All right, so now we are going to dive into discussion on configuration and verification
of OSPF version 2. So, that is for IPv4. The topology we're going to work with today looks
like this. So, we need to make sure we are aware of the boundary points of where we're
enabling OSPF versus where we're not. So, as I was describing yesterday, when you look
at the topology, something like this means OSPF is running here, OSPF is running here,
but it's not running here. So, I'm only going to be configuring on those two interfaces
for R1. R2, we're configuring it here, we're configuring it here, we're configuring it
here, but not here or here. So, that's going to be important for the certification exam
just to make sure you recognize those boundary lines. So, that way you're not configuring
it on the wrong interfaces, because if you do, you might have a bad config, a poor config,
or they might just simply say, well, you weren't supposed to configure it there, so you don't
really understand what you're doing. And as a result of that, well, we're going to have to
give you zero on this particular question or simulation or whatever it happens to be,
because we don't really know how they grade everything. That's a very well-kept secret
in the world of certification exams for Cisco. So, we just have to assume that if we don't do
exactly what they say, they're going to penalize us for that when it comes to the certification
exam. So, with that said, let's begin right now by taking a peek at, do we have OSPF running at
all? And the answer to that is no. Just before class, I went ahead and I disabled OSPF on all
of my devices. So, if I type in Show IP Protocols, you'll see there's nothing here related to OSPF.
So, if you go to every single device, OSPF has been disabled. So, nothing there for OSPF. It
would actually say OSPF in the output. So, there's nothing here listed. It's just the running
protocols application. So, that'd be like for software-defined networking features and stuff
like that. So, we won't get into that right now. Oops. Oh, I should have never highlighted that.
Show IP Protocols. Right. Again, nothing running there. And same thing with branch. So, we don't
have OSPF running at all. So, the first thing I want to do is I just want to focus on R1 right
now so we can understand the steps and procedures we need to go through. So, first of all, I'm going
to create a routing process. And for OSPF v2, we type in the keyword of router. Then we type in
OSPF. And then it asks us for our process ID. So, this process ID is just a locally significant
identifier for the OSPF process. That's it. So, this is something that does not have to
match on all the other routers. For those of you with EIGRP experience, you type in router,
EIGRP, and then you actually specify what is called an autonomous system number. So,
let me just show you that. You'll see how it says autonomous system number for EIGRP.
That is a number that has to match on all the routers that are going to be sharing information
with each other. So, if I was configuring EIGRP in this environment, that number would have to
be the same in all the routers. But for OSPF, it does not have to be the same in all the routers
because it's a totally different thing. It is a process ID instead. What does that mean? It means
on my router, I can run multiple OSPF processes. So, I could have like process one for something.
I could have process two for something else. When might you see that typically? With, for example,
like a service provider. A service provider might have multiple customers connected up to them.
So, for example, let's just say this is a service provider router up top, R1. Then I might have a
customer connected here. I might have a customer connected here. If that's the case, and I was
running OSPF with those customers, I would want to make sure that there's two different OSPF
processes, one for each customer. That way their OSPF, let's say process one, is for that customer,
and OSPF, let's say process two, is for that customer. And that'll make sure that those
processes are kept isolated and separate from each other. In addition, we want to do things
like VRFs and everything else, which is not part of this discussion. We'll talk about that later on.
But in the end, right, by having different processes, then I could have different instances
of OSPF running on my device for isolation purposes. So, the key here is, is that you're
going to pick a number that's locally significant for you and your device for OSPF, and it doesn't
have to match on every other router. It doesn't have to. I like to make it match just for simplicity
sakes for my brain. So, I'm just going to pick OSPF process ID one. All right. So, now what I
want to talk about, now that it's enabled on the device, and if you type in something like do show
IP protocols, you'll see that it is now running. OSPF process ID number one. Notice here there's
something called the router ID. We mentioned that router ID a multitude of times yesterday.
We saw the router ID was in the packet header or the OSPF header, I should say.
And what did we say the router ID was for? The router ID is a number that uniquely identifies
this router to all the other OSPF routers. Now, when you look at that, it looks like,
it feels like, it tastes like, I won't stick out my tongue, I promise you. All right. It smells like,
smells like an IPv4 address. It totally does. But what you need to learn here is that it is not
an IPv4 address. It is a router ID. And your router ID can be any number from 0001 all the
way up to 255, 255, 255, 255. That is your range for router IDs. You cannot do 000. And the reason
why is because 000 actually shows up in your database as the default route. And it's an actual
identifier for that default route and it can cause conflict. So that's just one of the reasons why
you can't use 000. All right. But other than that, you can use any other number as your router ID.
So what is a router ID? A 32-bit number that uniquely identifies that router to all the other
routers in the OSPF environment. And you saw the router ID is going to be in our what? OSPF header.
So for every message our router sends, it puts the router ID in it.
Now, how is this router ID chosen? Okay. The router ID is going to be chosen in one of three ways.
So what the router does first is it looks to see if you manually configured the router ID.
Well, I think we all know that I did not manually configure the router ID because you never saw me
manually configure the router ID. If I wanted to manually configure the router ID, I would use the
router ID command and then put in the router ID that I want to use in dotted decimal notation.
32-bit number in dotted decimal notation, any number in that range from 0001 all the way up
to 255, 255, 255, 255. If I do that, that is what's going to be used.
If I don't do that, then the router has to dynamically figure out what the router ID is.
And so what do we have on our routers that are also 32-bit numbers, folks?
What else do we have on our routers that are also 32-bit numbers? Chat in.
Well, not interfaces, not loopbacks. Okay, what do we have that is a 32-bit number?
IP addresses, exactly, right? An IP address. So since an IP address is a 32-bit number,
could the router use one of those as its router ID? Yes, of course it could. Of course it could.
So that's what it does. It looks for the IP addresses that are configured on this device.
And where do we configure our IP addresses? On interfaces. So if we type in do show IP
interface brief, there's the IP addresses that are configured on this device.
So here's what it does first. It says, well, since Raymond has not configured the router ID,
because it knows that I'm the one who configures it, Raymond, right? Of course.
Since Raymond has not configured the router ID,
then I need to look at the IP addresses that have been configured on this device.
And figure out what I could use as the router ID. I just need a 32-bit number.
So first though, it looks for what? It looks for loopback interfaces. Okay,
what is a loopback interface? A loopback interface is a virtual interface
that you can configure on your router and give it an IP address.
And then that loopback interface is reachable through any of the other interfaces on the device.
So think of a loopback interface like a centralized IP address on the device
that can be reached through any other interface and is always up,
up as long as one other interface is up, up on the device.
So it's going to look for loopback interfaces first.
Then it's going to go ahead and say, if there's a loopback interface,
I will use the IP address of that loopback interface. So in this case,
there's no loopback interface, right? So since there's no loopback interface,
what does it have to do? It has to then look at all the other interfaces that are on the device
that have IP addresses. And in this case, it has chosen what? The highest. It's going to choose the
highest IP address of those interfaces. So in this case, you can see it is going to choose the
highest. It's 203.0.1.13.90.
All right, 203.0.1.13.90. There you go. So if I configure the router ID,
such as router-id, we'll go 0.0.0.1 as an example.
We're going to pick that R1. I'm going to use 0.0.0.1 just to keep it simple for us as we
explore our device. Do show IP protocols. You'll see in this case, I'm now using 0.0.0.1.
Now, I did not have to restart the OSPF process in this case because I don't have any
neighborships right now. If I had any neighborships, then I would have to force
OSPF to reset itself. And you do that by typing in clear IP OSPF process. Now,
it will tell you to do that, meaning that if you have changed the router ID and you already have
neighborships, it'll say you've got to clear the OSPF process. So you type in this command,
you're good to go. All right, let's go over to R2 and try to demo this a little further.
Show IP route. No, show IP interface brief. All right, so take a peek at this. I've got
one loopback address right now, 10.2.2.2. Let's go ahead and create another loopback.
Oh my gosh, I'm having so much trouble typing today. Oh my goodness, what is going on? All right,
focus. All right, router. Oh, no, interface, interface, interface, loopback, 192. My brain's
all over the place. IP address, 192.2.2.2.2. All right, let's go ahead and try this again.
192.168.255.125.255.255.255.255. All right, so now let's go ahead and take a look at do show IP
interface brief. So now you'll see here that we have our interfaces with IPs and we have two
loopbacks. So let's go ahead and type in router OSPF1. So all I've done is enable OSPF. We haven't
set the router ID on R2, but what I want to point out to you is that the router says, hey, did you
configure router ID? No, you didn't. Okay, so now let's look for loopbacks. Oh, look, we've got two.
Which one has the higher IP address? That's it. Whichever one has the higher IP address is the
winner. So the router ID should be 192.168.255.1 in this case. Do show IP protocols. And you'll see
here that it is 192.168.255.1. So remember this for the exam. If it's not manually configured with
the router ID command, then what happens? The router looks for loopback interfaces.
If there is one loopback interface, that's the IP it uses. If there's more than one loopback
interface, then it's going to use the highest IP address of those loopback interfaces.
If there's no loopback interfaces, then it's going to use the highest IP address
of the remaining interfaces. All right, so now there was a chat that came in that says,
so it'll choose the highest IP address unless the interface is down. That's a good question.
Not something that would come up on the certification exam, all right? What I've
just told you up to this point is what you want to know for the exam. But you know what I think
is a really good idea? Let's test that right now, right? Let's go ahead and test that.
Let's go to branch. Let's type in show IP interface brief. What is our highest IP address?
It's this one right here, correct? Let's bring that interface down and see if it still uses it.
Let's just test it and see what happens. So, configure terminal, interface, gigabit Ethernet
0 slash 1. And let's go ahead and type in shutdown. So, then we'll take a look at the
output of show IP. Oops, I got to... Okay, so let's try this. 198.51.100.46 is now down, down.
Let's enable OSPF. Okay, so look at this. This one is down, administratively down, right?
This one, the next highest is down, down. This is going to be fun. So, let's see which one it picks
when it's all said and done.
Again, not something you're going to have to go this deep on the certification exam,
but take a peek at that. The interface has to be up. Wait, we got a loopback? Oh, you're right,
we've got a loopback. So, that was the winner. I didn't even notice the loopback there.
Yes, Casey, you said right, the loopback would be the winner. You're right.
So, the loopback destroyed me in that demonstration there. All right, no problem.
This is easy. Let's do this.
Let's also bring down the loopback. How does that sound? So, what I'll do is I will remove OSPF.
No router OSPF 1, so that's gone. Let's go ahead and type an interface loopback.
1, 2, 9, it looks like. 1, 2, 9. Let's go ahead and shut it down.
So, now we'll see that the highest IP is down. The loopback is down. The next highest is down.
So, let's see if it's still using that loopback even though it's down.
But you have 1716. Who's 1716? All right, take a peek at that. So, here's the moral of the story.
It won't use the loopback. It won't use the loopback. It won't use the loopback.
But you have 1716. Who's 1716? All right, take a peek at that. So, here's the moral of the story.
It won't use it if it's administratively down, but it'll use it if it's down-down.
For the exam, I wouldn't worry about that. For the real world,
maybe something you care about, but to be honest with you, I don't care.
Why? Because you should always manually configure your router ID.
Because when you manually configure a router ID, is there any chance it'll dynamically change on
you? Yes or no? No. So, with that in mind, isn't that the better option to go with? Absolutely,
that is the better option to go with in a production environment. But for the exam,
right, knowing stuff like you see on this page for the router ID,
it could be manually configured with the router ID, right? Let me just write up here 32-bit.
That's all it is, a 32-bit number, manually configured. If not, then it goes through this
process, right? In addition, as we saw, if the interface is administratively down, it won't use
it. But if the interface is down-down, it'll still use it. Now, exactly. Another thing
I want you to be well aware of is that OSPF is about what? It's about learning information
so you can do what? So, you can build your routing table. Let me repeat that in case you
blanked out. What is OSPF all about? Learning and sharing information so you can populate your
routing table. So, does the router ID have to be something that is routable? Does it have to be
something that's in your routing table? No, of course not. Remember how OSPF works. We are going
to be enabling routing for OSPF on this device, specifically on the interfaces. And after I do
that, I form neighbor adjacencies. Once the neighbor adjacencies is done, what do we say?
We're going to exchange LSAs. So, this router here sends out its link state advertisement.
For example, the type 1 LSA. What does R2 do with that? R2 makes a copy of that LSA
and then it floods it out all ports participating in OSPF. So, it makes a copy of it and floods
it out. So, if I got one in and I have two ports, I got to copy it twice and send it out to my
neighbors. So, when they get it, they're receiving a copy of the original, okay? Unmodified. An
unmodified copy of the original. So, this happens from neighbor to neighbor to neighbor to neighbor.
This happens before routing even happens, right? So, routing is not even set up yet in my environment.
But when I start enabling my interfaces, the fact that I send an LSA to my neighbor,
it makes copies of it and sends it to its neighbors who makes copies of it and sends
it to its neighbors, the flooding process. That is how, in the end, they learn and then they
populate their routing table. So, the router ID is not something that has to be in your routing table.
The other day, I got an email and that was the question I got, right? Well, the router ID,
why is that? Well, you know, why all of a sudden when we changed it in the lab? It was a CCNA
question. We changed it in the lab, but it's not in the routing table now. How in the world does
that work? Okay, well, the router ID doesn't have to be in the routing table because you're not
using it for routing. You're using it as an OSPF identifier so you know who's who and what they
know and what they're flooding. So, right now, we have what? We have, for example, on R1, what's
my router ID? 0001. Will I ever find that in the routing table? No, because that's not even a valid
IP address. You can't even put that as an IP address on any interface. That is an invalid
IP address. Just like what? Router ID 255, 255, 255, 254 is an example, right? Is that an invalid
IP address? Possibly. No, it is. Absolutely, it is, right? Because that's in the class E addressing
space. But it's a valid router ID. It's a valid router ID. So, don't let that throw you off. Don't
think that it has to be in the routing table. Never. Absolutely not. It's a router ID. All right.
Now that we got that out of the way and you're able to answer questions on the exam about it,
in case you said, that's why I'm a fan of using an invalid IP address. Same with me.
I'm like, I might as well use things that are not even IP addresses as my router ID. So,
for documentation purposes, it's so much easier for me. Makes so much more sense when it's all
said and done, right? Because now I can label this router as 0001. I can label this one as 0002,
003, 004, 005, 006, 7, 8, 9, 10, 11, 12, 30, right? Let's just do that. That's easy for me. I like
that. I really do. That's my preference. You don't have to do it that way, but that's my preference,
right? And based on documentation, that's how I know each router. And then when I look at my
database later, my database is going to be showing me information based on router ID. So,
I know, oh, that's router one, that's router two, that's so-and-so, that's so-and-so,
that's so-and-so, right? Based on my document, easier for me as an admin.
All right. So, now that we've got that done, what do we want to talk about next? We want to
talk about the fact that we have to now start enabling the routing process on interfaces.
So, enable OSPF on interfaces. So, right now, OSPF is enabled globally,
but it's not doing anything. It is literally not doing anything
because I have to have at least one interface participating in OSPF for this whole thing to
get started. So, let's focus on Gigabit Ethernet 050. So, why would I want to enable OSPF on
Gigabit Ethernet 050? All right. A couple of different reasons. So, reason number one,
so I can join multicast group 224.0.0.5. That is the all OSPF routers multicast
group, right? So, I join that multicast group. What can I do now on that interface?
I can send plus receive hellos to form neighborship.
So, I enable the routing process on the interface, so I can join that multicast group and then,
too, send and receive hellos so we can form neighborships. So, I enable on this interface.
I can send you hellos. I enable it on this interface. You can send me hellos.
And then, what are those states we go through? We said down, init, two-way.
Down, init, two-way. And then, xstart, exchange, loading, full.
So, what do we do after that? We then have the ability to sync with each other.
So, why? Sync with each other, essentially share info. So, why do we enable the routing process
on the interface? So, we can form neighbor adjacencies and share information. Okay. But
there's another reason why we do this, and most people are not taught this. I teach it in CCNA.
I teach it here. And this is probably even more important than what we've just talked about here,
in my opinion. Why? Because what we're doing is we're injecting network ID
of interface into link state database,
injecting the network ID of interface into the link state database. So, the network ID
of this interface gets put into my link state database. Why is that important? Why is that
important? Because I need to tell you about all the networks I am connected to, as well as
everything else I've learned from other devices. So, if I'm not injecting my own network IDs
into OSPF, you would never know that I'm directly connected to that network.
And if you don't know I'm directly connected to the network, how do you build?
What? How do you build? What's that thing that we have with OSPF? A topological map.
So, same thing is true about EIGRP, except you're not building a topological map with EIGRP, right?
But with EIGRP, you enable the routing process on interface, the network ID gets injected into
the topology table for EIGRP, and now you can tell the other routers, yeah, this is what I'm
connected to. But now your neighbor is the only one who knows that, but at least your neighbor
knows that, and it learns about those networks from you. All right. So, let me show you how we
enable the routing process on an interface and all this magic happens. So, what we're going to do,
first, we're going to type in do show IP interface brief.
And then we're going to type in interface gigabit Ethernet.
What are we doing? Zero size zero on our one right now? Perfect. All right. So, gigabit Ethernet,
zero size zero, we're going to enable the routing process on this interface, and it's up, up. If
your interface is not up, up, then it's not going to be able to participate in the OSPF process.
It'll be enabled on it, it just won't participate because it's down. So, any interface that is down,
the network ID doesn't get injected into OSPF. So, it's got to be up, up for the network ID to
get injected into OSPF. There is nothing here listing multicast addresses. So, right now,
we're not part of the group 224005. We're going to see this change here momentarily.
If you look at the IP addressing space, it's 240.23.0 slash 30 is the network ID. That's
what it would be. So, that's what we're going to find in our link state database after.
So, right now, let's type in do show IP OSPF interface. This will tell us what interfaces
are participating in the routing process, and you'll see no interfaces are participating in
the routing process. And if we type in do show IP OSPF database, you'll see there's nothing right
now in our OSPF database either. It's empty. The only thing we see is my router ID.
Uh-oh. There we go. That took a little bit of time to update. All right. A little networking
lag there between my systems. Hopefully, that doesn't last all day. But you'll see right there
how we have right now an empty database. So, first thing we're going to do is we're going to
go to interface gigabit ethernet 0 slash 0, and we're going to type in IP OSPF 1 area 0. I'm
starting to think I don't have a typing problem. I think there's a lag problem right now with me
in the demo environment because this is a demo environment that's somewhere else where we have
all of our racks set up, and I might be having a connectivity issue with it today as we just saw
with the lag. So, maybe I'm not typing that bad. We'll go with that story. All right. So,
now that the interface is enabled for OSPF, let's type in do show IP OSPF interface brief.
We'll see that we have this interface participating in the routing process now,
gigabit 0 slash 0, a part of OSPF process ID 1. It's in area 0, right? Area 0. That's what I
typed in there. So, I enabled that interface, put it in area 0. That's its IP address. That's
its mask. That's the cost. Right now, it's going through the DR BDR election process. That's why
it says wait. And you'll see it's still going through that process. It's about a 40-second
process. Once that's done, it has elected itself as a DR. So, we'll come back and talk about that
later on today what all of that means if you're not familiar with that. All right. But now,
I want to take a look at my database, do show IP OSPF database. Whoa. Look at that. What are we
looking at? We're looking at the type 1 LSA that I briefly introduced you to yesterday.
That's a type 1 LSA. How do I know? Because it says router link state. That's what that means,
type 1. More on that later today. We'll actually talk about those LSAs later today. But notice the
link ID is 0001. That's my router ID. Notice that the advertising router is me, 0001. Look at the
link count, one. One link. One of my interfaces is participating in OSPF. That's what that means.
One of my interfaces is participating in OSPF. Let's crack this open.
There you go. I have injected the network ID of that interface into OSPF locally.
For me. So, what does that mean now? It means when I form a neighbor adjacency with somebody,
I will send them this information. And they will now know that I am connected to this network.
Remember, we said a bunch of puzzle pieces, right? Bunch of puzzle pieces that all have to
be put together to build the puzzle. Puzzle piece, that's all it is. All right. What about our other
interface? Gigabit Ethernet, 0 slash 1 in our diagram up here. Okay, let's do that one. Interface,
Gigabit Ethernet, 0 slash 1. IP OSPF 1, area 0. Let's take a peek at our database now.
Crack it open. Now both of them are in there. So, you see, by enabling the routing process
on an interface, you inject the network IDs into your link state database, into your type 1 LSA.
So, that way there, when you form neighbor shifts with other routers, you can tell them, hey,
I am R1, and these are the links that are directly connected to me.
So, if every router does this, and every router gets this information, then they have the ability
to put puzzle pieces together. Now, there's more than just the type 1 LSA. That is part of the
puzzle building process. But this is your most fundamental LSA, the most important one, the one
that starts building everything, and the one that uses Dijkstra's shortest path first algorithm
calculation every single time in its most aggressive form that it can possibly be done in.
That's what you're dealing with in this case. So, remember we talked about multi-area, right?
Why multi-area? Because this LSA will never go over here. Type 1 LSAs never cross area border
routers. More on that later, and you'll understand why that is. Now, you might be saying, well, then
how do you get from here to there? Okay, because of other LSAs. You got to learn all, you got to
learn about five of them here for the exam. I'll teach you all five today. This is just one of them
so far. All right. So, now that we have that done, let's go over to DSW1. And on DSW1, we are going to
enable OSPF on gigabit 1 slash 0 slash 13. And as soon as we do that, folks,
we are going to do what? Form a dynamic neighbor adjacency. Why? Well, if we go back to R1
and we type in do show IP interface gigabit Ethernet 0 slash 0. Notice how I have now joined
multicast group 224005, the all OSPF routers multicast group. So, that means I'm sending
hello packets now. Do show IP OSPF hello. No. Do show IP OSPF packet hello. No. All right. Show.
Oh, no. Debug. I meant to type in debug. Debug IP OSPF hello. That's what I should have typed.
There you go. So, you'll see I'm sending out a hello packets out my interfaces.
There you go. So, I sent one out gigabit 0 0. I sent one out gigabit 0 slash 1.
Every 10 seconds by default. So, they're going out, but DSW1 isn't configured yet.
So, if we go to DSW1 right now, and we go to interface gigabit 1 slash 0 slash 1,
and we type in IP OSPF 1 area, what? Area 0. Remember, area has to match. Area has to match.
Okay. Type that in. We should see here. Boom. We just went from a net down to a external exchange
loading full. We're good to go. We just went through the whole thing. We're full on. We're
down to a external exchange loading full. We're good to go. We just went through the
whole thing. We're full already. That was fast, wasn't it? Woo. That was way faster
than yesterday when I explained it to you in, what, 45 minutes? All those different stages.
But now, let's go back to R1. And on R1, if we look at the output of show IP OSPF database,
what are you going to see? Whoa. I've got information from someone else now. Someone else.
I don't like that router ID. Let me show you what happens if I change it after a neighborship.
So, what we're going to do is we're going to type in router OSPF 1, router ID 0.0.0.3. So,
we're going to go 1, 2, 3, 4, 5. That's what we're going to do today.
It's telling me, remember what I said, you're going to have to clear the OSPF process because
there's already a neighborship. Let's do that. Yes, I want to do that. You'll see this
neighborship is going to flap. And then we're going to reform our neighborship.
And then once our neighborhood is reformed, we'll see over here on R1,
now we're going to learn from 0.0.0.3.
Come on. My impatience with OSPF runs strong today.
Okay. There we go. Just patience. That's all it takes. So, I'll go back to R1. You'll see now
0.0.0.3. And notice what it says. I have one link. So, if I open up the database right now in R1,
and we look at R1's database, and we look at the information inside of it,
especially the information from who? From DSW1. It'll say that that interface is participating
in the routing process. This one right here. And it has a certain IP address on it. Well, R1
then says, hey, I have an interface in that same network. So, that means we are connected together.
But I also know we're connected together. Why? Because we're neighbors. Right? So,
because we're neighbors, I already know that. But I know that this is what you call it. That's
what I call it. We're there. We can now build our quality, and we can share that information
with other people now. Other routers, I should say. But something I want you to realize is,
remember how we say everybody's got to be synchronized in the area? So, all four of
these routers in area 0, they're going to end up with the exact same database for area 0.
Go to DSW1 right now and type in show IP OSPF database. They're the exact same. Just pay
attention to this. Look at this. R1, DSW1. R1, DSW1. R1, DSW1. That's pretty incredible.
All right. Let's refresh this. Right now, they're perfect, except for the age timer.
The sequence numbers were off a bit. Let's try that again. Get that there. Get that there.
There you go. The sequence numbers were off a bit because they weren't fully, fully synchronized,
but now everything should be normal. Yep, there you go. Now, they're fully synchronized. Look at
that, except for the aging timer, and that's okay. Everything else is the exact same.
That's what is required in an OSPF area. If there's ever a tiny discrepancy in any of these
values except for the age, then that means you're not synchronized properly. And that is that,
because that means the routers are not seeing the topology the exact same way, which means you have
something wrong somewhere that you're going to have to figure out. All right. Great news is,
on the exam, you're not going to be digging this deep into the database to figure that stuff out.
But I'm just trying to give you a real-world picture of OSPF.
Every one of those routers have to have the exact same database, same information,
right down to sequence numbers, checksums, all of that stuff.
Let's go ahead and enable this interface now on DSW1, gigabit 1.0.0.14.
All right. Take a look at my database now. You'll see it now says two for DSW1.
Why? Because now we have those two interfaces participating in the
routing process with those two different network IDs.
Just like if we now type in do show IP OSPF interface brief, you're going to see,
there they are, 13 and 14, participating in the routing process.
That link count should match what you have locally configured.
I go to R1 now, right? Update the database. You'll see it now says two as well.
Why? Because we exchanged LSAs. We've updated each other about that information.
All right. But watch this. Are you ready? What is this network right here?
What is this network right here? Okay. It is listed as 10.40.23.4.30.
Is R1 directly connected to that? No, it's not.
Has R1 learned about that? Yes. Why? Because DSW1 injected that information
because DSW1 injected that network ID into its database and it shared that information with R1.
So if I go to R1 and I type in show IP route,
there it is. So R1 knows how to get there because DSW1 told it.
That's how OSPF works everywhere. Everywhere. So when we have OSPF running here eventually,
R1 will learn about that through link state advertisements.
It'll learn about this network both from DSW2 and from R2. Because don't forget R2 is part of
that network. R2 will send out an LSA and say, hey, I belong to that link, that network. DSW1,
DSW2 does the same thing. So R1 then says, okay, you're both, you're both telling me the same
thing. That means you two are connected together. That's how R1 is going to be able to figure that
out. Yeah. Pretty cool when you think about it that way. So all these different pieces of the
puzzle, the database come together and then R1 can say, okay, so you're connected to that,
you're connected to that. What's the quickest way to get there? Is it quicker to go this way
or is it quicker, let's say, to go this way? Well, obviously it'd be quicker to go this way
because it's only one link to get there. If I go this way, it's two links to get there.
If I go this way, it's two links to get there. So based on cost,
R1 will install the path this way in the routing table to get here.
It's learned about it two different ways, but in the end, both OSPF, meaning administrative
distance is the same. And then through metric, it figures out that going this way is faster.
Therefore, it puts that one in the routing table.
Now, let me ask you this question. Do we need to enable OSPF on our SVIs?
Yes or no? I mean, because think about it. Join the multicast group,
send and receive hellos, so that way there I can synchronize with routers.
What do you think, folks? Do I need to enable OSPF on my SVIs?
I mean, is there anybody I need to form a neighbor adjacency with?
No. Therefore, do I have to join the multicast group to send and receive hellos?
No. Do I have to share any information with anybody out those SVIs? No.
No. But the answer is yes. You need to enable OSPF on the SVIs. Why? Why? Because of number four.
Inject the network ID of, oh, it says off, of interface, there you go, into the link state
database. How is R1 going to learn about my networks? If the interfaces are participating
in the routing process, that's how R1 is going to learn. I need the network ID injected into OSPF.
Okay. So, enable the routing process on the interface. Let's look at this.
Interface, VLAN 10, IP, OSPF, one, area zero. Let's take a look at the database here on DSW1.
It now says three. Let's go take a look at R1 and see if it learned. It now says three. Let's
crack that open, though, on R1. So, we'll type in router 0.0.0.3. Let's look at router three's
information while we're on router one. And, oh, my gosh, look at that. Boom. I now know about what?
The network ID of the SVI. So, if I type now in, we have a conflict here, don't we? We do. Okay.
Hang on a second. Show run pipe to include IP route. I think we have a conflict here. We do.
Okay. Hold on. Administrative distance conflict. I got to get rid of this from our last session.
I remember configuring that. So, no IP route. That was a static route, remember? All right.
So, pretend that wasn't there. It wasn't there. Okay. So, let's look at our database right now.
And, look, we know about 10.0.0.0 slash 24. So, if we take a look at a routing table now,
show IP route, it's magic. There it is. OSPF 10.0.0.0 slash 24 out gigabit ethernet 0 slash 0
because that's the best way to go right now. That's why we enable the routing process on the SVIs.
So, interface VLAN 20. Oops, wrong button. There we go. Interface VLAN 50. Interface VLAN 200.
Now, let's go back to R1 as an example. Take a look at the database.
The database should now say, let's try that again. Look at just the database.
We'll see it now says six for DSW-1. Six interfaces. The four SVIs plus gigabit 13 and 14.
That's what that means. Let's crack that open. And you'll see SVI, SVI, SVI, SVI.
SVI. There they all are in our routing table now.
If this is the first time in your life you've seen OSPF explained to you this way,
let me know, please.
Right. And when it's explained this way, it makes a lot more sense, as John said.
So, that's how it really works. Yeah, that's how it really works.
It's really how it works behind the scenes. Okay.
So, what does that mean? It means I have to go to every single interface in our topology
and just keep enabling interfaces. That's what I've got to do.
That's how you do it. And then once you have all the interfaces you want participating in
your routing process, then all your routing tables are going to be updated,
as long as you configured it properly. So, let's continue going through this,
because there's a few more things I have to show you. So, don't fall asleep on me just yet, folks.
Don't fall asleep on me just yet, because if we go to DSW-2,
I have to show you another way that you can enable OSPF on interfaces.
So, the way I've shown you right now is what we call the interface enable command.
So, if we go back to DSW-1 as an example, I type in do show IP OSPF interface gigabit
ethernet 1.0.0.0.13. You see what it says? I enabled it, even though it says attached via,
I enabled it using the interface command. That's what that means. What's the interface command?
IP OSPF, the process ID, the area you want the interface in. That's the interface command.
But there's another command that exists. Does anybody know what that command is, that you can
use? Yes, it's the network command. The network command. The network command. So, I'm going to
type in configure terminal router OSPF 1. I'm then going to type in router ID. Let's set that
up first. 0.0.0.4, because I said 1, 2, 3, yep, 4. Now, the network command is right here in router
OSPF configuration mode. Router OSPF configuration mode. Look what it says. Put in a network number.
All right. Let's just put in 0.0.0.0, just for learning purposes.
Let's put in a question mark. It says wildcard bits.
Folks, where else do we hear the term wildcard bits?
Wildcard bits.
Access control lists. What do wildcard bits allow us to do?
All right. They allow us to specify a range of IP addresses.
That's right. In an access control list, when you have the network number first,
and then the wildcard mask combined, they identify ranges of IP addresses. Notice,
I did not say subnets. No. Ranges of IP addresses and nothing more.
So, what do you think this does, then? Specifies a range of IP addresses and no more. So,
let me put in a wildcard mask of all 255s.
What range of IP addresses is that, folks?
Everything. Yes. Everything. So, I am telling the router right now,
find every single IP address on this router. There they are.
And then, enable OSPF on those interfaces. Let me repeat that. Look for every single IP address
on this router and enable OSPF on their interfaces. So, what area, though? Now,
I got to specify the area. This command is not done yet. Area zero. Now, for EIGRP,
if you're EIGRP fans and you use EIGRP, you're familiar with the network command,
but it's only this long for EIGRP. That's it. Just what I've highlighted. And it means the
same thing. It means the exact same thing. Look for what? All IP addresses on the router,
enable OSPF. So, let me do that right now. Boom. Now, we're going to see a lot of
neighborhoods that are formed here. We'll talk more about this a little bit later.
But what I want to point out to you is we type in do show IP OSPF interface brief. We're going
to see that I have OSPF enabled on all of the interfaces that had an IP address, no matter what.
Every single one of them. So, we grab our interface list.
And I type in do that. There you go. Every single one of them.
Now, the question is, is this really? Is this really what you want to do? The answer is
absolutely not. No. Absolutely not. This is not a recommended best practice. What I just did.
If you did this on the exam, Cisco would frown considerably at you and mark you incorrect.
Because you have just said, going forward, from here on out, if any interface is created
on this device, with any IP address, it automatically participates in OSPF, no matter
what.
Here we go. I created an interface. It's now participating in OSPF.
That is a no-no because of security reasons. Yeah. It's kind of reckless to do that. I would
have to agree with that statement. Even with passive interface, Joshua, not worth it. Okay?
Not worth it. Doesn't matter. I will talk about passive interface and why it's really important.
But no matter what, you really don't want interfaces enabled if they don't need to be
enabled. What does that mean? It means this version of the network command is not acceptable
on a certification exam or potentially in the real world for you. Keep that in mind.
All right. What does that mean? It means that you need to look at your interfaces,
especially on the certification exam, and you need to identify which of the interfaces need
to be enabled. All right? Now, I showed you the interface command, for example, on DSW1 and R1,
and that one was pretty straightforward, right? IP, OSPF, just go to each interface and do this.
But what if Cisco says you're not allowed to do that? You must use the network command. Or what
if you're troubleshooting a scenario that is using the network command? That's why I have to teach
you this. I prefer the interface-level command myself. That's what I use in production
environments. That's what I use in the real world. I really am not a big fan anymore of the network
command. When I have something that is better, more specific, and gives me 100 percent control
of what I'm trying to do. But the network command, I can accomplish the same thing.
But if I can do with the network command the same thing that I did on the interface command,
I might as well just use the interface command because then I know that interface, that interface,
that interface based on the configs is enabled for that. But let me show the network command.
So let's look at another example. If we said network, for example, now,
and I said 10.0.0.0, what if I put a wildcard mask of 0.255.255.255?
Okay, what does that actually mean?
Okay, what does this actually mean? So Conrad, yes, 0.0.0.255.255.255 is considered reckless.
But let's get better. Let's get non-reckless, right? So in this case, this is every single
IP address from 10.0.0.0 to 10.0, no, 10.255.255.255. Now, if you don't know how I did that,
I will teach you wildcard masking and shortcuts so you can do that in your brain for the certification
exam. So I'll teach you that during our ACL discussion, not here right now during OSPF,
because we've got so much more to cover than to teach you how to read this, okay?
But when you learn that in ACLs, you can come back and this will make more sense if you struggle
with this. But this is every single IP address from 10.0.0.0 to 10.255.255.255, area 0. So that
means it'll be every single one of these addresses except for this one, because that address doesn't
fall in that range. This address does not fall in that range. So if we look at the output now,
we'll see that everything's there that starts with 10, 10.0.0.0 to 10.255.255.255. So the 192
is no longer there, the 172 is no longer there. But again, not good enough, because in our scenario,
what interfaces do I want participating in the routing process? I want this interface,
this interface, and my four SVIs. I don't want these ones right here at all. Oops, too many.
I don't want these ones here at all based on my scenario. So again, right, not good enough,
not good enough. So we could keep playing around with this and trying to get as creative as
possible to accomplish our objective. But there's really two Cisco approved,
recommended ways of accomplishing this. Andrew, I'm going to come back and talk about that. You
got to be careful with that word summary in this case. All right, because this has nothing to do
with summarization, or summarizing networks, or anything like that. It purely just says,
enable OSPF on these interfaces, inject their network IDs, and share those network IDs with
everybody. There's no summarization going on whatsoever. No summarization going on whatsoever
in that case. That's not what the network command does, right? I've seen documentation where it
says the network command tells you to advertise this network. No, it doesn't, right? That was
something that was written in books a long time ago in the world of RIP, V1. And yes,
that made sense for RIP V1 back in the 80s and early 90s. That's right, I said 80s and 90s.
Okay, that's not how it happens today. It hasn't been that way for 30 years approximately,
maybe, yeah, about 30, 27 years, okay, with the advent of variable length subnet masking.
And with that case, it is purely straight up. Find the IP addresses, enable it on those
interfaces, inject their network IDs, and, right, so we'll talk about summarization later today.
So, and we do that totally different. And this is true for EIGRP and OSPF. Both of those
would be the same application for that concept. All right, so Cisco's recommended best practice,
so these are really your two options for the certification exam. If they tell you,
we want you to enable the routing process, let's say, on this interface using the network command,
okay, two options for that. Option number one is to use a network ID and a wildcard mask
that matches that exact range of IP addresses for the subnet. So, when you look at this particular
subnet of slash 30, a slash 30, okay, what would the IP addressing space be for this particular
network? So, what network is this? This is going to be network 10.40.23.12 slash 30, right? So,
even though it says 14, remember, that's the IP address of the interface. So, what network does
that belong to? Well, based on my diagram, it's dot 12. So, let's put that in here.
We'll put in 10.40.23.12, and the wildcard mask that would match a slash 30
is what? No, sorry, I put the wrong number there. Three, there you go, three. Yes, Andrew,
good job typing that in. Perfect. Okay, so there. So, this is every IP address from 10.10.23.12
to 10.10.23.15, and it should be not 10.10, it should be 40, right?
40, yeah, thank you. Let's look at that. Right, so that says look for every single IP address
in that range. Now, always remember this, you can only have one IP address on that router
in any given subnet. Did you know that? Yeah, that's true. So, if you have a Cisco router or
a multi-layer switch, you can only have one interface on that router in any given subnet.
You cannot put two interfaces on a single router in the same subnet.
Okay. So, with that in mind, that means when you type in this command,
even though it's a range of addresses, there could only ever be one match on this router.
That's it. Because if you try to add another interface on this router in that same range,
it would yell at you and say, nope, cannot do it. One interface on this router,
cannot do it. One interface per subnet on your router. So, if we look now at the output,
a show IPOSPF interface brief, you'll see that one interface has been enabled.
What about this interface here as an example? So, 10.40.23.10, that is actually in the .8 network.
So, let's do the same command, but let's change this to a .8. So, if we had .8.0003,
then that would mean everything from 8, 9, 10, 11. And so, the interface is what? The interface is
10. So, it falls within that range. So, let's hit enter there, and we'll see that the end result is
we are now participating in the routing process. Okay. So, that is one option. Specify the network
ID range of addresses, because then it would only match one and one interface. That's it.
That's the recommendation. So, the recommendation nowadays, it's been this way for a long time,
but I say nowadays, is when you use a network command, it should only affect one interface.
Okay. Well, if I'm using the network command and it only affects one interface,
why don't I just use the interface command instead of typing in a network command for
every interface? I mean, I have to type in the same number of commands, don't I? Sure. Yeah.
But that is the recommendation. Okay. What is the other option we have? This is a lot easier.
Why not just specify the actual IP address? So, for example, I want this interface participating
in the routing process. So, what do I do? Why not just say, hey, find this IP address,
and whatever interface it's on, enable it for OSPF. How do you do that? That's really simple.
Use your network command, type in the IP address of that actual interface, so 10.0.0.2,
and then put 0.0.0.0. Now, I'm not even messing around with wildcard mess,
and then I type in the area number, and boom. It looks for that exact IP address, and when it
finds that exact IP address, it enables it on that interface. So, that is another option you have
that would be perfectly acceptable on the certification exam. Cisco will be very proud
of you if you use that option or the option of the network. The question is, you know,
what is going to be accepted, whatever they tell you to use? If they tell you to use the exact IP
address, then you better use this option. If they tell you to use a range of IP addresses,
then use the network ID and craft a wildcard mask for that. Yeah. All right. So, I'm just
showing you the different options because if it shows up on the exam, right, are they really
testing you on real-world awesome knowledge? Not really. Not in my opinion. In this case,
they're testing you on, do you know the difference between the network command and the interface
command and how to use a wildcard mask? That's really what they're testing you on, which to me,
it doesn't matter for the real world. It doesn't matter. That doesn't prove your skills, right?
But they could do that to you, and I want you to be ready for that.
Hey, it's getting good. It's getting good. Let's keep going. Let's go to R2. Now, I'm going to go
a lot quicker here, right, folks? Because I've gotten everything out of the way that I want to
cover in regards to the interfaces. So, right now, on Router 2, we have to be super careful now,
and this is where you got to pay attention on the exam for Encore. What is this? Okay,
this is going to be one of those area border routers. It's an area border router. Why? Because
it has interfaces in area 0 as well as interface where? In area 1. You see that? You have to be
super, super, super careful that you don't mess this config up because this is where you're going
to get busted on the Encore exam. See, CCNA is single area, area 0. That's it. Encore is
multi-area. So, you got to get this config right if you have to do it or troubleshoot it or anything
like that. So, on R2, what do we do? Router-ID, because we already set up our process earlier
when we were looking at the Router-ID, 0.0.0.2 today. Do show IP protocols. We'll see in our
output here that we, yep, that's good right now. All right, let's get this party started.
Interface, gigabit Ethernet, 0 slash 0, IP OSPF 1, area 0. Interface, gigabit 0 slash 1,
IP OSPF 1, area 0. Now, for this one here, interface, fast Ethernet, 0 slash 1,
0, IP OSPF 1, area 1. Do show IP protocols. Look at this. It says you are an area border router.
Why? Because I have interfaces in area 1 and I have interfaces in area 0.
What does that mean from a database standpoint now?
Remember, your database has to be synchronized with every other router in that area.
How is R2 even going to do that if it's connected to two different areas?
Well, area border routers have a database for each and every single area. Let me repeat that.
Area border routers have a database for each and every single area that they are connected to.
So, if right now we type in do show IP OSPF database, here's the database for area 0.
Now, we start a database for area 1.
So, I'm going to have different LSAs for each and every single area.
So, R2 now has to keep track of everything here, separate from everything here.
This will all be synchronized together. This will all be synchronized together.
And if you're still wondering, how do we share the information between areas? We'll get to that.
We'll get to that. All right. Let's go to branch now. And in branch, I think we shut down some
interfaces. We did some crazy things. So, do show IP interface brief.
Let's type in interface. We have to bring this one back up.
Interface.
What other one did we shut down? Loopback 129. Let's bring that one back up.
Router OSPF1. What else do we want to say? Router ID is going to equal 0.0.0.5.
Okay. Do show IP protocols. Let's double check. OSPF is running, 0.0.0.5. Do show IP
interface brief. Make sure all those interfaces I want up and running
are up and running for right now. And I think we look good.
Okay. So, let's go to branch right now, and let's purposely make a mistake to answer
the question, would placing an interface in the wrong area generate a mismatch area ID message?
Let's check it out. Let's do that here on purpose. So, interface, gigabit ethernet,
0 slash 0, IP OSPF1 area. Let's say 0. See what happens. So, we got area 0 here. We got area 1
here. I don't see anything yet on this router. Okay. On this router, though, I am getting an
area ID. Yes. There you go. So, I am getting it on R2 right now. I'm not getting it on branch.
Let's see if we type in do show logging if logging is turned on.
Yes, it is. Okay. But it is quite possible we're not getting the log messages on branch
because it is area 0, right? It is area 0, and that's area 1. So, I'm only getting the
messages on the one that's area 1. So, this router thinks it's misconfigured where this
router thinks it's not misconfigured because it's area 0. I think that's why we don't get
the message on branch because it's area 0. It thinks it's right where this side thinks it's
wrong because area 0 is always like it's the backbone. So, area 0 is like the best area. So,
it's never wrong even though you might be wrong. So, let's go to branch, and let's fix that problem
right now, and we'll just type in IP OSPF 1, area 1, and we'll see if now we form our neighbor.
There you go. Problem solved. All right. Interface loopback 129, IP OSPF 1, area 1,
and then let's not forget about
our subinterfaces. So, we'll go to this interface here
and type in the same command, area 1, and then we'll go to our other subinterface,
and we'll type in area 1.
So, with that said now, in the end, if I've done everything I needed to do on all of the interfaces
properly, what we should ultimately have here in the end is branch A in its routing table,
it has the SVIs from over here.
Okay. Good.
And what else? Any other interfaces. Look, all those other links too,
all those other links in between that are participating in the routing process. Why?
Network IDs injected into the link state database for all the different routers,
and then the links between them are all being routed. So,
are participating in the routing process. Why? Network IDs injected into the link state database
for all the different routers. They send out their LSAs. All those LSAs go where they need
to go to all the different routers they need to go to. The routers then take that information,
build what they need to do, the topological map, the puzzle, if you want to call it a puzzle,
with all the different LSAs, puzzle pieces, and then boom, they figure out what's the best place
things to put in the routing table, and there you go. Now, if we go to DSW1, let's think about
these networks here, right? These ones right here. DSW1 should now know about those.
So, if we go to DSW1, and we type in do show IP route, there they are.
Beautiful. Absolutely beautiful. And notice, it shows you the one size zero slash 14. Why?
Because that's the best path to go. Will I have learned that I can possibly go this way as well?
Of course, right? I know everything that's going on in this area. Everything. Meaning, I know I
can go this way. I know I can go this way. I choose this way because it's shorter based on
the cost, the metric. In this case, look at this. I'm load balancing for all of these. Okay.
Here's a problem that I want to talk about next,
since we have our entire environment configured. What is the problem?
Well, right now, you see that network? Where is that network? Dot eight. It's right here.
And who are we on right now? We're on DSW1. That's who we're on.
So, we know that we can get there, gigabit one size zero slash 13.
That makes sense, right? Yep. We also know we can get there from VLAN 20, 50, and 10.
So, we know that we can get there from VLAN 20, 50, and 10.
Okay. What about VLAN 200? Why is it not listed there? It's not listed there. Why?
Because you can only load balance on four paths at a time.
See what it says? Maximum paths is four for load balancing. Let's change that. Let's change that.
Let's go to router, OSPF1, and let's say maximum paths is now going to be 10.
Do you show IP protocols? We'll see that the now 10 equal path load balancing. Let's see if that
changed my routing table. Oops, wrong button. Okay. So, let's go to the routing table.
Yep. There it is. So, the reason why only four was showing up is because the maximum
path for load balancing is four by default. But if there are more paths we could use,
then we can get them put in there. All right. So, now, there we go. There's another one.
Folks, is that a problem? Yes or no? Is this a problem?
It is. Yes, without a doubt. Why? I want you to remember how traffic flows in and
out of your subnet VLANs and broadcast domains. Think about it for a second.
Your goal is to have traffic doing what? In and out, in and out, in and out, in and out.
Right now, DSW1 is saying, I can go from here through the layer two network and back out.
And we're only looking at this link right here.
But what we need to be very careful of is that if we allow these two routers to form neighbor
adjacencies, and we allow them to use that as a path under certain circumstances, that could crush
that layer two environment from a performance standpoint. Watch this. Let's say this link went
down. Let's say this link went down. The only way to get over here or over here or over here now,
if traffic's coming in this way, is how? By using a layer two network.
Or over here now, if traffic's coming in this way, is how? Through the layer two network.
Oh my gosh, that is bad. You never want to allow that to happen in your environment.
Never. That layer two network is purely for the traffic of those subnets, of those VLANs,
of those broadcast domains, and no one else. Always remember that. So we actually do not want
neighborhoods formed here, through that layer two environment. Because if we do,
it could cause that issue down the road. Right? And if you're like, well, I want to use it as a
last option, Raymond. Whoa. If you want to use that as a last option, you're designing your
network incorrectly. Why not just add another link here? Or why not add more links? Add more
links. Why not do something in here instead? Instead of using layer two as your path. Never.
If you're down to layer two being your path to go from here all the way over to here,
that's not a good design. That is like the worst thing you could have possibly done.
So what do we have to do here? What do we have to do here instead?
What we have to do is we have to stop the neighborhood from forming,
but ensure the interfaces are still participating in the routing process.
So let me ask you this, folks. How or what is used to form neighbor adjacencies?
All right. Look, I have four neighbor adjacencies right now with DSW2.
Four. I should have none in a well-designed network.
Okay. What is used to form neighbor adjacencies? What is the packet called? What is the packet
called? Well, it's not the LSA that's used to form neighbor adjacencies. What is used?
Yes, the hello packet. So right now if we type in debug IP OSPF hello, I have hello packets
going out. My interface is the SVIs. Look at the SVIs. Hello packets. Hello, hello,
hello, hello, hello. What does that mean? It means that every single PC in that Layer 2
environment has to receive those hellos and drop them as well. So wait a second. Not only are we
forming neighbor adjacencies here, we're also sending hellos to devices that don't need them.
What's another problem that could happen here? What if somebody adds a rogue router in that Layer
2 environment? What if somebody installs a virtual router on one of their PCs because
they're studying for the Encore exam? Could that possibly receive the hello
and then form a neighbor adjacency with the production router and then inject false
routing information into the routing environment and cause problems? Oh yeah.
So what is one of the best ways to make sure none of that can happen? Well,
how about we just stop the sending and receiving of hellos on those SVIs?
And now I've just protected myself from rogue routers. I protected myself from suboptimal
routing paths in certain scenarios and conditions. Yeah, let's stop the hellos. That's all we got to
do. So stopping those hellos is going to be a security feature, really, in the end,
as well as improve performance because we don't have to send this junk down there anymore
and have all the PCs drop it anyways, and the phones drop it.
So how do you do that? Joshua says passive interface. Yeah, watch this.
I'm just going to type in right now, router
OSPF1, right? So router OSPF1. There you go. You can see it. Now I'm going to type in passive
interface default. What does passive interface default mean, folks? It means
disable the sending and receiving of hellos on the interface.
Done. All done. So what have I just done? No more hellos. No more hellos. No more hellos.
No more hellos. No more hellos. No more hellos. Oops. Oops. We still need hellos there, don't we?
Yeah, we do. So I'm going to type a no passive interface, gigabit ethernet,
one slash zero slash 13. And now we'll send hellos out that interface again
and form our neighbor adjacency. So for all those interfaces that go down your layer two devices,
layer two network, make them passive. And this is one way to make every interface passive,
passive interface default. And then you type a no passive interface for the interface you
don't want to be passive. So there's now 14 is no longer passive either.
So we type in, I'm going to type in do you all to shut off my debug and then
do show run pipe to section OSPF.
And you'll see here that I have passive interface default and then no passive interface for the
interfaces I don't want passive. So here's something to keep an eye on the exam. If an
interface is accidentally configured as passive, would that stop you from forming a neighbor
adjacency? Yep. Right. So this is awesome. Now here's this is the actual way I recommend you do
it in a production environment. Why is that? Because what I want to point out to you right now
is that any interface now you enable for OSPF will not be able to form a neighbor adjacency
with anyone else. That's right. At all. Unless you do what? Unless you also type in no passive
interface for that specific interface. It gives you actually a little bit of extra security.
Meaning that if an interface accidentally gets created with an IP address and it accidentally
gets enabled for OSPF, it still won't be able to form a neighbor adjacency with anybody until
you type in the no passive interface command. Because you're saying every interface is passive
unless otherwise specified. So basically default deny unless explicitly allowed,
which is pretty cool. So I like that as a real world option. I like that as a real world option.
I do. So if you go to DSW2, I'll do the same thing on DSW2. So router config router. So we'll say
passive interface default and then no passive interface gigabit ethernet one slash zero slash
13 and 14. So same idea. Now we go over to somebody like our router over here, our branch
router, right? Just to show you another example, you may not want to do passive interface default.
So what if on the exam you weren't allowed to do that? Or it wasn't one of the valid options
that you could pick in order to stop the sending and receiving of hellos on your sub interfaces?
Well, then all you have to do is go into router OSPF configuration mode.
And then just do it on an interface by interface basis. So you can just turn around and say
passive interface fast ethernet zero slash zero slash zero dot 24. So you can just do it one at
a time if you want to. So passive interface default says all interfaces and then you know
pacify the interfaces you don't want to be passive. Whereas this one says all interfaces
are not passive except these ones that I've typed in. So the other one, the one I showed you,
the one I showed you on our distribution routers, this is a better option.
This is a better option because it gives you that little added extra layer of security
where this one doesn't. Because this one still ensures all interfaces are not passive.
And so if somebody does connect or enable an interface, I should say for OSPF and so on and
so forth, well then it can form a neighbor adjacency at that point in time because it's
not passive by default. Whereas over here, it is all the interfaces are passive by default.
Just something to keep in mind for the real world. All right, so do show IP protocols. You'll
see that now when we look at this output, it even tells you what interfaces are passive on your
device. So it tells you what interfaces are participating in the routing process,
what interfaces are passive. We type in do show IP OSPF interface brief, we'll see all my
interfaces that are participating, whether they're passive or not. Now EIGRP, just to let you know,
because I know some of you use EIGRP. EIGRP, if I did the same thing, the interfaces don't show up
here that are passive. So with EIGRP, none of these would show up here if they were passive.
With OSPF, they still show up here. So with EIGRP, it's a little more trickier in troubleshooting
the passive interface because they don't show up here at all. Whereas in this case, I know all
these interfaces are participating in the routing process. And then when I look at this, I can see
that they're passive. So now I know that all of these are passive and they're participating in the
routing process. Where the EIGRP is a little more trickier because you got to figure out, okay,
they are passive, but are they really participating in the routing process? So you'd have to look up
here to double check and triple check that. So just a little different things to keep in mind
for EIGRP versus OSPF in the real world, not for the exam. For OSPF for the exam, you're seeing
what you need to see right now. Okay, what is the other command? Oh, yeah. So if I take a look at
ShowIPOSPF interface and we look at a very specific interface like VLAN10, what I want
you to see here is that it actually says no hellos, passive interface as well in this particular output.
Conrad asked earlier, Conrad, he's there. Okay, you asked any major differences in the ShowIPOSPF
command when looking at interfaces added using the network command versus the interface command.
So you'll see here that if you're using the interface command in this output,
ShowIPOSPF interface, whatever, it'll show you that it's attached via interface
enable. If you look at it for the network command, so Do Show IP
OSPF on this router interface, we did the network command on this one,
you'll see that it says network statement. Is that the answer you were looking for, Conrad?
Is that what your question was about?
All right. No, that's about it. So for example, we type in Do Show.
Show IP protocols will be different. Okay. So Show IP protocols shows it like this instead.
So Show IP protocols actually shows you your network command. All right. So that's different.
This is so misleading. I really despise this output. I really do. This output was created,
this title, Routing for Networks, for RIP version 1. Okay. And so with RIP version 1,
it was class full addressing and no variable length subnet masking. So that title made sense
for RIP version 1, but the title doesn't make sense for RIP B2, EIGRP, OSPF, ISIS. It doesn't
make sense at all, right? Because I am not routing for this network. Does that look like
a network to you? No. I am routing for the network of the interface that was enabled
by this network command. That's what it should say. That's what it should say, but it doesn't.
So that's what it shows up if you use the network command and IP protocols.
But if you use the interface command in Show IP protocols, it shows up as what? As we saw earlier,
the actual interface. All right. That's why I am a fan of using the interface level command,
because this is so much easier to read and view than something like this. This is silly. This is
nonsense in my opinion. All right. It makes it harder for you to troubleshoot looking at
something like this than something like this. So yeah. What this really means is that's your
network command that you use to enable the routing process on that interface.
Let's take a peek at something like Do Show IP OSPF. I don't really think there's anything
there, because this is not about the interface. This is purely about the process that is running
on the device. So here it says there's six interfaces, but it doesn't tell you how they
were configured. So that's fine there. So Show IP OSPF interface. Yeah. So that's about it.
That's about it, Conrad. Yeah. For your question. And there's really not anything else that I can
think about off the top of my head. But if it comes to me as we continue this adventure, I'll
definitely bring it up and tell you right away when it comes to my head. Yeah. Oh, great questions.
Great questions. So just to wrap up the oops, wrong thing. Wrap up our passive interface
discussion here, just so you're aware. Right. I have a little slide. Suppress the sending and
receiving OSPF message on an interface. Interface is still participating in the OSPF process.
It's about reducing the amount of OSPF traffic in the layer two network. And ultimately,
the answer is rogue routers, rogue devices in that layer two network can't form neighbor
adjacencies with routers and infect our link safety database with false information. So
think of it security, security, security and performance, both at the exact same time.
All right. And lastly here, just before we wrap up this discussion, let me just double
check my slides, my notes. Yeah. This will be our last thing before we take a little breather.
And then we'll have our config totally done. And then we can start looking at all the other
things we need to cover for the rest of today's session. So right now, if we analyze our environment,
we'll see that we can reach every place that is inside our organization. So by doing something
like show IP route, you'll see that all the networks listed are networks inside of our
routing domain. So everything that's inside here, everything that's inside here, everything that's
in the blue area circles, that is what we can reach. Same thing if I go all the way to branch.
Same idea. Okay. So what are we missing? What are we missing? The ability to get
everywhere else, the ability to get to every other network we do not know about.
So for example, right now, if we want to go to the internet, folks, can we go to the internet?
No. For example, my PC right now, if I try to go to the internet, I can't. Why? Look at DSW-1.
DSW-1 only knows how to get to everywhere in your own organization. So yeah, we're missing what?
We're missing the, what type of route is it called? We're missing the, starts with a D,
starts with a D. Default route. Yeah, absolutely. So right now though, if we go to R2,
if I type in show IP route, do I have a default route, folks, on R2 right now?
I do. There it is. 0000 slash zero. So R2 can get to the internet.
If we type in show run pipe to section IP route, take a peek. There's our default route. I actually
have a floating static default route configured here as well.
Now, what are my options? Well, we could go to all of our routers and configure static default
routes, but that would be silly. What would be a better option here, folks? What would be a better
option? What if we took this default route and we imported it into OSPF? What if I take that,
bring it into the link state database? Right now, there is nothing here about a default route. If
there was, it would show up as a type five, LSA would actually say as a title type five,
and then you would see 0000. That is the default route in your link state database. It's not here
anywhere. So how do we do that with OSPF? It's different than EIGRP, that's for sure.
With OSPF, we have a very special command we can utilize. And what is that very special command?
It is default dash information originate. Now, when I type that, what that tells the router to do
is it says, I am having a little bit of issues here. One second, folks. Let me refresh my
student screen right now. Anybody else having buffering issues?
No, a little bit of lag, right? Just a little bit. Yeah, okay. So right now, I am having zero
issues streaming, but it looks like my client is having trouble, right? So if you're not receiving
any issues, that's fine. But I am not having trouble streaming, I'm just having trouble
receiving right now. So my stream is fine. Okay. So it's a receiving problem on my end,
you might not be affected by it. Good. All right. So default information originate
is the special command. And what does it say? It says,
look in the routing table for 000 slash zero. It doesn't matter how it got in there.
It could be in there because of a static default route. It could be in there because you learned
it via BGP. It could be in there because you learned it via EIGRP. It could be in there,
it doesn't matter how it got in there. If it is there, no matter how it got there,
take that and import it into the link state database. That's it. That's what that command
does. So now we look, it'll always be listed at the bottom, folks, just to let you know.
And there you go. Type five, we'll talk more about that later. But 000 advertised by me,
router number two. So now that it's in the link state database, am I going to tell everybody else
about it? Yep, that's exactly what I'm going to do. And now everybody's going to have an OSPF
default route. Look at that. Now we can get to the internet because that will cause traffic to
go from me to R2 out to the internet and back. Likewise, branch would be the same way now.
Branch would have that in its routing table. And so branch, even though it has an internet
connection, I don't have a static route set up for that. Why? For the demonstration purposes,
where we can go from here over to here now and then up because of that route that's in
the routing table. Now, could we also have this used as an exit point if we want to? Sure,
of course we could. What about R1? Could we have that too? Sure. Let's go see if R1 has a
static default route. Look at that. R1 has a static default route, folks. Therefore,
notice the OSPF route is not in there, is it? Why is the OSPF route not in there
and the static route in there? What's the magic word? Two words.
Lower administrative distance. Beautiful. Beautiful. Great answer. Perfect answer.
So, if I type in show run pipe to section IP route. Let's take that out for a second just to show you.
I'm removing it. And you'll see the OSPF one's in there now.
Not bad. Not bad. Perfect example, again, of your what? Administrative distance, how that works.
All right. So, I just put it back in.
All right. Now, let's do this. Since we have a static default route here, let's type in router
OSPF one. Let's do it here as well. Default dash information originate. So, what does that mean now?
So, what does that mean now? It means I'm also going to inject the default route now.
So, now we have it twice. Once for me and once from R2. Look at that. Twice.
So, let's go over to somebody like DSW1.
I can go two different ways if I wanted to the Internet. Why? Because it's equal cost
pass to both of those gateways that we have. So, if one fails, the other one can still be used. If
the other one fails, the other one can still be used. Not bad. Pretty cool. We could even do it
over on branch if we wanted to as well. And therefore, no matter what, if any of these
links fail to the Internet, we'd have still the ability to go to the router that still has a
connection to the Internet. And you can even manipulate this more. I teach you how to manipulate
this even further in the advanced routing course called an RCENARSI for exam 300-410. I'm just
looking over there at the numbers I got on my list. Yeah. So, we teach you how to manipulate
that even more. So, you can control like under normal conditions, I want to go here. If and only
if that fails, then I want you to fail over to that one for OSPF. If and only if that one fails,
I want you to fail over that one for OSPF. So, yeah, you can really get creative with these
right here if you needed to. All right. But that is beyond the scope of Encore. But there you go,
folks. What did we learn? We've learned how to enable OSPF on all of our routers, enable it on
all the interfaces, so we can inject the network IDs of all the different interfaces participating
in OSPF in the link state database, so we can share all that information with everybody.
And we had fully populated routing tables now. And then what do we do? We looked at passive
interface. And on top of that, we looked at what else? Default information originate.
Know all of that if you plan on being successful on the certification exam.
Config, verify, troubleshoot, very important skills to have for all of that information right there.