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Cisco CCNP ROUTE 642-902

OSPF Routing: Area Types and Options

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Video Titles Duration
1. Cisco ROUTE: Cisco Certification and Getting the Most from this Series
2. Lab Foundations: GNS3 Overview and Operation
3. Lab Foundations: Network Design and Documentation
4. EIGRP Routing: Concepts and Planning
5. EIGRP Routing: Implementing Basic EIGRP
6. EIGRP Routing: Implementing Advanced EIGRP
7. EIGRP Routing: Implementing Advanced EIGRP, Part 2
8. EIGRP Routing: Best Practices and Design Options
9. OSPF Routing: Foundation Concepts, Part 1
10. OSPF Routing: Foundation Concepts, Part 2
11. OSPF Routing: Implementing Basic OSPF
12. OSPF Routing: Implementing OSPF over NBMA
13. OSPF Routing: Implementing OSPF over NBMA, Part 2
14. OSPF Routing: Area Types and Options
15. OSPF Routing: Area Types and Options, Part 2
16. IPv4 Redistribution: Controlling Routing Updates
17. IPv4 Redistribution: Implementing Simple Redistribution
18. IPv4 Redistribution: Implementing Advanced Redistribution
19. BGP Routing: Foundation Concepts and Planning
20. BGP Routing: Implementing Basic BGP
21. BGP Routing: Implementing Basic BGP, Part 2
22. BGP Routing: Tuning Attributes
23. BGP Routing: Tuning Attributes, Part 2
24. Path Control: Configuring Path Control
25. IPv6 Routing: Understanding and Implementing IPv6 Addressing
26. IPv6 Routing: Implementing IPv6 Routing and Routing Protocols
27. IPv6 Routing: Implementing IPv6 Routing and Routing Protocols, Part 2
28. IPv6 Routing: Transitioning to IPv6 and Certification Review

Cisco ROUTE: Cisco Certification and Getting the Most from this Series

Lab Foundations: GNS3 Overview and Operation

Lab Foundations: Network Design and Documentation

EIGRP Routing: Concepts and Planning

EIGRP Routing: Implementing Basic EIGRP

EIGRP Routing: Implementing Advanced EIGRP

EIGRP Routing: Implementing Advanced EIGRP, Part 2

EIGRP Routing: Best Practices and Design Options

OSPF Routing: Foundation Concepts, Part 1

OSPF Routing: Foundation Concepts, Part 2

OSPF Routing: Implementing Basic OSPF

OSPF Routing: Implementing OSPF over NBMA

OSPF Routing: Implementing OSPF over NBMA, Part 2

OSPF Routing: Area Types and Options

00:00:00 - It's time for OSPF to take a huge step in the world of efficiency,
00:00:04 - as we look at our special area types and options that we have
00:00:09 - at our disposal. First thing that we'll talk about as we get
00:00:12 - into some of these special options of OSPF is the place of virtual
00:00:17 - links. You'll find out very quickly virtual links do not belong
00:00:21 - in your network but maybe there if you have a potentially band-datable
00:00:26 - situation. You'll see that in just a moment. We'll then look
00:00:29 - at the special OSPF area types which is one of my favorite topics
00:00:32 - just because of the names of these area types and what they can
00:00:36 - do for you in terms of efficiency. The whole time going through
00:00:40 - this, I plan on doing live demonstrations of these areas so that
00:00:43 - we can see the implementation and verification to make sure that
00:00:47 - these areas are doing what they said they should.
00:00:51 - Let's start things off by breaking the rules. That's what OSPF
00:00:54 - virtual links is all about. Now, looking at the network diagram
00:00:59 - that you see on the screen, you should have one word in mind
00:01:02 - and that is, "Impossible!" You can't do that. You can't have
00:01:06 - multiple areas daisy chained away from area zero because it violates
00:01:11 - the OSPF design boundaries, which are, every single area has
00:01:15 - to be directly linked to area zero. Well, this is an exception
00:01:21 - to the rule and that is what virtual links are all about. First
00:01:24 - thing I'll say about virtual links is that they are a poor design
00:01:29 - criteria. You would never design a network like this with virtual
00:01:34 - links in mind. What virtual links are therefore, are sort of
00:01:38 - a band aid process. Kind of just a way to make things work until
00:01:41 - you can redesign a network. For example, maybe area zero represented
00:01:45 - the hundred routers that you had at the corporate offices in
00:01:49 - California. Area one represented about 20 different branch offices
00:01:55 - you had located in Australia. Well Australia got aggressive and
00:02:00 - took over the competing Australia company and with a hostile
00:02:03 - takeover, you know merged maybe the Nabisco headquarters in Australia
00:02:10 - with the Hasbro headquarters in Australia. Now I don't even know
00:02:15 - what those two companies have in common but they acquired each
00:02:19 - other, and so for the time being you have the need to link in
00:02:23 - the Hasbro networks directly into the offices in Australia and
00:02:28 - they don't have a direct connection back to area zero. That's
00:02:32 - a place where the virtual link can come into play. Now as of
00:02:35 - right now I have a configuration set up to where router four
00:02:40 - is completely immersed in area zero and it's already configured.
00:02:43 - Router three has one interface in area zero and one in area one
00:02:47 - making it an area border router and it is already configured.
00:02:50 - Router two is yet un-configured, because I want to show you what
00:02:55 - exactly happens when we set this up. So I'm going to start off
00:02:58 - on router two to do a show IP protocols, verify there are no
00:03:03 - routing protocols running. A little quick show IP interface brief
00:03:06 - and you can see that I have my link over from router two, I got
00:03:10 - a WAN link to router three up here and that is this guy
00:03:17 - I also have a LAN link in area two that is over here
00:03:22 - that we're going to get up and running. So let's set this up.
00:03:26 - We are going to router OSPF one. First thing I'll do is set my
00:03:30 - router ID to,
00:03:32 - and by the way, we'll find router IDs are of the essence at this
00:03:37 - point. You'll see that in just a moment. I'm going to type in
00:03:40 - the network and we'll focus on the WAN link first
00:03:46 - is going to be in area one. That is the WAN link going
00:03:51 - from router two up to router three, and sure enough we see the
00:03:55 - neighbor relationship form and I want you to see that as of right
00:03:59 - now everything is fine. There is no error messages happening
00:04:02 - because that is a valid design. Just having router two sitting
00:04:06 - in area one has not broken any design constraints. Now I'm going
00:04:10 - to add in the LAN interface. I'm going to say network,
00:04:18 - all zeros and we'll put that in area two, which makes router
00:04:22 - two an area border router and now violates all of the OSPF design
00:04:28 - rules that we have put in place because area two is not directly
00:04:31 - connected to area zero. Now what's going to happen as that gets
00:04:37 - added to the process is router, let's see, we are on router two
00:04:41 - right now, router three is going to start barking. And you can
00:04:46 - see the end of some little message coming through right there.
00:04:49 - But I'm going to just give it sometime, pause the recording right
00:04:53 - here sitting on router three for the error messages to start
00:04:57 - coming through. Well, after waiting 38.3 hours the error message
00:05:02 - never came. With some of the newer IOS versions that actually
00:05:06 - will report an error whenever a virtual link is needed, meaning
00:05:11 - it will all come in and say, "Hey, router two is reporting that
00:05:13 - it's got area two and that's not allowed here." So it helps you
00:05:17 - troubleshoot. In this case, we don't see any error messages but
00:05:21 - we're not going to get that route. Router two if you jump up
00:05:25 - over here had the
00:05:28 - network over here, an Ethernet zero and that route is not showing
00:05:32 - up at router three, I'll do and show IP route. You can see nothing
00:05:36 - there and it's definitely not showing up over at router four
00:05:41 - which is receiving the inter-area route. I It's receiving the
00:05:45 - WAN link between router three and router two, however it's not
00:05:48 - receiving this 10.1. network back here, this Ethernet network.
00:05:53 - So what we need to do is configure a virtual link between router
00:05:58 - three and router two. Here's the syntax to do it. First thing
00:06:03 - is you need to know that this is dependent on the router ID.
00:06:07 - The name of the router. This is that one criteria I was telling
00:06:11 - you that if the router ID suddenly changes, this virtual link
00:06:15 - will break. It will no longer function correctly. The way you
00:06:18 - set it up is you go on router three, I'll start it off with router
00:06:22 - three, the one that is linking it into the backbone,
00:06:25 - and going to
00:06:29 - the router OSPF process
00:06:32 - and you type in the command virtual link, oh sorry, not virtual
00:06:37 - link, you type in area followed by the area number, and in this
00:06:40 - case we are looking at area one. Area one is acting as the virtual
00:06:44 - link area, followed by the command virtual link. You can see
00:06:48 - area one virtual link question mark and it's saying, "What is
00:06:52 - the IP address or the ID? That's the one to keep in mind associated
00:06:58 - with the virtual link neighbor. This is the router ID. So I'm
00:07:01 - going to say router two's ID is
00:07:06 - Enter. That builds the bridge over to router two to say, you
00:07:11 - now have a virtual link. Now I want to mention that router three
00:07:14 - and router two are directly connected over that WAN link. But
00:07:18 - the command would be the same even if there was 20 different
00:07:21 - routers in between them. There could be, you know, router three
00:07:24 - linked up to router nine right here, that's linked to router
00:07:27 - 10, it's linked to blah, blah and you know, this link goes on
00:07:29 - and on and on. Eventually it links to router two. But the point
00:07:33 - is I would type in the same command. The virtual link is formed
00:07:37 - with that neighbor. We're looking for the other ABR that is linking
00:07:42 - us to the discontiguous area, if you will. Now, we're not done
00:07:46 - yet because I have to go over to router two
00:07:50 - on this side and form the virtual link the other way. The command
00:07:54 - is going to be the same, meaning I'm going to go into the router
00:07:57 - process and type in area one virtual link, but now I'm going
00:08:00 - to type in the router ID of router three. So I'm going to jump
00:08:05 - back over to router two here. Get into global configuration mode
00:08:09 - followed by router OSPF one. I'll type in area one. Again the
00:08:14 - area that the virtual link belongs to, space, virtual link. and
00:08:19 - then I'm just going to type in the router ID of the neighbor,
00:08:23 - What will happen when I hit enter on that command is
00:08:28 - a virtual link is formed between those two neighbors.
00:08:33 - Now a virtual link is a tunnel. I don't know if you've had experience
00:08:38 - with tunnel interfaces, but it is a tunnel that makes router
00:08:41 - 2 believe it is directly connected to area zero. As a matter
00:08:46 - of fact in the CCIE lab, one of the things that you may be asked
00:08:50 - to do is to form virtual links without using the virtual link
00:08:54 - command. Meaning you have to resort to using tunnel interfaces
00:08:58 - because they do exactly the same thing. The tunnel interface
00:09:02 - tunnels the packet through so that, router two in this case,
00:09:06 - believes it is plugged right into area zero. Now look at this.
00:09:09 - It says the process OSPF VL zero is going from loading to full
00:09:15 - when loading is done. Type in show IP OSPF neighbor, you can
00:09:18 - see that the neighbors looked the same. We have that same neighbor
00:09:22 - with router three but when I typed in show IP OSPF virtual link,
00:09:28 - it shows this new point to point virtual link that is a tunnel
00:09:34 - interface. Now the tunnel interface doesn't actually show up
00:09:37 - in the show IP interface brief or anything like that. It's just
00:09:40 - showing right here and this is your way of being able to check
00:09:43 - the status. Just type in this command and verify that the link
00:09:47 - is up. The only reason it would fail is if we typed in a bad
00:09:51 - router ID, or the router ID somehow changed between those two
00:09:56 - neighbors. Let's check the process over on router three. That
00:10:01 - virtual link should be up. I'm going to type in show IP route,
00:10:04 - and sure enough, look at that. It has an inter-area network
00:10:12 - that it now has picked up from router two. That sees Ethernet
00:10:16 - zero interface over here in area two that it wasn't picking up
00:10:21 - before because that was seen as a discontiguous network. Now,
00:10:24 - we should also see that over on area, oh sorry, rather four to
00:10:29 - show IP route over here
00:10:33 - and sure enough, there it is. The
00:10:38 - route shows up as
00:10:41 - it has now appeared coming from that one neighbor. So that tunnel
00:10:46 - interface is successful and router two is able to advertise its
00:10:49 - discontiguous routes over across the network. Now you can do
00:10:53 - virtual links within virtual links. I'm not going to show it
00:10:57 - to you because it is really ugly, but what you could do is, let's
00:11:01 - say you had, you know, another hostile takeover that took place
00:11:04 - and then ended up with area three over here with a router connected
00:11:08 - like that. You can virtual link these routers together and then
00:11:12 - virtual link rather router two and router three together. It
00:11:15 - gets very ugly and very confusing, but it is possible and allows
00:11:19 - those routes traverse over. Again, this is not a way that you
00:11:23 - would purposely design a network, but rather a band aid that
00:11:26 - helps it work until you can redesign it to link all the areas
00:11:29 - directly. Now, before we get in to the next topic, I want to
00:11:34 - do a little review on the OSPF areas as in their purpose. Remember,
00:11:39 - we divide the network into areas when the SPF algorithm has begun
00:11:44 - to run too often. Updates had become too numerous because the
00:11:47 - network has grown too large. So by splitting into multiple areas,
00:11:52 - we make that topology database smaller for the routers within
00:11:56 - those areas so they have to run the algorithm less often. The
00:12:00 - reason that it is because we can do summarization at this point.
00:12:03 - We can summarize at the area boundaries.
00:12:07 - As soon as we do summarization, we get those new LSA types that
00:12:11 - we've talked about in the previous video. The LSAs are the building
00:12:16 - blocks of OSPF. They advertise routes. They advertise
00:12:21 - routers connected to the same switch or the same subnet, That's
00:12:24 - the LSA type two. The LSA type three and four, the summary LSAs
00:12:28 - that get generated anytime. We have an ABR that passes routes
00:12:32 - from one area to the other. Those are always marked as LSA type
00:12:36 - three. LSA type four identifies the ASBR, its IP address, its
00:12:41 - location. Then the type five LSA was the LSA that the ASBR generated
00:12:47 - anytime it sent external routes into the OSPF domain. I wanted
00:12:51 - to do that review because the function of these special area
00:12:57 - types that are coming up help you to manage and filter these
00:13:02 - LSAs. Let's take a look. Behind the scenes, I went ahead and
00:13:07 - built the network that you see here on the screen right now.
00:13:10 - Three different areas, five different routers. Router three being
00:13:14 - the ASBR bringing RIP routes, redistributing them into the OSPF
00:13:18 - domain, and we broke them up into multiple areas because the
00:13:22 - router was getting a little crazy. We want to manage our routing
00:13:25 - tables. But let's take a look at router one. I'm going to jump
00:13:28 - into router one on the terminal and do a show IP route and you
00:13:33 - can see that router one is getting all of the inter area routes.
00:13:38 - You can see the WAN links that are coming from other areas, we've
00:13:41 - got the external routes that are being shut in from that RIP
00:13:45 - router, you can see them as the E2 routes. So even though I've
00:13:50 - implemented multiple areas, router one is still getting all of
00:13:54 - these different routes and the irony of these all is that router
00:13:58 - one's only way out of area two is router two in the first place.
00:14:03 - So why on earth would I want to fill router one's routing table
00:14:06 - with all of these routing information and all these detail about
00:14:10 - the WAN links and the other areas, the RIP external routes, when
00:14:13 - router one doesn't care. I mean router one just knows to go to
00:14:18 - router two to get out in the first place. It's almost as if router
00:14:22 - one is better fit for just a static default route than it is
00:14:26 - to run the full OSPF, but at the same time we are running OSPF
00:14:31 - and one of our administrative challenges has been to remove all
00:14:35 - the static routing. So we want to run OSPF but, hah, do you see
00:14:39 - our dilemma? Well, that's where this concept of stub and totally
00:14:44 - stubby areas come in. I love this concept for the sure fact that I
00:14:49 - love saying those names. I'm convinced that whoever created this,
00:14:53 - they had to come from California because they were probably thinking
00:14:57 - of like, "Yeah, let's create an area. Let's call it the stub."
00:15:02 - And a stub will have the criteria that it will block the type
00:15:07 - five LSAs from entering that area. But you know, we wouldn't
00:15:12 - step it up even more. Do you feel the California coming in here?
00:15:16 - And maybe we want a different kind of area that's like, totally
00:15:22 - stubby man, and that totally stubby area is going to block all
00:15:27 - the LSAs from other areas, like type three, type four and type
00:15:31 - five. Those will all be blocked from entering these areas. That's
00:15:36 - my envisioning of how this process was created. So that's the
00:15:41 - two different kind of areas. It's the stub area, or what's called,
00:15:44 - the stubby area will block type five LSAs from entering. Now
00:15:49 - think back, we did the fly-by-review. Was that the type five
00:15:52 - LSA? It was the external routes. Any route that was sent in from
00:15:59 - router three, will be blocked from entering a stubby area. These
00:16:05 - are piece of cake to configure. I'm going to go into my router
00:16:10 - and let's start off and see. On router two over here, the ABR,
00:16:14 - and I'm just going to type
00:16:18 - in the OSPF process. Area, and this is area two. Area two is
00:16:25 - a stub, that's it. As soon as I do that, area two is now configured
00:16:30 - as a stub and the neighbor fails. Because if you remember back
00:16:35 - to the HELLO packet, one of the things that must agree
00:16:39 - in my neighbor relationships is the stub flag. It's the one that
00:16:43 - was way down on the list and I said, "Ah we'll talk about this
00:16:46 - stub later." This is where we talk about it. The stub flag has
00:16:50 - to agree between neighbors so that means I have to go back to
00:16:53 - router one, go into router OSPF process
00:16:58 - which has to be done from global config mode. I'll get into the
00:17:01 - router OSPF and I'm going to type in area two stub, same command.
00:17:08 - Now as soon as I do that, we're going to see the neighbor relationship
00:17:11 - reform between router
00:17:14 - two and router one, these two router right here. Now router one,
00:17:18 - I don't think reports the neighbor relationship up and down to
00:17:21 - the screen. It's the logging method I have turned off. I'm going
00:17:25 - to type-in and show IP OSPF neighbors and sure enough it has
00:17:28 - reformed to that neighbor relationship. But let's check out what's
00:17:32 - different. I'm going to start over on router two and do a show
00:17:36 - IP route.
00:17:37 - Router two is the router that is connected right here to the
00:17:42 - backbone and area two. Now router two shows no change in the
00:17:47 - routing table. It's still seeing those external routes, the routes
00:17:51 - that the stub area was supposed to stop. Oops, my slide got jumped
00:17:56 - there. The stub area was supposed to stop but that's okay because
00:18:00 - router two is the ABR. It has all the info from area zero and
00:18:05 - all the other areas that are being injected and all the info
00:18:08 - from area two. The point of the stub area is it's supposed to
00:18:12 - filter the information from reaching the routers in the area,
00:18:17 - not the ABR. The ABR is always going to have all the info. So
00:18:21 - let's jump over to router one and see if that's really taking
00:18:24 - place. Then type in show IP route and,
00:18:29 - sure enough you can see it in action. All of the external routes
00:18:33 - have disappeared from router one's routing table and been replaced
00:18:38 - by this route right here. A default route is automatically generated
00:18:43 - by the ABR that says, "Hey, I know I'm filtering the routes but
00:18:47 - you can send anything that you don't know about to me because
00:18:51 - I know all those routes still and I will be able to get you there."
00:18:56 - We've effectively shrunk router one's routing table from something
00:19:00 - that looks like, let's scroll up here,
00:19:04 - right there. That was its old routing table. Something that looks
00:19:07 - like this with all the external routes all the way down to this
00:19:11 - that has just the default route here in play. Now, I know it
00:19:14 - doesn't look like much, of course in lab environment because
00:19:16 - there is only three external routes coming in. But man, that
00:19:19 - can have a huge impact if you have a ton of external routes,
00:19:22 - that are being redistributed into the domain. Well, let's take
00:19:26 - a look now at the totally stubby area, over here in area one.
00:19:31 - Remember, these types of areas should block everything from coming
00:19:36 - in. So, I'm going to bring up my prompt and hop on to route five.
00:19:39 - That's the router way over on the right hand side. Just to verify
00:19:43 - right now, show IP route, that it's getting all of those routes.
00:19:48 - Yeah, you can see external routes are flooding the table, other
00:19:51 - areas are coming in flooding the table. We got a huge routing
00:19:54 - table here. Huh! relatively speaking. So I'm going to change
00:19:58 - this area into a totally stubby area. Now the first thing I want
00:20:03 - to mention is TSA. It's for totally stubby areas, our Cisco proprietary.
00:20:08 - This is not an industry standard thing although many other vendors
00:20:12 - have implemented in their own ways. This is something that is
00:20:15 - supported only on Cisco routers. So I'm going to jump over to
00:20:18 - the ABR first, router four
00:20:23 - and go into the router process to turn this feature on. Now,
00:20:28 - even though this is a Cisco proprietary feature, the only one
00:20:33 - that has to be a true Cisco device is the ABR. Router four is
00:20:40 - going to be doing the filtering, stub areas, the stubby area
00:20:44 - feature is an industry standard. So as long as router four is
00:20:47 - an industry standard capable router, and can run the stub area
00:20:51 - flag, then it can handle the totally stubby area just fine because
00:20:55 - router four is the one really the one doing all the filtering.
00:20:58 - Did I say router four, I meant router five. Router five is the
00:21:01 - one that's just receiving what router four has to say. Here's
00:21:04 - the command to type in. Just one more step, area
00:21:09 - one will be a stub and we'll take it one step further and type
00:21:15 - in no summary. Stub, no summary, enter, converts that into a
00:21:21 - totally stubby area. They can see router five immediately fails
00:21:25 - because the stub flag doesn't agree anymore. You can see the
00:21:28 - neighbor relationship has been reset so I'm going to come over
00:21:30 - to router five, and just to prove it to you, I'm going to OSPF
00:21:33 - and just type in, area one stub. I'm not going to turn on the
00:21:38 - no summary flag, we're going to keep this one industry standard
00:21:41 - and not use the Cisco proprietary feature. That should bring
00:21:44 - the router relationship back online. There's
00:21:51 - my router, it's back online. I'm going to type in show IP route
00:21:56 - on router five. Now what should we expect to see before I hit
00:22:00 - that enter key? Router four is a totally stubby area blocking
00:22:04 - type three, four and five LSAs. That is, any external route that
00:22:08 - is type five, any ASBR
00:22:11 - IP address, let's type four, and any intra area routes, that's
00:22:17 - type three, those are supposed to be the summaries from other
00:22:19 - areas. So I should see just
00:22:23 - a default route. And sure enough we do. You see router five has
00:22:28 - received nothing but a default route from router four. Everything
00:22:33 - else has been removed from its routing table. Now, this was a
00:22:36 - real area, it would probably have more routers in it. We'd see
00:22:39 - other routes coming from our own area but router four effectively
00:22:44 - filters everything, from router five's routing table, and its
00:22:50 - topology database. So router five should have a completely clean
00:22:55 - database. I'll do a show IP OSPF database which has very little
00:23:00 - information, just saying, Hey, this is the router that's advertising
00:23:04 - your one summary route, which is our router right there. But
00:23:08 - everything else has been minimized down to nothing. Talk about
00:23:11 - savings and processor cycles. That's what the stub and totally
00:23:15 - stubby areas do.
00:23:18 - Now if the stub and totally stubby areas did not convince you
00:23:22 - that some beat surfer in California created this concept, this
00:23:26 - one definitely will. It is, no joke, a not so stubby area. Again,
00:23:33 - I can see the conversation because here's what happens on the
00:23:36 - screen. You can see that area five used to be a totally stubby
00:23:41 - area and the guy was like, "Oh yeah, the totally stubby area
00:23:45 - stops all LSAs..It's good." And then all of a sudden some design
00:23:52 - flaw jumps in the midst of thing, and router five gets connected
00:23:56 - to an external RIP network. And the California guy goes, "Oh,
00:24:00 - no way. Huh! Then I guess this is like a not so-stubby area.
00:24:09 - Well, but it's totally stubby, so maybe it's a not so stubby
00:24:15 - totally stubby area dude." Yeah that is, I kid you not, the technical
00:24:21 - term for what area one would be. Take a look. I've got router
00:24:25 - five sitting in area one. I'll do a show IP route. You can see
00:24:29 - it's still configured as a totally stubby area. I've got to get
00:24:34 - out of that voice. But it's because it is still getting the default
00:24:37 - route, all of the OSPF routes have been filtered, but the problem
00:24:41 - is its RIP ended up, or sorry, router five ended up connected
00:24:44 - to a RIP network out here. So now you have router five in area
00:24:48 - one that's essentially an ASBR, right? Because it's needing to
00:24:53 - send this RIP routes to the rest of the OSPF domain but in itself,
00:24:57 - it violates the whole rule of a totally stubby area anyway. Do
00:25:02 - you see what I mean? I mean, how can you have an ASBR sitting
00:25:05 - in area one when area one is still a totally stubby area, just
00:25:10 - like it was before. Well, that's where the not so stubby area
00:25:14 - comes in. What it does is it passes external routes through a
00:25:20 - type seven LSA.
00:25:22 - This LSA was engineered to kind of trick the area one. Even though
00:25:29 - area one is still a totally stubby area and it denies type three,
00:25:32 - four and five LSAs. The people that be created these areas and
00:25:36 - said, "Well, I'm just denying those three LSA types and, you
00:25:41 - know, we need type four and five to really have an ASBR sitting
00:25:45 - in area one. Let's just go ahead and trick it. Let's make up
00:25:49 - some other LSA types. Let's make it type seven. And type seven
00:25:53 - LSAs will tunnel through these areas, so as router five sends
00:25:58 - those RIP routes over to router four, they come across this type
00:26:02 - seven which all the routers in that area, if there were other
00:26:05 - routers, would just say, "That's a different LSA. We're not filtering
00:26:10 - that even though we're totally
00:26:12 - stubby area." Router four gets it and immediately realizes, "Aha,
00:26:16 - type seven LSAs. Those are external, so as I send them into the
00:26:21 - rest of the network, I will send them as type five LSAs." It
00:26:26 - converts them back to the original form that they were or the
00:26:30 - original form that they should be to be considered external routes.
00:26:34 - So type seven, just like we saw virtual links kind of tunneled
00:26:38 - areas through each other, these LSAs types sort of tunnel through
00:26:42 - stub and totally stubby areas and that's by the way where the
00:26:46 - name comes from. A not so stubby area represents a stub, a not
00:26:50 - so stubby, totally stubby area represents a totally stubby area.
00:26:56 - So here's what the config looks like. I'm going to go on router
00:27:00 - five and go into router OSPF one and the first thing I'm going
00:27:05 - to type is, this is area one. I'm going to type in area, one,
00:27:10 - stub and then put a note in front of that. I'm turning off the
00:27:14 - stub capabilities because I need to convert this into a not so
00:27:19 - stubby area. The way I do it is type in area one, instead of
00:27:23 - a stub I'm going to type in NSSA. That
00:27:27 - stands for a not-so-stubby
00:27:29 - area. Just so you know I didn't make that word up. Now I have
00:27:33 - to go over to router four, okay.
00:27:36 - Router four is the one, and I don't know where I am at here.
00:27:40 - Router four is the one that originally converted this into a
00:27:44 - totally stubby area. I'm going to type in no area one stub, no
00:27:49 - summary which is the totally stubby flag. I'm going to type in
00:27:53 - area one NSSA,
00:27:56 - not so stubby area plus no summary. That's how we put the,
00:28:03 - oh, did I, I just need Just type in no area one stub to turn
00:28:09 - off the stub flag. There we go. Area one NSSA no summary, which
00:28:15 - now says this is a not so stubby totally stubby area and it will
00:28:19 - still be filtering those routes out. Before we do the redistribution,
00:28:23 - let's go over to router five and sure enough, we should be able
00:28:26 - to see router five is, oops,
00:28:31 - ah there you go, just took a second. Router five is now receiving
00:28:34 - that default route from router four just like it was configured
00:28:38 - as a totally stubby area but now router five would be able to
00:28:43 - redistribute those RIP outs to router four and router four will
00:28:47 - receive them as those type seven LSAs. Let's do that. I'm going
00:28:51 - to go into router OSPF one and again, I know we haven't talked
00:28:54 - about redistribution yet. But I'm going to type in the command
00:28:57 - redistribute RIP which sends all RIP routes in the OSPF and it
00:29:02 - just set flag of subnets, and I'm going to set
00:29:08 - the default metric of this routes to just, let's put them at
00:29:11 - ten. Now, I'll explain that whole command later on. That sends
00:29:15 - the RIP routes into OSPF. Now, actually before I do that, I'm
00:29:19 - going to type in show IP OSPF database,
00:29:23 - and you can see, look at this, we have type seven
00:29:29 - external link states. Routes that are being received via RIP.
00:29:33 - Now I have some routes in here that shouldn't be there but that's
00:29:37 - just because I'm kind of simulating the RIP network behind us.
00:29:40 - These are the routes that are coming in your RIP, okay.
00:29:43 - You can see all of them in the routing table, RIP routes jumping
00:29:46 - in here that are being advertised in the database as type seven
00:29:51 - LSAs. Now let's hop on over to router four to show IP OSPF database
00:29:58 - and you can see they are being received by router four. Look
00:30:02 - at this, router four is receiving them as type seven LSAs as
00:30:07 - well, but it is advertising them out as type five LSAs. Now the
00:30:14 - list shrinks down here, you can see I have a bunch of type seven
00:30:17 - and it shrinks down to just one of them. The reason it shrinks
00:30:20 - down is because, as I mentioned, some of these should not be
00:30:23 - showing up in the RIP routes, they just are because I am simulating
00:30:26 - them. So it's correctly adjusting them as it's advertising them
00:30:29 - out as type five. Now if I were to come up here to, let's jump
00:30:33 - over to router two. Router
00:30:38 - two should not see type seven LSAs at all. It should only see
00:30:42 - the type five because router four is doing the conversion back
00:30:46 - to type five. Type seven is only between routers and that not
00:30:50 - so stubby area. So I'm going to type in show IP OSPF database,
00:30:53 - and just as expected, type five LSAs are the only thing we receive.
00:31:00 - You see the summaries, those are the type threes and fours, the
00:31:03 - router that's type two, some other summaries over here, some
00:31:08 - other router link states, which are type two, type one but overall,
00:31:12 - we can see that there are no type seven LSAs. They've all been
00:31:15 - successfully converted back to the type five.
00:31:19 - Last thing I'll say on not so stubby areas is that they are usually
00:31:23 - designed goof ups. They are usually set up where you had the
00:31:26 - stub or totally stub and then oh, we have some external network
00:31:30 - that we merged into or whatever the case maybe, and we have to
00:31:33 - redistribute. So in the interim, while we were redesigning the
00:31:37 - network, we'll convert it to a not so stubby area to let things
00:31:40 - work in the meantime.
00:31:43 - Last thing I mentioned in general, with the stub and totally
00:31:46 - stubby areas, is that you've now seen a major method you can
00:31:50 - use to reduce the routing tables and topology database in huge
00:31:55 - ways on the routers and these fringe areas.
00:31:58 - With those design options comes one major criteria, and that
00:32:03 - is there should only be one exit point from a stub or totally
00:32:08 - stubby area. You can have multiples for redundancy, but if you
00:32:12 - do have multiple, keep in mind that you have now dual default
00:32:17 - routes that are going to be injected into a specific area, making
00:32:22 - the routing potentially inefficient. If you design it poorly,
00:32:26 - meaning that you end up having load balancing happening, when
00:32:29 - load balancing shouldn't be happening because router one doesn't
00:32:32 - really have an idea of what is beyond its own area depending
00:32:37 - on the type of stub you deploy. So that's why they call them
00:32:40 - stub and totally stub is because those areas are supposed to
00:32:44 - be just a stub of the network. There's only one way in and one
00:32:48 - way out of them. Now that known, let us wind things down. We
00:32:52 - started off this whole video by taking a look at Virtual Links
00:32:56 - which is essentially a band aid for the network, a way to patch
00:33:00 - the network, while you redesign it so all areas are directly
00:33:03 - connected to area zero. We then got into the special OSPF area
00:33:07 - types which are for the stub, the totally stub and the not so
00:33:11 - stubby area and saw the implementation of those one by one as
00:33:15 - we walk through a live topology and saw the effects of each one
00:33:19 - of those area types on our routing tables. I hope this has been
00:33:23 - informative for you and I'd like to thank you for viewing.

OSPF Routing: Area Types and Options, Part 2

IPv4 Redistribution: Controlling Routing Updates

IPv4 Redistribution: Implementing Simple Redistribution

IPv4 Redistribution: Implementing Advanced Redistribution

BGP Routing: Foundation Concepts and Planning

BGP Routing: Implementing Basic BGP

BGP Routing: Implementing Basic BGP, Part 2

BGP Routing: Tuning Attributes

BGP Routing: Tuning Attributes, Part 2

Path Control: Configuring Path Control

IPv6 Routing: Understanding and Implementing IPv6 Addressing

IPv6 Routing: Implementing IPv6 Routing and Routing Protocols

IPv6 Routing: Implementing IPv6 Routing and Routing Protocols, Part 2

IPv6 Routing: Transitioning to IPv6 and Certification Review

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Jeremy Cioara

Jeremy Cioara

CBT Nuggets Trainer

Cisco CCNA, CCDA, CCNA Security, CCNA Voice, CCNP, CCSP, CCVP, CCDP, CCIE R&S; Amazon Web Services CSA; Microsoft MCP, MCSE, Novell CNA, CNE; CompTIA A+, Network+, iNet+

Area Of Expertise:
Cisco network administration and development. Author or coauthor of numerous books, including: CCNA Voice 640-461 Official Cert Guide; CCNA Voice Official Exam Certification Guide (640-460 IIUC); CCENT Exam Prep (Exam 640-822); CCNA Exam Cram (Exam 640-802) 3rd Edition; and CCNA Voice 640-461 Official Cert Guide.

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