OSPF LSA Types for IPv4

one of the requests I had was to go the common LSA types used with OSPF and I commented back I said okay I promise the very next video I publish up on YouTube I will cover the common LSA types so here's our beautiful little network right here and it's got seven routers I've got router one router to router three and then across the bottom going left to right four five six and seven now something you need to know about each of these routers is that each router has a loopback interface now loopback interface is assigned an IP address or can be and I gave each router an IP address for its loopback that matches the router number so on our one it would be one 1.1.1 on our to be 2 2 a 2 a 2 and so forth and I made that a slash 32 so there's no room for extra host addresses on those logical networks but we really don't need to it's just a loopback interface secondly I want to point out a couple pieces for this network that are important we've got each router has an interface that goes off into cyberspace so on the bottom for the network goes southbound and I've got the 172 16 for Network here the 172 16 5 and then over on the right-hand side I've got 2 192 168 6 matching the router number and 182 168 7 again that third octet matching the router number so the common links going between r1 and r2 I call 10 0 12 between 1 and 2 10 0 13 between 1 & 3 & 10 0 23 between r2 and r3 see how that works the third octet gives it away as far as where that network lives in the topology the green circled area includes all the interfaces that belong to area 0 see in OSPF a router doesn't literally belong to an area you can be in you're only in my area really it's the interfaces that are participating in areas and the IP addresses on those interfaces so in this network r1 all of its interfaces are in air zero it has four it's got three that we can see gig 1 0 2 0 + 3 0 + it's got the loopback interface which is also participating in OSPF r2 has 4 interfaces in OSPF area 0 it's got this guy here gig 1 0 gig for zero gig 5-0 it also has this loopback in area 0 + r3 is treated similarly if we go down to here - aerial 1 hour 2 has two interfaces in area 1 and it our 4 has 3 interfaces in area 1 1 loopback and the two physical and our 5 has 3 as well over on the right hand side in red we have OSPF area 2 our 6 has 2 physical interfaces 1 loopback interface inside of OSPF and our 7 check this out it's got its loop back in OSPF it's got gigabit - / 0 in OSPF area - but this interface gig 1 slash 0 it's an e IG RP it's not running in OSPF at all this interface isn't but what we've done is we've redistributed this routing protocol II IG RP the directly connected interface and anything else that we may have learned through EIGRP we've redistributed those into OSPF that's that little cool arrow going into the red zone there so that's our network to start with and i've created all of this so i could demonstrate the 5 most common type of LSAs and what they do for a living so let's start on our one on our one if we want to do a show is the fun part IP route it's going to show us the entire routing table and there's a bunch of routes I'm gonna scroll up a little bit so there's a boatload of routes but they're all right here and so our one knows about every single route now they're not OS all OSPF routes it knows some of them because it's directly connected so it's directly connected to the loopback and these three interfaces but everything else outside of those directly connected networks those are all OSPF learned and routers in the backbone they're lucky they get to know everything and let's take a look at how our one came to know about all of these networks and that'll discuss will discuss the LSA types as we do it to see the database the links database information show IP ospf database just like that so there's the command highlighted and we're going to start off by taking a look at LSA type ones so LSA type ones beginning right here our router LSAs see a router and OSPF is so happy about being a link state route and it's going to advertise about what it's directly connected links are so router one is going to tell everybody hey guess what everybody I have four directly connected networks that are running OSPF in this area I've got the gig one zero two zero three zero and my loopback interface which are all participating in LSP F to take a quick peek of that we can do a show IP ospf interface brief and sure enough there's the four interfaces and they're all participating in OSPF so we look back at the show IP ospf database r1 this LSA from our r1 is saying hey I've got four links that are connected and if we want to see more details on those we could do it which do a show IP ospf database and ask for the router LSAs which is the equivalent to the LSA type ones and then put in the router ID for the router you want them from and here's the command the very top and it's going to give us the details on the four networks that router one is connected to so a router LSA the LSA type one isn't just who oume road or it's hey I'm a router and here's my current networks that I am directly connected to it's like the foundation building blocks for link state routing protocols so we went through the list it would have all four interfaces so we have the loopback interface here it's calling it a stub network because there's no other OSPF router that he has an adjacency with on that loopback that makes sense then we have the network of 10.0 13.1 this guy right here and he's saying that the designated router for that segment is dot three so he didn't win the election if these were all powered up at the same time it would be because router 3 has a higher router ID than router 1 and if they both came up at the same time that would be a logical reason why router 3 would win it so that's one of us now works he's got the twelve dot 10.0 about 12.1 network that's here and he's also saying I'm not the dr for that so there's two OSPF speakers on the network I'm not the dr I'm probably the backup dr but not the dr itself and then I've got this network here as well 1001 goes northbound it's an active up interface but it's not considered a quote-unquote transit area because there's no other OSPF speaker out there from an OSPF perspective is the end of the world it's a stub and so we're not going to be you know we are a dr on that segment but we're not going to see a whole bunch of dr advertisements because there's no one else out there and our one knows it so that's the art the router lsas the from our ones perspective and if we went to any router let's go to our three for example we'd see this exact same information so our three to show IP ospf database router specific meaning the LSA type ones for one dot one dot one dot one it's the same information because everybody's sharing the same link state database he says okay here's everything I know about r1 he's got this stub network for his loopback interface yes we know he's got a connection to the thirteen network but he's not the dr our threes which were on our three snickering saying it's me I'm the DRC I got a little it's like a shout out in a in a book so he gives you a shout of hey and I want to say hello to anyway and this is also saying that router one has a connection ten zero twelve network using ten zero twelve one the dr is ten zero 12 - which is our - and then last but not least if we go down a little further he's also knows about ten zero one zero see the thing is a link state database everybody's got copies of these so this is an example of the LS 8 type ones specifically for our one and we can look at the ones for our - and our three for this area and they'd be the same now here's a secret about LSA type ones what happens in Vegas stays in Vegas that's also true for these ll sites so these LS A's are flooded everywhere in this area but the LSA type ones are not going to make it down into PFF area one or area 2 they don't have to worry about or know the details of each of those individual routers that are outside their area so our fours not going to ever see the LLC's for our one just isn't we can go take a road trip say dear mister are for show IP ospf database do you know any of the LSA type ones for our one he's gonna say nope all I know is our two because our two is part of my area area one and I know about our fours that's me and I know about our 5s and that's it so LSA type ones what happens in the net in the area stays in the area for LSA type ones okay let's move on to the next one let's go back up to our one as a constant frame of reference here for our network and we'll do a show IP ospf database the next type is the network lsas an LSA type two and what that is that's the designated routers advertising on behalf of a network they're connected like a broadcast network or a non broadcast multi access network where they happen to be the dr so from our ones perspective he's saying oh there's a link ID of 10.0 12.2 and what that really is that's the IP address of the interface of the dr on the segment where that dr lives so 10 0 12 2 is this guy right here 10 0 12 2 is our two's IP address the last octet always matches the router number in my topology here so what this is saying is that our 2 for this segment is the dr and he is going to be sending out the clearinghouse messages if you will for that segment if we looked at the details for that let's do it let's look at the details for that LS 8 type 2 because every router in OSPF area is 0 is going to have that information we'll do a show IP ospf database and with the question mark and i want to see network this guy right there so I'll put in network and then I can also specify this specific one so the network if we want to take a look at this one I'm going to copy and paste it in I want 10 0 12 2 so the link link state ID for the network lsas is the interface IP of the dr which happens we are - so I'm going to say that I want to do it based on that so this is the command I just put in and this is just showing us the details for the LSA type - that's being generated by the dr for that segment so he says this okay here we go the link state ID is 10 0 12 - which means it's the IP address of the dr on that segment and the advertising router is art - that's art Tuesday router ID it's me says r2 and then the attached devices to this network segment are these two routers right here and if there's 15 routers they would all be in the list so that's an LS 8 type 2 is simply describing a broadcast network where the dr exists and the link state ID for that is the IP address of the dr on that segment so that's they all say type - that's the dr clearinghouse for the segment okay so let's move on to ll say type 3 what is that all about let's go back to our our standard basic starting point and that is the show IP ospf database command on r1 and i'm going to go up just a little bit and these summary network link states those are all representing LS a type threes now what is that all about well a network summary is only done well there's all there's all kinds of summaries right there's like I'm going to summarize the 172 16 and the 172 17 and 172 18 into one address that's a good example of a summary but as far as LS he types go whenever you see the word network summary I want you to think an ABR did that an area border router generated that information what do you mean Keith well here on this network segment we've got in this topology we have two ABR's are - because he's a area border router between the backbone and area one he's an ABR r3 is also an ABR between the backbone and area - so who generates these LSA type threes is the ABR's so here's what our two does for a living he says I'm going to take all the networks because our and r6 they don't see the LSA type ones for these guys so r2 says I'm going to take all the information for the networks that I've learned from this area and I'm going to pop them over onto the other area and they call it a network summary so if there is 42 networks over here we'd have 42 network summaries that r2 it advertised into the backbone not only would we put those 42 networks in the backbone this router here our three would take those 42 networks that he has learned from the backbone plus the backbone routes which are maybe now total 60 and he would create those as a BS summary routes Network summaries LSA type threes and put them into area 2 so eventually every single router is going to know about every single other route in the network if they're not routes inside of the area they're at their routes that they learn through a network summary courtesy of an ABR an area border router so let's take a look at them this is the LSA type threes right here we've got these four right here and these the link ID is important is the network address so for the LSA type threes the link idea the link state ID equals the network you're trying to reach I've got 32-bit networks 4 4 4 4 4 4 5 5 5 5 6 6 6 6 & 7 7 7 7 so although they look like router IDs here those are just the 32-bit routes for each of their loop X so our to saw all those routes those two routes and it's the advertising router 4 4 4 & 5 5 and it sent those into the backbone so we're looking at our one our one is saying hey I've got routes 4 4 4 4 4 & 5 5 5 5 those are LSA type threes because and only because the area border router took those routes and advertised them into the backbone so these four are the loop backs of the bottom two areas if we take a look at the additional routes these are the ones that are to has sent in our to knows about the ones going to do 16 4 5 24 and 25 that's these four networks in blue here it generated them as LS 8 type threes and them over into the backbone also if we take a look at these routes on the bottom where they come from all these routes were taken from our three took these routes pop them into the backbone and the this our two area border router pop those routes into area one so we went down to our four just as a road trip for a moment and we said that's come in for help show IP ospf OSPF database it would show us that our four knows about those networks from the far right and it knows them as LS a type threes because the routes were here they got put in the backbone area and this border router on this side of the network r2 took all those routes and put them in area one so everybody knows about all the routes and that's what a network summary is back when you see network summary I want you not to think I'm summarizing networks what's up Oba I want you to think this is an LSA type generated by an area border router to help out the people on the other side of the fence so he's helping out the backbone by telling about the routes here and he's helping out area one by telling us about the routes that we've learned via the backbone which could include other areas that were put into the backbone as well as far as the routes are concerned and last but not least let's take a look at LSA type five and then I'll get to LSA type 4 an LSA type 5 is an LSA type 4 a rat network that has been injected into OSPF it wasn't put there with a network statement native to OSPF but it was redistributed most likely from another routing protocol into OSPF so let's go take a look at our six if we get our six and we do a show IP ospf database it knows about the LSA type ones in its area the LSA type twos from the DRS in its area it knows about the LSA type threes from the area border router thank you very much and you see from our sixes perspective the only person who's feeding them LSA type threes is our three so from our sixes perspective everything has been advertised by the area border router which is if you look at the topology that's the only way we're going to get to all those routes networks outside of our local area and then finally down here we have an LSA type 5 now this LSA type 5 is an external link state meaning it's a it's a route to network a prefix that we can reach but it's not native to OSPF so r7 redistributed that route into OSPF and the link ID this is important the link ID just like in a network summary the link ID is the actual network that you're trying to reach so if this is the 192 168 7 Network the link ID is going to show up as 192 168 7 tada that's the link ID now how do we get there our success what if I need to find out how to get to that network well obviously if you look at the topology the only way we're going to get to this network segment is through our 7 so inside this area it says oh the advertising router is 7 7 7 7 and r6 says oh that's not a problem because we scroll up a little bit I happen to know all the details about 7 7 7 what interfaces it's connected to what networks it's connected to and I can get there no problem because I know 7 7 7 he's the default gateway where the the path if you will to this external route and that's the LSA type 5 so inside the area here there is no LSA type 4 we have LSA type 1 each of the routers I'll say type 2 the designated routers LSA type threes generated by the area border router and we have the LSA type 5 referring to an external route through a router that's in our area so what is the deal with 4 by the way r7 would be called an autonomous system boundary router because it's linking together OSPF and some non OSPF domains such as grip or EIGRP or is is or something else so what is the deal with this links the LSA type 4 why do we need it well here's the rub let's go back to our one good ol mr. r1 if we look at the bottom we have this information that says hey guess what if you want to get to 180 once today at 7:00 the advertising router is 77077 now the LS 8 type ones for seven seven seven seven for this router never make it out of the area so r1 has no clue on anything about seven seven seven seven that router it doesn't know what networks it's connected to or how to reach it and so the area border router r3 in this case it also adds itself if you will as the advertising router and it's an LS 8 type 4 so an LS 8 type 4 is the router ID of the asbr the autonomous system boundary router and for the benefit of r1 and r2 and everybody else who ever might need to reach that network this basically says hey to get to 7 7 to find out information on how to get to 7 7 7 7 this LS a type 4 is the information on how to reach it which basically says dear mr. r1 or whoever else is looking at this to get to to get to the external network the router ID is seven seven seven seven but because you pourcel's don't know anything about that router ID and it's directly connected networks the advertising router is three three three three and check it out that router ID is in this area and these devices know how to get there so it's like connecting the dots together if we go up a little bit you'll notice we have a ll say type 1 4 3 3 3 3 which includes all the links that are 3 is participating in so the r1 can forward so that's it that's a that took a little longer than I thought it was going to but that's the 5 common types of LSAs I'd like to review them with you an LS a type 1 is just about the router itself and it's directly connected networks everybody in area 0 is going to have all the same information they'll all know about all the interfaces and all the routers that are participating in those PF area 0 the people who get to be designated routers on a segment where there's more than one OSPF speaker are going to generate LS a type twos the ID for that is going to be the interface IP address of the dr for the segment is the dr 4 so that's the LS 8 type twos it describes everybody who's to do that segment it's a wonderful thing an LSA type-3 is only generated by an area border router so the routes from area one the only way they get put into the backbone is as LSA type threes network summaries there's just the reason they call it a summary is that we're sending the network routing information but we're not giving the details behind the scenes on the individual routers in their link States so I guess in that sense it really is kind of an overview saying hey guess what world you want to reach these networks go ahead and come through me says mr. r2 and because that's the advertising router and external LSA type 5 is generated by a router that doesn't that has routes that are not native to OSPF so EIGRP redistributed in that LSA type 5 goes throughout the entire network everybody sees it life is good the problem is only these guys know about router 7 so in addition the ABR is going to add the ASPR the LSA type 4 which is gives the rest of the world a way to reach the actual asbr I've enjoyed it I've had a lot of fun I appreciate you praising paying attention and if there's other requests let me know I'll be happy to do them and I wish you the best of success with OSPF or wherever your routing takes you thanks everybody you you

Channel: Keith Barker

Views: 147,915

Rating: 4.9589744 out of 5

Keywords: Cisco, ccna, Open Shortest Path First, ccnp, ospf lsa types, OSPF, ospf routing protocol tutorial, cisco, router, networking, link state advertisement types in ospf, ospf lsa type 3, ospf lsa types cisco, ccna certification, 200-301

Id: 7LzrvCvb-Ro

Length: 23min 57sec (1437 seconds)

Published: Mon Nov 07 2011