OSPF Area Types

hi everyone my name is Narvik coach Aryans and I'm here to talk about OSPF area types so let's get going so let's say we have area zero and in this area we're advertising 100 routes so that means that if I go to a given router with an area zero and I do a show IP route OSPF I'm going to see spot area zero here I'm going to see 100 all routes these are intra area routes so let's write intra area here so now let's add area one to area zero so I'm going to have an ABR here and I'm going to connect area one to area zero area one is also advertising 100 routes so if I go back to the same router in area zero and now I do a show up here at OSPF I'm going to see my own routes as intra area routes and I'm going to see hundred routes as ia or inter area routes these are routes coming from area one you see traffic from an areas perspective can be intra area traffic or inter area traffic or the traffic could be external if the traffic is intra area traffic this is traffic within our area if the traffic is inter area traffic this is traffic entering my area from another area within the same routing domain but if the traffic is external it means that traffic redistributed this is traffic from another routing domain that we have redistributed into our OSPF routing to me so now let's add areas two three four and five I'm going to put an ABR here you're going to add area to another ABR so we can add area three and this is area for and of course area five these areas are also advertising 100 routes so now if I go back to the rattling area zero and I'll do a show IP route OSPF I'm going to see my own route these are 100 routes these are inter area routes now I'm going to see 100 routes coming from area 100 rats coming from area to another 100 from area 3 another 100 from area for another one from area 5 so that means 100 200 300 400 I'm going to see 500 I a route so now let's add some ASPRS I'm going to add for ASPRS I'm going to add an a SVR in area 3 1 in area 4 third one - area 5 and the final one or the last one - area 0 now in asbr and this asbr is redistributing 100 routes this arrow means that I'm redistributing hundred routes into my OSPF routing domain same thing over here and this ASPR is also redistributing 100 rounds so my third ASPR is also redistributing 100 routes but the ASB are in area zero he is redistributing 500 rounds so now if I go back to the router in a year area zero and I do a show IP route OSPF I'm going to see my own route as intra area routes I'm going to see 500 routes coming from other areas these are inter area routes now I'm going to see 100 over here external routes plus 100 is 200 300 plus 500 I'm going to see 800 external route by default they will show up as e to total number of routes 1,400 routes so the administrator of area 1 gives you a call he says narvik 1,400 routes are too many routes can you do something to reduce the size of our link state database of course we can but before we configure area 1 the question is do they like to see the inter area routes these are routes coming from the other areas in their routing table and he says yes I definitely need to see the inter area routes in my routing table so in this case what I can do is I can configure area 1 as a stub area so let's do this we're going to say this area is going to be stub and I'm going to go to the ABR and I'm going to say area 1 stub now this entire command needs to be repeated on every router within area 1 so the areas flag matches so I'm going to go on all routers and I'm going to do area one stop so now let's see what LSA is I'm allowed to propagate within area one and what lsas are going to be blocked so the ones that I'm allowed to have I'm going to put them in blue there was that I'm going to block I'm going to put them in red so here I can have my own LSAs these are entry area routes type ones and type twos type fries are routes coming from the other areas plus a default route who injects that default route the ABR injects that default route and he injects that default route as LSA type 3 so now let's see what LS A's are blocked who blocks these Alice's the ABR does that he's going to block lsas fours and fives so basically he blocks a let's say four fives if LSA fives are blocked and LSA fours provide reach ability to the asbr then it's useless to have a less a tie for words when I cannot have an asbr or type 5 LS A's in my area so for that reason 4th and 5s are blocked so now let's go to a router in area one and do show IP route OSPF and see how that affected our routing table so I'm going to go to area one and I'm going to do a show IP route OSPF I'm going to see my own hundred routes these are LSA ones and twos I see the inter area routes these are 500 routes coming from other areas and I'm also going to see a default route the default route is injected as ia total number of routes is 601 and this is what makes always we have so scalable so now the administrative area to gives you a call and he says if you're giving them or if you're going to give us a default route like you did in area one can we not use that default route to reach inter area routes of course they can they can use the default route to reach any destination that is not in the routing table so it says can you block inter area routes sure we can how do we do this what we going to do is we're going to go to the ABR and I'm going to say area - stop no - summary now this portion of the command these two repeated needs to be repeated on every single router within area 2 so on all routers we're going to say area to stop now what Ella says am I allowed to propagate in area 2 I can have my own LS A's ones and twos now I can no longer have LSA type freeze because I'm blocking them who's blocking them the ABR is going to block LSA type freeze now whenever L sa type trees are blocked the ABR has no choice but to inject the default route so in this case he is going to inject a default route the default route is injected as LSA type 3 you see the ones that are that we're blocking a route coming from the other areas even though the default rat shows up as L Shi 3 this is not coming from another area this is originated by a br for area two and this is why I'm allowed to have a single LS a type three that originated by a br and that propagates the default route into that area so what Ellis's are blocked by the ABR threes fours and fives so now let's go to a router in area two and do a show IP route OSPF and see how that affected my routing table so I'm going to go to area 3 or area - sorry I'm going to see my own 100 route these are ones and twos and I see a default route and the default route is injected as ia total number of routes 101 routes now this is called totally stubby totally stubby now why is it totally stubby because we cannot have LSA type threes the administrative area 3 gives you a call obviously with a similar problem now when you look at area three you realize that they have an asbr so these guys want to be stubby but they don't want to be that stubby not to have an ASP are so what do we call them not so stubby so now we're going to configure area three as not so stubby area how do we do this we're going to go to the ABR we're going to say area three NSSA and we're going to repeat this entire command on all routers within area three so I'm going to go on all routers I'm going to say area three NSSA so what Ella says am I allowed to propagate within area three here I can have ones and twos you see I'm not blocking trees like I did in a totally stubby area so I can have fries I have an a SPR and this ASPR is redistributing on red routes and those routes will show up as LS a type 7s and that's all I'm going to have you see in a regular nut so stubby area the ABR does not inject a default route the assumption is that one of the routes that the ASPR is redistributing happens to be a default route so if the asbr is injecting a default route and the ABR is also injecting a default route you're going to go this way to connect to a given destination so what Ella says are blocked over here we're going to block fours and fives so now let's see how that affected the routing table in LS in area 3 so I'm going to go to area 3 I'm going to do a show up here at OSPF I'm going to see my own 100 routes these are entry area routes I see LSA type fries these are 500 ia routes these are inter area routes I see type sevens these are the routes that the ASPR is redistributing into that routing domain into this routing domain so that's 100 by default and 2 routes and these are external total number of routes 700 routes you know what we forgot to write that these are inter area routes and these are inter area so the administrative area 4 gives you a call obviously you're receiving a lot of phone calls days and obviously has identical problems so in this case the administrator says that they need to reach the external routes that are redistributed in other areas within our riding domain basically what they're asking for is a default route notice in a regular NSSA area the ABR does not inject the default route but obviously these guys want to have a default route so in this case what I'm going to do is I'm going to configure the ABR by saying area for NSS a default information originated now this portion of the command needs to repeat it needs to be repeated on every single router within area 4 so let's go on all routers we're going to say area for NSS a now let's see what LS A's are propagated in area 4 so here we can have type ones type twos we haven't blocked LS a type Riis so we're going to have freeze we have an ASB R that's going to be that's redistributing 100 routes those will show up as type sevens the only difference between the two areas area 3 and area 4 is the fact that the ABR is now going to inject the default route now since we used default information or originated the default route will be injected as external routes in this case it will be injected as n2 so we're going to have a default route what Ella says are blocked fours and fives so now let's go to a router in area 4 and do a show IP route OSPF and see how that affected our routing table so an area for we're going to do a show IP route I'm going to see my own routes as ones and twos as intra area routes I see LS a type trees these are 500 routes showing up as I a these are inter area routes I see type sevens these are the 100 routes that their own ASPR is redistributing into a spear flowering domain so they're going to see 100 by default as in - I'm also going to see a single default route that's injected by the ABR this default route will show up as n2 so total number of routes 701 route the administrative area 5 is having an identical per similar problem but he sees what we've done for area for and he says you know what if you're going to give us a default route can we not use that default route to reach inter area routes it's kind of similar to area 2 here of course they can so we know that the minute we say node I summary the ABR will inject the default route and we cannot stop that so in reality I don't have to say no summary default information originated because by saying no summary the ABR is going to inject the default route anyway so now what we're going to do is you're going to go to ADR and we're going to say area 5 and SSA know that summary now this portion of the command needs to be repeated on all routers within area 5 so I'm going to go on all routers within area 5 and I'm going to say area 5 and SSA now what LSA is are we propagating over here you're going to have Alice's ones and twos we're blocking 3 so we cannot have fries but we can have 7 plus a default route what LS A's are being blocked by the AVR threes fours and fives you see fours and fives are always blocked fries are only blocked when we say no summary and the minute we say no summary the ABR will inject the default route if you notice in area 2 we said no summary and the default route was injected by ABR as LS a type 3 the same thing happens over here in area 5 the minute we say node I summary the ABR is going to inject the default route as ia so let's see what happened to the routing table in area 5 so an area 5 we're going to do show up here at OSPF we're going to see our own hundred routes as intra area routes we don't see LSA type threes but we see LSA type sevens these are hundred routes by default they show up as and - and we see a default right here the default rod is injected as I a total number of routes 201 routes now what if what if our ABR in area 3 redistributes a loopback interface or redistributes a whole bunch of routes from another routing domain so let's say here I'm going to put a loop back and figure a loop back on that ABR and I'm going to redistribute it up you redistribute that loop back into SPF routing to make that loop back will show up in area 0 as external type 2 and you'll show up in area 3 as n2 but what if I wanted to redistribute the route such that only the routers in area 0 can see the route meaning what meaning that I don't want any router within area 3 to see the redistributed routes so here we have our ABR our ABR happens to be an ASB R and any route that he redistributes should not be redistributed in area 3 they should only go into area 0 in this case all we need to do is just say no redistribution once we say no redistribution the routes will not be redistributed into area 3 they'll only be redistributed into area 0 so now let's talk a little bit about why do I need to repeat this command on all routers in areas 1 & 2 now in OSPF two routers will use hello messages to form an adjacency if I look at those hello messages in white shark or sniffer in the options field I'm going to see the EBIT set when I configure these areas as stub the hello messages that these ABR's are sending or are generating will have their EBIT cleared why is the e bit cleared because we don't have external routing capability so if I cannot have external route capability these areas it's useless to set the e bit in the hello messages but the router to which these ABR's are directly connected to by default they don't have the e bit cleared so if they don't have the e bit cleared when they receive a hello message from the ABR they're going to discard that hello message if they discard for hello messages in a row the adjacency is torn down so this is why we need to repeat that command on all routers within that area when it comes to not so stubby area instead of a bit the ABR sets the N bit obviously if the N bit is not set on the router to which I'm directly connected to he is going to tear down the adjacency in the same manner the last item that I wanted to cover over here is how can we utilize the default route that is injected by the ABR now over here in area for the default route is injected as external in area five the default route is injected as ia now how do we utilize that to our benefit so let's say I have an ABR here ABR one he has a connection to routers in area zero and he has another connection to area one I've configured this ABR as area one NSSA no dice summary now what routes is he going to inject into area one if I say no die summary LS a type threes are not going to be in my area one instead I'm going to get a default route and the default route shows up as ia so let's say we have another ABR here a B or two now this ABR is configured as area one and as I say default information originated now since I said default information originated the ABR is going to originate a default route but in this case the default route will show up as and - but since we're not blocking LS a type threes is also going to give me individual L Shi trees so now let's assume that you are a router in area one over here if you are a router in area one and you need to connect to the individual LS a type Ruiz you're going to go this way why because he's the one that gives you the individual the specific routes coming from the other areas but for any other route for any other route you're going to go this way why because in OSPF ia routes are preferred over external ones so you see by utilizing these these two commands we have achieved some type of a load sharing capability over here now this is it for area types in the future Oh SPF lectures I'm going to go a little bit deeper into the bits and bytes into P bit and the other bits and we're going to talk about tenth occasion and other features of OSPF thanks for listening

Channel: CCIE Quick Study

Views: 120,336

Keywords: CCIE, OSPF, NETWORKING, Cisco, routing, switching, protocols, router, narbik, study, ccie, ospf, networking, cisco, technology, IT, Area, types, area, quick, quick study, ccie quick study, Quick, CCIE Quick Study, Study

Id: cM3OI_ZyRuQ

Length: 28min 4sec (1684 seconds)

Published: Wed Sep 14 2016