How STP works 2 - Video By Sikandar Shaik || Dual CCIE (RS/SP) # 35012

[Music] so now in this section we'll continue again about spanning tree protocol which we have discussed in the previous in a previous video we have seen the first two process selecting the root bridge the root base will be circuit based on the best bridge ID and then clicking the root port root port is again the shortest part of the root bridge and it is selected based on the three conditions the first it will see the cost if there is a time the first is you see the forwarding bridge ID if there is a time the forwarding page ID then the least port number of the upstream of swing device now the last condition and based on that conditions if you if you just try to figure out this on those conditions in my scenario this is a root port and is a root so in this diagram there is a the root word is liquid based on the cost in the next second diagram is the first diagram actually and in the second diagram this one the the the root port will be fretted based on this on the bridge ID or in bridge ID and in the third device there is a time the bridge ID so the root what is that root put expected this on the upstream port number okay so if I go with this topology here now the next thing they have to decide what port should be in the forwarding what pour should be in the blocking now now again the shortest path will be always the root put the root port or the shortest path will always be in the poverty now whichever the switch becomes the root bridge the root bridge ports all the ports will be in the forwarding state so forwarding means they always you don't have any blocking ports on the root bridge so when any switch is indicated as a root it says I am the root bridge and in multi port will be always forwarding and also the the root port which was selected they also will be in the forwarding because they are the shortest part of the root bridge so which means they will be always forwarding the traffic now out of and out of deciding the other ports what are the leftover ports they will decide them as either forwarding apply so let me just write down first this is forwarding this is forwarding and then this is also forwarding port or designated ports you can call it as poverty now whatever the left over port is a this or this any one of this port will go into blocking state so which means all the traffic flow will go through the root bridge and any one of this port will be in the blocking state because there are only two routes one is forwarding other one should be blocking now again the decision will be taken based on the same conditions what we discussed in in terms of in terms of the root port so it's going to see first it's good to see the cost now in my scenario the cost is Thai on both the sides the cost is 19 and 19 and the next condition is going to see the forwarding bridge ID sort of these two devices of the forwarding page ID now in case of designated ports it's not going to see the forwarding bridge ID it's going to see the local course okay so but we need to ensure that it's not it's not interfering with the root ports root ports always will be the forwarding it's going to see the local bridge ID where if you try to see the priority value in the Microsoft these two devices 0 0 0 2 is going to win which means this port goes into blocking state now which means this particular port will go into blocking state based on the local bridge ID information in case of designated ports it's going to see the local bridge ID instead of forwarding and then also it will see the power local port numbers are advancing the forwarding port it works so but the conditions are same in case of root port it will see the up up upstream port numbers whereas in case of designated and blocking ports it's going to see the local port number information so the port works in the blocking state because the bridge ID of the switch 2 is much better than switch 3 and it is going to put this port in the blocking state so all the traffic going from switch 2 2 3 3 will go by our switch 1 as I said this root bridge will be the central switch or the central focal points for all your traffic and all the traffic that's into any network will be going wire will bridge and because this is a central switch from ways all your traffic flows and this port will be in the blocking state as long as your main link is working okay so these are default HTTP process and this process happens automatically whenever you connect multiple switches we are not going to add any single command for this to work and but we need to understand how exactly the STB process happens three different steps now let us add some more information before we actually verify verify the spanning tree behavior on the command line so the three steps which we discussed just now selecting the root bridge cells in the root port and selecting the designated and non designated ports designated ports or the ports which are in the forwarding and non designated ports ports which are in the blocking State now there are some other information like as a discussed there is something called hello messages which is sent by the switches between them and this hello messages are sent for every two seconds so at the time of initial process initial on the first steps if you remember selecting the root bridge now every switch will by default advertise itself as a root bridge it says I am the root bridge now switch to also will say harm the root bridge now the switch to will compare its own bridge ID and the neighbour BJT and it says that I'm not the root who is the root which one is the root now they they come to a conclusion based on the BPD messages so at the time of initial process which everyone will think I am the root they all send D free messages but once they elect a common root now the root bridge will start sending the DPD messages to all the features now the non-religious will not send the VPD messages initially in case of normal panics and it is sent for every two seconds and in case if the link goes down due to some reason I am NOT receiving the hello messages this interface the switch is going to wait for a maximum of 20 seconds that's what we call as maximum each time before it starts using the alternate port into poverty okay so the maximum weight it is going to wait or we can say at that time is 20 seconds and then this entire has to be process whatever we are going to discuss it happens in in the in the time frame of 30 seconds now we call them and listening and learning stages so whenever you power on the switch for the first time by default every port goes through listening state where it is going to listen to the BPD messages and decide the root bridge and then decide some route ports and forwarding for designated ports so the entire process whatever I discussed it happens in the frame of 30 seconds before it actually puts the ports into either forwarding or in the blocking stage depending upon the calculation problems okay so there's something what we are going to verify when we start getting into the command line more in detail so right now we just go with the theory anywhere okay so the different status message port state now by default if any port is in the blocking state due to internet links and that port believe in the blocking state or maybe 20 seconds or there is no limits as long as your main link is working this port will be in the blocking State and if something goes wrong here let's say if this link goes down then the blocking port will be transitioned into forwarding and it's going to take somewhere around 50 seconds default for alternate port now we call this as alternate port transitions into forwarding because it has to wait for 20 seconds or 20 seconds of maximum time and then if there is no BPD messages coming from this way because of the link is down in that case it says that it has reached the maximum time and after that it goes through listening state where it is going to go with the same calculation process again and the learning stage find the root bridge and before it puts supports into power straighter so the entire timer is going to take 50 seconds if any of the link failed the default convergence time in case of spanning trip will be around 50 seconds in case of indirectly dis links in case of the local link fails if there is if this link fails it will take a default convergence time of 30 seconds because this link is on the local switch so it's not going to take that 20 seconds time so the default convergence time in case of spanning tree if your main link fails either it will be 30 seconds or 50 seconds depending upon the kind of the link if the link on the same switch goes down as the blocking port it will take around 30 seconds if any link fails which is not on the same switch we call it as indirect link which is going to take somewhere around 50 seconds default convergence time now this is something we'll be verifying more in detail in our next section which will practically verify the behavior okay [Music]

Channel: Sikandar Shaik

Views: 91,765

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Id: eHRf6VeGRlQ

Length: 9min 54sec (594 seconds)

Published: Thu Jan 19 2017