Understanding OSPF STUBS and TOTALLY STUB

okay so in this video we will be discussing on a new topic called OSPF stops okay so before we get into that so SPF stop is one of the most widely used option because it really helps administrators to minimize the number of advertisements it also minimize the size of the routing table so let us see how exactly provides a good option so if you remember we did some stops in eh RP also near jarppi also there is a concept of stop but it is totally different when we compare with OSPF stops so let's try to understand OSPF stops helps in reducing the size of the routing table that is something I can say what is the use of stars means I can simply say it sells in reducing the size of the routing table and also minimizes overhead on the routers especially on the end outers you can see the end routers so to understand this what I am doing I did is I got some routers here I will explain you my topology it's not much clear you can see these routers these area routers so is it all the routers used in area 0 these are the area 0 routers so I got some routers here assume this is my head office connecting to some of our branch offices these are the 3 branch offices which I am using and then these are all my end locations I got a very big network assume that I got more than 200 place networks in my organizations it's a very big and complex network design so head office connecting to all my branch offices and then all my branch offices are again connecting to my end locations so very small small branch offices and as it is a very big network so what we did is we designed them into multiple areas so we designed in such a manner that area 0 is at the center so assume that is your area 0 and then I got some multiple areas this is my area 10 and also this is my area 20 and this mariya 30 so what I did is I group some routers into multiple areas and I designed them in multiple areas ok and also I got some routes coming from external torques external route means the routes which are dyes I got some more branch offices see on this side this part you can see on the left side where I wrote EHR pen r.i.p so these branch offices or these are the locations which are not running OSP or protocol but they are running something other than who is p of like EHR PR i-- p or it can be any other protocol and we are doing the distribution of these routes into OSPF so which means automatically these routes are also coming here into my routing table so it's a very big network assume that I will give some I'll use some rough figure rough number for understanding so I'll be giving some assume that there are some 50 networks present in area 0 as you just assumed ok there are some 50 networks LAN van everything includes 50 networks present in area 0 and also have some 50 networks in area 1050 networks in area 20 and 50 networks in area 30 so 50 50 50 means around 200 networks I have inside the OSPF and I have some 100 networks 100 networks I have something coming from external routes nothing but come and learn from different protocol and they are redistributed inside those ok so now if I go to any router so let let's try to understand what is the problem in this topology there's no problem it was fine because you know area 0 is at the center everything is ok but we can make it more better by using a concept of stops so let's try to understand what is the general problem we have in this type in this type of network where we have very big topology and we have a lot of big network size so if I go to any one of these routers any one of these routers especially the end routers and if I issue a command called show IP route OSPF so when I give the command called show IP doorways you don't know if you go to any one of this router and you show IP row is view generally you'll see ports so the meaning of over rocks if you remember we discussed in the last session or represents our routes coming from the same area which means from the same major you'll see how many over outs so I'm talking about the routers in the anyone watering intake so you'll see only the routes coming from the same mirror means I think I can see around 50 networks or 50 lines as over outs it can mean a tendon 23rd unit or whatever the networks we have I can see something around 15 it works right because they are from the same area so or outs you'll see how many 50 because from the same area I can see the routes next thing you can also see not only or do you also see something or oh I errors oh yeah nothing but the routes coming from a different area different area means if you see the diagram here I go I'm missing the route from area 20 area 10 in area zero so these are considered as different area routes other than my area so as of now my area is area 30 so any routes coming from different areas nothing but OSPF inter area routes so how many lines you can see so we are assuming each area is having 50 networks so you can see 50 networks from this area 50 networks from this area and 50 network from this theorem which means you can easily see 150 lines on 150 networks displayed as oh I a and also one almost 150 lines and also apart from that you can also see something called a 100 a - you know u1 or OE - represents OSP of external routes it can be metric type 1 metric type 2 we know is pure which means the routes coming from different protocol and they are getting redistribute into the OSP F so you'll also see the routes coming from this side but they will be displayed as different output even it adopts so now how many or even it routes 100 extra loss so if you just figure out if you count the total number of networks you can easily see not 200 it's more than 300 networks because you know if you have at least 100 branch offices assume the 100 branch offices and each branch office is having 3 networks so you know 1 land two vans or it can be more than that so easily you will get 300 networks in your routing table so now which means from this we can conclude that from this second from this basic understanding can come to a final conclusion that your routing table is very big this is something what because you know 300 it's too big so my routing table is very big and it's really because you know if you have a big routing table it really uses more resources to see a specific route in the routing table and also it has more overhead so now this won't be a problem with these routers because maybe this is a core router it's a very high speed router running 7 7000 series routers maybe these routers also don't have any problem maybe they are running 3600 series routers distribution level routers so they may have enough memory to maintain those routing tables and process them but now the problem issues comes with these low level doubters where we are running your 1600 1700 SILS doubters 2,500 2,600 routers which are generally low level silly routers maybe 800 series routers they don't have enough memory to maintain such a big routing tables maybe if they even if they have the enough memory to maintain such a big routing tables still it requires a lot of processing to maintain such a big table and to do lookup because you know every time there may be a lot of traffic moving from here in there because you know every time a packet comes on the router from the LAN or from the van it has to check the routing table forward the packet so it really uses lot of resources so we need to minimize it so this is something what default we cannot really stop this this is ready for beer but we can optimize these things by using concept of stops so OSPF they added a concept of stub where by using this concept we can really minimize the size of the routing table and also which again in turn minimizes the routing table size and also in turn it minimizes the overhead on the routers ok so which again in turns increases the efficiency of the routers especially the low series of artists so they reduce something called stops so let's try to understand what is stop stop here we can make a specific area system we cannot make a single order to stop here we are making a complete area system and in this stub there are two options so first one is stop stop what it is going to do is it is going to stop external rocks it is going to stop the external nodes instead of external routes it is going to send a single default route it is going to send a single default road instead of external laps now what is exactly that means so it means it is very simple here so just need to understand the basic methodology so if you see so here what I am going to do is this is the default routing table which we discuss just now the default routing table will have OSP of routes coming from the same area where is P of interior routes coming from a different area and also OSP of external routes coming from redistribution through redistribution we can say so when I use a normal area it increases the my size of the routing table so what I can do is I can make a complete area as system so you cannot make a single router as a stop so I'm going to make area 30 as a stop now once I do that what happens so once you do that what happens is automatically your routing table looks slightly different so how it looks is so there won't be any changes here much changes like you will see the same over outs as it is how many routes or odds same 50 no changes same and also you will see over outs also same how much 150 networks maybe 150 lines but but the difference between the normal routing table and after configuring the stubby's you will not see this you will not see this one instead you will see oh a stick ia has one line you will see a single default part now this default is something not I am creating I am just config only one command when I come to the lap I will show you the practical implementation of steps but just try to understand what exactly it is going to do it is going to stop these external routes which we will remove the external routes from the routing table and replaces with a single deep water so but now the question is automatic it will do that after adding one command but now what is the impact of this and why it is doing that let me explain you so why it is required because you know all the external doubts if they really want to access or enter into the stub area whichever the area you want to make a stop they should go wire which router right they have to go buy a Aryabhata router which means if you want to reach any external route so in simple I can say reverse I can tell like this if any of your internal router the all these routers inside the area ten area thirty which is supposed to be stub which way you are supposed to contain a stub if they want to go to any external route any external or means any of these hundred routes it should go via area border which means there is only one route you know wherever you want to go you have to go buy a bottle order only so now when you have only one single rod you don't really need to maintain all this rod so what we can do is once I configure these are stuff so counting stuff is very easy just one command area 30 stop inside the router mode so practical part don't worry it's just one line command but the main reason here is to understand why we do that and what is the impact on the routing table or what is the impact once we configure that command and once we do that automatically you'll see over outs as it is no changes over out as it is 50/50 whatever whatever is here whatever is same and Hawaii remains the same no changes but this external dots will be replaced with one single Depot w0s Takaya which means all your internal routers in simple I can see all internal orders means maintain the default route so that default route is actually a replacement for external dots so that's what I said here it is going to stop the external dots and instead of external node there will be a single default road which means so when these external nodes are coming from here when you configure it as a stop this border router says these are actually stop routers tub area and there is no external router load inside but instead of external doubts I am going to send a default which means if any of this router want to reach any external ops they will say please come to the my daughter that is border router and I am the one who is going to maintain a more specific route so now the behavior will be like this so let me explain you the behavior here so the border router whichever is area water router is going to maintain a more specific route which means the border router will maintain each and every external route information but when it sends to internal out us it is not going to send those external dot it says you are a starter area you don't need to maintain the external route information I am going to maintain that but you maintain only a default rock so you maintain only one line information only default route and if you don't if you want to go to any network let's say this ignored 50 odd Network and I tell everyone to go to filter Network it will simply send to the bottles outdoor saying that I want to go to 50 Network but I don't have that information so the border router knows exactly where is 50 and how it is learned so it will make sure that it reaches the 50 on network in the packet report pack and then returns back to their destination so that is what exactly stub there is how stop exactly works so when a practical implement you really have some more clear understanding but the one thing you need to keep in mind just try to see the difference try to understand the difference in the output before conferring the stop this is actually before conferring the stop your routing table will have all the rocks nothing but you have or odds you have over hours you have even in two routes but once we configure stub all your external routes will not be sent in to the internal doubters but instead it is going to send only a single default on so this is very very useful concept and we're very widely used because you know internal routers no need to maintain information so they you're almost reducing hundred lines you can see here if you try to see the difference you are almost reducing 100 100 lines as per our assumption you're assuming that the 100 net was coming from external so in the real prediction network if you $1000 it was coming from external routes so you are minimizing many lines so this way we can really reduce the size of the routing table and also we can increase the efficiency of the routers so that they can process the packets much faster than a normal routing again so that is one concept of stops so to implement and verify this so we can implement it verify I will come to the implementation but before that let me explain you OSPF stop whisp your stub what we understood is all you are imani two routes will be replaced with one single d forward so output wise you will see something like this so now they also have one more option called OSP of totally stop so this total stub is little bit more advanced and far more better than normal stuff now how it is better because let me explain you how it is better like in the stuff we did we discussed that all your external routes will be replaced with single default route right when in case of totally stop not only external dots means in case of totally stop which is some advanced stop it is going to replace your external routes as well as it is going to replace your OSP of inter area routes with a single deep order now what is required again if I come to my diagram you if you try to see here if I configure this particular routers or area 30 as totally stop so when I convert or it is stopped any of the internal routers if they want to go to any other area any other area they should go via area border router if this inter outers if they want to go to any external route they should go wire so which means wherever you want to go you need to go by our area but an outer so which is really same thing we are into the same situation here so now in case of totally stop wherever you want to go let me just come down to the same thing so if you want to go to any external out extra lot means here or if you want to go to any other area go via area water order which means even if you want to exchange the route between the two or more different areas still you need to go via area water router right so that is what weighs PF totally stub is doing so as we have totally stopped is actually replacing not only your external routes it is also replacing your external routes is a single ever which means if you take the routing table over outs will be fifty if you take normal routing table have 300 lines now you'll see over remains the same but in stop these two you will have a single default which means we are minimizing almost 250 lines as per our assumption okay so there is a basic difference between so now to configure there's only one one command just one line command there is no difference but understanding this stop and total stuff is important so let's let's try to verify practically I got a simple demonstration of a lab here okay so NSS is not so sloppy I will come to this in our next session okay so we'll be discussing on that so is few stops and totally stops so to implement and verify again you

Channel: Sikandar Shaik

Views: 80,845

Keywords: OSPF stub, totally stub, OSPF

Id: D1cNIfqpIyU

Length: 19min 45sec (1185 seconds)

Published: Thu Sep 12 2013