Transcript for:
OSPF Study Areas: Stub, Totally Stub, Not-So-Stub, and Totally Not-So-Stub

hello and welcome to irony so today in this webinar we are going to be talking about OSPF study areas totally stub not so study area and totally not so study area before we stop this webinar I just want to have a quick introduction so first of all I'd like to thank you guys for attending this webinar and my name is Rohit Pardo Sonny and I am a full-time instructor wait i nee I have five CC is en route switch security voice collaboration and service provider so without wasting much time let's quickly jump in to OSPF study areas totally study areas not so study areas and totally not so study areas so what exactly we would be learning in this webinar we would be basically focusing on LSA types so again illicit type is it's kind of needed for you to know the different OSPF LSA types you really need that because if you want to understand your OSPF study areas or totally study areas you really need to have at least some background knowledge of the different types of ell essays which can come in inside the study areas or totally study areas so we would be focusing on the LSA types again it it won't be really in depth to a point where we are looking at a CCI level is just going to be introduction to the LSA types because our main focus is going to be on the study areas so we would look at illicit types and the next thing that we would look at is going to be stubby areas configuring study areas totally stubby areas the differences between stubby and totally stub then we would look at not so stubby areas and then totally not so stubby areas again this webinar is not just going to be theoretical concepts it's also going to be a lab demonstration so I would actually implement stubby areas totally stubby areas not so study areas and totally not so snobby areas and we would look at the logs the b-bugs and look at the database to see what do you actually learn or what routes are being basically learned in those areas so let's quickly start off with the different types of Alice's now as you know in Alice's there are West bf has different different types of Alice's we have many Alice's but our main focus in this webinar is going to be only on a few LS is that I'm going to touch base on so first of all what exactly is an LSA so as you know SPF uses LS DB which is the link state database and it fills this database with Alice's which is link state advertisement and instead of using LSA one packet OSA has different OSPF has different types of NS n so it's not just one LSA OSPF is not about just one LS say that I'm just gonna send one type of LSA for all different types of routes it's actually different types of Alice's that you would see in your link state database so what we would focus on is going to be Alyssa one which is called as the router LSA we would look at LS h 2 which is type 2 which is called as the network LSA and then we would look at NSA 3 which is called as the summary NSA we would focus on LS f 4 which is the ASB our summary LSA and then LSA type five which is external LSA basically the routes you learn from an ESP are and then lastly we would look at LS is 7 which is basically not so stubby area and s is again it's it's basically NSS a external LSA so these are the only LSE's that I would majorly focus on in this webinar so what exactly is NSA 1 which is router LSA now router LSA is basically it contains a of information so every router which is running OSPF would be generating LS a one LS if one is only flooded within the area it's something that cannot go outside the area so if you did have multiple area areas in your configuration let's say if you were deploying a multi area OSPF then you would see LS a one but this LS a one does not cross the border it's only within the area so each router within the area will flood type one and si within that area and so what exactly does this LS actually contain well LS a one contains prefix information so every router let's say if I have a router that has three interfaces and all those three interfaces are basically running OSPF OSPF is basically activated in that case that router is going to generate elesif one and that LSA one would contain the three prefixes that he is advertising so it's not that because I have three prefixes I am going to advertise three NS is no it's just one LSA and let's say one one single LSA which contains the list of links that is basically running OSPF so that is LSA one so it contains a list of all the prefixes that arava has it also contains the cost of each of those links so when I advertise a route to him to my neighbor so when I'm advertising LSA one as an update to my neighbor when I'm advertising that I will give you the list of all the links which is basically running OSPF at the same time I will also give you the cost of those links so LSA one also contains the cost it also contains the neighbors router ID however this actually depends on the type of network connectivity that you have between the two neighbors for example if you and me are running OSPF and and you and me are basically running OSPF and our connectivity type is a point-to-point connection which is maybe a ran link in that case when I advertise the update LSA one to you I would insert the neighbor's route ready so I would basically insert your neighbor ID in my update so neighbor ID neighbors router ID is there in the LSA one however if your connection to me if you and me were neighbors in a broadcast network type in that case the neighbors router ID information is basically lost that information is only by the dr which is basically LS it - so if there was a broadcast segment you would see LS a - otherwise you would only see NSA one you would not see LS it you so if my connection to you is a broadcast segment in that case I don't send the update to you directly I send the update to add ER and the dr gives the update to you so in that case in that kind of an environment you would see LS a - which is network LS a so so if the network type is broadcast instead of the neighbor router ID you would see the IP address of the dr so this is LS a1 so remember Allah say one is prefix information it contains the list of all the networks which I'm advertising to you including the cost including the neighbors router ID the neighbor route ready may change to the dr's IP address in case if it's a broadcast segment so this was LS a one the next one is basically LS a qu in ELISA - like I said it's only LS it - only comes in when there is a broadcast segment so when there's a dr present so it's the dr who sends the update to everyone LS it - is not prefix information it does not contain prefixes it only contains router ID information of all the routers in that broadcast segment or broadcast domain so let's say if there were three routers me you and maybe one more router we all are connected through a switch in one subnet and we all are running OSPF in that case one of the router would be elected as the er the second router would be the BDR and maybe the third router would be dr other so if the dr other wants to give an update he would give the update to the dr and the dr would give it to everyone else so the prefix information is still an sm one and i said to only contains the list of all the routers connected in that broadcast environment which is basically three routers you me and that third router so the router ID information would be basically in lsah to see the thing is that with point to point i see the neighbours router ID so i know okay this router connects to an ex router i have the neighbours router ID in that information but if it's a broadcast segment router ID information is lost and you need to you need to basically look at LS it Chu to find the router ID of the neighbour who is connected on that segment so that information is in network LS a it only contains router ID information it does not contain prefix it does not contain cost again LS it to is something which you would only find within the area it cannot go outside the area it cannot cross the border so LS f1 and Alyssa to is only contained within the area so if I am advertising to my neighbor that neighbor cannot give it outside the area so Allah say 1 & 2 would not go outside the area it's basically blocked but if you look at LS a 3 LS III was summary NSA summary LS a is a prefix information that is only generated by the ABR only the ABR can generate LS a 3 which is basically containing the list of networks which he's learned through LS a 1 so for example if you look at this diagram here I have router a who is basically advertising 1 1 1 1 to his neighbor now which LS a would he send as a prefix information to Radha be that would be LS a 1 because only LS f1 is prefix information would there be Alessa to in that area too would there be LSA to maybe yes maybe not that really depends on how the two routers a and B how they are actually connected with each other so if they are connected through a broadcast segment if my network type is a broadcast in that case yes there would be illicit - also besides LS a1 so router a would not give the LSA one update directly to rather be instead router a would give it to add ER and the dr would give it to rather be again i maybe the dr and a normal router so it's not net don't think of dr as a separate router or maybe like a router which which you've designated as a dr it's a virtual kind of system so but think of it as a separate router virtually so let's say if B was the dr a does not give it to be the router he gives it to be the dr and the dr gives it to be so so if it's a broadcast segment yes you would see LS it to also but prefix would be LS a one now when now when that update which is one one one one when that route reaches rod of B he cannot send that update you rather see as Alice a one because the rule says that LS a one update cannot go outside the border so what does Ark Radha be do what he does is he blocks LS a1 he blocks ELISA to and now he generates a new LS a which is LS a3 some reality now again this name is kind of confusing because you would think that summary LS a means summarization it has nothing to do some with summarization though with multi area you have support for summarization because with single area I really cannot do summarization so that's kind of the limitation of single area with multi area you can do summarization so if you look at this diagram LSA one let's say if all the links between all the routers were point-to-point so there's no dr there's no LS at 2 at all because all the links are point to point so Rara a would send LS a one advertisement which contains the list of prefixes which he has he sends that to rather be as soon as Radha begets that he blocks Alice a1 generates a new LSA for the prefix now see there's a desert difference in NSA one it was one single LSA which contains the list of prefixes so let's say if r1 was advertising for networks so he would send one singular let's say LSA one with which contains four links but when our route of B gets that what he does he blocks Alice a1 and now he generates a new LSA which is LSA three and he would generate one LSA three four link so there were four routes coming from Radha Wan Rara B would send four LSA three updates to area zero now as you know the rule of OSPF is that everybody within the area needs to maintain the exact same copy of the database so varis he gets that he sees that that a new update has come in for one one one one and the advertising router is router be he sees that he does not know anything about router a lara C would not know anything about lara a because radha is NSA did not reach radha see rather be was basically blocking type one and sending type three with him being the originator or the advertising router of that NSA so Radha's he gets that and everybody in area zero would see that the advertising router for one one one one is router B so if I want to get to that Network I need to reach vara be now what happens next Rolla C needs to now send that update to router D but because the border is changing the border is changing from area zero to area one Rossi will modify the LSA he would modify ELISA tree insert himself as the advertising router and then advertise LSA three again to area one so now everybody in area one they don't know anything about Rara rather be they don't know anything about that for them the advertising router is louder see so you think of the ABR like like maybe an airport you know so it's something like that let's say if I was in New York and let's see if I'm sitting at home and I need to reach maybe Las Vegas right so I need to reach there so so what's going to happen is that I I don't really need to run SPF see the whole point of multi area was to reduce the SPF calculation because if this whole thing was one single area Rara D would see the advertising router as rada a so think of Rock area one as maybe New York and I am rowdy I am sitting in my house and I need to reach Las Vegas which is maybe area 2 I need to reach there if this was one single area I would see the advertising router as router a and not rather see because in single area everybody needs to maintain the exact same copy of the database it can't change so nobody can change the the advertising router so as me is sitting in New York if I need to reach Vegas I would need to find the best path to reach Vegas the how many ways can I reach Vegas I could fly or I could take I could drive all the way there there would be thousands of ways to get to Las Vegas and that really becomes a problem from SPF perspective because it would take the convergence would be affected and it would take a lot of time for me to find the best possible path to reach Las Vegas from New York but now when I have multi areas and Rada C is changing the Ellis III to himself as the advertising router what's going to happen I'm sitting at home I need to reach Las Vegas and I don't need to find how much how much is it going to cost me to reach Las Vegas what I see is I'm sitting at home I see a big billboard maybe an advertisement from American Airlines but says hey we have a direct flight from JFK which is Rada see think of the ABR as an airport so we have a direct flight from Rada see qu Rada B which is the airport of Vegas and from there we would have a limousine waiting for you they would pick you up from the airport take you to the Las Vegas Strip maybe to MGM wherever you want to go so I don't really need to find out how much how much fuel do you think the the plane or American Airlines is going to spend to fly from New York to Las Vegas I don't need to think about that what would I do if I'm sitting at home in New York and I see a billboard of American Airlines which says okay reach Las Vegas destination MGM to reach there I I have an all-in-one inclusive cost which is the SPF of Rossi I have an all-in-one inclusive cost of maybe five let's say five dollars mommy let's keep it as $500 just to be realistic so let's say five hundred dollars so I don't need to calculate what's the cost of the flight to reach Vegas how much is he paying to over to reach MGM how much is he paying for a meal in MGM I don't really care about that the the Billboard says come to JFK from there we have a flight which goes to Vegas from there we have a limousine to take you to MGM from there we have a reservation all-inclusive dinner package for you and that is $500 so what do I do all I do is booked an uber to JFK which is rather see add the cost $500 plus my uber cost to the airport that becomes my total cost to reach that destination so multi area really helps a lot in reducing SPF because I don't need to run SPF to destination I instead I run SPF to just the ABR so if you look at this diagram LS f1 update comes in within area 2 then the ABR of area 2 which is rather be blocks that generates LS 8/3 which himself being the advertising router and everybody in areas you know would see Larabee as the advertising router when it crosses the border again rather see would would modify and put himself as the advertising router along with his SPF and then advertise to area 1 so everybody an area one knows if I need to get to Vegas I need to take an American Airlines flight from JFK which is fallacy all I do is run the SPF to the ABR and I get my best path cost so this is LS a3 which is prefix information of inter area it is represented in the routing table as oh I a the next one is LS f for LS f4 is a SBR summary LS a now again LS f4 is not prefix information it is router ID information of the SBR so the minute there is an airs we are present in your OSPF domain for example if you look at this diagram I have router a which has a rip domain somewhere though nowadays nobody uses rip but but let's say if there was maybe repo AI GRP so rada a in this diagram has rip running somewhere and he is redistributing those routes in OSPF so the minute he redistributes he becomes an e as we are and now he would start generating LSA 5 and let's say 5 is prefix information and I said 4 is not prefix information so what's going to happen is that router for order a he's sending LSF I'll order a is not sending LSA for remember LS f 4 does not come from the ASV are only an ABR can generate LS f for so LS a 5 is being generated by router a he sends that he floods that throughout the OSP of domain as soon as the ABR gets to know that ok I have received an LSA five external LSA update rod of B whose the ABR he generates LS a for summary ESB our summary LS a and floods that to area 0 and then Rossy modifies that to himself being the router ID as the advertising router and then forwards that to rudder D so if you look at this diagram I have type 1 LS a being received now why type 1 in fact I just said some time back it was type 5 so how does it actually work see what's going to happen is that the minute I give the redistribution command on router a Radha a would send his prefixes rip updates or ripped routes which go into OSPF those updates are sent as LS l 5 l SL 5 goes unchanged throughout the West PF domain I'm not really talking about Alyssa 5 but how does rather be know that Rada a is an SBR how does he know that so what happens is that the minute I do redistribution router a would basically set a bit he would turn on a bit which is basically he basically flips a bit to let the ABR know that I am an a SVR and this happens in LS a1 so the minute Rada B receives LS a1 updates normal OSPF updates not external routes normal OSPF updates he sees that in the update in the LSA one a bit is flipped which basically means that router a is an SBR that's how B knows that okay he is an SBR because his bit is flipped so when B gets to know that he generates LSA for SBR some Riel sa remember SBR some realice a is not an update it is router ID of the SBR that's why if you look at this diagram I have type 1 LSA coming from router a2 rather be I'm not talking about the prefix of rip right now what I'm talking about is the minute I do redistribution when router a is sending his OSPF routes not externally his normal OSPF routes he flips the bit just to let the ABR know that I am also an SBR that's why I brought a B generates type for a SB are some realice a which contains the router ID information of the a SBR which is rod a when it gets to see C modifies that LS f4 and puts himself as the advertising router to let area one know that there is an a as we are present in our OSPF domain so that is LS f4 and then we have LSF 5 like I discussed LSF 5 was exact prefix information prefix information learned through redistribution that comes from the asbr so LS F 5 is a prefix a quick way to actually remember this is all the odd ones or LSA is LS a 1 and s 3 and s f5 l SS 7 they are all prefix information updates elissa to is not a prefix information unless a 2 is router ID of all the routers in that broadcast segment when there's a dr present and LS f 4 is the router ID of psvr all the odd ones 1 3 5 7 they are prefix information so here I have LS l 5 this comes from the asbr and that does not change that goes unchanged throughout the OSPF domain by the asbr so yes we are advertises that throughout though SPF domain and it does not change at the border every router in every area would see router a as the advertising router for those rip routes again that really depends on if if it was multi area without maybe without not so stubby because it not so stubby something changes but let's say if there was no not so stubby configuration it was just normal multi area configuration in that case every router which is running OS PF would see router a as the advertising router for those external routes which is learned through redistribution that is type 5 and then the last one that we need to look at or focus on is going to be LS a 7 I mean there are more l essays but again we are not looking at that at this point of time in this webinar so LS s 7 only gets generated when there is a not so stubby area configuration so if you look at this diagram here area to which has an ASB R which is vara a area 2 has been configured with not so stubby as not so stubby so the minute router a redistributes from rip to OSPF normally he generates type 5 LSA which is here outs either a 1 or we to default is OE 2 but he generates type 5 LSA but if i configure area 2 as not so stubby he would not generate NSF 5 because there's a rule for not so stubby that that type 5 LSA cannot go inside not so stubby area so instead he generates type 7 LSA which is not so stubby area LSA or externally let's say for not so stubby he generous type 7 which again is prefix information for the rip routes learned through redistribution so he generates type 7 type 7 cannot go outside the area unlike type 5 which was flooded throughout the OSPF domain type 7 is only within NSS a area so as soon as radha begets a type 7 update he blocks that he blocks that and instead he generates a type 5 LSA and floods that throughout the OSPF domain so for outside areas for example area 0 or area 1 for them the asbr is not router a the asbr is Radha B now why does rather be generate type 5 a let's say he's not an ESB are he's not doing redistribution the reason he does he generates type 5 LSA because router a will will instruct rather be to to generate a type 5 so this is done with the P bit so the router a actually sets a pbut which you can actually see in the database if you actually look at the database you would see that router a is is is setting the payment which basically means that translate the LSA seven to LSF five because not so stubby area LSA cannot go outside the area if I cannot advertise that outside the area how would other areas know about that update so that's why the robber a which is the SBR which is the true a SBR he sets the pbut which tells Rada be that translate LSS seven to LSF five and then send update through OSPF domain so this was LSA seven so now that we know about the Ellison's let's now go and look at the stubby area totally stubby area not so stubby area and also totally not so stubby area so the first thing that we will look at is going to be stubby areas now the first thing that comes to our mind is everything is working fine I have multi area configured why do I need to configure stubby areas what's the need for configuring stubby areas see the thing is that think about from perspective of why do we do multi areas because but single area I cannot do summarization number one and the number of LSAs would really drastically increase and there would be too much SPF calculation as your topology increases so we configure multi area now what if I had some routers which were lower end routers maybe does not have enough CPU or enough memory so it cannot handle one thousand routes so I want to reduce the routing table imagine if I had 50 routes from external BGP being redistributed into OSPF maybe I had 50 more of rip routes being redistributed in OSPF maybe I had hundred more routes of Eid RP being reduced to buted in OSPF in that case there would be 200 external routes going throughout the OSPF domain which basically means that my routers need to process all those updates so if i have lower end routers maybe the cpu is is not that that big or strong maybe the memory is low well maybe the router is running at 90% utilization so the CPU is always at 90% because it has to process so much updates so what I could do is I could configure an area as stubb the minute I do that the minute I configure an area a stub that area would not receive type 5 LSA and would not receive type 4 NSA so there are limitations of stubby areas there are rules for stubby area the first rule is that you cannot configure area 0 a stubby area you cannot do that you cannot have a virtual link going through a stubby area and you cannot have an SBR present in the stubby area so based on these three rules area two cannot be configured a stubby area why is that because I do have any SBR in that area which is var a so I cannot configure area to a stubby area area 0 cannot be configured a stubby area the only area we can configure as for this diagram is area 1 area 1 I can configure a stubby areas let's say we did that the command to configure stubby areas is just a single command area the area ID and then stop however the stop flag must match for you to establish OSPF adjacency so if you could figure one router a stubby area but stubby area in an area you have to configure all the routers in that area as stubby otherwise you would not establish OSPF adjacency you would not establish so so if you look at this diagram here I have I have Radha a which is basically redistributed the routes from from rip to OSPF goes to be unchanged because ELISA type five B sends to see unchanged once C gets it C will block LSA five and C will not generate LSA four instead C would send a default route to area one because if he does not do that then rather D would not have any reach ability to that external route because how was D getting how was D reaching that external route because earlier he was getting external routes in his database and in his wearing devil but now what's going to happen is that C which is the ABR as soon as he gets LS a five he blocks that he does not generate LS a for he does not send LS f for in area one instead he sends a default route to that area which is a type three default route so that those routers can still reach the external network this is stubby area so in stubby area only type five and type four is blocked that's the only thing which is blocked the next thing that we have is totally stubby area totally stubby area is pretty similar to stubby areas the rules are still the same that you cannot configure area zero a stubby area or you cannot configure an area that has an es BR and you cannot have a virtual link so the only area that I can configure as totally stub is going to be area one again stop flag must match so if you configure stub on one browser you have to do that on all the router so when you configure totally stub you are basically telling the ABR to not send type three LSA also by default with stub it blocks type five and four but when you configure totally stub it blocks LSA three also which means in Terraria LSS also gets blocked so let's say our type five NSA was coming from a SBR and type three LSA was coming from Rada B which is the ABR rather see as for the diagram would basically block five four and three and instead he would send one default route which would be a type three default route some really say so only one type three is allowed in the totally stubby area so he has to use the default route to go to inter area or even to get to to external network that is totally stub where your routing table drastically reduces which means the only LS is that you would have in your database would be LS a1 intra area prefixes elicit 2dr information and one type 3 NS a which is the default route this is totally stub now to configure totally stub the command would be area one stub know summary now this command can only be done or it should only be done on the ABR because only the ABR generates LS a three on the other routers you would just give the command area one stub but on the ABR you would say area one stop know summary which basically tells the ABR that besides blocking five and four don't send summary LSA which means five four and three basically gets blocked in two totally stubby area the next one that we will look at is going to be not so stubby area now not so stubby area is pretty similar to stubby area with one limitation relaxed which is you can have an SBR in the not so stubby area so the other limitations like you cannot have a virtual link that still exists so when you configure an area as not so stubby you cannot have a virtual link going through it and you cannot configure area zero as not so stubby you can have any SPR so if you look at this diagram I have area one which is configured as not so stubby now even though area one has an asbr I have router D which has TIG RP connected and EIGRP is being redistributed in my OSPF so rod OD becomes the asbr but because this area is configured as not so stubby the router D would not generate type v LSA let me in fact tell you what's happened now if you look at this diagram carefully I have two asbr one a SBR is an area to outside the NSS area it's an area to which is Rada a and 1/8 a SBR is router D which is inside the NSS area let's talk about the routes coming from outside which means routes being redistributed on router a how would those routes be seen in the not so stuffy area so router a would when he redistributes he would send LSA 5 LS f 5 goes throughout the OSPF domain once it reaches router c rather see would block LS f 5 and would not generate LS f 4 towards area 1 so ellisa 5 and 4 basically gets blocked going into area 1 so would router D be able to reach the route of our of router a no you know why that's the main difference between stub and not so stubby in stub the ABR block 5 and 4 but Center default route as type 3 in not so stubby the ABR blocks 5 & 4 coming into the area but does not generate a default route as type 3 it does not do that for you to tell the ABR to generate a default route you have to give an additional command which is area 1 NSS a default information originated when you give that command the ABR Rara c will generate a default route and this default route would not be a type 3 default route it would be a type 7 default route so if you look at this diagram the green line the green arrow so it's coming from Rada a a type 5 reaches rather C gets blocked 5 & 4 gets blocked and then Radha's C generates type 7 default route towards the NSS area that's why rowdy would be able to reach rip routes off router a using that default route but this default route does not come automatically you have to give the command B full information originated under NSS a so the command is area 1 NS s ad full information originated that's one part of it what about the routes of router D the eigrp routes now the rule of NSS a is that you can have an ESB are however type 5 LS a cannot be generated so what's going to happen is that rod of D when he redistributes a I GRE into OSPF instead of generating type 5 he generates type 7 and type 7 is only within the NSS a area so it goes to everyone in area 1 as soon as Rada see who's the ABR gets type 7 he also sees a flag being turned on which is translated 7 to 5 so rather see translates the LSA 7 to LS f5 and sends Alice a 5-2 outside to everyone in the other areas throughout was beer domain unchanged so if you look at the type seven coming from rowdy reaches router c letter c blocks type seven and since type five throughout OSPF domain this is an ssa the next one that we have to look at is the last one which is totally not so stubby totally not so stubby is a lot like like totally stop it blocks five four and three LSA five well it's a four and unless a tree coming into the area so again if you look at this diagram let's talk about the routes coming from rip router a through OSPF so rather a sense type five LSA throughout the west PF domain besides that i have in Terraria OSPF routes coming from the ABR so LS a five and LSA three prefix information is coming to our R to R Odyssey which is the third router ABR when he gets that he blocks LS a five he blocks Alice f4 and he blocks and acid-free going into the NSS a area so will rather D be able to reach the external route will he be able to reach in the area routes the answer is yes the reason he is able to reach that that external network or even in the area because in totally not so stubby the ABR generates a default route automatically I don't have to give the command default information originated it generates that default automatically like totally stub and it's a type three default route so if you look at the diagram again five came from outside three came from outside got blocked and then ours Radha C generates a default route of Type three automatically that's why Radha D would be able to reach rip routes of a and also in Terraria routes what about the routes of Eid are beyond rowdy that part is the same like like not so stubby type 7 LSA is generated not type 5 because type 5 cannot go inside not so stubby so rowdy whose the ASV are instead of generating type 5 he generates type 7 that goes throughout the NSSA area and when the ABR gets it he translates 7 to 5 and since type 5 throughout the OSP of domain outside of the NSSA area this is totally not so stubby so what we are going to do now is I will show you a diagram we would actually implement all of this we will test all of this and we will confirm if those Ellis's are being blocked so let's do that let's actually lab it up and see how we can configure first up then we will modify it to do totally stop then we will do not so stubby and then we will do totally not so stubby so let me quickly show you my diagram which is pre-configured with OSPF what I've done is not to waste time for this webinar I have pre-configured OSPF throughout my topology I have pre-configured that and it's multi area topology and I haven't configured stub or totally stub or not so stubby or totally not so stuffy I have not configured that I have only configured multi area so based on that we will actually test all of these four features or for SPF alright so here is my topology which is pre-configured with multi area OSPF let me quickly show you what's configured so I have area 0 which is here that's my area 0 which is here I have area 1 which is here and then this is area 2 and here is where I have area three now all of these routers are basically pre-configured I have all the routes in my routing table and I have full connectivity I have not configured any stubby or totally stubby or not so stubby so what I'm going to do first is let's in fact make router nine which is an area to let's make him into an SBR so what I'm going to do is I'm going to create some routes first I'm going to create some loop backs and let's read is to Butte those low backs in OSPF so let's stop that off so what I'm going to do is go to my router and on run a nine let's create some low backs so config T interferes loop back nine let's give the IP address as as 99.99 dot 99.99 to 5 5 to 5 5 to 5 5 to 5 5 let's also create one more loop back let's say 199 and give the IP address as 199 199 199 one ninety nine to five five two five five two five five two five five so I have these two loop backs and I will go to my OSPF let's changed my router ID to be nine nine nine nine and let's redistribute connected subnets so once I redistribute these routes these two routes would be redistributed in OSPF and since I did not specify the metric type the default metric type would be e two routes so throughout my OSPF domain i should see these routes it means that quickly show you the routes in the routing table and also in my database if you remember I told you that LSF five was advertised by the asbr throughout the OSPF domain and it remains unchanged so if I go to router 9 and do a show IP ospf database external self originated you would see that router 9 is advertising 99 99 99 99 in OSPF his router ID right now is 151 nine nine I did change the router ID but because I did not restart my OSPF process my router ID would still be the old one so anytime you change your ID you should go and restart your OSPF process let's quickly do that clear IP ospf process and let's say yes now once I do this and if I go back to show IP ospf database external self originated r9 who is now the SBR he is advertising LSA five and that NSF I would would remain unchanged throughout the West Pier domain so if I check here now he is advertising 99 and $1.99 as a prefix so to NSA is one for 99 one for 199 and the advertising router is nine nine nine nine if I look at my checksum value it's 0x FC f one and if I go to router ten if I look at the diagram r9 is here and our 10 is ik at the other end which is an area three so if I go back to our ten and do a show IP route OSPF first I see the routes in my routing table as each you routes which you can see here and even here for 99 and 199 so it is in my routing table as e 2 because default metric type is 2 and if I look at my database show IP ospf database external you would see that the checksum value for 99 is FC F 1 which is the same which r9 had advertised so this basically proves that the LSA 5 remains unchanged throughout the OSPF domain now the problem is how do I get to this network I always do an SPF towards the advertising router what's my SPF what's my advertising rada it's nine nine nine nine is that a prefix no it's it's a router idea of r9 so how do I get to the SBR to reach the SBR I look at the LSF for show IP ospf database ESB our summary you would see that to reach this router ID which is the SBR I should go to my airport or my local ABR which is our five so if I look at the diagram again for our 10 the local ABR is router 5 which is the ABR so ABR gets that LSA he generates an LSA and sends that down to other areas so r5 is the advertising router so again not going into the LSA types in detail we would quickly move forward with stubby areas now if you remember what was to be areas doing it was blocking type 5 LLC and type 4 LS it going into the area but can they still reach the external Network yes because the ABR generates a type 3 default route so let's do one thing let's configure area 3 as stubby area ok so we will configure this area here as tubby let me in fact write it down for you so we will go back to our router and we will configure all of these routers in area 3 as stubby area now again if you remember for configuring stub my stuff flag must be the same since my stuff flag has to be the same I have to configure all the three routers in area 3 r5 the ABR r8 and our 10 so let's go and configure that as of right now they all have external routes in their routing table let me go and do a show run section bar OSPF or in fact show IP route OSPF include o e routes so I have to routes in my routing table as of right now and I see LSA five also I see LSF or also in my database now if I want to reduce my routing table at the same time I want to reduce my processing of the LSE's so I can configure this area a stop let's do that so I will start with route of 10 where I would go and say a config T router OSPF 1 if I can spell that right router OSPF 1 and here I would say area 3 would be stub now the minute I do this you would see that I lose my neighbor ship with router 8 the reason I lose the neighbor ship is because the stuff flag must match so if I go back to 8 and do a show IP ospf neighbor you would see that my neighbor shape with router 10 is going to go down in about 13 seconds more and my neighbor ship would not form with our 10 in fact if I do a debug debug IP ospf maybe I think adjacency should probably show me that I have an issue of stop flag mismatch if it doesn't show you here you can probably give the command IP show IP ospf debug IP ospf hellos in fact it should show you here also so I should see a message that I received a packet or a hello packet from our 10 but mismatched stub flag like I said even you configure stubby area you have to configure the entire area all the routers in that area as table area you cannot configure area 0s stuff you cannot have a virtual link going through it and you cannot configure an area as tub if there's an ASB are present so I have to go and configure this on all my routers so on our 8 also router OSPF one area 3 stub and lastly would be our 5 where I would do the same thing router OSPF router OSPF one and area three as tub the minute I do this you would now see that our five who's the ABR he would block type five NSA and block type four unless they going into area three let's quickly verify that so if I look at our five who was the ABR if I look at his database show IP ospf database external he has type five why does he have type five he's getting type five from from here basically five is coming from nine going to seven three and then coming to five five is going to block it and he will not send five he would not send LSA five and four down let's quickly verify that so let's go back to our router and look at maybe our tens database show IP ospf database external if I look at his external database he has no type five Allah says it's completely blank and if I do a show IP ospf database SBR summary which is NSF or he does not have LSA for all so now it kind of makes sense because why do we use Alice f4 to reach the router ID of the SBR if I'm not giving you external routes what's the point of me giving you type for NSA that's why in stubby areas and it's a five and LSF four they both are block five blocks the prefixes and four is not generated because you don't need to reach those prefixes so I don't need to generate LSA for also so five and four is blocked does that mean that the routers in the stubby area can they reach that external network let's do a ping so ping to 99 99 99 99 can they reach the external network yes why is that if I look at my routing table you would see that a default route got generated automatically I did not generate this let's look at the database who generated this default route show IP ospf database summary 0/0 zero why am I giving summary because this route shows up as oh I a OSPF in the area if you remember from the slides that a br blocks five and four and automatically generates a type three default route so if i look at show IP ospf database summary for the route zero zero zero zero you would see in fact that's a lot of zeros so zero zero zero zero you would see that the default route was generated by the ABR are five so he generates the default route and now what's happened with stubby area is that my routing table has drastically reduced and my database has also drastically reduced because I don't need to process external Ellis's I don't need to process sv RLS ends I don't have to do that so I'm only concerned with one default route to reach all destinations I still have inter area routes so if I look at my database show IP ospf database let's do a show IP ospf database router LSA I still have a less a one which is intra area routes and I should have NSA - also because my connectivity between our 8 and our 10 is a broadcast environment I did not change it to a point point so I should see Network LSA also which I do and if I do a show IP ospf database summary I have LS it 3 also I just don't have LS a 4 + LS f5 so my routing table drastically shortens or reduces and my database also reduces that's the advantage of using study areas now let's say if you wanted to reduce your routing table even further maybe I don't want so many routes maybe I have 1000 inter area routes I don't want all the interior routes I just want to be for route just to go out of the area why should I maintain in the area routes and LSA is also so I can reduce that also by configuring totally stop now to configure totally stub what you should do is configure stub first configure all the routers in the area as tab and then go to the ABR which is our five tell him that besides blocking five and four because of stub you're blocking five and for the besides that also block NSA three so for that all I would do is go to Rada OSPF one and say area please stop know summary so once I say no summary what you're effectively telling are five that block five and four and also block summary illnesses so don't send summary NSA so with this if I look at the the routing table of are ten now show IP route OSPF you would see that his flowering table has drastically reduced how many routes do I have now look at the order table before before I configure this if you look at my routing table let's scroll back up we had a lot of routes if you see I had so many interior routes and before configuring stub I had so many external routes also so with you configuring totally stub all I have now is a few routes which is my intra area routes so maybe five six ten routes in try area routes and I have one inter area route the default route which is automatically generated in totally stub like I said earlier that totally stop blocks and let's say five LS f for and LS III and the ABR will generate one ELISA tree which is the default route so the only summary LSA which is allowed in totally stub is the default route so this is totally stub now what is the problem we totally stub or stub the problem is that for this area to go anywhere let's say if it if it has to go to inter area or if it has to go to the Internet so for all destinations this area would have to go all the way from ten to eight to five and then go wherever he has to go it has to exit from our five the problem with stubby and totally stub is that what if our 10 had a connection to an ISP through the internet so maybe he had another eius be connected there and maybe he wanted to go out to internet directly maybe there's an ESB are present so the problem with stub and totally stub is that I cannot have an ESB are present in the stubby or totally stubby areas that limitation was reduced or eliminated so that was that was eliminated in not so stubby and totally not so stuffy so in Turin not so stubby and totally not so stubby basically you can't have an ASPR but one difference you will not generate LSA 5 as an ASP are within the NSSE area instead you will generate LSA 7 let me in fact show you that to demonstrate that what I will do is we will configure one more ESB are you remember in my slide I had one ASB R which was outside their necessary ax and I had one more asbr inside the NSS area what we'll do is we will configure router for as the asbr which is outside the NSS a area so this is still totally stub what we will do is since we have an ESB are here also this is also an ASB our we will configure area to as not so stubby so what's going to happen are 9 which was earlier generating LSA 5 this time he will not generate lsah 5 because he knows now I connect to a not so stubby area I cannot send a LSA 5 there so instead he generates LSS seven and sets a flag which tells the AVR to translate 75 now who's the ABR for area - only r3 r3 is the ABR r6 is not an ABR because for you to be an ABR you need to be connected to an area zero r6 connects to area one and connects to area 2 but he does not connect to area zero so our citizens not an AVR only our tree is an ABR so when nine generates Ellis is seven he sets a flag which says translate LS is seven to five so our three will translate LS is seven to five and send that an LS f 5 goes unchanged throughout the OSPF domain so basically from here till here I would see LS a 7 then it gets blocked here and then r3 generates a LS a 5 and that 5 will remain unchanged throughout the OSPF domain let's see that and we will also see this asbr his routes when it comes to the ABR ABR blocks if you remember even not so stubby is like total ease it's like stubby area so it blocks 5 & 4 going into the area let's in fact see that so the first thing what we will do is we will just work on this I will go to router 9 and in fact I'll guru area qu and configure that as not so stubby so as of right now our nine who is the ASB are show IP ospf database external self originated he is generating LSA 5 at this point of time to NSF 5 updates 1 499 prefix 1 for $1.99 so now I will go to config T router OSPF 1 and say area to NSS a again the stop flag must match NSS a is also a stub it's it's not so stop but it's still considered as stub so my neighbor ship would go down because stuff flag must match so I have to configure all the routers in that area not so stubby so r7 would also be area to not so stubby and r6 would also be not so stubby rod OSPF one area to not so stubby and lastly the ABR r3 router OSPF one area to not so stubby so now let's go to our nine and do a show IP ospf database external self originated you remember earlier he was generating type five LSA is he generating that anymore no he's not doing that anymore why because when I redistribute by default generates type 5s ty5 allowed in stubby or totally stub or not so stuffy is it allowed now so instead of generating five he generates LS s7 which you can see here show IP ospf database NSS a external so NSS a external self originated you would see that he generates type 7/4/99 and $1.99 and if you look at the flag look at this flag this is the flag I was talking about the P bit which basically r9 is telling the ABR that hey you cannot send my prefixes LS s7 cannot go outside the NSA area you cannot send my prefixes outside as steps as as LS s7 you need to translate this from seven to five so as soon as r3 gets the LSA seven he generates LSA five now is our tree an ESB our Oh only an SBR generates LSA five right but because our nine has said the flag to translate 75 our three will generate LSA five so show IP ospf database external self originate now our three is generating LSA five for 99 and 199 and he is the advertising router and this would remain same throughout my oh s be domaine obviously it won't go to this area area 3 because that's configured as totally stub but if I check on maybe let's say r2 if I check on our two you would see that show IP route OSPF you would see I have external routes e two routes and if I do I show IP ospf database external so IP ospf theta B is external you would see that the advertising router is not our nine it is our three so for the outside areas they don't know our nine they know r3 r3 is the advertising router for the LSA five update and it's not our nine because unless a seven cannot go throughout the West beer domain it gets blocked and translation happens seven to five so this was an ssa but this was only one part where the SBR inside the NSS area is sending LSS seven that gets converted to seven to five and then that that goes throughout the worst fear domain what about the SVR routes from the outside of the NSS area let's see that so if I go to r4 let's make him into an ESB are so on our for let's create one loopback 44 interface loopback 44 and say IP address 44 44 44 24 to 5 5 to 5 5 to 5 5 to 5 5 and let's go to Rado SPF one redistribute connected subnets if I look at r2 r2 would have the 44 Network which he if you see here he has 44 in his database type 5 LSA now our four is not an SSA it's a normal area so he's an ESB are so he generates type 5 and type 5 goes remains the same throughout the West Pier domain however once type 5 LSA comes from our 4 so our four ascending type 5 everywhere so this is type 5 type five and once it reaches our three our three blocks that he blocks five and he would not generate LSF four into this area so he blocks for all so let's verify that if I go to two let's say our seven which is inside the innocence area and if I do a show IP ospf show IP ospf database external I have no external innocence show IP ospf database asbr summary I have no LSA for do you think he would be able to ping the routes of the external external routes behind our forum would he be able to bring that in stub and totally stub I was able to ping the external network that seemed not so stubby so ping 44 44 44 44 I am NOT able to ping why is that if you remember I told you that not so stubby is a bit different from stubby it still blocks 5 & 4 but it does not generate a default route automatically you have to give one command you remember that command I had told you that that we had to give the command area to NSS a default information originated I have to tell the ABR to generate a default route towards the NSS a area only then they can reach the external network which is outside the NSS a let's do that lets go to the ABR and give the command rado SPF one area to NSA default information originated once I do that on our 7 if I do a ping I should be able to pin which I can and again if you remember I told you that this default route is not a type 3 LS a default route it is a type 7 so show IP let's do a show IP route OSPF let's do include all n you would see that I have type 7 factors to a show IP route OSPF I should see a type 7 default route we Edge's yeah so it's not a type three totally stub is Type three automatically a BIA generates that automatically stub generates Type three automatically NSSA does not generate type three or he he in fact does not generate any default route by default you have to give the command area area number n SS a default information originated and only then he would generate a default route and that's not going to be die three it's going to be in LSS seven this is not so stubby now let's do totally not so stubby totally not so stubby is a lot like totally stop it blocks five four three coming into the area and generates a default route automatically so I don't have to give default information originated your asbr generates seven which gets translated to five by the ABR let's see that so all I have to do is go to r3 which is my ABR and I will remove this command I don't need this command anymore and I will give area to NSS a no summary so if I look at my OSPF config I don't have the default information originated I only have any at unsa with know summary what this basically means if I look at seven show IP ospf database external do I have type five no do I have type 4 no it was blocked do I have type three summary no I only have one type 3 which is the default route coming from r3 so it came automatically and that's a type 3 LS a default route so look at my routing table now I have only the type 1 LS 8 intra area routes I have type 2 LS a 4d are being present and I have type 7 LS a within NSS a external routes which is type 7 foil SSA so so what's basically happening is that my router this is the SBR when he sends the routes are three blocks five four and three and sends here a default route 0.000 which is an O I a summary NS a default route and this SVR who's redistributed he sends LS a7 which are three will forward ahead as LS a five so 75 translation happens so you see configuring stubby areas or not so stubby areas or even totally starboard totally not so stubby it's pretty straightforward it's just one command area area ID and stub or area area ideas not so stubby or you do you add the keyword no summary on the a on the ABR and that makes it totally stub or totally not so stubby I hope this webinar was informative to you and thank you for watching