Configure and Troubleshoot OSPF | Cisco CCNA 200-301

[Music] even in skies [Music] and welcome everybody hey thanks for joining me I'm glad that you are here for those of you who are brand new to this channel my name is Keith Barker glad to have you eyes looking at the cue I see a lot of familiar faces we are gonna focus on another CCNA topic and this one is going to be OSPF open shortest path first and we're gonna get right into it and the challenge today is to have a plan configure OSPF and then verify OSPF and if we have hiccups or problems along the way it'll give us the opportunity for unite to troubleshoot those together so let's go ahead and bring up the topology here and here here it is I worked I worked for minutes on this so here's our topology let me explain it to you real quick and then we'll we'll go to work configuring it and one of the benefits that we may discover as we plan this and configure together if you're brand new to us beautifully give you a good idea how it works and also if you've seen all SPF before but thought oh what's this or was that there may be some insights as well we are gonna focus on single area OSPF which is part of requirements for cisco CCNA and that's for 200 - 300 one there Cisco certification alright so here we have 4 routers routers 1 2 3 & 4 and we've got some connections between them we've also got the switch it's a layer 2 switch so it's got some access ports connecting r1 and r2 together and then there's a PC hanging off of gig 0/0 on r1 it's actually going through a switch and then off of r4 there's a switch it goes to a PC over here and there's your IP addresses so tip 4 you know I love I love creating network topology so when we're learning and and practicing things that are pretty easy to interpret so we're not getting lost in the where's that networker where is that Network let me show you how easy this is to decode so base so these routers I used the 10 0 Network for everything so we are gonna make a single area for OSPF it's gonna be area zero so all the routers all the networks on all these routers are all gonna go into this giant area called area zero and the benefit of areas in larger networks think of it like a room with a hundred people in it and if we had a room with a hundred people and then we were asked okay you're gonna get a little bit of information from every single user every single person and you have to keep that all in a database and remember all of it that's a lot of overhead so in OSPF to make it more manageable we can carver a network up into smaller chunks maybe we have smaller rooms it's like having a room of 10 people versus a hundred and then all we have to do is just memorize the people in that smaller room and it's less to manage there's less than our database and it's easier to calculate so that's the benefit of having multiple areas so in our topology we're just going to use one area and we're going to put all of our it's like a one room we're gonna have all of our routers sharing all their routes with their rails in that same area and in this topology 10-0 is gonna be the first two numbers of all the IP addresses and then between routers 1 & 2 it's going to be 1 & 2 I put the two numbers together like x and y so this network is 10 0 12 between r1 and r3 it'd be 1003 n-- between our 3 and our 4 1003 4 and I just put in there so we get when you see a route you'll say oh that's what that is also each of the routers their last octet the last number of their ipv4 address I'm using the same as the router number so our one's gonna be dot 1 on all its interfaces our 3 is gonna be dot three our four is gonna be dot four and our - yeah dot two so in this topology I've got all the IP addresses already configured so we can focus right on no SPF so let's let's make a plan for OSPF and here's what I propose we do we'll have all the all the networks in area zero which means all these routers and all their interfaces that will tell them that any networks that are going to be an area 0 and let's include every interface that begins with 10.0 we want to put that into OSPF now we had a separate stream on network statements and wildcard masks and so if all of these routers if we wanted to add any interfaces that start with ten zero which is all of these that were all these Ethernet networks the network statement would look something like this network ten zero and then we follow it through with two more octet so 1000 10000 a space and then if we want to match on these first two octets these first two numbers what we do is in our network statement would say we care about matching on the ten with a zero a zero for the wild-card mass as we care about matching on the second number and then for the wild-card mask I'll put these in a different color every better so the wild-card mask let me go ahead and grab then you grab black like I don't care what they are how them so dark so a 255 in the wild-card mouth says I don't care what that third octet is and a 255 here in this last octet means I don't care what that last octet is so what this means to the router is okay I get it I'm gonna look at all my interfaces say the router and I look for anybody any interfaces they begin with 10.0 and if they do boom I will have those interfaces participating in OSPF participating in OSPF I hate that term any interfaces that match ten zero what it means is those interfaces whatever networks they're connected to those networks are going to be in OSPF and if there's a neighbor like another OSPF router off of one of those interfaces and we see there hello messages back and forth we can become a neighbor with those and start sharing information with them as well that's what it means so that's what the network statement works and then we're scanning specified that we are going to put these into area zero so that's our plan right there boom so oh one more thing let's go ahead and each of these routers has a loopback interface and it matches the router number so router one has the loopback the one-one-one-one and router two has a loopback of two - two - so if we don't get a question for you if we don't specify the router ID in configuration mode we don't go say router ideas this or router ideas that what I what I D is the router going to use for the OSPF router idea and if you know this I'd like you to think about what that is if you're not familiar yet with what it's gonna use here's the pecking order it's three things my finger no longer hurts I smashed it in a door we can have a go of it no longer hurts hopefully I'm keeping the nail sir I'll give you this side I'll give you the friendly side so there's three things it's gonna use for the router ID if you have the router ID manually configured it uses that if there is no router ID manually configured the next thing is going to use when OSPF comes up it's gonna go out when it when it starts it's gonna use the IEP address on the highest IP address numerically on any loopback interfaces and if there's no loopback interfaces and you haven't configured the router ID it then says okay I'm gonna take the highest IP address on any other interface like a physical interface and that's what uses so a router ideas is it dotted decimal format like you like it I looked it looks like an ipv4 address however it doesn't have to be I mean you could use like 250 dot v dot v dot v it doesn't care so even though it kind of looks like a dotted decimal address it just happens to be represented the same way with four numbers three periods and that's the route ready all right so as far as our plan goes because I have loop backs on all these I'll just go ahead and let those loop backs because it's the highest IP address it's the only loopback the router ID will automatically be 1 1 1 1 for our 1 and 2 2 2 2 for our 2 and so forth so great that's it let's let's go ahead and implement this plan so let's start on r1 and you know I'm also gonna do I'm also gonna do what I would do in a production environment unless I was using network automation which we even faster but if I knew my configs I had an idea what I'd probably use Notepad or some text editor put the commands in verify them and then just paste them in especially if they're very very similar so let's see those well let me go ahead and clear the screen and let's go ahead and get to lab and make sure it's up and hey it's still responding that's great or so I'm gonna bring up my favorite tool one of my favorite tools I have a few notepad and so we're gonna just go into each these routers routers 1 2 3 & 4 go to configuration mode and let's see here do a view and format let's do this real quick format font and the skill bigger that way you you can read it with me there we go easier to read good so config T and then we're gonna get a router OSPF process ID I'll use one and then we'll simply say network I just tap that out you know this Cisco router you tap it out it gives you the whole command but here it's it's saying Keith I don't you mean so I will spell it out here so we can see it so the network statement I mean network 10.0.0.0 and we care about the first two octets so the wildcard mask would be 0 0 which means I care about the 10 and 0 matching but I don't care about the third octet says that 255 all bits on and I don't care about matching on the last octet that means the third and fourth octet on this routers interface once we apply it could be anything doesn't matter as long as the first inner the first two numbers or 10 0 it's gonna match and then we're gonna put any networks that match that into area 0 just like that and I think I think that's it we could we could paste this command in all 4 routers and it would work so let's I'm gonna copy that I'm just gonna highlight it and right-click and copy it into my buffer on this local virtual machine that's running this lab and I've got a question for you before we apply this what is if you've been with me for a few these streams you probably know them a big fan of verifying what device we're on with a simple show command before we start plowing in or pasting and configs so I'm gonna strongly recommend that in here just verify that we're on router 1 that the interfaces that we think should be there are there before we start configuring so in our topology we're expecting our one to have this interface 1 / 0 + - / 0 and zero zero with these networks 10.1 10.12 and 10.13 so let's let's just quickly verify that sanity check to make sure that's the case absolutely a show IP interface brief and sure enough there's our three interfaces with those respective IP addresses which is great and then I also have a loopback down here so I'm on the right device so I got a I got a little a mistake I just made I highlighted some text in the CLI and as a result when you highlight with most terminal emulators it copies so if I paste it now I'd be pasting a bunch of those numbers so I didn't go back to my text document and copy again before it based oh by the way I think I told some of you that I brought down a whole network once many years ago and this is how I did it I was I was in a config I was pasting in something and I grabbed something else two things I was on the wrong device and I had the wrong copy because I was highlighting something else anyway nasty business that mistake never happened twice in production alright so let's go back to notepad and here notepad will copy that and we'll go to our warning boom alright that seemed painless let's do some verification commands because it's a two-step process config and verify so let's do a show IP protocols so that verifies that OSPF is running here's the router ID and here's the network statement that we just put in saying that we care about these first two numbers don't care about the last two for matching purposes and any networks that match that are gonna go into area zero that looks good do a show IP ospf interface brief and that looks good to wait the status wait because each of these network segments are Ethernet the default network type is broadcast and default network type of broadcast says we're going to assume that we're using a designated router so this is this router simply waiting I believe us three times are the dead interval beef or it starts to go ahead and become the dr it wants to make sure there's no other dr out there so it's waiting for a moment and then finally because nobody else is out there it'll become the designated router for all three segments now a couple things that happen with OSPF um in lsbf there's a lot of data that's being shared now if you only have if you'll have one router it's gonna there's not a whole bunch of data however in no SPF but routers generate what's called a router LSA now link-state advertisements are how two routers let's say it's you and i we're both routers we see each other's hello messages we send frequently and if say hey we're on the same segment we agree about the network we agree about the area let's become neighbors and we can go ahead and start sharing our information with each other and so each router creates a link state advertisement and a link state advertisement think of it like it's all about me not man times know but the router was is router one would say it's all about me here's my link state advertisement and in this link state information is talking about all my links and it pulls out the details that says here are the details i'm connected to network a and network b and network c and those are these states of its links that's called a link state routing protocol so every router is gonna generate its own router router LSA and it's also referred to as an LSA type one so if you ever hear of a router LSA or a LSA type 1 is simply the router I'm so happy says mr. r1 here's a link state advertisement but they have I'll put in my database and it has informational as three networks so I thought what would be cool instead of just like here in the theory about this let's go take a look I mean router one at this moments the only one running OSPF so the OSPF database think of a database like a collection of LS A's and it gets pretty gnarly after a while there's a lot of about 20 routers you're gonna have at least 20 router l essays plus some additional designated router l essays network LSA is come out to so well we just have one router let's take a quick peek at the LSA and this is a handy tip because by building a step-by-step and learning the individual pieces like starting with CCNA which is the perfect place it helps when you start getting to the professional and enterprise and advanced levels an expert level by by having a solid foundation so let's do that how do we ask for that first of all do it up arrowkey so mm-hmm router 1 is now the designated router for each of its broadcast network segments and that's because it's pretty easy to win when you have no competition there's no other routers reading the OSPF yep all right so router 1 is the deck it doesn't get router and if we do a show IP ospf database okay let me give you let show you a question work there's a lot of information that we could look at regarding the OSPF database but think of it like this think of the OSPF database as the collection of all the lsas that are being advertised and synchronized in the entire area so if there's 20 or 40 or a hundred the LS all those else a's collected on a router would be called the link state database so right now we should just have one that's what I'm banking on let's take a look so if we do a show IP ospf database I love it ok so this is a router link state no a router link state if this was in English it would say this you would say LS a type 1a router LSA because that's what this is so this routers an area 0 so this LSA is gonna be found on every router that's in the area because we share we have identical copies of the link state database we advertise with their neighbors and we propagate the information but right now it's just router 1 so if we want to take a look at the details of that what we here's what we'd expect to find what we would expect to find is that if we said to this router hey what's in your LSA router I want to say well well I have three interfaces I've got 0 0 I've got 1 0 and I've got 2 0 Gus is right yeah and those networks are respectively zero zero is the ten dot zero dot one dot zero network and 1 slash 0 is 12 10 dot 0 dot 12.0 and 2 0 is 10 0.13 whoops me 13 there we go so and they're all up at the moment so if we looked at that LSA that router type 1 LSA is literally gonna show us that he's got those 3 links now at the moment he's the only router that cares because nobody else is running those PF yet but it's handy to be familiar with what to expect and also a quick way of how to see it so let's take a look at the interface and take a look so to do this we'll just do a show IP ospf database and then we'll type in router and that's a fancy way of saying please show me the LSA type ones which is the router LSAs and there's like one of them and this is it right here this basically says that this LSA this link state advertisement was generated by the router that has the router ID of 1 1 1 1 which is router 1 that's his OSPF router ID and if we hit the spacebar which I'll do right now and go through these check it out he's got three links we're not surprised we do right we knew based on the theater faces he had and the network stateman that we used that he'd have these three networks connected and they are the 10 30 10 0 13 Network which is the interface off gig 2/0 and then we have the 10.12 network this bad boy and that is the gig 1/0 network and then there's the 1001 network which is gig 0/0 so the cool thing is by looking at this when you don't have 15 routers and lots and lots of different LSA types flying around it's a great way to help get your get your feet wet with the basics of understanding LSAs and in CCNA a single area so you don't don't worry about anything beyond that and there's only two LSA types in a single area SPF as long as we're not doing redistribution which is beyond CCNA so they and the first one of those is a router LSA LSA type one that we're looking at right here okay so the next step that we are going to do let me clear this off is we need to bring up some other people to the party so let's take a look at our topology and let's go ahead and use those same commands this the configuration commands to bring up r2 now it's interesting I think it's really interesting when we bring up another router so right now it's like a prized possession this is our one this is my LSA it's part of my link state database it's the only thing in there because he's the only router but once we have another router this imagine that I'm gonna make this a carrier so here's the link state database for router one so router two shows up and start sending little hello messages and those little messages are sent to a multicast address the little hello messages and router one says oh oh oh I see you over there and I see that you see me and they go through a process of states as they start to discover each other and then if everything is lined up meaning if they agree they agree on what the network is between them they agree with the authentication like our using authentication if you are what's the password or if you're not using education they have to agree on the network type are we gonna use the dr or no dr yeah they have to agree on the timer's the hello interval which on Ethernet is by like 10 seconds by default and the dead interval is 40 so they have to agree on that assuming they do they can see those in these little hello messages they'll go ahead and start to negotiate and then they'll say hey uh great welcome aboard now router two who just came up doesn't know about this yet he doesn't know about the link state advertisement for outer one so what they'll do is they'll share again like us so router 1 and router to basically router want to say hey here's my link state advertisement so you know all about me and that's bad news yellow and r2 is can have its own router LS a type 1 talking about its links and what it has up and can reach and this is gonna have that and it'll show that information over with I'm tapping in the link states inside that LSA and they'll share that with our one so at the end of the day every router did you say every router yeah every router in the same area is going to have identical copies of the link-state advertisements and the collection of all those is called the link state database so it's not rocket science they basically share information and make sure they're synchronized and then once our router has all the details it can then calculate from where it is in this topology it can calculate its best path based on longest match and then metrics and so forth of how to forward packets all right so let's bring all that's to say let's bring up router two so if we go to our lab which I'll do and get a notepad I think this will work so I'm gonna copy that this basically says I'm going into configuration mode I'm an abling OSPF I'm gonna use process ID 1 now the process ID doesn't have to match between routers in the same OSPF area it's just locally significant on the router and then network 10000 and matching on the first two based on with that wild card math says and put those into area 0 so great I will copy all of that right click copy we'll go to r2 and verify that we're on our to show IP interface brief before I paste this in all right so great so r2 is configured let's take a look at the IP addresses r2 should be connected to this network right here which is the 10.0 12 the 10 0 24 it also has a gig 0/0 interface going to 1002 but Mill seeds 10 12 and 20 24 10 12 + 10 0 24 or what we're looking for I verify on the right device and sure enough okay so I'm on the right interface right devices and I will right click and it's done so in a matter of time through the hello messages R 2 and R 1 should discover each other become neighbors and life should go on let's go ahead and go to our three from the topology our 3 is this bad boy right here it has two interfaces in area zero and maybe three do I have a gig zero zero as well but two that we care about 1 0 & 4 0 we'll go ahead and paste the configuration there so here we got our 3 and our 4 same thing and then we'll do a show IP ospf in a face brief and great so he's in a wait state and after the dead interval we do a show IP ospf interface for gig to slash 0 so that command show IP ospf internet gig to 0 will show you lots of really cool information including let me get my pin out including what the network type is so if the network type is broadcast that means we are going to be using a designated router if it's if the type is non broadcast that also means we're using a designated router and any of the other network types point-to-point point-to-multipoint it sort of they do not use a designated router but so that's my screen move dummy so it's good to so it's good to know that's how you verify what the network type is and we can manually change that here is the hello interval and the dead interval they have to match if you want to be neighbors they have to match and based on these network statements these console messages we just went into a full state now full means that we found each full means we found each other says r4 to r3 and r4 to r2 we found each other and we agreed on all the parameters the network address the area the authentication and we got so excited about seeing each other that we shared each other's LSAs and we got updated copies so now if we have three routers that's good if we have three routers or four routers in the OSPF area once those neighbors get into a full adjacency that means they have synchronized and have identical copies of the link-state advertisements in their link-state database so we should see is that on any router once we're fully synchronized router one two three and four that if we looked at the link state database with all the router LLC's and now we're gonna have designated Network Alice's as well because of the DRS that have transit devices on them they're all gonna be identical so the link state database identical on all four devices alright fun times fun times now let's take a look at se our objectives our objectives as I recall were to plan which we did configure we did and verify all right so let's do some let's do some verification all right so let's go ahead and I've got a PC out here PC one and let's go to UM let's get our four let's go to Pete let's go to our four and check a few things just to verify that OSPF is working so here on our four fantastic couple things we can do one show IP protocols that shows you what routing protocols are running here's OSPF one it's router ideas four four four four fantastic as far as the number of areas this router is connected to it is one it's in the single areas area zero and here is the network statement which says we matched on the first two octets on the interfaces and those interfaces became part of OSPF and we've learned information from the router ids of 1 1 1 1 3 3 3 3 and 2 2 2 2 and that's because our 4 has an exact copy of the full link state database which includes information from R 2 and R 3 and R 1 and if we went to R 1 it would say oh yeah I haven't I've learned through the link-state advertisements from two three and four because they're all shares so we have a neighbor ship we share all the information we have and effectively we're synchronizing the link state database on every single router okay so testing yeah like where you going now key where you going now let's go ahead and verify routes how about that let's do a show before we do that let's do a show IP ospf press enter and this is gonna show us a lot of great details about OSPF including the process ID again the router ID again a lot of stuff in here that we may not need right away but it also shows us the number of interfaces in the backbone which is three so area zero is the backbone area and and here are some other parameters as well this looks this looks great um one aspect is this though reference bandwidth unit is 100 megabits per second let me explain how that works in fact I'll just do it on the whiteboard right here if we had a 10 megabit per second interface like Ethernet and we used the reference bandwidth of 100 megabits so there's 100 megabits and we divided 10 into a hundred the result of that would be a cost of 10 if we had a hundred megabit network interface card and the reference bandwidth which is a hot is 100 still his and we divided 100 into 100 the cost is 1 and you know what that was fantastic for like a decade ago maybe more but now we've got interfaces that are easy a gig so that's 1,000 megabits per second and so if we have the reference bandwidth of 100 and we're dividing 1000 into that that is a fraction and here's what Cisco does I'm gonna round up to one so even though it would be like 0.1 it rounds up to one and that means that OSPF by default cannot tell the difference cost-wise between a gigabit interface and a fast ethernet interface that's like a mistake of tenfold so that's just the fact of the matter and so we need to correct that as well but I just wanna make sure we have adjacent seas and make sure we have basic route information and then we'll tweak that if we need to as part of our troubleshooting all right so on our floor still and here he is in the topology just to make sure on the same sheet of music we're looking at r4 and on our for if we do a show IP in OSPF interface briefed on my favorite commands that's great and what that's showing us is clear that off is showing us that we've got these four interface these three interfaces all in area zero there's their interfaces that got them in and so the first two octets are ten zero and as a result that's why these interfaces are in there their cost is all a cost of one they are all currently designated routers no in OSPF if there's a network segment and there's five or six routers on it it would be a nightmare to do full of Jason sees with all the routers with everybody else there'd be a lot of redundancy you don't need it so instead on a broadcast or non broadcast network type there's gonna be a clearinghouse it's like the King Kong and the network of that segment and that's called the designated router and the does and router is gonna build full of Jason sees with every other device on that network segment and that way you don't have to have if you have 10 devices you don't have to have 10 devices with full adjacencies and sharing all their information without all the other nine you just have them exchange information with the designated router instead having a full of Jason see between the common dr other but Amnon does need a router with the designated router there's also a backup designated router as well for fault tolerance but that's how that works so this router because now why did he win well he won on some of these interfaces he be that doesn't answer on this guy because there's nobody else out there see that that means there's no other neighbors out there no no other OSPF speakers out there but on these two he won the designated router role because he is has a higher router ID that's the reality of it so when a router went when two routers loved each other very much but they have to decide you know who's gonna be the designated router and who's not the one that has the highest priority on the interface is gonna be the dr unfortunately the default prairie is one so that's the same on everybody and if when - - that would win but the default one so if they both are powered up at the same time the one that wins the designated router role is going to be the one who has the higher bridge ID all other things being equal the other thing in too is if a router got booted first like it's running OSPF I got powered on and five minutes later some other router came up the designated router doesn't give up his role it's like nope on it I'm at ICU yeah great priority everything else but I'm still it so it's not pre-emptive a new router coming up is not gonna boot the existing dr out of his role it's keys gonna keep it but they both put it at the same time and we installed OSPF pretty much at the same time the one with the highest priority on the interface wins and if that's the same the one with the highest route ready so router four out of all of our floor routers has the highest router ID that's white one okay curious minds want to know so let's next check and verify our neighbor ships so we'll do a show IP ospf neighbor won't you please won't you be my neighbor and i like doing these two commands in this order because this command right here show IP ospf interface brief is all about me says the router r4 so i on these interfaces i'm the dr i'm the dr i'm the dr and we need to show IP ospf neighbor it's about them the other device so this output show IP ospf neighbor is saying okay I've got two neighbors let's pick 3 3 3 3 which is the router idea of r3 because that's his loopback that he used for the router ID and my state with that guy is full meaning that's a full of Jason see think of a full adjacency as you share everything so if my link-state database is this is all these LS days from all over the place I in that area I'm gonna share everything with them and ask for updates and communicate with them that's a full of Jason see that's what that means all right and then this second part here means that that device is the BDR the backup designated router in case the primary doesn't need a router goes away sometime and there is the interface that we learned about him on okay so let's uh let's do some testing I'm game I think we've configured OSPF let's go ahead and do some testing from let's go to PC one oh we didn't do brows I want to verify brows I take it back so like take a look at the routing table so show IP route the whole reason for this is the routes show IP route and we'll limit it just to OSPF these are the OSPF learned routes so our four knows how to get to 1001 1002 1003 1000 13 and he's directly connected to 34 and 24 and that's why they're not showing up as OSPF learned routes ok so that looks good so let's go ahead and test a ping let's go to PC 1 which is a little virtual machine and let's do a ping from this address which is 1001 10 and let's ping over to 1004 10 which is PC for down here so the network space is I get my pin up here there we go so here's the network space PC one is on 1001 PC 4 is on 1004 if you need any assistance with networking and subnetting please join me for subnet saturdays where that is the complete focus and we'll bring you right up speed on all that ok so let's go to PC one and we'll make that test so I have a tab here for PC one and here's his IP address and let's do a trace so on Windows it would be the command we trace our T TR AC er T on Linux boxes would be traceroute yeah and so we're also on a Cisco IOS router should be traceroute so here on this PC it's trace and let's go to ten dot 0 dot 4 dot 10 that's the pc IP address of pc 4 and i'm gonna do a - p space 1 now Keith why are you doing a - capital P space 1 by default on Linux and UNIX and a lot of same thing on Linux platforms and on Cisco routers when they do a traceroute command to trace the path the packet takes to the network here's how it works they send the first packet out with a TTL at time to live of 1 the first router sees it's a time to live expired because every time a packet layer 3 packet goes over a router it decrements the TTL the time to live field and so if you send out a packet with a TTL of one the first router kills it sends a message back saying I killed your packet and you're saying that's what I wanted and so a traceroute we can send a few packets with the TTL of one and then a few more with the TTL of 2 which makes it past the first router into the second router and that's how we're tricking the network sorry about that that's how we're tricking the network to give us information on the path that the pack is taking through the network this is the trick so with Linux and with Cisco IOS it uses UDP at the transport layer and with Windows with trace RT it uses ICMP so the benefit using ICMP is that it just looks like a ping request to the destination device instead of some kind of looking for an unknown port that it's not listening on so one other thing here is I'm just trying trace in this virtual machine which is just a proprietary to this virtualized environment that I want to use protocol number one and protocol number one is ICMP just what's happening here so we'll go ahead and do a trace and do to the magic of having numbers that are all lined up the first hop let's take a look real quick the first top says PC one was my default gateway 1001 1 which is router ones address because the last octet matches the router number no accident there then the next hop is router 3 and then the next hop is router 4 and then it went finally to PC 4 so 1 3 4 10 yeah I see that and I'll say I also don't like it let me share with you I don't like that very much let's go back to our topology this says that our path and I'll use a different color here I'll use green for the path it went like this one three four and then find this this PC so use this path now this link right here and I'll put this in black this is fast ethernet and all the other interfaces in the network for the routers they're all gigs he'll gig here gig here gig here gig here and so if we look at the costs the default cost on a gigabit interface for oh I know it happened yeah that's the problem I talked about earlier so unfortunately because the auto cost reference bandwidth is set to a hundred megabits per second basically it means that the fast ethernet looks like a cost of 1 and the Gigabit Ethernet also looks like a cost of 1 and so oh s PF as brilliant as it is with the default configuration in the cisco environment thinks that the cost to go to this network right here to the 10.0 for network is and I'll put these in kind of a pink color here the cost the exit cost here was 1 and the exit cost here is 1 and the exit cost here is 1 so it's 3 and it sees this top path that's an exit cost here of one exit cost here one and wouldn't this be an exit cost here one also mmm very curious now why that shows that path and not the other let's take a look let's go ask it part of the Trojan is okay so if the fast ethernet is being treated like gigabit still why did it use this path let's go to r1 and let's ask it about the route to 1004 and just take a look at what its decision points are in getting there and then we'll fix the auto cost reference bandwidth to make the fastethernet looked like a cost of 10 and make the gigabit look like a cost of 1 so let me go ahead and clear that off and let's go take a look at our one alright I am actually very curious I wasn't expecting him to use that I mean I can see why you might use that path but why did he show IP route OSPF here are OSPF learned routes 1004 he has one path he has one path are to 1004 okay so okay time to uh time to get in the mind of Keith ah there should be two routes there there should be two routes because if if router one it was saw the cost going through the bottom path of it as a cost of three which it does by the way it's right here this is the number I'm looking out here this equates to the egress interface costs as it goes out of our one out of our three out of our four so the cost is three but my question is why didn't it also see an equal cost route going through the upper path and that upper path is right here so I would expect that the cost going this way I'll use a different color excuse me for a moment let's go ahead and use about that color I would expect the cost going this way to be a cost of three and until we fix the fastethernet mistake there that also cost us three let's just count them up real quick so from our ones perspective a cost of one two and three yeah and this path B cost of one two and three oh yeah yeah so it we should have two because that's what OSPF does and many of the routing protocols too if there's two equal cost paths where the metric is the same for the same exact network there should be two paths but there isn't so uh let's do this for him so now Keith is going keep talking to the third person um let's solve one problem at a time well as first of all solve the problem we're OSPF believes that every interface gig and fast ethernet is Atlantic cost is a cost of one let's fix that first so let's take a peek at our four and this link right here on the bottom this is actually Fast Ethernet and everything else is gigabit so let's take a look at our four and verify that then we'll fix it so I promised a little trouble shooting today you got it so go to our four and on our four with this show IP ospf interface brief yeah sure enough so the fast ethernet has a cost of 1 and the gigabit has a cost of 1 and that is because of this factor right here show IP ospf and a space bar it's because of this bad boy right there the reference bandwidth is 100 so anything faster than 100 megabits per second is also gonna have a cost of 1 that includes 10 gig 40 gig etc so to solve that what we're gonna do is get out notepad again and go into configuration mode now let's do it on one and then I'll copy it on the others we're gonna go into configuration mode and go into router configuration for OSPF same process ID and specify auto cost auto - cost reference bandwidth and then put a bigger value as a reference than the hundred megabits per second so it's done in megabits per second let's go for instead of 100 I'm gonna add one more zero and make it a thousand press ENTER and now saying hey please make sure you do this consistently across all your other devices so I'm going to go ahead and copy that and go to notepad config T router OSPF 1 paste and and then I'll do a show IP ospf interface brief they'll save me that typing all right so it's gonna do that for all the rest copy and this guy is already done for is done so go to one auto cross-reference bandwidth boom r2 auto cost reference being with three auto cost reference bandwidth and although I did it on four already Oh check it out so on our three look at that it has a fast interface announced these as a cost of 10 perfect we've now solved the problem now now what I would expect is that if we went back to our topology that this path here going a path B this is path B I would expect a path B would be a cost of 1 and this is now fastethernet so this can be a cost of 10 and out here oh that's gigabits that'll be a custom one so the cost should be 10 11 should be 12 well the cost of the high road here should be a cost of one here one here and one there which would be a cost of 3 so OSPF when it sees those two paths should choose path a every time and path B should not even make it to the routing table because it's not an equal cost paths so let's go check and let's go see what happened so we fixed the auto cross reference bandwidth challenge let's go back to our lab let's go back to our PC one let's hit the up arrow key and do that same ping okay and we had a timeout on the fourth one I'm gonna do that again hit the up arrow key alright so we have the same path 1 3 4 10 I got to be careful we asked for as I said I said there would be some troubleshooting okay so so PC wants so r1 is not using this top path at all to get over there and so to troubleshoot this what I would do first is I would say let's troubleshoot the neighbor ships let's start it our for and make sure that our 4 is the neighbor with our 2 and then we go to our to make sure our choose the neighbor with our 1 because if any of those are misconfigured or if there's a broken link that would explain why this path isn't being used so let's go to our 4 and check them out so here we are on router for show IP ospf neighbors so our 4 going up to r2 is fully adjacent meaning we're sharing everything and that r2 is a backup designated router which means we're the designated router so there's no problem there let's go to our three I think about look at my topology let's go to r2 and verify the neighbor ship beat on r2 and r1 alrighty so our to make sure I'm on the right device so IP ospf interface brief so I've got OSPF on all three interfaces and it's gig to zero that goes over to to the router so we can do a show CDP neighbors just to verify you know basically so my local interface gig to zero oh it's going to this pitch you know some days it just gets like that so the challenge here is just an identify basic connectivity is that because r2 is connected to a switch as far as CDP is concerned and it's a Cisco switch it's gonna just tell us about that connectivity to the switch it doesn't give us connectivity directly over to r1 because that's not our directly connected neighbor from a physical perspective it's a switch so we can still solve this so we are connected to port I'm gonna document this as we go so from our two's perspective on our local gig to zero we are connected to the switch on its port gig to zero so let me go and update my documentation here let me add a layer documentation is there can be our best friend so on the switch this is port 2/0 and let's also verify that r1 is connected also to the switch that'd be a good test so we'll go over to r1 and a show IP STP neighbor yeah okay so on router one its local gig 1/0 is connected to the switch on gig 1/0 so let's document that as well oh that was easy okay so it's one zero on the router ones here on the switch on router 2 is 2 0 & 2 0 sounds like somebody was thinking ahead there as far as training purposes and let's do a show IP ospf interface brief make sure that we have on gig 1/0 OSPF running and over on r2 if we do a show IP ospf interface brief make sure we have OSPF running there which we do all this they both think they're DRS on we have no neighbors oh yeah there we go so r1 and r2 both believe though the does V and router and they don't see each other so if we do a show CDP neighbors sorry as CDP on the brain we do a show IP ospf neighbors we have a neighbor ship to r4 but we do not have a neighbor ship with r1 and if we get r1 and do I show IP ospf IP ospf neighbors yeah r1 is the neighbor with r3 but it's not a neighbor with R - all right so we have a we have a problem houston we have a problem so let's yeah they can't see each other so the network Ethernet broadcast from OSPF perspective so there can be saying multicasts and they should be able to see each other's multicast let's try a ping from R 1 to R 2 and if that doesn't work we'll continue the troubleshooting so here on r1 the IP address of our two it is 10 0.12 - okay all right I'm doing a control shift 6 just came Fela anyway who's gonna stop the pink um no connectivity so let's let's go check the switch so on this switch these two ports 1 0 and 2 0 should be in the same VLAN if we want R 1 and R 2 to form an adjacency with each other they have to be on the same network segment from a layer 2 perspective as well as a layer 3 perspective for the OSPF part let's go check out the switch so on the switch we will go to the core switch and oh well spending trees running that's handy let's do a show VLAN brief and there's your problem right there so gig 1 slash 0 which goes to R 1 is in VLAN 10 and gig to slash 0 which goes to switch to our router 2 is in VLAN 20 so we could either move them both to VLAN 1 or we can simply move one of those ports to VLAN 10 or via just put in the same VLAN is the answer to that let's go ahead and take VLAN port gig to 0 and put it into VLAN 10 and that way they can be in the same VLAN so configuration mode interface gig 2/0 switch port mode it's already an access port switch port access you Leon 10 verify our work for the show VLAN brief ok they're both there and that's to show spanning tree for VLAN 10 just to make sure they're both forwarding all right so this edge means we have portfast enabled otherwise it may take 30 seconds or something close to that for the forwarding to happen so now that we have layer 2 connectivity for router 1 and router 2 through the switch let's go ahead and verify that we have connectivity so we'll go back to the lab go back to our one and okay that's a very that's that's a very good sign so they found each other now that they can see each others clothes they then went through the steps of becoming fully adjacent which involved them sharing and making sure they have the latest and greatest updated copies of their databases of their links days and if we did a show IP LSPs interface brief oh look at this so router one I gave 1/0 is the BDR and because they just came together you can't have two DRS and router two had either a better priority on the interface or or it simply had the higher router ID which would be the tiebreaker all right so now now if we go back to this client PC one and we do a trace to ten zero dot 4 dot ten this this is PC one just get right here going to PC for the cost through this top path should be a cost of three and the path the cost of the bottom path which is so high it's not even in the routing table won't be used and won't even be in the routing table fact that we can verify that on our on our one if we do a show IP route and let's go ahead and put in 10.0 dot 4 dot zero this is basically saying the details for that route is that the egress interface last update from ten to twelve dot zero up to that the what am I looking at oh my brain it's been a very very long day let me take a look at the relative to IP route OS yeah 10.0 not for what oh I'm kiddie was going out the top interface I was like why is it going on the top interface why does it go at the top interface that's because that's where the route is the best and that's why when we're looking at the details for the route here and it was showing that the egress interface was gonna be a gig 1/0 I was like what what that's how it should be that's the better path also if you notice that the route with the next top of there out for 10.04 with the next top of our three doesn't he doesn't exist it did not make it into the routing table because the routing table only likes winners it's the best route and if it's not the best route and doesn't make it into the routing table and as a result that's why we see the winner here alright so I think I think we I think we did it I think that's everything let's go ahead and just RFI from our ones perspective that we can do some things so if we do leave some traces from here to so if we do a trace and let's go ahead and do a trace [Music] see here 10 0.4 dot 10 space and we can use the source option here now let me tell you what the benefit is of the source option the benefit of using a source is that we can mimic what we like coming from the PC so when our one pings this IP address or traces to it it's going to use by default as a starting point the interface closest to that based on its routing table if we say source it from 0 0 or from the IP address here on this interface we then have a more accurate picture of what that traffic flow would be like if it's coming in from a PC so that's why I mean this would be out of the source option there so let's go back to the interface and will say source and we'll say a lot of options Villegas zero zero is what I want we could also plug in an IP address so there's our trace and I'll do that one more time there we go so the first hop was our two and then our four and then the client at ten wonderful all right so our objective let me go back and make sure I look at our objectives here our objectives were I had a lot of fun by the way thanks for going through that with me objectives were to plan configure and verify OSPF and do troubleshooting along the way so the challenges that we faced were that the auto cost reference bandwidth was by default 100 megabits per second so gigabit links didn't look any better than fast ethernet until we went across the whole board and router config and told himself we had a problem with r1 and r2 being able to see each other they were in the same VLAN so they can form a neighbor ship but once we did they were great other things that could cause problems would be if there's a a mask difference like one side believes is the 25 bit mask and the other side leaves the 24 bit mask they're not gonna work if the authentication doesn't match they're not gonna work is the timers don't match it's not gonna Burtt work if one side believes there should be a designated router and the other side believes there should be no designated router like network or non broadcast type versus a point-to-point they won't become neighbors so those all have to agree so I want to thank you all for joining me for this OSPF configure and verify session also I had an idea I like to run by you and I think it's gonna be great and I like some ideas on a name for it I'm building out the CCNA playlist every week we have two or three new videos or live streams that go into it I hope you're enjoying that tell your friends subscribe hit the alert Bell have a party be here with us enjoy study and grow um eventually there's gonna be so I do sundaes CCNA Sunday subnet Saturday and also last year on Wednesday which we are right here so at some point the subnetting Sunday or the Wednesdays are gonna become I'm gonna have a full library in the playlist so you can enjoy the full thing so here's I was thinking I was thinking of taking the topics from the live streams so you go to the master playlist and go like dynamic carp inspection or layer two trunking or router on stick or inter VLAN routing with the multi-layer switch or OSPF or whatever it is and those various topics and taking each one of those and then having a challenge that somebody meant the reason I got this idea was somebody mentioned a channel a YouTube channel where you just watch old people try to do stuff like me um and that's literally where I got the idea I was like oh yeah let me do this I would love to your ideas on this is getting a topic from something we've done in a live stream where I've elaborated on it and gone through it and uses a challenge for maybe call it packet tracer panic or the rushed networker or slip and what we do is based on the topic that you would give me I would go ahead and do a live stream of like 15 minutes and ten of that would be my time limit to design and implement and verify the solution or the technology that is recommended by you and it'd all be CCNA level stuff stuff that I've done in the live streams so I think it would be a hoot because not only say it let's pick let's say we just did OSPF that's on my brain let's do spanning tree or something like that or pour fast or or port security so give me a topic and then basically from nothing like with packet tracer building the whole topology you know thinking about it for a few moments and then in ten minutes building the whole topology implementing it and verifying it and then hit the stop button like a 10-minute limit I think it'd be great because that way it could be like a series that we could all check in together meet a lot of fun get your recommendations you could grade me at the end like okay the scale of one to ten how do you do like oh total fail couldn't get dynamic inspection working or whatever it is but the the time would be the critical thing because that's so fun to set a timer I could put the timer on the screen as well and just go ahead so take the topic that's been recommended set it up logically tell you what I'm gonna do and then from from nothing just take packet tracer drop in the devices dropping the configs configure it and I would just talk through it doesn't doing it and that would help reinforce it so that way people are you know when they've been studying various topics like routing or switching or whatever it might be it'd be nice concise 10 to 15-minute way to do a refresher on it from soup to dessert and everybody watching could do it themselves you say Oh Keith topics today so so and just as you watch the live stream get out packet tracer and oh I know you could oh yeah so that's my that's my thoughts um if if you think that's something that is worth pursuing I'm excited about it I need two pieces of help though if you'd help me one is I need a name I thought you know the packet tracer pendemonium or something like that so that implies hey this is a ten minute window for a keith to build and configure and verify some technology he's covered in one of the streams the second thing I would need is a topic and so if you would I'm not in the livestream topics because sometimes those aren't available after the fact depends on what button I click but if you could once this video is live or if you're watching later the recording that is if you could chat in a recommendation or two on the technology something we've done the livestream you just go to my master playlist look at the playlist say oh this topic yeah and so well this is all let's pick one and as I start that series I'll do it weekly I'll pick one and then I can go ahead and just demo and have a lot of fun I think I'd be a good reinforcement for those topics for every who's watching also be a lot of fun because I will not be able to get it all done in ten minutes every time and but I will try my darndest to do it and then we can see how I succeed or fail under pressure which is it's fun to see alright so that's it for this livestream on configuring verifying planning configure configuring and verifying OSPF I've enjoyed haven't yet the next livestream is coming up in just a couple days that would be subnet Saturdays that's going to a playlist followed by a CCNA Sunday and then we'll come back to this Wednesday as soon as I get those recommendations I would I would love to start that for that the pushy packet or whatever I call it also if you come up with a title for this series and I use it I would be happy to send you an original gangster white t-shirt a themed shirt like mister sloth is yeah that he's wearing um just let me know your size so again your recommendations on the name and the topics would be great and the person who picks a name that that I ended up using for that series you've got it all right thanks everybody they find some exit music here it is and I'll see you in the next dream don't forget to subscribe like and study art bye everybody [Music] life is a winding road no telling where it goes driving through days and my own stuff a traffic light [Music] you can say oh that's my mine I will keep on holding my head high even the skies falling down [Music] jumping from Cliffs or high trust in a leads to fight sometimes of crashing down but we get up and stuff from the ground [Music] even if further down I will keep on switching from my house you can say oh that's more mine I will keep on holding my head high even if the sky is falling [Music] even skies [Music]

Channel: Keith Barker

Views: 21,951

Rating: 4.9807692 out of 5

Keywords: ccna, ccna 200-301, ccna certification, ccna study, ccna training, cisco, cisco ccna, cisco certifications, cisco training, ccnp, ospf network statement, cisco wildcard mask explained, cisco wildcard mask, wildcard cisco, Cisco wildcard, wildcard, ospf configuration, ospf routing protocol tutorial

Id: IQj1eIxy9CQ

Length: 68min 35sec (4115 seconds)

Published: Wed Jan 29 2020