Packet Tracer 2.3.11 - Determine the DR and BDR (NET 225)

hi everyone this video walks through completing packet tracer assignment 2.3.11 determining the dr and bdr which is the designated router and backup designated router this packet tracer assignment is a part of the enterprise networking security and automation ccna version 7 curriculum in the cisco networking academy so for this lab we've got three routers there r a rb and rc attached to s1 all of them are utilizing ospf to know where each other are um as well as we've got a loopback interface don't let the loopback throw you off they just kind of simulated a separate network here so that would be like if there was even another network connected off of rb sometimes we do that with other routers or sometimes we do that with a pc or a local area network to show us really needing to divide the network up so with this one um they just kind of use the loopback interface um don't call it lazy or anything but that's just a way to uh look like another um lan or another network okay so in this design here they're using ospf it's already configured for us and basically remember with ospf not only do we use the shortest path first or spf we also look at um how those neighbor adjacencies are formed so it sends out those advertising packets and forms a neighbor once it knows about each other and it adds it to its routing table now there is also a backup designated router as well as a designated router and then there's an uh other basically you don't fit into either one of those categories that's kind of looked at as like the main router that keeps everything up today and then of course you got a backup because in case that one goes down then the backup assumes responsibility for the network so we're gonna figure out even how to figure out which one is the designated router which one's the backup and then look at how we even make that change by forcing it okay by turning off some uh interfaces so first we need to look at the directions here it says wait to all these link lights turn green so they're not that amber or orange color anymore so they've negotiated everything and we're going to go to each one of them go to the cli tab and we are going to type in the command let me zoom in here and we're going to type in the command show ipospf so enable show ip ospf and what we're looking for here oh sorry that's just the basic stuff we want to do neighbor all right so what we're looking for here is off of the g00 interface all right we know about 192.168.31.33 which is the name of the router okay remember how we do when we're configuring our ospf stuff from our previous lab uh when we configure it we can figure it with a router id that's kind of looked at like its name okay so it is the dr our designated router it's the boss in charge okay the other one whoever is dot 22 is the backup designated router okay now if we go to each one we should see some consistency here so if we do enable show ip ospf neighbor then we should see some consistency so on that one you saw that dot 33 was the the designated router here we also see 33 is the designated router whoever.11 is is the other okay and i'll show you how to see also while we're here if you do a show ipospf you can see who is 192.168.31.11 again that's just the name that is not the ip address for connectivity or anything and that is ra okay so our a is dot 11. so when we look at dot 11 it is the other so it is not serving as the designated router or the backup okay when we looked here we saw that dot 22 is the backup all right so who is dot 22 if we do a show ipospf the backup is right here rb alright so they are the backup okay so the designated by process of elimination should be rc here because they are the dot 33 name however let's type it in just to prove a point so enable show ip ospf neighbor and right here we see that the backup is dot 22 which was rb the other is dot 11 which was r a so rc if we do a show ipospf is dot 33 all right so uh rc right now is the designated router if you want to put that in your notes right quick uh rb is your backup designated router and our a is other so it is not the backup or the designated router all right so important things to know when you're looking at your topology okay so you can answer those questions there okay so it says turn on ipospf adjacency debugging with the debug command so we do debug ipospf adj for on r a and r b so let's go to that's rc i don't need you all right so let's go back over here to rb and we want to do the debugging commands we're going to turn those on so we can monitor what's going on here all right so also remember our question mark so if you want to turn on any type of debugging which will alert you with a lot of messages every time changes happen remember you can type debug question mark space question mark and you're like okay uh let me try ip all right then we see ospf there and then we want to know about adjacency events which are our neighbors all right so that's what we want to type there until we turn it on so we want to type the same thing on ra debug ip ipospf adj so debug ipospf adj and debugging is on so any changes should alert us all right so we're going to go to disable g00 on rc so if we look at it rc here the g00 is this port right here so we're going to disable that so it will no longer be able to communicate you see that's the only way in and out of rc to talk to it so if we disable it we're gonna go to config t all right and interface g zero zero and we're gonna type shutdown or shut and you see it says they're detached so it no longer knows about our neighbors anymore okay so let's go to rb and ra and see maybe what comes up or what might happen once it actually figures this thing out we should get some messages starting to pop up and it says it waits about 30 seconds for the dead timers to expire that's ospf checking to make sure everybody's still uh good to go there's no new routes or anything and we can fast well there we go no need to fast forward so now you can see that process taking place so it says the dead timer is expired to talk to the dot 33 router okay so it's saying hey we can't communicate interfaces down or detached right so now it says all right let's do this is doing that election process right now it's saying okay who's gonna now be the uh designated router so it's going from backup to designated and now you see it let's uh number 11 which is ra know hey you're now going to be the backup designated router so if we do an ipospf show ipospf neighbor all right we only see one in the dot 11 router which is ra is now the backup designated router okay and then if you go to r a and do the same thing you should see those election process taking place and now 22 which is rb is the designated router okay so now i want you to actually turn uh g00 back on on rc so let's go to rc we're already under g00 if not remember interface g00 and do shut or sorry no shut or no shutdown so basically turn it back on and we're going to wait and see what happens now so we enabled it so now we want to see did any changes happen so is rc gonna now become the designated router again like it was before now that rb is the designated router and ra's the backup so what's going to happen what kind of election process is going to take place here so we're going to see okay it looks like the link lights are up all right it's sending is showing the election process the lsas are being sent out the link state advertisements to basically let everybody know who they are it's going through that election process and then if we do a show ip ospf neighbor let's see if it's been long enough it has so it shows 33 back again which is rc right but instead of it being the designated router now it went kind of to the back of the line and now it is the other router all right so the designated other so it is no longer the designated router okay so rb has stayed the designated router and even when we go to rc and kind of exit exit and do a show ipospf neighbor you now see the designated router is dot 22 which is rb the backup designated router is ra all right where ra used to be the other okay so it doesn't really go back to the state it was if everything's flowing good it just does the whole reelection process again okay so then it wants you to disable the g zero zero and rb and see what happens so rb config t interface g zero zero shut down all right and then you wait a little bit and let that election process take place you can always use this forward arrow here it kind of jumps time so that way that election process can go ahead and happen and if you look on our a we should have had you see now the designated router is now our a the backup designated router is now rc because rc is the dot 33 so again if we do a show ipospf neighbor we only have one neighbor now and it's the backup designated router if we go to rc and do that same thing again all right it is the designated router is ra all right so you can now see in my topology rc is the backup designator router our a is the designated and rb is technically off the map right now right so then we want to restore connectivity on rb so we go back to rb and we're going to do no shut on this interface to turn it back on and i am going to speed up the time here all right let's get that election process in and when i show my neighbors here now you see that the designated router has now went back to the 22 the 11 is now the designated route or other once it did the election process all right an rb here we go um you see now that the 11 is back to the dr other so now it's back like it was in the first time all right so you can kind of see that election process take place um as it goes through and now we can turn off debugging um un-debug all on uh our a and rb so that way when we continue in this lab it will not continue to show us every little thing all right now to change the dr and bdr because you might be wondering what in the world happened how did that and you you might have thought that ra was going to stay but it kind of kicked our a to the back of the line and made it the other again so what happens is the priority so that's the next section we're going to go through where we can actually force these elections to happen instead of letting them take place but it has to do with the priority that it assigns and it looks at that uh router id for assigning the priority for designated and backup designated router so here we are going to do the ipospf priority command on each port that is receiving the interfaces to actually make that choice for us okay so the default priority is one remember in um so the default fault priority is one we're going to set that on rc rb we're going to use 100 and re we're going to do 200 so we're going to go to the interface this is on c so under interface config t interface g zero zero and we're gonna do ipospf priority and then we're gonna set it as one then we're going to go to rb config t ip or interface g00 ip ospf um priority and 100 i believe it was yes 100 for rb and then we're going to go to ra and do config t interface g00 ip ospf priority 200. all right all right so once we set all three of those priorities it says force an election by resetting the osf process ospf process on all routers starting with router a issue the clear ip ospf process on each router all right so let's go here we're going to do exit exit one more time all right clear and you see all our options here uh ipospf process reset we want to do yes here all right and then it asks us to do the other one so let's go do the other ones clear iposps process yes and same thing here exit exit clear ip ospf process oh i type new yes all right so we'll wait a few seconds and why actually just go ahead and press the fast forward button let a couple minutes go by and now it says verify the br and bdr elections were successful this should take a few minutes so let's see here who is who all right so we're going to do show ipospf neighbor and now you see the priority here next to each one

Channel: Anthony Lucas

Views: 392

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Id: KlfzlFHOu84

Length: 17min 14sec (1034 seconds)

Published: Fri Sep 11 2020