root bridge so the first one broke the tie there he gets the desing Airport right what about this so we've got we've got this guy cost of eight to get there and look at all these guys man third third all these our guys are direct to the root bridge so they win they got the better cost so does he a port and yeah yeah yeah yeah didn't now he knows I know that maybe like oh well that that's bad we want that guy should have it well honestly it doesn't really matter because at the end of the day we're gonna fall down to rule number three block anything that's left these three rules will give you a perfect spanning tree Network every single time so it goes around and goes up it looks like right there block looks like right there block block block block block block ah a block my fire guard right block block bada-bing so let me do this that so that by the way that is how you figure it out and that is gonna be on icnd2 right I can't say that hypothetically speaking that might be on icnd2 not not that diagram but a spanning tree question like this where you got to figure out the topology that's that question from networking a negotiator what about alternate ports same thing huh Locke so so when we were talking about to hang let me let me hide my scratch for a second because I think I got a switch I use such good grammar I got a switch right here check it out I'm gonna do a show spanning tree on this guy see this right here block is called alternate it's just rapid spanning tree uses the name alternate whereas the original spanning tree just said block right so oh hang on okay you can see I was using my slide right from right from the the series so let me let me do this cuz because this this will thanks Chris she can join too Chris come on let Chris finish drawing the spanning tree protocol all right so I'm gonna scribble out look at look at this this is what your final topology looks like I'm going to scribble out all the links that are blocked Chris sorry if I gotten in trouble that would totally get me in trouble so scribble scribble scribble scribble right right right did we get them all oh yeah I think so so then let me let me take I'm going green let's go green yeah yeah uh-huh see Network diagrams like painting like that get some happy little trees you know duh there's a fire yeah good that is your spanning tree put topology that is that is the final topology that that your switches will use which I mean if I could remove all of those red links half of your network would go down and that's fine because that's what spanning tree does blocks the redundant links now if let's just say this switch fails right here it's going to just flip over and you're gonna have all of the red links light up right so that's that's the beauty of what spanning tree can do for you that's how you figure out the spanning tree topology that's probably the part of spanning tree that people struggle with most if you can remember and and I would encourage you so what why don't I do this why don't I do this I'm gonna take this this little house Manning tree works saying I'll make it a separate YouTube thing right so you can re-watch it a thousand times if you remember these three rules that's how a switch figures out the best way to get around their network and these three rules this is how the spanning tree process works you've got spanning tree you just have to practice it and do it again and again and again it's cool cool cool cool lots of questions let me so let me let me glance at the questions real quick now and that's that's gonna be by the way that's just gonna be what what time we get three 42 three 42 I'm good so I'm just going to take a few a few questions thank you guys by the way so someone someone earlier asked if I'm able to do CCNP route and switch material before February ah maybe I'm not sure because I see in d2 that's gonna take a while to get through the practice exams and do stuff like this maybe but I think right now I'm just doing CCNA till February because might'n I'll tell you my heart goes out to people that are like I'm jumping into this game CCNP is like you're in the game keep going so so so I that's so that's that if you ever want to know why does Jeremy always run to talk about CCNA that's because I connect with those those people the most I just I'm not there's just something that jives really well so good good good and I think I think that's I think that's it easily three port number three port number like layer 1 layer 4 what port number is the same oh oh oh oh yeah yeah actually that's a great question I I got you easy so here's what that me so let me grab let me grab it different let go go black so spanning tree protocol let me just draw draw this so typical spanning tree topology first thing is let's just say this is the root bridge the switches will try and find the lowest-cost to the root bridge and you know so let's just say these are all four and that so these two are switches they're gonna go okay that's the best think that's a bit that's how they find but what if you've got a switch down here right that's where it's tied he got 40 so it's like so that's where it uses that bridge ID so so easily is saying well what what does this mean this topology you won't you won't actually get there the bridge ID will always break the tie you run into rule number three if you do this like that kind of thing would instigate rule number three where it's like okay same cost same bridge ID so port number one port number two port number one will be the preferred port number two will end up getting blocked right so that's that's how that works hopefully hopefully I answered the right question with that I was I was taking a stab at understanding it cool so guys I think that's that's probably the the most valuable way I know how to help you with spanning-tree in the least amount of time without just dumping a whole ton of stuff so so watch that again I'll throw it up on YouTube watch that again if you if you can do that you've got Spanish tree that's the hardest part right there is figuring out how to do that cool well guys it's Friday happy Friday have a great weekend enjoy your studies be blessed I'll see you next time

Channel: Viatto

Views: 23,096

Rating: 4.9854722 out of 5

Keywords: Keeping IT Simple, Jeremy Cioara, STP, it blogs, it specialist, information technology (industry), information technology, it, tech, networking, it jobs, it fundamentals, how to, learn IT, networking tutorial for beginners, home network, Master Spanning Tree, Learn STP, Learn RSTP

Id: 1RPMCnJStec

Length: 20min 54sec (1254 seconds)

Published: Wed Nov 20 2019